Application of Nanotechnology in the Agro-Food Sector

Abstract

Nanotechnology is an emerging field of research that has been widely applied in different scientific and engineering areas. The agro-food sector is not an exception, which considers its applicability in several areas of major interest for both consumers and producers. This review considers major concepts related to nanostructures and nano-based instruments used in the food sector, as well as their applications in agro-food products. Food safety through the use of nanosensors for pathogen detection, smart packaging, and valorisation of food products by nanoencapsulation/nanodelivery of food ingredients (e.g. flavours) are examples of important areas of nanotechnology. Consumers' apprehension regarding food stability and safety issues is also considered. [PUBLICATION ABSTRACT]

Headnote

Summary

Nanotechnology is an emerging field of research that has been widely applied in different scientific and engineering areas. The agro-food sector is not an exception, which considers its applicability in several areas of major interest for both consumers and producers. This review considers major concepts related to nanostructures and nano-based instruments used in the food sector, as well as their applications in agro-food products. Food safety through the use of nanosensors for pathogen detection, smart packaging, and valorisation of food products by nanoencapsulation/nanodelivery of food ingredients (e.g. flavours) are examples of important areas of nanotechnology. Consumers' apprehension regarding food stability and safety issues is also considered.

Key words: nanostructures, nanofiltration, food safety, food packaging, consumer safety

Introduction

Despite the scientific and technological progresses achieved in the new millennium, the aim to gain com- petitive advantage and market share in the agro-food sec- tor requires a continuous update and the development of innovative strategies to improve production efficien- cy, food safety and food characteristics. In this context, a growing interest in the use of nanotechnology has been observed in different domains of food processing, food packaging, food safety and farm production systems (1-8), and so far it seems to have been a success due to the ob- tained value-added food and agricultural products. De- spite the several nanotechnology applications that can be explored in the agro-food industry, their wide use is still very limited mainly due to the consumers' fears. In fact, several of the safety issues raised by consumers and regulators result both from the complexity and from many forms of nanotechnology that can be applied.

Although the food products are naturally composed of nanomaterials, based on the dimension of the particles and structures that constitute them, other nanostructures could be intentionally added or applied to manufactur- ed food products. Over the past few years, nanotechnol- ogy has had an impact on various segments of the food and agricultural industry including the production, pro- cessing, storage, safety, authenticity and waste reduction. Several examples are reported in the literature concern- ing the development and application of different nano- structures ranging from intelligent packaging (1,7) to inter- active food (i.e. in the sense that food products contain nanostructures, which can modulate the release of bio- active compounds, e.g. flavour or colour enhancers or nu- tritional elements, in response to nutritional deficiencies or allergies, detected through nanosensors, or personal taste preferences based on the concept of 'on-demand de- livery') (9). Currently, major food researchers are using nanotechnology strategies (10-14) in order to: (i) improve the quality, safety and biosecurity of food products (e.g. nanosensors to detect pathogens or contaminants, and nanodevices to identify preservation and to track stocks); (it) increase the range of food texture, colour and taste (e.g. encapsulation of flavour or odour enhancers) and decrease the use of fat, (tit) improve the efficiency of nu- trient supplements and natural health care products (e.g. preparing carriers for protecting or delivering several antioxidant agents and nutraceuticals, such as quercetin, glycyrrhizinate and ellagic acid, resulting in higher sta- bility and oral bioavailability); (iv) increase the efficiency of liquid filters; and (v) improve the shelf life. Nanotech- nology applications are expected to provide more precise food manufacturing equipment, new packaging mate- rial, new methods for rapid identification of the authen- ticity of the products, as well as non-polluting, cheaper, and more efficient food processing techniques (2).

The present paper provides a comprehensive review of the latest achievements in nanotechnology applied to foods and food-related systems. Covered topics include nanostructures, nanofiltration, food safety, food packag- ing and instruments used in this area. An overview of food stability and consumer safety is also briefly dis- cussed.

Concepts of Nanotechnology in Food Industry

Even though there is no precise definition of nano- scale material in the food sector, nanotechnology is com- monly associated with the characterization, design, pro- duction and/or manipulation of structures, devices or material with submicron diameter (15). Nanostructures are defined as having one structural dimension with a dia- meter smaller than 100 nm (16), which are comparable to those of subcellular structures, including cell organel- les or biological macromolecules like proteins (17). On this scale, the structures should display functional prop- erties that are significantly different from the properties of macroscale material composed of the same substance (7). Consequently, interest and activities in this research area have greatly increased over the past years. Some of their characteristics comprise changing important orga- noleptic properties (e.g. colour), good physical stability, conductivity (heat and electrical), chemical reactivity, op- tical and magnetic properties, which when incorporated into products can enhance or improve their existing prop- erties (e.g. enhance oral bioavailability) (18,19).

Regarding food applications, nanostructures can be produced by two different approaches, either 'bottom- -up' or 'top-down' (20-22). The 'bottom-up' approach re- fers to the manipulation of single atoms and molecules which produce more complex molecular or supramole- cular structures by a design based on self-organization of chemical or biological compounds. For example, in the biological application, the organization of casein mi- celles or starch and the folding of globular proteins and protein aggregates are self-assembling structures that produce stable entities (21). Alternatively, the 'top-down' approach is achieved by reducing the size and refine- ment of the smallest structure to the nanoscale dimen- sion by physical or chemical techniques (e.g. mechanical milling, homogenization, ultrasound, lasers and evapo- rization followed by cooling) (22,23). For example, the antioxidant activity of green tea powder has been im- proved by using dry milling technology (24).

One important concept in this area is the so-called 'delivery system', which has essentially originated from research in the pharmaceutical field. However, similar concepts have been explored in foodstuffs. Delivery sys- tem is defined as a vehicle that is used to carry a bio- active compound (e.g. drug, functional food ingredient) to a desired site of action. In recent years, nanotechno- logy has been used in the agro-food sector to prepare carriers for delivering several functional food ingredients, such as quercetin, ß-lactoglobulin, hesperetin, or tea cate- chins (13,25-30). In order to target a specific site, nano- systems have to be able to control the bioactive release (26,29,30). Additionally, nanocarriers can protect the bio- active compounds against degradation (e.g. chemical and/ or biological) during processing, handling, storage, and utilization (14,26,31,32) maintaining the functional ingre- dient in its active state. Another requirement is its com- patibility with other components, with physicochemical benefits and qualitative outcomes (e.g. texture) of the fi- nal product (33).

Nanostructures

A huge variety of nanostructures has been devel- oped to be used in agriculture and food fields. The de- velopment of nanostructures to entrap or nanocarriers to deliver functional food ingredients (e.g. nutrients, sup- plements and additives) has been widely explored. As delivery systems, the aim is to develop biocompatible nanocarriers, in which the functional food ingredients (e.g. vitamins, probiotics, bioactive peptides, antioxidants and natural health products) are incorporated within the matrix, thus allowing a controlled bioactive release. This approach is very useful as it can protect the sensitive compounds against a range of environmental influences such as in the gastrointestinal tract (e.g. pH, enzymes, presence of other nutrients) and conditions encountered in food process (e.g. temperature, oxygen, light), but it is also capable of improving their stability and solubility. Consequently, the bioavailability and targeted bioactive delivery can be increased (34-36).

Within the agro-food chain, metal or metal oxide- -based nanostructures (e.g. nano-Ag, nano-ZnO, nano-Cu, nano-TiOo) have been investigated as pesticides (37,38). These particles are known to have different structures and shapes, which can be (homogeneous or heterogeneous) spherical, tubular, irregularly (non-spherical) shaped, or can exist in fused aggregated or agglomerated forms (39).

There are several types of nanostructures used to deliver functional food ingredients (e.g. nanoemulsions, micelles, liposomes, nanoparticles, cubosomes) (25), which can be based on lipids, proteins, polysaccharides, poly- meric networks, and even combinations of these com- pounds (40). As far as food is concerned, delivery sys- tems based on lipids, proteins, and/or polysaccharides are the most widely used and promising materials due to the biocompatibility concerns. Nanostructures based on polymers are prepared by the polymerization of more than one type of monomer, frequently combinations of hydrophobic and hydrophilic monomers are used, creat- ing a carrier with opposite affinities for aqueous solvent (41), and therefore more versatile in terms of application. Different natural polymers such as albumin (protein), gelatin (protein), alginate (saccharide), collagen (protein), chitosan and pectin (saccharides), ?-lactalbumin (milk pro- tein) and zein (corn protein) have been applied (14,21, 26,29,30,40,42,43).

The use of protein-based nanostructures to encapsu- late compounds is particularly interesting because pro- teins present: (i) unique functional properties, especially those derived from food, (ii) high nutritional value, and (iii) a less dangerous application in food (44). Moreover, proteins offer additional advantages since they are rela- tively easy to produce and capable of forming complexes with polysaccharides, lipids or other biopolymers, allow- ing them to be used in a wide range of applications.

Polysaccharide-based nanostructures are also inter- esting for encapsulation of food ingredients due to both biocompatibility and biotolerability properties. Polysac- charides are polymers of monosaccharides (carbohydrates) that are linked together by glycosidic bonds. In the or- ganism, these polymers are broken down to saccharides by the colonic microflora and are able to protect func- tional food ingredients from hostile conditions, such as those found in biological systems (e.g. stomach acidic pH). The glycosidic linkages are hydrolyzed on arrival in the colon, which triggers the release of the entrapped bioactive compounds. Two polymers frequently used are chitosan and pectin (40).

In the last years, several copolymers have been syn- thesized and used to prepare different nanostructures, such as micelles, nanospheres, polymersomes and nano- capsules (45). Polymeric micelles are described as nano- scopic core/shell structures formed by amphiphilic block copolymers. The inner core of these nanostrutures is com- posed of hydrophobic regions of the amphiphilic mole- cules in which hydrophobic compounds can be encapsu- lated (e.g. lipids, flavouring agents, antimicrobial agents, vitamins, antioxidants) (44). Polymeric nanospheres are solid colloidal particles in which compounds are dissolved, entrapped, encapsulated, chemically bound, or adsorbed to the polymer matrix (41). In some situations, it is not easy to differentiate between micelles and nanospheres if the inner core becomes more or less solid-like depend- ing on the copolymer composition (44).

Nanocapsules and polymersomes are vesicular sys- tems of colloidal size in which the compound is inside a cavity surrounded by a polymer, which is usually an am- phiphilic synthetic block copolymer, membrane or coat- ing. A nanocapsule is formed if the core is composed of an oily liquid and the surrounding polymer is a single layer, which is able to entrap hydrophobic compounds (e.g. lipids, hydrophobic vitamins, antioxidants). If the core of the vesicle is an aqueous phase and the sur- rounding coating is a bilayer polymer, the particle is considered a polymersome.

