CHEMICAL AND PHYSICAL CHARACTERIZATION OF CACTUS CLADODE (OPUNTIA FICUS-INDICA) POWDER

Headnote

ABSTRACT

Some physical and chemical characteristics of cactus cladode powder and the influence of concentration, temperature and pH on the viscosity of a water suspension were studied. The powder showed low water activity (0.53). The total dietary fiber content was 42.99%, and the ratio of insoluble fiber to soluble fiber was 2:1. The pH significantly influenced the viscosity of the powder suspensions at low concentration and temperature. The concentration significantly affected the viscosity at all temperatures and pH values. The IDF/SDF ratio suggests that the main physiological effect would be to regulate intestinal functioning, depending on other factors such as daily intake.

- Key words: cactus cladodes, cactus pads, cactus powder, dietary fiber, Opuntia ficus-indica, semiarid plants -

INTRODUCTION

In recent years, interest in healthy foods has increased markedly. Consumers prefer lowcholesterol, low-fat, low-calorie and high-fiber foods. There are many studies about the effects of fiber in humans (GALLAHER and SCHNEEMAN, 2001; CHAU et al, 2004; NAS, 2005; NELSON, 2001). Consumers are aware of the relationship between fiber consumption and the control of cholesterol and the prevention of illnesses such as diabetes and obesity. Dietary fiber can also contribute to the prevention, or treatment of illnesses, like gastrointestinal disorders, that are associated with a lack of dietary fiber intake. Thus, the trend is to search for new, natural sources of dietary fiber for the development of food ingrethents. Cactus cladode Opuntia ficus-indica) powder appears to be a promising source to obtain this kind of ingrethent. This powder could be considered a natural food supplement to be used in solid or liquid foods. The age or size of the cladodes and the climatic conditions prevailing when they are harvested have some influence on their physical and chemical composition (RODRÍGUEZGARCÍA et al, 2007). BETANCOURT-DOMÍNGUEZ et al (2006) observed that during the development of young cladodes (called "nopalitos" in Mexico), the insoluble fiber increased from 29.87 to 41.65% and the soluble fiber decreased from 25.22 to 14.91% in cladodes from 60 to 200 g, respectively. PIMIENTA (1990) reported an increase in crude fiber as a function of their maturation, from 12 to 17% in 1- and 3-year-old cladodes, respectively.

ZAMBRANO et al (1998) studied some properties of young cladodes (1-3 months), as a source of fiber. The dried product had 20.4% dietary fiber as well as other interesting physico-chemical characteristics: water absorption (5,8 mL/g), water retention (4.7 g/g), organic molecule absorption (0.69 g/g), and cation exchange (0.49 Meq H+/g), which could explain the role of "nopalitos" in intestinal health. HERNÁNDEZ et al (1998) and DUQUE et al (1998) tested the effects of blanched "nopalitos" (11% fiber) consumption in rats and observed that while the amount of fiber in the diet increased, the deposition production increased, but the rats lost weight and showed some signs of malnutrition. HERNÁNDEZ et al (1998) concluded that the consumption of fresh "nopalitos" must be carefully controlled in humans. The use of cactus cladode powder in food is completely different depending if the prepared food is a solid or a liquid. SAENZ et al (2002a) replaced a portion of wheat flour with nopal powder (from old cladodes) in biscuits and got good results with up to 15% addition, but also observed that the use of nopal powder in preparing a vegetable soup had a negative effect on the viscosity of the soup when the amount of powder approached 15% (SAENZ, 2006). Other studies in powdered dessert formulations showed that the use of up to 16% of nopal powder gave products with good texture (SAENZ et al, 2002b). Recently, in México, young cladodes ("nopalitos") have been included in typical "tortillas" (a thin bread made with corn flour), in order to increase the dietary fiber intake because this product is massively consumed, instead of bread, in this country (SAENZ et al, 2006). In a complete review about the chemistry of cactus stems, STINTZING and CARLE (2005) concluded that much research is needed to get an insight into the multitude of bioactivity properties reported in the literature.

The objectives of this study were to determine the physical and chemical characteristics of cactus cladode powder, from mature pads, as a source of natural dietary fiber for foods and the effect of the concentration, temperature and pH on the viscosity of the powder suspensions in water.

MATERIAL AND METHODS

Cactus cladodes (1-, 2- and 3-year-old, blends in the same ratio) from Opuntia ficusindica from an orchard located in the semiarid central region of Chile were used. The flour was obtained according to the method described by SEPÚLVEDA et al (1995), which involves drying the cladodes in a forced air tunnel (70°-80°C for 6-8 h; 2 ms-1) and milling. The milling was done first, using a knife mill with a 1 mm diameter sieve and then in a lab mill (Mills 3800) with a 150 µm sieve.

Physical and chemical analysis

The following analyses were performed on the cactus cladode powder: particle size using the official method of the A. A. C. C. (1989); moisture (A.O.A.C., 1996), water activity (aj, with a Lufft equipment model 5830 (Fellbach, Germany); color parameters (L*, a*, b*, C* and h°) with a reflectance colorimeter Minolta CR-200b (Osaka, Japan); water absorption index (W.A.I.) according to the method described by QUINN and PATTON (1978); total dietary fiber, soluble (SDF) and insoluble (IDF) (LEE et a?., 1992); calcium, sodium, potassium and phosphorus (A. O. A. C, 1996); and calorie content using the FAO Atwater factors (FAO, 2002).