Nanostructures, such as surfactant micelles, vesicles, bilayers, reversed micelles, and liquid crystals, have been widely used to encapsulate and deliver polar, nonpolar and/or amphiphilic functional ingredients (46). They are thermodynamically favourable systems whose formation is normally driven by the hydrophobic effect. A different type of nanostructure depends on: (i) the nature of the resultant structures, (ii) the concentration and molecular characteristics of the surfactant, and (iii) the established environmental conditions. Among these colloidal sys- tems, nanoemulsions are defined as non-equilibrium, heterogeneous systems, which are composed of oil drop- lets dispersed in an aqueous medium and stabilized by a surfactant. Nanoemulsions differ from conventional emulsions in nanometric droplet sizes (normally in the range of 10-100 nm), which makes them more stable for longer periods (47), being often produced by high-pres- sure valve homogenizers or microfluidizers. Functional food ingredients can be incorporated within the nano- droplets or in the continuous phase of these nanoemul- sions (48). They are an example of lipid-based nanostruc- tures. Particularly, the nanostructures based on lipids represent one of the most attractive encapsulation tech- nologies due to their additional benefits since after oral administration they are expected to undergo similar me- tabolic pathways as the food-ingested lipids. Moreover, when compared to other nanostructured materials, lipid- -based systems present additional advantages, such as: (i) they can be produced using natural ingredients, which are usually similar to the physiological lipids and have Generally Recognized as Safe (GRAS) status for oral and topical administration, therefore, a biocompatible and bio- degradable nanocarrier is expected; (ii) they have high capacity of modulating the bioactive delivery; (iii) they can entrap efficiently compounds with different solubil- ity, and (iv) they require low-cost production techniques, avoiding the use of organic solvents, and are easily scaled up to industrial production (49-51).

Other interesting lipid-based nanostructures that have been reported as useful for food technologists are na- noliposomes, archaeosomes and nanocochleates (52,53). Nanoliposomes are structures of bilayer lipid vesicles (<30 or 30-100 nm). Due to their typical composition, nanoliposomes are versatile colloidal carriers capable of both hydrophilic and hydrophobic compound entrap- ment within a unique particle (52). Moreover, it has been reported that the lipid bilayer of nanoliposomes can fuse with physiological bilayers (e.g. cell membranes), medi- ating the release of functional ingredients into the cells (e.g. encountering specific cellular enzymes, due to pH or thermo sensitivity or after the binding of antigen with the tagged antibody) (54). In addition, these lipid-based nanostructures have demonstrated good biocompatibili- ty, low toxicity, lack of immune system activation and, therefore, high versatility in use as colloidal carrier sys- tems (55). Nanoliposomes have been used in the food industry to encapsulate and control ingredient delivery in functional food (e.g. flavours and nutrients), enhanc- ing their biovailability, stability and shelf life (e.g. milk proteins) and, more recently, have been investigated for their ability to incorporate antimicrobials that could aid in the protection of food products against microbial con- tamination (53).

Archaeosomes represent another variant of liposome vesicles, which are prepared from archaeobacterial mem- brane lipids (56). The archaeobacterial lipids exhibit un- usual lipid structures, which contribute significantly to the vesicle stability (e.g. thermostable and stress resis- tant) and are well tolerated in vivo (murine models) (57). Archaeosomes have proved to be an ideal carrier for pro- tection of food supplements, such as antioxidants, during food processing (e.g. against chemical influences) (56).

Nanocochleates are obtained by the addition of cal- cium ions to small phosphatidylserine vesicles and they comprise a multilayered structure consisting of a contin- uous, solid lipid layer sheet rolled up in a spiral fashion with little or no internal aqueous space producing a na- nocrystalline structure (i.e. microstructural features on a nanometer scale) (52), which can also encapsulate and deliver both hydrophilic and hydrophobic compounds. It is well documented that the structures of crystalline and intercrystalline regions vary with decrease in crys- tallite size. These lipid-based nanostructures deliver their inside content to target cells through fusion mechanisms. Their solid layer protects the 'encochleated' material from harsh environmental conditions (e.g. pH) or enzymes, being able to resist the degradation in the gastrointesti- nal tract, which makes them attractive carriers for oral delivery (58). They protect micronutrients and antioxi- dants from degradation during manufacture and storage (2)·

Furthermore, nanostructured lipid carrier (NLC) and nanosized self-assembled structured liquid (NSSL) are also demonstrating successful achievements in food tech- nology. NLC is composed of a blend of solid lipid (melt- ing point above 40 °C) within very tiny nanocompart- ments of liquid lipids (oil), which is solid at both body and room temperatures. NLC usually provides a high pay- load and prevents bioactive expulsion during storage (51,59). Hentschel et al. (60) reported a sucessful encapsu- lation of ß-carotene in NLC to be dispersed in beverages. NSSL involves the development of minute compressed micelles called 'nanodrops'. These nanodrops serve as liq- uid carriers, allowing penetration of health components, such as vitamins, minerals and phytochemicals, which are insoluble in water or fats. This technology has been used in the canola active oil by Shemen Industries and they report that the phytosterols added to the micelles can pass effectively the digestive system without break- ing down (61). Additionally, these colloidal systems com- pete with cholesterol from the micelles produced by bile acids, inhibiting the move of cholesterol from the diges- tive system into the blood stream (62).

Another interesting nanostructure with potential ap- plication in food systems and industrial food processing equipment is the nanotube membrane. Carbon nanotubes represent a newer generation of nanostructures. Carbon nanotubes are tube-shaped structures which are construct- ed of a hexagonal array of carbon atoms. These struc- tures have interesting features that make them useful in food packaging to improve its mechanical properties. Moreover, Kang et al. (63) have reported that carbon nanotubes demonstrated powerful antimicrobial activity and that Escherichia coli died on immediate contact with long, thin nanotubes.

When combined with molecular biological tools, the developed nanostructures may offer new biotechnologi- cal applications including bioanalysis (64). This type of nanostructures has already been applied for different pur- poses such as bioimaging, biosensing or bioactive deliv- ery, with an enormous potential still to be explored (65), increasing the prospects of nanotechnology transfer to other scientific and technological areas.

Applications in the Food Industry

Applications of nanotechnology in the food industry are emerging quickly. Considering food, there are two areas of interest, the first which involves food packaging (i.e. nanotechnology application outside the food prod- uct), and the other concerning the product per se (i.e. nanotechnology application inside the food product). Therefore, according to Moraru et al. (66), the four main topics in food industry where nanotechnology could have a significant impact are: (i) encapsulation of nutraceutic- als and other functional food ingredients to develop new functional material, (ii) micro- and nanoscale processing, (Hi) product development, and (iv) design of methods (e.g. nanofiltration) and instrumentation (e.g. nanosen- sors) for food safety and biosecurity.

In the last years, some successful examples of food- -related nanotechnology applications have included the development of smart delivery systems of nutrients or other food ingredients, rapid sampling of biological and chemical contaminants (i.e. food safety), and nanoencap- sulation of nutraceuticals for controlled release, water purification and cell-wall rupture (10,11,44,67,68). Sever- al applications of nanotechnology in food have recently been reported, but only some examples will be explored.

Application in product per se - food manufacture and encapsulation of food additives

Functional ingredients are essential components of a wide range of industrial products, including pharmace- uticals, natural health-care products (e.g. quercetin, glycyr- rhizinate, tea cathechins, ellagic acid), cosmetics, agrochem- icals, and foodstuff. Examples of functional ingredients used in food products include vitamins, antimicrobials, antioxidants, probiotics, prebiotics, peptides and proteins, carotenoids, omega fatty acids, flavourings, colourants and preservatives, and they can present a variety of dif- ferent molecular and physical forms. In general, they are not administrated directly in their pure form, but they are often incorporated into the delivery system (e.g. nano- structures). Functional ingredients are incorporated into food matrices to develop innovative functional food, known as nutraceuticals. Even though the involvement of these products in physiological functions is not yet fully un- derstood, it is widely accepted that their addition to food systems may have physiological benefits or disease pre- venting properties (69). An example of the benefits is the antihypertensive effect of dietary peptides derived from milk proteins, mediated by angiotensin-converting en- zyme inhibition (70).

Concerning encapsulation and delivery nanotechnol- ogy application, functional food ingredients can be in- corporated, absorbed, or dispersed in nanostructures. New food products containing nanostructures have been in- troduced or are being currently developed for different purposes (2,25,40,71): (i) to protect nutraceuticals against degradation during manufacturing, distribution and stor- age, improving their stability, (it) to enhance the bioavail- ability of poorly soluble functional food ingredients (e.g. hydrophobic vitamins), improving their nutritional value, (iii) to increase food shelf life, (iv) to produce low fat, carbohydrate or calorie products (e.g. mayonnaise, spreads and ice creams), (v) to optimize and modify the sensory characteristics of food products creating new consumer sensations (e.g. texture, consistency, development of new taste or taste masking, flavour enhancement, colour alter- ation), (vi) to control functional food ingredient delivery (e.g. flavour, nutrient). Additionally, nutraceutical diges- tion or absorption may increase or decrease depending on the structural, chemical, and physical state of the de- veloped nanostructures and the entrappement of the functional food ingredient. Therefore, reducing the size of the encapsulates can be related to prolonged gastroin- testinal retention time caused by bioadhesive improve- ments in the mucus that covers the intestinal epithelium (72).

Nanostructures (e.g. nanoemulsions, liposomes) con- taining functional food ingredients (e.g. polyphenols, min- erals, and micronutrients) can be used to protect them from oxygen and water (73), and from harsh conditions of the GI tract (74), improving their shelf life. Nanostruc- tures of certain inorganic materials have also been studied as food additives in form of coating to provide moisture or oxygen barrier (e.g. silicon dioxide (E551), magnesium oxide (E530), titanium dioxide (E171)) (75), and antibac- terial 'active' coating, especially silver (76). However, very little is confirmed about the specific effect of silver-based nanoparticles on human health which limits their addi- tion directly to foods. The administration of ?-3 polyun- saturated fatty acids can be of major importance due to their effectiveness in preventing diseases (77,78). How- ever, due to their high sensitivity to oxidation, they re- quire both stabilization procedures and protection against deterioration factors. A recent study by Zimet et al. (68) reported about two systems based on casein (casein nano- structures and reformed casein micelles) that showed a remarkable protective effect against docosahexaenoic acid oxidation. These systems proved to have a good colloi- dal stability and to preserve the effect of their functional ingredient up to 37 days at 4 °C. Recently, natural dipep- tide antioxidants (e.g. L-carnosine) are receiving increas- ing attention due to their potential application as bio- preservatives in food technology. However, their direct application in food can result in a decrease of their activ- ity due to stability issues (e.g. proteolytic degradation and a potential interaction of peptide with food compo- nents). In this context, Maherani et al. (79) have success- fully encapsulated these natural antioxidant peptides by nanoliposomes to overcome the limitations related to the direct application in food. BioDeliverySciences Interna- tional has developed Bioral(TM) nanocochleate nutrient de- livery system, which is a phosphatidylserine carrier (-50 nm), derived from soya bean (GRAS status). This system has been used for protecting micronutrients and antioxi- dants from degradation during manufacture and storage (76).

Although several benefits can be claimed in the de- velopment of nano-sized food ingredients, the main aim appears to be the improved uptake, absorption and bio- availability of these ingredients. In this context, nanotech- nology renders hydrophilic substances fat soluble and liphophylic ones water soluble, allowing nanostructures of some functional food ingredients (e.g. carotenoids, phytosterols, and antioxidants) to be dispersed in water or fruit drinks (10). Nanostructures of the synthetic form of tomato carotenoid, lycopene (particle size of 100 nm, from BASF's US patent US5968251), have been devel- oped and accepted as GRAS substance by the Food and Drug Administration (FDA). The water-dispersible lyco- pene nanostructures can be added to soft drinks to pro- vide colour and health benefits (80). For example, the men- tioned authors demonstrated that synthetic lycopene in association with vitamin ? can inhibit the growth of pros- tate cancer in nude mice. Lycopene has been included in other products such as baking mixtures and blanc- manges (76). Another example of nanostructure applica- tion in nutraceuticals is related to coenzyme Q10 (CoQIO), which is an antioxidant agent with well-established phar- macological activities. However, CoQIO is only marketed as a nutritional supplement without any claim of its ther- apeutic activity probably due to its poor physicochem- ical and biopharmaceutical properties leading to its low oral bioavailability, which does not allow it to reach its therapeutic concentration easily. Ankola et al. (81) dem- onstrated the potential of nanotechnology in improving the therapeutic value of molecules like CoQIO, facilitat- ing its usage as first-line therapeutic agent for prophy- laxis and therapy by overcoming the problems associ- ated with its delivery in physiological conditions. These authors developed biodegradable polymeric nanostruc- tures based on poly(lactide-co-glycolide) (PLGA), using quaternary ammonium salt didodecyldimethylammoni- um bromide as a stabilizer. Essential oils present poor water solubility, which limits their application. Recently, Wu et al. (43) have demonstrated that the entrapment of essential oils within zein nanostructure allows their dis- persion in water, enhancing their potential for use as anti- oxidant and antimicrobial in food preservation and control of human pathogenic bacterium, Escherichia coli. Another example includes catechins (natural health care prod- uct), which are present in tea and can act as an antioxi- dant agent. However, the oral bioavailability of tea cate- chins is known to be very low probably due to digestive instability and poor intestinal uptake/transport (82,83). Recently, Tang et al. (30) developed self-assembled nano- structures composed of chitosan and an edible polypep- tide, poly(y-glutamic acid), for oral delivery of tea cate- chins, which can be used as food additives for drinks, foods and dietary supplements. Li et al. (13) reported that solid lipid nanoparticles are valuable as an oral delivery carrier to enhance the gastrointestinal absorption and, thus, the bioavailability of quercetin, a natural health care product. There are many other nutraceuticals that are poorly absorbed, such as vitamin K2, vitamin ? and many phytonutrients, especially the polyphenols and ter- penes (e.g. carotenoids, chromanols, limonoids and sapo- nins), where nanotechnology has or can have a great po- tential to enhance the bioavailability and to generate new nutraceutical products.

In this area, different commercial products are cur- rently available. Nanotea, from Shenzhen Become Industry & Trade Co., Ltd., Shenzen, China, is a nano-selenium- -enriched tea, which is claimed to enhance selenium up- take and bioavailability in certain regions of China that lack this mineral, providing health benefits (2). Novasol® from Aquanova® AG (Darmstadt, Germany) is a nano- -micelle based carrier system for use in food and bever- age. Such system can encapsulate a variety of functional food ingredients (e.g. benzoic acid, citric acid, vitamins A and E, soya bean isoflavones, ß-carotene, lutein, ?-3 fatty acids, CoQIO). An increase in bioactive bioavailabil- ity with Novasol® has also been claimed. Nutralease®, developed by the scientists of the Hebrew University of Jerusalem, Israel, is a technology used to improve func- tional food ingredient solubility and bioavailability (84). It is a nanosized self-assembled liquid structure that can carry different nutraceuticals such as coenzyme Q10, lu- tein, lycopene, vitamins, or phytosterols. Applying this technology, Shemen Industries Ltd. (Haifa, Israel) devel- oped a canola active oil fortified with supplements (e.g. phytosterols) (85). In this area, another example of a commercial product is Nutri-Nano(TM) CoQ-10 Solgar (Le- onia, NJ, USA), a commercial product which enhances the absorption of fat-soluble nutrients through their con- version into water-soluble ones.

Cushen et al. (22) reported that the use of nanoemul- sions in food products can be a good alternative to re- duce significantly the quantity of fat needed. The prod- ucts produced using these nanoemulsions are as 'creamy' as conventional food products, without compromising the mouthfeel and flavour, being an alternative to full-fat food products. Cushen et al. (22) suggested that as the size of the droplets in an emulsion is reduced, it is less likely that the emulsion will break down and separate. Therefore, nanoemulsions may reduce the need for cer- tain stabilizers. Such products include low-fat nanostruc- tured mayonnaise, spreads and ice creams (2,86).

Additionaly, the undesirable tastes of functional in- gredients can be minimised in the finished food product if they are carried in nanostructured delivery systems. Some examples of food additives entrapped into nano- structures are the ones that have been used to mask the taste and odour of tuna fish oil added to bread for health benefits and the addition of live probiotic microbes to promote gut functions (2). Wen et al. (87) described food industry applications of liposomes for oral delivery of functional food ingredients such as proteins, enzymes, flavours, and antimicrobial compounds. An example of this application is the entrapment of proteolytic enzymes in liposomes for cheese production (52,88), thus reduc- ing the production time to half without losing flavour and texture properties. The use of zein nanostructures, a major protein found in corn, has also been explored as a vehicle of flavour compounds and essential oils (e.g. thy- mol and carvacrol), because they have the potential to form a tubular network resistant to microorganisms (21, 43). Another nanostructure proposed to encapsulate nu- traceuticals (e.g. vitamins) or to mask disagreeable fla- vour/odour compounds is the ?-lactalbumin nanotube, which can be obtained from milk protein (42,89). Based on the origin of these nanostructures, milk protein in the case of ?-lactalbumin nanotubes, or corn protein in the case of zein nanostructures, can both be regarded as food grade, which makes their common application in the en- trapment of functional food ingredients easier (22).

The enhancement of food flavour through the in- crease on the surface area that hits the taste buds has also been explored. NanoCluster(TM), from RBC Life Sci- ences® Inc. (Irving, TX, USA), is another delivery system for food products. Different products have been devel- oped based on Nanoclusters(TM) system, such as Slim Shake Chocolate, which incorporates silica nanoparticles that are coated with cocoa to enhance the chocolate fla- vour.

Furthermore, as far as sensorial properties are con- cerned, the colour of the food products can be altered by nanoemulsion technology. Astete et al. (90) reported the use of ß-carotene, an oil-soluble pigment compound, to colour water-based foods.

Nanofiltration

Nanofiltration includes several aspects of food tech- nology and it may be divided into several fields of ap- plication: (i) water treatment for reuse, (it) product qual- ity improvement, and (iii) molecule isolation.

The application of nanofiltration in water treatment is linked directly to the worldwide increase of human population, which leads to a rising demand for food supply. The growth of food needs has been pressuring the agriculture sector in order to intensify production through the increasing usage of pesticides, herbicides and fertilizeres. The huge amount of residues produced by these practices is emerging as water contaminants. The same is true when considering animal farms, which have problems related to animal detritus and also to the antibiotic and hormone usage. Nanofiltration has been successfully applied in drinking water treatment plants (91-93). However, not all pesticides presented in the guidelines for drinking water by World Health Organi- zation (94) have been considered in the referred study.

Nanofiltration has been reported to be directly used in combination with powdered activated carbon to re- move effluent organic matter from a municipal waste- water (95). The combined effect revealed to be a promis- ing treatment for high quality water reuse applications, especially for direct injection. Many membrane technolo- gies have been applied to the dairy industry to treat wa- ter for further reuse in its processes (96).

Olive oil production at an industrial level produces large amounts of wastewaters that are considered highly polluting for the enviroment, since the contaminants are highly concentrated (97). A combined process using micro- filtration followed by nanofiltration allowed to recover almost all available polyphenols, which are considered as pollutants, and to use these subproducts for prepar- ing food, cosmetic and pharmaceutical formulations (98).

Because nanofiltration can separate low-molecular mass solutes from mineral salt solutions, the technique is very attractive for industrial applications in the food and pharmaceutical industries. In dairy industry nano- filtration is also used to improve the quality of the prod- ucts (96), and to separate mineral salts from lactose, after removing the proteins by ultrafiltration. Both proteins and lactose can be used as raw materials to prepare a variety of products. Whey is the main by-product obtained from cheese production. Worldwide an increasing amount of whey is industrially processed to produce whey pow- ders and other high-quality, protein-rich products meant for human or animal consumption. However, whey con- tains high salt levels which need to be removed. The only way to achieve this goal is through its concentra- tion and demineralization, which is only possible using nanofiltration. Nanofiltration membranes have a high per- meability for (monovalent) salts (e.g. NaCl or KCl) and a very low permeability for organic compounds (e.g. lac- tose, proteins, and urea). The separation mechanisms are still not clear, and are determined by complex steric and electrical effects or electroneutrality principle such as in Donnan effect (99). The nanofiltration membrane behav- iour is influenced by the feed solution characteristics (100) and by the membrane material properties (101,102).

Similar applications may be found in other by-prod- ucts. Processing xylan-containing raw materials in aque- ous media under suitable operational conditions gener- ates xylooligosaccharides, which have food, medical, and pharmaceutical applications. It was possible to frac- tionate and purify xylooligosaccharides from monosac- charides and other low-molecular mass materials, such as salts, from rice husk xylan using nanofiltration; the concentrate presented a purity of over 91 % and an over- all yield of 71 % (103).

Nanofiltration application in the processing of rose- mary extracts achieved an extract at a concentration that would allow a direct application as preservative and func- tional ingredient in the food, cosmetic, nutraceutical and medical areas (104). The capability of the Duramem® 200 (Evonik MET Ltd., Wembley, UK) nanofiltration mem- brane to separate monophenolic acids from higher mo- lecular mass antioxidant compounds in the extracts was observed with a molecular mass cut-off of 200 Da at a pressure of 20 bar (105). These results open a new field of application on a variety of aromatic plants.

Anthocyanins comprise the largest group of water- -soluble pigments in plants. They are highly appreciated by the food industry for their colouring properties and also because of their potential antioxidant properties (105). Cissé et al. (106) were able to concentrate roselle extract from 4 to 25 g of total soluble solids per 100 g, with 100 % retention of anthocyanins using ten nano- filtration flat-sheet membranes and eight tight ultrafiltra- tion membranes.

Food safety

Quality and safety assurance in food products is of extreme importance since it is a major demand imposed by consumers. The stringent regulations imposed by governmental agencies are used to ensure food product safety and feed hygiene (107).

One of the major problems related to food safety concerns is the detection of microorganisms, which rep- resent a challenge, because the initial levels of contami- nation are generally very low and the food supplies have limited shelf life, requiring an adequate sampling which is usually difficult to achieve (108). Therefore, rapid de- tection and determination of pathogens with a high de- gree of specification and sensitivity are crucial for main- taining a safe and high quality food supply (108).

Methods based on immunosensing or nucleic acid detection are advantageous for both pathogen recogni- tion and for adulterous detection through the food chain. The immunosensing is based on the interaction between antigens presented on the target cells and antibodies im- mobilized on surfaces. The nucleic acid-based sensors detect DNA or RNA originating from target cells by ex- ploring the complementary property of nucleic acid se- quence interaction. Normally, biomolecules are conju- gated to nanomaterials using covalent reactions. The nanodevice approach can use aptamers, single-stranded oligonucleic acid-based binding molecules and antibod- ies that can bind a wide range of targets with high affin- ity and specificity.

Synthetic DNA barcodes, such as nanobarcodes, have been used in the last years to detect the presence of food pathogens by measuring the reaction using a fluorescent probe under ultraviolet light. When the DNA barcodes, present in the films, conjugate with the tagged patho- gens, the derived compound fluoresces, allowing to moni- tor the presence of a defined pathogen (23). The conjuga- tion of biomolecules with nanomaterials is the foundation for nanobiorecognition, which has been explored for the detection of contamination and infectious diseases (109).

Amagliani et al. (110) detected the contamination with Listeria monocytogenes cells of 10 CFU/mL in milk sam- ples using immobilized oligonucleotide probes to mag- netic nanoparticles. However, this detection included a PCR reaction that confirmed a dose-dependent inhibi- tory effect.

Researchers at the University of Pennsylvania (Wal- nut, PA, USA) and Monell Chemical Senses Center (Phil- adelphia, PA, USA) have used nanosized carbon tubes (as transmitter) coated with strands of DNA (as a sen- sor) to create nanosensors with the ability to detect o- dours and tastes (23). Using similar technologies, elec- tronic tongue nanosensors are being developed to detect substances in parts per trillion, which could be used to trigger colour changes in food packages to alert consum- ers when food is spoiled (111).

Boehm et al. (112) have constructed a microfluidic sen- sor for bacterial detection based on measuring the impe- dance in a fixed-volume chamber containing cells func- tionalized with antibodies specific to target cells. These authors were able to discriminate two bacterial strains, E. coli and Moraxella catarrhalis, in a few minutes. The sensor was able to detect 9-105 CFU/mL of E. coli cells.

Other types of technology have been developed in order to achieve the same goal, using various approaches: atomic force microscopy (AFM), which allows both qual- itative and quantitative microorganism determination, using as reference pre-isolated strains of E. coli; the main advantage of this approach is the rapid determination of microorganisms (113); nanofunctionalized gold electrode applied for rapid quantification of bacteria in milk, based on the catalysis of lipid peroxidation on cell membrane of bacteria by nanoporous gold film (detection range 1.1·103-2.5·107 CFU/mL within 1 h) (114); and function- alized single-walled carbon nanotubes with multivalent carbohydrate ligands on their surface, which allowed an efficient capture/detection of pathogenic E. coli cells (115). Several examples concerning this line of research are presented in a review by Heo and Hua (116).

Some of the advantages that have been found with these nanodevices for foodborne pathogen detection are referred to by Yang and Wang (113), Tallury et al. (109) and Magnuson et al. (11) as: (i) rapid and real-time de- tection, (ii) detection sensitivity improvement, (iii) si- multaneous detection of multiple pathogens due to their high selectivity, (iv) low cost, and (p) portability. Con- sumer health can be protected considerably with these devices.

Food packaging

Research on the use of nanocomposites for food pack- aging started in the 1990s. Protective coating and suit- able packaging handling by the food industry have be- come an interesting topic due to their potential capacity to increase the food product shelf life (117). Food pro- cessing and packaging industries spend around 15 % of the total variable costs on packaging materials (118). It is estimated that in the next decade, nanotechnology will have an impact of 25 % on the food packaging market, currently valued at $100 billion (119). Consumers' needs and demands request innovation in food and beverage packaging, which is influenced by changes in global trends, such as life expectancy and the decrease in the number of organizations responsible for food production and distribution (120). The most important factors in terms of food packaging are environmental conditions such as heat, light, moisture, oxygen, pressure, enzymes, spuri- ous odours, microorganisms, insects, dirt and dust parti- cles, gaseous emissions, among others (23,121). All these environmental conditions, when not controlled, can cause food deterioration (23,121).

The use of nanotechnology to improve food packag- ing material may introduce many innovations in the form of barrier and mechanical properties, pathogen de- tection, and smart and active packaging (e.g. containing nanosensors and antimicrobial activators), resulting in the increase of food safety and quality benefits for the food product (23,100,119).

Silver nanoparticles are the most widely used mate- rials for antimicrobial purposes (122,123), due to their capacity to restrain bacterial growth. Motlagh et al. (123) studied the effect that micrometer-sized silver particles had when included in low-density polyethylene (LDPE) packages in terms of microbial and sensory factors of dried barberry. Both microbial growth inhibition (bacte- ria and mould) and sensorial parameters (taste, aroma, appearance, and total acceptance) were significantly in- creased when 1 to 2 % of silver particles were added to LDPE packages.

In order to improve barrier and mechanical proper- ties of plastics, inorganic aluminium platelets have been self-assembled into wagon-wheel (nano-wheel) struc- tures (124). Montmorillonite clay has also been widely used as nanocomponent of polymers such as polyethyl- ene, nylon, polyvinyl chloride, and starch. These silicate nanoparticles are interspersed in polyamide films func- tioning as oxygen and carbon dioxide blockers, promot- ing an increase of the moisture of fresh meat and other food. The final package based on these nanoparticles is considerably lighter, stronger, and more heat-resistant in comparison with others (125).

With the increasing amount of food packaging dis- posal, a new field of research has been developed that considers biodegradable nanocomposite food packages. By pumping carbohydrates and clay fillers through high shear cells, films can be produced with exfoliated clay layers. These are very efficient as moisture barriers and increase the film strength significantly. Starch and chito- san are two of the most studied biodegradable matrices (33). However, efficient mechanical, oxygen and mois- ture protection are not achieved with starch-based poly- mers. Recently, starch/clay nanocomposite films have been obtained by dispersing montmorillonite nanopar- ticles via polymer melt processing (126). Nevertheless, ef- ficient mechanical, oxygen and moisture protection were not achieved with these starch-based polymers. Mechan- ical characterization results demonstrated an increase of modulus and tensile strength, overcoming the problems of starch films (126). Recently, Arora and Padua (127) used montmorillonite and kaolinite clays, which showed good potential as compatible filler-polymer systems. How- ever, new studies need to be conducted in relation to the processing technologies. Carbon nanotubes can also be used in food packaging, improving mechanical proper- ties and having powerful antimicrobial effect (23,120).

Active cellulose-based packaging materials have been prepared through lysozyme binding to paper modified with anionic polyelectrolytes, which was optimized with carboxymethylcellulose or polygalacturonic acid (128). This type of packaging guarantees the lysozyme lytic (and therefore, antimicrobial) activity against the Micro- coccus lysodeikticus cell wall (128).

The addition of nanosensors to food packages can be anticipated in the near future. Nanosensors could be used to detect chemicals, pathogens, and toxins in foods. A colour-changing film that could find its way into food packages is a polymer opal film. It belongs to a class of materials known as photonic crystals (129). These photo- nic crystals could be used to produce unique food pack- aging materials that change colour (23). Photonic crystal fibres were successfully used in apple juice to evaluate sugar composition and can be applied to other food prod- ucts to determine quality parameters (130).

The nanocomposites used for packaging purposes have been studied and reports have suggested an im- provement of properties regarding: durability (131), tem- perature resistance (132), flame resistance (133), barrier properties (134), optical properties (131), processability due to lower viscosity (135), and recycling properties (136). With this it was possible to develop a group of nanoparticle-reinforced polymers that normally contain up to 5 % (by mass) nanoparticles. Recently, new con- cerns related to food packaging have arisen because studies reported on the migration of nanoparticle com- posites used in packaging to food (137), leading to a new field of investigation (119).

Instruments Used for Nanoparticle Characterization

The main interest in developing and using nano- sized materials in food industry is the fact that they can exhibit new and improved physical, chemical and bio- logical properties, phenomena and functionality of food products (138). However, characterizing these materials can be a demanding task. This is also, by itself, an emerg- ing field with old and new characterization techniques being evolved and developed to cope with the challenges imposed by the nanosize (139). In these materials there is a strong relation between the dimension, shape and surface morphology and the exhibited properties, and that fuelled the research activity on the invention of charac- terization techniques of nanomaterials.

Traditionally, in food science, optical microscopes are used for sample observation. Nevertheless, optical aber- rations and the wavelength of visible light limit the ob- servation, with reasonable resolution, to the microscale features, rendering these instruments useless for the ob- servation of nanosized materials and therefore other im- aging techniques have to be used.

One of the most versatile imaging techniques is the scanning electron microscopy (SEM). This instrument uses a high energy beam of electrons to scan the sample sur- face. The interaction of these electrons with the sample atoms generates secondary electrons, scattered electrons and characteristic X-rays that contain information about the sample surface topography and composition, among others. The generated images are black and white and can reveal details down to 1-5 nm in size and achieve magnifications up to 300 000 times. SEM has been used to observe the morphology of polysaccharide nanopar- ticles (140) and to study protein nanospheres for the en- capsulation of essential oils to maximize the antimicro- bial properties of the oils (141).

Generally, when a SEM is associated with an energy dispersive X-ray (EDX) system, it can be used to analyze the surface composition and estimate the element pro- portion. The incident 10-20 keV beam generates X-ray emission from the sample and the energy from these emitted X-rays depends on the atomic number of the surface constituents. With this technique, the composi- tion of nanoparticles near or at their surface can be esti- mated provided they contain some heavy metal ions.

Another technique using a beam of electrons is the transmission electron microscopy (TEM). In this tech- nique the electron beams are transmitted through an ul- trathin sample and interact with the sample structure as they pass through it. A TEM system is capable of resolu- tion of the order of 0.2 nm (142). It has already proved to be a suitable technique to image and characterize var- ious kinds of food nanoparticles, as in milk protein-based nanotubes (42), the shape of serum albumin nanoparti- cles (143), and the fabrication of protein-functionalized microtubes (144). More recently, it has been used to char- acterize the structure of gold nanoparticles deposited on ß-FeOOH nanorods for detecting melamine in aqueous solutions (145).

One of the most suitable techniques for the quanti- tation of surface roughness on the nanometer scale and for visualizing the surface nanostructure is the atomic force microscopy (AFM). This is a nondestructive tech- nique where a sharp tip of a probe (around 10 nm) lo- cated near the end of a cantilever beam is raster scanned across the surface of a specimen using piezoelectric scan- ners. When the tip is brought into the proximity of the sample surface the interaction forces between the tip and the surface change the cantilever deflection. Moni- toring the change in this deflection when the sample surface is scanned provides the information required to create a high resolution image of the scanned area. The AFM can detect different types of forces, depending on the particular situation, including mechanical contact forces, van der Waals forces, capillary forces, magnetic forces, electrostatic forces, etc. It presents several advan- tages in relation to other microscopes, such as: (i) it does not require a vacuum chamber to operate, (ii) it can de- tect atomic-scale features, (iii) it does not need previous sample preparation, maintaining the sample native sta- tus, (iv) it can acquire 2D and limited 3D images, (v) it is possible to observe real-time processes, and (vi) it can be used to manipulate and research the interactions be- tween macromolecules (146). AFM has been applied to investigate fine food molecular structure and molecular interaction on nanoscale. It has been successfully applied in qualitative and quantitative analysis of macromole- cule structure, molecular interaction, and molecular ma- nipulation (147). AFM was also used to obtain the sur- face morphology of chitosan-capped quantum dots and their size distribution, which can be used for the detec- tion of waterborne bacterial pathogens (148).

The chemical behaviour of nanostructures is also a key aspect that needs to be fully characterized and under- stood. Some of this information can be acquired using specific spectroscopy techniques. Of the several types of spectroscopy techniques available, we will describe only two in their most basic configuration that have been broadly used for the characterization of nanomaterials: Raman spectroscopy and ultraviolet-visible spectroscopy.

Raman spectroscopy can be used to study vibra- tional, rotational, and other low frequency modes in a system. To obtain that information a monochromatic la- ser is used to interact with phonons or other types of ex- citations in the sample resulting in inelastic scattering (also called Raman scattering). As a consequence, the energy of laser photons is shifted up or down and the detection of this energy shift provides the information about the phonon modes in the system, which is very specific for the chemical bonds in molecules. It can then be used to fingerprint the molecule present in the nano- material. Most of Raman systems have the detection wave- number range between 500 and 2000 cm-1. The recent development of surface-enhanced Raman spectroscopy, a new variant, where metal nanoparticles are added to the analyte, enhancing the Raman scattering by several orders of magnitude, allows the development of inspec- tion tools for food safety applications (149,150).

Ultraviolet-visible (UV-VIS) spectroscopy also uses propagation of light through the sample to obtain the absorption spectra. A UV-VIS spectrometer uses a light source to create reference and a sample beam, a mono- chromator and a detector. The source beam propagates through the sample and when the wavelength corre- sponds to one energy level, the energy is absorbed. The detector will then record the ratio between the reference and the sample intensity. This technique was used to characterize ZnS quantum dots doped with Mn2+, which can be used for sensing and identification of waterborne bacterial pathogens (148).

The size of nanoparticles can also be assessed using a non-invasive technique called dynamic light scattering (DLS). The constituent particles or molecules of a sus- pension have a Brownian motion imposed by the sol- vent molecules that are also in movement due to their thermal energy. If this suspension is illuminated with a laser, the intensity of the scattered light will fluctuate at a rate that is dependent on the particle size. The analysis of the intensity fluctuations will give the velocity of the Brownian motion and the particle size (151,152).

Another well-established technique for nanoparticle characterization is X-ray diffraction (XRD). This tech- nique is broadly used in materials science to retrieve in- formation about the crystalline structure, quality and grain size dimension. In this technique, a beam of X-rays is steered to the sample and its crystalline structure will diffract the beam of light into specific directions. From the angles and intensities of these diffracted beams, the mean position of the atoms in the crystal, their chemical bonds and also their disorder can be determined. This technique was used to characterize MtCu2+/LDPE nano- composites, which have a potential use in food packag- ing (153).

Nanotechnology in Food Stability and Consumer Safety

The application of nanotechnology in the area of food science and technology is appealing because of all the benefits and new openings it promises, namely the stability of the new products. In the last few years, many researchers have demonstrated that encapsulation of bio- active compounds in colloidal carrier systems is realistic and can overcome issues associated with slow and low uptake and thermodynamic instability (25). Graveland- -Bikker and De Kruif (42) described the stability of the ?-lactalbumin nanotubes under a variety of conditions. The application of nanotechnology to improve food pack- aging material may introduce many innovations in the form of barrier and mechanical properties, detection of potential pathogens, and smart and active packaging with food safety and quality benefits (23).

The ultrasmall size of nanostructures associated with the chemical composition and surface structure provides not only unique features and huge potential applications but also potential toxicological properties (154). Although the potential benefits of nanotechnology in several areas are well emphasized, it adversely affects the safety as- pects of its application in food production, and the in- corporation of manufactured nanostructures into food products is not well known. Therefore, it is imperative that regulatory frameworks for nanotechnologies ap- plied to food are defined based on scientific arguments, mainly due to the fast emergence of nanotechnology ap- plications in the food area and the uncertainty about its negative impacts on biological systems (2,39,154-156). In a recent publication, Bouwmeester et al. (39) have of- fered an updated overview concerning the scientific is- sues that need to improve the existing risk assessment methodology, good governance and regulatory frame- work of the application of nanotechnology in the food sector. In another publication, Chau et al. (67) suggest different criteria and recommendations that should be considered for the development of standards, definition, control measures, and regulations for nanofood prod- ucts. Abbott and Maynard (157) point out the real chal- lenges that need to be addressed when evaluating the unique characteristics of nanostructures present in the nanofoods. These authors suggest that in order to evalu- ate the real effect of the nanostructure, basic characteris- tics of nanoscale materials (e.g. particle number mass size distribution, charge) and different exposure assess- ments to the nanomaterials (e.g. occupational, consumer and environmental) may have to be considered, which are not suitable for measuring functional or structural properties when food is altered during digestion and the function may change during this process. As the appli- cation of nanostructures in consumed products is recent, the literature on its potential toxicity is quickly increas- ing (2,39,67). However, toxicity results are often obtained for individual nanostructure type and size. When con- sidering only the nanostructure size, the interaction with the biological system may alter significantly with this unique property and affect both toxicokinetic and toxi- codynamic applications. In the use of novel nanofood products, the particle size should be considered as an explicit criterion to trigger a reassessment process. The consumer safety implications from nanotechnology ap- plications in food are related to the physicochemical na- ture of the developed nanostructure (i.e. chemical compo- sition, size, particle form, surface functionalization and charge, porosity and aggregation tendency) and the like- lihood and extent of exposure through consumption of nanofoods (2,16,158). According to Dreher (159), several aspects may be considered in order to evaluate the nano- toxicity: (i) exposure assessment of nanostructures, (it) toxicology of manufactured nanoparticles, (Hi) possibil- ity to use existing toxicological databases of nanostruc- tures, (iv) environmental and biological fate, transport, and persistence of manufactured nanoparticles, and (v) transformation and recyclability, and overall sustainabil- ity of nanostructures. Although a nanostructure might cause harmful effects beyond expectations, some studies have also demonstrated that the development and pro- cessing procedure may not necessarily produce products with such effect (160).

Regarding the application of nanotechnology in food packaging material, the main risk of consumer exposure is through potential migration of nanostructures into food and beverages. Up to date, there is a lack of infor- mation on the extent of such migration. Avella et al. (126) reported that the migration of metals would be minimal. Another way of exposure to nanostructures can occur through the ingestion of food matrix which contains them (engineered organic or inorganic) by de- sign (22).

To conclude, in food industry, despite the amount of regulatory framework to control the potential risks, most current frameworks are not designed to cope explicitly with the new challenges created by the advent of nano- technology (57). For nanoproducts, there are no special regulations that go beyond the general food law pre- scriptions. In the EU the Regulation (EC) No 178/2002 is laying down the general principles and requirements of food law, established by the European Food Safety Au- thority and describes procedures in matters of food safe- ty (161). Several organizations are already involved in nanotechnology research, regulations, and guidelines, in which risk assessors work alongside toxicologists and food technologists among others (22,67,162). Regarding the impact of nanotechnology on food products and pack- aging materials, deficiencies in regulations were already detected by the Institute of Food Science and Technol- ogy in 2006 (163). However, nanostructures can be natu- rally present in food products, e.g. milk (milk proteins, casein), with a significant difference between such 'natu- ral' nanostructures and many engineered nanostructures in their totally different biological degradation behav- iour (158).

Conclusions

With regard to the application of nanotechnology in food industry, promising results have already been de- veloped in several areas including food manufacturing, packaging, safety and storage. The incorporation of nano- structures into final food products will improve different properties: protection and stability of functional food in- gredient, bioavailability and shelf-life improvement, de- velopment of new consumer sensation and efficient de- livery of bioactive substances into biological systems.

The most widely applied nanocarriers consist of nat- ural molecules, such as lipids, proteins or polysaccharides. The reason for their wide application is based mainly on the excellent biocompatibility presented by such carriers. Nevertheless, these vehicles are also able to overcome the harsh conditions that food products are submitted to during digestion allowing the release of intact functional ingredients in desired sites.

Recent research has taken place in the area of nano- filtration, with exciting results in the reuse of wastewater and in the recovery of compounds of interest in several areas of application. However, due to its novelty, there are still lots of uncertainties that need to be explained and attended so it can be more widely applied.

The application of nanosensors in food products is an emerging area of utility, and it is very relevant when considering the consumer protection and safety. The inclusion of biosensors into different packaging material may increase significantly the consumer protection against foodborne pathogens, toxins and adulteration, mainly because it can result in quick and visual detection. A wider application of such intelligent packaging may in a long term save a large number of lives. However, con- cerns related to the security of the nanoparticles used for food packaging (e.g. stability, toxicity, etc.) can limit their wider application because their properties are not well studied.

Nowadays, more studies are requested in several ar- eas considering the emerging applications of nanotech- nology in the food sector, nanotoxicity, regulation and potential risk evaluation and benefits to sustain its de- velopment. For regulatory consideration of a nanofood product, it is necessary to establish the nanotechnology product statutory classification.

Acknowledgements

This research was supported by the Portuguese Found- ation for Science and Technology, Portugal (FCT) through the projects PTDC/AGR-ALI/69516/2006, PTDC/AGR- -ALI/117341/2010 and strategic project PEst-OE/EQB/ LA0023/2011.

References

References

1. C. Chawengkijwanich, Y. Hayata, Development of TiOo powder-coated food packaging film and its ability to in- activate Escherichia coli in vitro and in actual tests, Int. ]. Food Microbiol. 123 (2008) 288-292.

2. Q. Chaudhry, M. Scotter, J. Blackburn, B. Ross, A. Boxall, L. Castle et al., Applications and implications of nano- technologies for the food sector, Food Addit. Contain. A, 25 (2008) 241-258.

3. A. Alemdar, M. Sain, Isolation and characterization of nano- fibers from agricultural residues - wheat straw and soy hulls, Bioresour. Technol. 99 (2008) 1664-1671.

4. M.A. Augustin, P. Sanguansri, Nanostructured materials in the food industry, Adv. Food Nutr. Res. 58 (2009) 183-213.

5. K. Buonasera, G. D'Orazio, S. Fanali, P. Dugo, L. Mon- dello, Separation of organophosphorus pesticides by using nano-liquid chromatography, /. Chromatogr. A, 1216 (2009) 3970-3976.

6. S. Neethirajan, D.S. layas, Nanotechnology for the food and bioprocessing industries, Food Bioprocess Technol. 4 (2010) 39^7.

7. T.V. Duncan, Applications of nanotechnology in food pack- aging and food safety: Barrier materials, antimicrobials and sensors, J. Colloid Interface Sei. 363 (2011) 1-24.

8. DJ. McClements, H. Xiao, Potential biological fate of in- gested nanoemulsions: Influence of particle characteristics, Food Fund. 3 (2012) 202-220.

9. J. Dunn, A mini revolution (http://www.foodmanufacture.co. uk/news/).

10. H.D. Chen, J.C. Weiss, F. Shahidi, Nanotechnology in nu- traceuticals and functional foods, Food Technol. 60 (2006) 30-36.

11. B.A. Magnuson, T.A. lonaitis, J.W. Card, A brief review of the occurrence, use, and safety of food-related nanomater- ials, /. Food Sei. 76 (2011) 126-133.

12. G. Sharma, J.L. Italia, K. Sonaje, K. Tikoo, M.N.V. Ravi Kumar, Biodegradable in situ gelling system for subcutane- ous administration of ellagic acid and ellagic acid loaded nanoparticles: Evaluation of their antioxidant potential against cyclosporine induced nephrotoxicity in rats, /. Con- troll. Release, 118 (2007) 27-37.

13. H. Li, X. Zhao, Y. Ma, G. Zhai, L. Li, H. Lou, Enhancement of gastrointestinal absorption of quercetin by solid lipid nanoparticles, /. Controll. Release, 346 (2008) 160-168.

14. Y.C. Chen, S.H. Yu, G.J. Tsai, D.W. Tang, F.L. Mi, Y.P. Peng, Novel technology for the preparation of self-assembled catechin/gelatin nanoparticles and their characterization, J. Agrie. Food Chem. 58 (2010) 6728-6734.

15. A.M. Augustin, Y. Hemar, Nano- and micro-structured as- semblies for encapsulation of food ingredients, Chem. Soc. Rev. 38 (2009) 902-912.

16. G. Oberdörster, ?. Oberdörster, J. Oberdörster, Nanotoxi- cology: An emerging discipline evolving from studies of ultrafine particles, Environ. Health Perspect. 113 (2005) 823- 839.

17. S.E. McNeil, Nanotechnology for the biologist, /. Leukoc. Biol. 78 (2005 ) 585-594.

18. Q.R. Huang, H.L. Yu, Q.M. Ru, Bioavailability and deliv- ery of nutraceuticals using nanotechnology, /. Food Sei. 75 (2010) 50-57.

19. D. Horák, M. Babic, H. Macková, M.J. Benes, Preparation and properties of magnetic nano- and microsized particles for biological and environmental separations, /. Sep. Sei. 30 (2007) 1751-1772.

20. G.A. Silva, Neuroscience nanotechnology: Progress, oppor- tunities and challenges, Nat. Rev. Neurosci. 7 (2006) 65-74.

21. N. Sozer, J.L. Kokini, Nanotechnology and its applications in the food sector, Trends Biotechnol. 27 (2009) 82-89.

22. M. Cushen, J. Kerry, M. Morris, M. Cruz-Romero, E. Cum- mins, Nanotechnologies in the food industry - Recent de- velopments, risks and regulation, Trends Food Sei. Technol. 24 (2012) 30^6.

23. A.L. Brody, B. Bugusu, J.H. Han, C. Koelsch Sand, T.H. McHugh, Innovative food packaging solutions, /. Food Sei. 73 (2008) R107-R116.

24. T. Shibata, Method for producing green tea in microfine powder. US patent US6416803B1 (2002).

25. J. Weiss, ?. A. Decker, D.J. McClements, K. Kristbergsson, T. Helgason, T. Awad, Solid lipid nanoparticles as delivery systems for bioactive food components, Food Biophysics, 3 (2008) 146-154.

26. L. Chen, M. Subirade, Chitosan/ß-lactoglobulin core-shell nanoparticles as nutraceutical carriers, Biomaterials, 26 (2005) 6041-6053.

27. ?. Shimoni: Nanotechnology for Foods: Delivery Systems. In: Global Issues in Food Science and Technology/, G. Barbosa- -Cánovas, A. Mortimer, D. Lineback, W. Spiess, K. Buckle, R Colonna (Eds.), Academic Press, San Diego, CA, USA (2009) pp. 411^24.

28. M. Fathi, J. Varshosaz, M. Mohebbi, F Shahidi, Hespere- tin-loaded solid lipid nanoparticles and nanostructure lipid carriers for food fortification: Preparation, characterization, and modeling, Food Bioprocess. Technol. 6 (2013) 1464-1475.

29. B. Hu, C. Pan, Y. Sun, Z. Hou, H. Ye, X. Zeng, Optimiza- tion of fabrication parameters to produce chitosan-tripoly- phosphate nanoparticles for delivery of tea catechins. /. Agrie. Food Chem. 56 (2008 ) 7451-7458.

30. D.W. Tang, S.H. Yu, Y.C. Ho, B.Q. Huang, G.J. Tsai, H.Y. Hsieh et al., Characterization of tea catechins-loaded nano- particles prepared from chitosan and an edible polypep- tide, Food Hydrocoll. 30 (2013) 33^1.

31. A. Ghosh, A.K. Mandai, S. Sarkar, S. Panda, Ν. Das, Nano- encapsulation of quercetin enhances its dietary efficacy in combating arsenic-induced oxidative damage in liver and brain of rats, Life Sei. 84 (2009) 75-80.

32. A. Shpigelman, G. Israeli, Y.D. Livney, Thermally-induced protein-polyphenol co-assemblies: ß-lactoglobulin-based nanocomplexes as protective nanovehicles for EGCG, Food Hydrocoll. 24 (2010) 735-743.

33. J. Weiss, P. Takhistov, D.J. McClements, Functional mater- ials in food nanotechnology, J. Food Sei. 71 (2006) 107-116.

34. D.V. Ratnam, D.D. Ankola, V. Bhardwaj, D.K. Sahana, M.N. Kumar, Role of antioxidants in prophylaxis and therapy: A pharmaceutical perspective, /. Controll. Release, 113 (2006) 189-207.

35. V.P. Torchilin, Targeted pharmaceutical nanocarriers for can- cer therapy and imaging, AAPS ]. 9 (2007) E128-E147.

36. P. Anand, H.B. Nair, B. Sung, A.B. Kunnumakkara, V.R. Yadav, R.R. Tekmal, B.B. Aggarwal, Design of curcumin- -loaded PLGA nanoparticles formulation with enhanced cellular uptake, and increased bioactivity in vitro and su- perior bioavailability in vivo, Biochem. Pharmacol. 79 (2010) 330-338.

37. K.P. Lisha, T. Pradeep, Enhanced visual detection of pes- ticides using gold nanoparticles, /. Environ. Sei. Health B, 44 (2009) 697-705.

38. L. Kiaune, N. Singhasemanon: Pesticidal Copper (I) Oxide: Environmental Fate and Aquatic Toxicity. In: Reviews of Environmental Contamination and Toxicology, Vol. 213, D.M. Whitacre (Ed.), Springer, Cham, Switzerland (2011).

39. H. Bouwmeester, S. Dekkers, M.Y. Noordam, W.I. Hägens, A.S. Bulder, C. de Heer et al., Review of health safety as- pects of nanotechnologies in food production, Regul. Toxi- col. Pharmacol. 53 (2009) 52-62.

40. D.M. Luykx, R. J. Peters, S.M. van Ruth, H. Bouwmeester, A review of analytical methods for the identification and characterization of nano delivery systems in food, /. Agrie. Food Chem. 56 (2008) 8231-8247.

41. M. García, T. Forbe, E. Gonzalez, Potential applications of nanotechnology in the agro-food sector, Ciênc. Tecnol. Ali- ment. 30 (2010) 573-581.

42. J.F. Graveland-Bikker, C.G. De Kruif, Unique milk protein based nanotubes: Food and nanotechnology meet, Trends Food Sei. Technol. 17 (2006) 196-203.

43. Y. Wu, Y. Luo, Q. Wang, Antioxidant and antimicrobial pro- perties of essential oils encapsulated in zein nanoparticles prepared by liquid-liquid dispersion method, LWT - Food Sei. Technol. 48 (2012) 283-290.

44. L.Y. Chen, G.E. Remondetto, M. Subirade, Food protein- -based materials as nutraceutical delivery systems, Trends Food Sei. Technol. 17 (2006) 272-283.

45. K. Letchford, H. Burt, A review of the formation and classi- fication of amphiphilic block copolymer nanoparticulate structures: Micelles, nanospheres, nanocapsules and poly- mersomes, Eur. ]. Pharm. Biopharm. 65 (2007) 259-269.

46. J. Flanagan, H. Singh, Microemulsions: A potential deliv- ery system for bioactives in food, Crit. Rev. Food Sei. Nutr. 46 (2006) 221-237.

47. H. Chen, C. Khemtong, X. Yang, X. Chang, J. Gao, Nano- nization strategies for poorly water-soluble drugs, Drug Discov. Today, 16 (2011) 354-360.

48. M.M. Fryd, T.G. Mason, Advanced nanoemulsions, Annu. Rev. Phys. Chem. 63 (2012) 493-518.

49. W. Mehnert, K. Mader, Solid lipid nanoparticles: Produc- tion, characterization and applications, Adv. Drug Deliv. Rev. 47 (2001) 165-196.

50. P.M. Bummer, Physical chemical considerations of lipid- -based oral drug delivery-solid lipid nanoparticles, Crit. Rev. Titer. Drug Carrier Syst. 21 (2004) 1-20.

51. R.H. Müller, R. Shegokar, C.M. Keck, 20 years of lipid nano- particles (SLN and NLC): Present state of development and industrial applications, Curr. Drug Discov. Technol. 8 (2011) 207-227.

52. M.R. Mozafari, J. Flanagan, L. Matia-Merino, A. Awati, A. Omri, Z.E. Suntres, H. Singh, Recent trends in the lipid- -based nanoencapsulation of antioxidants and their role in foods, /. Sei. Food Agrie. 86 (2006) 2038-2045.

53. M.R. Mozafari, C. Johnson, S. Hatziantoniou, C. Demetzos, Nanoliposomes and their applications in food nanotechnol- ogy, /. Liposome Res. 18 (2008) 309-327.

54. T.M. Taylor, P.M. Davidson, B.D. Bruce, J. Weiss, Liposo- mal nanocapsules in food science and agriculture, Crit. Rev. Food Sei. Nutr. 45 (2005 ) 587-605.

55. A. Jesorka, O. Orwar, Liposomes: Technologies and analy- tical applications, Annu. Rev. Anal. Chem. 1 (2008) 801-832.

56. G.B. Patel, B.J. Agnew, L. Deschatelets, L.P. Fleming, G.D. Sprott, In vitro assessment of archaeosome stability for de- veloping oral delivery systems, Int. ]. Pharm. 194 (2000) 39^9.

57. A. Omri, B.J. Agnew, G.B. Patel, Short-term repeated-dose toxicity profile of archaeosomes administered to mice via intravenous and oral routes, Int. ]. Toxicol. 22 (2003) 9-23.

58. L. Zarif, Nanocochleate cylinders for oral & parenteral delivery of drugs, /. Liposome Res. 13 (2003) 109-110.

59. R.H. Müller, R.D. Petersen, A. Hommoss, J. Pardeike, Nano- structured lipid carriers (NLC) in cosmetic dermal prod- ucts, Adv. Drug Deliver. Rev. 59 (2007) 522-530.

60. A. Hentschel, S. Gramdorf, R.H. Muller, T. Kurz, ß-Caro- tene-loaded nanostructured lipid carriers, /. Food Sei. 73 (2008) N1-N6.

61. N. Garti, A. Aserin: Microemulsions for Solubilization and Delivery of Nutraceuticals and Drugs. In: Microencapsula- tion: Methods and Industrial Applications, Drugs and the Phar- maceutical Sciences, Vol. 158, S. Benita (Ed.), CRC Press, Tay- lor and Francis Group LLC, Boca Raton, FL, USA (2005) pp. 345^28.

62. M.J. Shin, J.H. Lee, Y. Jang, Y.C. Lee-Kim, E. Park, K.M. Kim et al., Micellar phytosterols effectively reduce cholesterol absorption at low doses, Ann. Nutr. Metab. 49 (2005) 346-351.

63. S. Kang, M. Pinault, L.D. Pfefferle, M. Elimelech, Single- -walled carbon nanotubes exhibit strong antimicrobial ac- tivity, Langmuir, 23 (2007) 8670-8673.

64. H.S. Yang, Y.F. Wang, S.J. Lai, H.J. An, Y.F. Li, F.S. Chen, Application of atomic force microscopy as a nanotechnol- ogy tool in food science, /. Food Sei. 72 (2007) R65-R75.

65. W.C.W. Chan, Bionanotechnology progress and advances, Biol. Blood Marrow Transplant. 12 (2006) 87-91.

66. C.I. Moraru, C.P. Panchapakesan, Q. Huang, P. Takhistov, S. Liu, Nanotechnology: A new frontier in food science, Food Technol. 57 (2003 ) 24-29.

67. C.F. Chau, S.H. Wu, G.C. Yen, The development of regu- lations for food nanotechnology, Trends Food Sei. Technol. 18 (2007) 269-280.

68. P. Zimet, D. Rosenberg, Y.D. Livney, Re-assembled casein micelles and casein nanoparticles as nano-vehicles for co-3 polyunsaturated fatty acids, Food Hydrocoll. 25 (2011) 1270- 1276.

69. R. Elliott, T.J. Ong, Science, medicine, and the future - Nu- tritional genomics, BM], 324 (2002) 1438-1442.

70. S.M. Groziak, G.D. Miller, Natural bioactive substances in milk and colostrum: Effects on the arterial blood pressure system, Br. ]. Nutr. (Suppl.l), 84 (2000) 119-125.

71. J. Rao, D.V. McClements, Food-grade microemulsions and nanoemulsions: Role of oil phase composition on forma- tion and stability, Food Hydrocoll. 29 (2012) 326-334.

72. C. Medina, M.J. Santos-Martinez, A. Radomski, O.I. Corri- gan, M.W. Radomski, Nanoparticles: Pharmacological and toxicological significance, Br. ]. Pharmacol. 150 (2007) 552- 558.

73. S. Leclercq, K.R. Harlander, G.A. Reineccius, Formation and characterization of microcapsules by complex coacervation with liquid or solid aroma cores. Flavour Fragr. ]. 24 (2009) 17-24.

74. W. Krasaekoopt, B. Bhandari, H.C. Deeth, Evaluation of en- capsulation techniques of probiotics for yoghurt, Int. Dairy J. 13 (2003) 3-13.

75. P.L. Beyer, T.E. Jach, D.L. Zak, R.A. Jerome, F.P. Debrincat, Edible products having inorganic coatings. US patent 5741505 (1996).

76. Q. Chaudhry, K. Groves: Nanotechnology Applications for Food Ingredients, Additives and Supplements. In: Nanotech- nologies in Food, Q. Chaudhry, L. Castle, R. Watkins (Eds.), RSC Publishing, Cambridge, UK (2010) pp. 69-85.

77. C.J. Lavie, R.V. Milani, M.R. Mehra, H.O. Ventura, Omega- -3 polyunsaturated fatty acids and cardiovascular diseases, J. Am. Coll. Cardiol. 54 (2009) 585-594.

78. C.H.S. Ruxton, S.C. Reed, M.J.A. Simpson, K.J. Millington, The health benefits of omega-3 polyunsaturated fatty acids: A review of the evidence, /. Hum. Nutr. Dietet. 17 (2004) 449^59.

79. B. Maherani, E. Arab-Tehrany, A. Kheirolomoom, F. Cley- mand, M. Linder, Influence of lipid composition on physi- cochemical properties of nanoliposomes encapsulating nat- ural dipeptide antioxidant L-carnosine, Food Chem. 134 (2012) 632-640.

80. J. Limpens, F.H. Schröder, C.M. de Ridder, C.A. Bolder, M.F. Wildhagen, U.C. Obermiiller-Jevic et ah, Combined lyco- pene and vitamin ? treatment suppresses the growth of PC-346C human prostate cancer cells in nude mice, /. Nutr. 136 (2006)1287-1293.

81. D.D. Ankola, B. Viswanad, V. Bhardwaj, P. Ramarao, M.N. Kumar, Development of potent oral nanoparticulate for- mulation of coenzyme Q10 for treatment of hypertension: Can the simple nutritional supplements be used as first line therapeutic agents for prophylaxis/therapy?, Eur. ]. Pharm. Biopharm. 67 (2007) 361-369.

82. L. Zhang, Y. Zheng, M.S.S. Chow, Z. Zuo, Investigation of intestinal absorption and disposition of green tea catechins by Caco-2 monolayer model, Int. J. Pharm. 287 (2004) 1-12.

83. R.J. Green, A.S. Murphy, B. Schulz, B.A. Watkins, M.G. Fer- ruzzi, Common tea formulations modulate in vitro diges- tive recovery of green tea catechins, Mol. Nutr. Food Res. 51 (2007) 1152-1162.

84. J. Wolfe, Safer and guilt-free nano foods (2005) (http://www. forbes.com/2005/08/09/nanotechnology-kraft-hershey-cz_jw_0810 soapbox_int_print.html).

85. B. Bugusu, U.V. Lay Ma, J.O. Floros: Products and Their Commercialization. In: Nanotechnology in the Agri-Food Sec- tor - Implications for the Future, L.J. Frewer, W. Norde, A. Fisher, F. Kampers (Eds.), Wiley-VCH Verlag Gmbh, Wein- heim, Germany (2011) pp. 149-170.

86. J. Hall, How super-cows and nanotechnology will make ice cream healthy (http://www.telegraph.co.uk/finance/2920953/ How-super-cows-and-nanotechnology-will-make-ice-cream-healthy. html).

87. H.W. Wen, T.R. Decory, W. Borejsza-Wysocki, R.A. Durst, Investigation of NeutrAvidin-tagged liposomal nanovesicles as universal detection reagents for bioanalytical assays, Ta- lanta, 68 (2006) 1264-1272.

88. P. Walde, S. Ichikawa, Enzymes inside lipid vesicles: Prep- aration, reactivity and applications, Biomol. Eng. 18 (2001) 143-177.

89. P.R. Srinivas, M. Philbert, T.Q. Vu, Q. Huang, J.L. Kokini, E. Saos et ah, Nanotechnology research: Applications in nu- tritional sciences, /. Nutr. 140 (2010) 119-124.

90. C.E. Astete, C.M. Sabliov, F. Watanabe, A. Biris, Ca2+ cross- -linked alginic acid nanoparticles for solubilization of li- pophilic natural colorants, /. Agrie. Food Chem. 57 (2009) 7505-7512.

91. J.A.M.H. Hofman, E.F. Beerendonk, H.C. Folmer, J.C. Kruit- hof, Removal of pesticides and othermicropollutants with cellulose acetate, polyamide and ultra-low pressure reverse osmosis membranes, Desalination, 113 (1997) 209-214.

92. P.A.C. Bonne, E.F. Beerendonk, J.P. van der Hoek, J.A.M.H. Hofman, Retention of herbicides and pesticides in relation to aging RO membranes, Desalination, 132 (2000) 189-193.

93. B. Cyna, G. Chagneaub, G. Bablon, Ν. Tanghe, Two years of nanofiltration at the Mery-sur-Oise plant, France, Desa- lination, 147 (2002) 69-75.

94. Guidelines for Drinking-Water Quality, World Health Orga- nization, Geneva, Switzerland (2011) (http:llwww.who.int/water_ sanitation_health/publications/2011/dwq_guidelines/en/).

95. C. Kazner, T. Wintgens, T. Melin, S. Baghoth, S. Sharma, G. Amy, Comparing the effluent organic matter removal of direct NF and powdered activated carbon/NF as high qual- ity pretreatment options for artificial groundwater recharge, Water Sei. Technol. 57 (2008) 821-827.

96. B. Cuartas-Uribe, M.I. Alcaina-Miranda, E. Soriano-Costa, A. Bes-Pia, Comparison of the behavior of two nanofiltra- tion membranes for sweet whey demineralization, /. Dairy Sei. 90 (2007) 1094-1101.

97. ?. Fezzani, R.B. Cheikh, Thermophilic anaerobic codiges- tion on olive mill wastewater with olive mill solid wastes in a tubular digester, Chem. Eng. ]. 132 (2007) 195-203.

98. E. Garcia-Castello, A. Cassano, A. Criscuoli, C. Conidi, E. Drioli, Recovery and concentration of polyphenols from olive mil wastewaters by integrated membrane system, Water Res. 44 (2010) 3883-3892.

99. X. Xu, H.G. Spencer, Transport of electrolytes through a weak acid nanofiltration membrane: Effects of flux and crossflow velocity interpreted using a fine-porous mem- brane model, Desalination, 113 (1997) 85-93.

100. A.W. Mohammad, M.S. Takriff, Predicting flux and rejec- tion of multicomponent salts mixture in nanofiltration membranes, Desalination, 157 (2003) 105-111.

101. M. Minhalma, V. Magueijo, D.P. Queiroz, M.N. Pinho, Op- timization of "Serpa" cheese whey nanofiltration for efflu- ent minimization and by-products recovery, /. Environ. Manag. 82 (2007) 200-206.

102. Y. Li, A. Shahbazi, Κ. Williams, C. Wan, Separate and concentrate lactic acid using combination of nanofiltration and reverse osmosis membranes, Appl. Biochem. Biotechnol. 147 (2008) 1-9.

103. R. Vegas, A. Moure, H. Domínguez, J.C. Parajó, J.R. Alva- rez, S. Luque, Evaluation of ultra- and nanofiltration for refining soluble products from rice husk xylan, Bioresour. Technol 99 (2008) 5341-5351.

104. D. Peshev, L.G. Peeva, G. Peev, I.I.R. Baptista, A.T. Boam, Application of organic solvent nanofiltration for concen- tration of antioxidant extracts of rosemary (Rosmarinus officiallis L.), Chem. Eng. Res. Design, 89 (2011) 318-327.

105. J. Sun, J.Y. Yao, S.X. Huang, X. Long, J.B. Wang, E. Garcia- -Garcia, Antioxidant activity of polyphenol and anthocya- nin extracts from fruits of Kadsura coccínea (Lern.) A.C. Smith, Food Chem. 117 (2009) 276-281.

106. M. Cissé, F. Vaillant, D. Pallet, M. Dornier, Selecting ultra- filtration and nanofiltration membranes to concentrate antho- cyanins from roselle extract (Hibiscus sabdariffa L.), Food Res. Int. 44 (2011) 2607-2614.

107. S. Neethirajan, D.S. Jayas, Nanotechnology for the food and bioprocessing industries, Food Bioprocess. Technol. 4 (2011) 39^7.

108. S.E. Hanna, C.J. Connor, H.H. Wang, Real-time polyme- rase chain reaction for the food microbiologist: Technolo- gies, applications, and limitations, /. Food Sei. 70 (2005) R49-R53.

109. P. Tallury, A. Malhotra, M.L. Byrne, S. Santra, Nanobio- imaging and sensing of infectious diseases, Adv. Drug Deliv. Rev. 62 (2010 ) 424-437.

110. G. Amagliani, E. Omiccioli, A. del Campo, I.J. Bruce, G. Brandi, M. Magnani, Development of a magnetic capture hybridization-PCR assay for Listeria monocytogenes direct detection in milk samples, /. Appl. Microbiol. 100 (2006) 375-383.

111. M. Scampicchio, D. Ballabio, A. Arecchi, S.M. Cosío, S. Man- nino, Amperometric electronic tongue for food analysis, Microchim. Acta, 163 (2008) 11-21.

112. D.A. Boehm, P.A. Gottlieb, S.Z. Hu, On-chip microfluidic biosensor for bacterial detection and identification, Sen- sors Actuat. B, 126 (2007) 508-514.

113. H. Yang, Y. Wang, Application of atomic force microscopy on rapid determination of microorganisms for food safety, J. Food Sei. 73 (2008) N44-N50.

114. X.Y. Wang, F. Gu, F. Yin,Y.F. Tu, Rapid detection of micro- organisms in milk using an in-situ prepared nano-func- tionalized gold electrode, Chin. ]. Anal. Chem. 40 (2012) 657-662.

115. L. Gu, P.G. Luo, H. Wang, M.J. Meziani, Y. Lin, L.M. Veca et al., Single-walled carbon nanotube as a unique scaffold for the multivalent display of sugars, Biomacromolecules, 9 (2008) 2408-2418.

116. J. Heo, S.Z. Hua, An overview of recent strategies in path- ogen sensing, Sensors, 9 (2009) 4483^502.

117. A. Sorrentino, G. Gorrasi, V. Vittoria, Potential perspec- tives of bio-nanocomposites for food packaging applica- tions, Trends Food Sei. Technol. 18 (2007) 84-95.

118. R. Esse: Flexible Packaging End-Use Market Analysis, Flex- ible Packaging Association, Linthicum, MD, USA (2002).

119. W. Han, Y.J. Yu, N.T. Li, L.B. Wang, Application and safe- ty assessment for nano-composite materials in food pack- aging, Chin. Sei. Bull. 56 (2011) 1216-1225.

120. J.B. Lord: The Food Industry in the United States. In: Developing New Food Products for a Changing Marketplace, A.L. Brody, J.B. Lord (Eds.), CRS Press, Boca Raton, FL, USA (2008) pp. 1-23.

121. L. Rashidi, K. Khosravi-Darani, The applications of nano- technology in food industry, Crit. Rev. Food Sei. Nutr. 51 (2011) 723-730.

122. S.K. Jun, K. Eunye, N.Y. Kyeong, K. Jong-Ho, J.P. Sung, J.L. Hu et al., Antimicrobial effects of silver nanoparticles, Nanomed. Nanotechnol. 3 (2007) 95-101.

123. N.V. Motlagh, M.T.H. Mosavian, S.A. Mortazavi, A. Tami- zi, Beneficial effects of polyethylene packages containing micrometer-sized silver particles on the quality and shelf life of dried barberry (Berberís vulgaris), ]. Food Sei. 77 (2012) E2-E9.

124. D. Mössinger, J. Hornung, S. Lei, S. De Feyter, S. Höger, Molecularly defined shape-persistent 2D oligomers: The covalent-template approach to molecular spoked wheels, Angew. Chemie Int. Ed. 46 (2007) 6802-6806.

125. T. Lan, G. Bayer: Introduction to Flame Retardancy of Poly- mer-Clay Nanocomposites. In: Thermally Stable and Flame Retardant Polymer Nanocomposites, V. Mittal (Ed.), Cam- bridge University Press, Cambridge, UK (2011) pp. 161- 185.

126. M. Avella, J.J. De Vlieger, M.E. Errico, S. Fischer, P. Vacca, M.G. Volpe, Biodegradable starch/clay nanocomposite films for food packaging applications, Food Chem. 93 (2005) 467- 474.

127. A. Arora, G.W. Padua, Review: Nanocomposites in food packaging, /. Food Sei. 75 (2010) R43-R49.

128. E. Mascheroni, G. Capretti, M. Marengo, S. Iametti, L. Mora, L. Piergiovanni, F. Bonomi, Modification of cellulose- -based packaging materials for enzyme immobilization, Packag. Technol. Sei. 23 (2010) 47-57.

129. O.L.J. Pursiainen, J.J. Baumberg, H. Winkler, ?. Viel, P. Spahn, T. Ruhl, Nanoparticle-tuned structural color from polymer opals, Optics Express, 15 (2007) 9553-9561.

130. A.V. Malinin, A.A. Zanishevskaja, V.V. Tuchin, Y.S. Skibi- na, I.Y. Silokhin: Photonic Crystal Fibers for Food Quality Analysis. In: Biophotonics: Photonic Solutions for Better Health Care, III, Proceedings of SPIE, Vol. 8427, J. Popp, W. Drexler, V.V. Tu chin, D.L. Matthews (Eds.), SPIE, Bellingham, WA, USA (2012).

131. K.H. Wang, C.M. Koo, I.J. Chung, Physical properties of polyethylene/silicate nanocomposite blown films, /. Appl. Polym. Sei. 89 (2003 ) 2131-2136.

132. S. Torres-Giner, ?. Gimenez, J.M. Lagarona, Characteriza- tion of the morphology and thermal properties of zein pro- lamine nanostructures obtained by electrospinning, Food Hydrocoll. 22 (2008 ) 601-614.

133. S.S. Ray, P. Maiti, M. Okamoto, K. Yamada, K. Ueda, New polylactide/layered silicate nanocomposites. 1. Prepara- tion, characterization, and properties, Macromolecules, 35 (2002) 3104-3110.

134. B. Xu, Q. Zheng, Y.H. Song, Y. Shangguan, Calculating bar- rier properties of polymer/clay nanocomposites: Effects of clay layers, Polymer, 47 (2006) 2904-2910.

135. B. Schartel, P. Potschke, U. Knoll, M. Abdel-Goad, Fire be- haviour of polyamide 6/multiwall carbon nanotube nano- composites, Eur. Polym. ]. 41 (2006) 1061-1070.

136. S.A. McGlashan, P.J. Halley, Preparation and characterisa- tion of biodegradable starch-based nanocomposite materi- als, Polym. Int. 52 (2003) 1767-1773.

137. P. Simon, Q. Chaudry, D. Bakos, Migration of engineered nanoparticles from polymer packaging to food - A physi- cochemical view, /. Food Nutr. Res. 47 (2008) 105-113.

138. R. Landsiedel, L. Ma-Hock, A. Kroll, D. Hahn, J. Schne- kenburger, K. Wiench, W. Wohlleben, Testing metal-oxide nanomaterials for human safety, Adv. Mat. 2 (2010) 1-27.

139. M. Joshi, A. Bhattacharyya, W. Ali, Characterization tech- niques for nanotechnology applications in textiles, Ind. ]. Fibre Text. Res. 33 (2008) 304-317.

140. I. Bertholon, C. Vauthier, D. Labarre, Complement activa- tion by core-shell poly(isobutylcyanoacrylate)-polysaccha- ride nanoparticles: Influences of surface morphology, length, and type of polysaccharide, Pliarmaceut. Res. 23 (2006) 1313- 1323.

141. N. Parris, P.H. Cooke, K.B. Hicks, Encapsulation of essen- tial oils in zein nanospherical particles, /. Agrie. Food Chem. 53 (2005) 4788^792.

142. Z.L. Wang, Transmission electron microscopy of shape-con- trolled nanocrystals and their assemblies, /. Phys. Chem. B, 104 (2000) 1153-1175.

143. V. Vogel, D. Lochmann, J. Weyermann, G. Mayer, C. Tzia- tzios, J.A. van den Broek et al., Oligonucleotide-prota- mine-albumin nanoparticles: Preparation, physical prop- erties, and intracellular distribution, /. Controll. Release, 103 (2005) 99-111.

144. K.T. Johnson, K.R. Fath, M.M. Henricus, I.A. Banerjee, Self- -assembly and growth of smart cell-adhesive mucin- -bound microtubes, Soft Mat. 7 (2009) 21-36.

145. J. Yue, X. Jiang, Y.V. Kaneti, A. Yu, Deposition of gold nano- particles on ß-FeOOH nanorods for detecting melamine in aqueous solution, /. Colloid Interface Sei. 367 (2012) 204- 212.

146. Atomic Force Microscopy - Biomedical Methods and Applications. In: Methods in Molecular Biology, Vol. 242, P.C. Braga, D. Ricci (Eds.), Humana Press, Totowa, NJ, USA (2004).

147. H. Yang, Y. Wang, S. Lai, H. An, Y. Li, F. Chen, Applica- tion of atomic force microscopy as a nanotechnology tool in food science, /. Food Sei. 72 (2007) R65-R75.

148. S. Mazumder, J. Sarkara, R. Dey, M.K. Mitra, S. Mukher- jee, G.C. Das, Biofunctionalised quantum dots for sensing and identification of waterborne bacterial pathogens, /. Experim. Nanosei. 5 (2010) 438^46.

149. J.F. Li, Y.F. Huang, Y. Ding, Z.L. Yang, S.B. Li, X.S. Zhou et al., Shell-isolated nanoparticle-enhanced Raman spectro- scopy, Nature, 464 (2010 ) 392-395.

150. J.R. Anema, J.F. Li, Z.L. Yang, B. Ren, Z.Q. Tian, Shell-iso- lated nanoparticle-enhanced Raman spectroscopy: Expand- ing the versatility of surface-enhanced Raman scattering, Ann. Rev. Anal. Chem. 4 (2011) 129-150.

151. Dynamic Light Scattering: An Introduction in 30 Minutes, Technical Note, Malvern Instruments, Malvern, UK.

152. M. Alexander, D.G. Dalgleish, Dynamic light scattering tech- niques and their applications in food science, Food Bio- phys. 1 (2006) 2-13.

153. J.E. Bruna, A. Penaloza, A. Guarda, F. Rodríguez, M.J. Ga- lotto, Development of MtCu2+/LDPE nanocomposites with antimicrobial activity for potential use in food packaging, Appl. Clay Sei. 58 (2012) 79-87.

154. A. Nel, T. Xia, L. Madler, N. Li, Toxic potential of ma- terials at the nanolevel, Science, 311 (2006) 622-627.

155. K. Donaldson, A. Seaton, The Janus faces of nanoparticles, J. Nanosci. Nanotechnol. 7 (2007) 4607-4611.

156. J.L. Ferry, P. Craig, C. Hexel, P. Siseo, R. Frey, P.L. Pen- nington et al., Transfer of gold nanoparticles from the water column to the estuarine food web, Nat. Nanotechnol. 4 (2009) 441^44.

157. L.C. Abbott, A.D. Maynard, Exposure assessment approach- es for engineered nanomaterials, Risk Anal. 30 (2010) 1634-1644.

158. J.P. Matthieu, Nanoparticles: Aspects of safety and risk management, J. Verbr. Lebensm. 3 (2008) 308-311.

159. K.L. Dreher, Health and environmental impact of nano- technology: Toxicological assessment of manufactured nano- particles, Toxicol. Sei. 77 (2004) 3-5.

160. Q. Zhang, Y. Kusaka, X. Zhu, K. Sato, Y. Mo, T. Kluz, K. Donaldson, Comparative toxicity of standard nickel and ultrafine nickel in lung after intratracheal instillation, /. Occup. Health, 45 (2003 ) 23-30.

161. Regulation (EC) No 178/2002 of the European Parliament and of the Council of 28 January 2002, laying down the general principles and requirements of food law, estab- lishing the European Food Safety Authority and laying down procedures in matters of food safety, Off. ]. Eur. Union, L31 (2002) 1-23.

162. A.D. Maynard, Nanotechnology and Human Health Impact: A Framework for Strategic Research?, Project on Emerging Nanotechnologies (PEN), Woodrow Wilson International Center for Scholars, Washington DC, USA (2005) (http://nmrw.nanotechprojed.org/process/files/2741/18_ nano- technologyhumanhealthimpactframeworkstrategicresearch.pdf.

163. Nanotechnology, Institute of Food Science and Technolo- gy, London, UK (2006) (http://www.ifst.org/uploadedfiles/cms/ store/ATTACHMENTS/Nanotechnology.pdf).