All the physical and chemical analyses were done in triplicate and the coefficient of variation was calculated.

Microbiological analyses

A total count of aerobic microorganisms, total yeast and molds were determined (PASCUAL, 1982).

Viscosity measurements

The effect of the concentration (2.5, 5.0 and 7.5%), temperature (10°, 20°, 40° and 70°C) and pH (4.0, 6.0 and 7.0) on the viscosity of a cactus cladodes powder/water suspension was measured with a Brookfield viscometer model RVT (Middleboro, MA, USA), with different spindles according to the concentration.

The experimental design for the viscosity effects was totally random, with a factorial arrangement (3x3x4) with 4 replications. The results were analyzed by ANOVA applying a Duncan Test when differences were detected (p >0.05).

RESULTS AND DISCUSSION

The cactus powder had 77.5% of the particles between 150 and 190 µm and about 7.5%, of the particles larger than 190 µm. These results agree with LARRAURI (1994), who reported that products with high fiber content generally have particle sizes between 150 and 430 µm.

The water activity (Table 1) was 0.53, similar to that reported by LAHSASNI et al (2003) for dehydrated cladodes. The low a value indicates that this powder will be stable during storage mainly against microbiological attack.

The color parameters (Table 1), represented by L*, a*, b*, C* and h°, show that the powder is light green with a high L* value; similar to that reported by SEPÚLVEDA et al (1995) in a powder prepared with mature cladodes as in this study. The chroma (C*) and the h° value indicate a pale, yellow-greenish color. These parameters are important when the powder is used as a food ingrethent. This green color may need to be masked in some foods, such as biscuits, in order to make them more acceptable. However, if the powder is used in a liquid, the pale color is consistent with the color of other vegetable fibers.

The water absorption index (5.6 mL/g) was lower than that reported by ROSADO and DIAZ (1995) for dehydrated cactus cladodes and for cactus cladode fiber isolates 11.1 and 7. 1 mL/g, respectively. This can be attributed to the different raw material used, the cladode age, or to the particular analytical techniques applied in this study.

Table 2 shows some chemical characteristics of cactus cladodes powder. The water content (7, 14%) was similar to that reported by SEPÚLVEDA et al. (1995) and assures a good blend with other kinds of flour. Wheat flour commonly has a water content close to 12-13%, while flour from legumes has a lower water content (9.29.6%), suggesting the possibility of mixing cactus powder with legume flour, rather than with wheat flour, without caking or microbiological problems.

The total dietary fiber of cactus cladode powder was 43%, where 28.45% was insoluble dietary fiber (IDF), and 14.5% was soluble dietary fiber (SDF). The insoluble/soluble dietary fiber ratio was 2:1; which is a little lower than the 3: 1 reported by SALAS-SALVADO et al. (2006) for most vegetable products and for a powder prepared with from 2- to 3-year-old Tunisian varieties cladodes reported by AYADI et al (2009). It is generally accepted that fiber suitable for use as a food ingrethent should have an IDF/SDF ratio close to 2:1 (JAIME et al, 2002; SCHEENAM, 1987). RODRÍGUEZ-GARCÍA et al (2007) reported that dried young cladodes (7.31% moisture) from Opuntia ficus-indica, Redonda variety, harvested after 65 days had a total dietary fiber content of 56.56%, with 41.65% IDF and 14.91% SDF. The IDF content was greater than that observed in the present study with mature cladodes; the SDF contents were similar. The IDF/SDF ratio was close to 2.8:1, greater than that observed in the present study.

Total dietary fiber was similar to the 41.8% reported by AYADI et al (2009) for dehydrated spineless cladodes. ROSADO and DIAZ (1995) reported values of 50.4% and near 56.7%, in dehydrated cactus cladodes and isolated cactus cladodes, respectively. The variability between these values can be attributed to the climatic conditions where the plants were grown and also to the methods of preparation, as well as to the age and variety of the Opuntia cladodes used. The ratio between insoluble and soluble fiber was similar between the dehydrated cactus cladodes (ROSADO and DÍAZ, 1995) and the cactus cladode powder obtained in this study. The isolated cactus cladode fiber ratio was high (9:1), probably due to the ethanol used to extract the fiber which caused a loss of some soluble fiber. The cactus powder showed a higher value of dietary fiber compared with whole wheat flour (12.57%) and wheat flour (2,78%), There are many products with much higher dietary fiber contents, for example: Psillium plantago (87,3%), glucomannan (83,4%), and soybean extracts (68.8%) (ROSADO and DÍAZ, 1995). Among these three sources of dietary fiber, only glucomanann provides an appreciable proportion of soluble fiber, with an insoluble and soluble fiber ratio of 32: 1. FIGUEROLA et al (2005) reported total fiber contents between 60.7 and 89.8% for concentrated apple pomace, of which 4.14 to 14.33% was soluble fiber. The physiologic effect of cactus powder is not easy to define because it depends on many factors, such as the amount consumed, and also the other food constituents of the diet. IBAÑEZ-CAMACHO et al (1983), using another species of Opuntia, Opuntia streptacantha, reported a hypoglycemic effect in rabbits, associated with the soluble fiber content. More recently, GALATI et al (2007) proposed the protective effect of carbohydrate polymers from Opuntia cladodes against ethanolinduced ulcers in rat.

Dietary fiber is associated with several physiological effects, such as decreasing cholesterol levels in the blood GALLAHER and SCHNEEMAN (2001). There is a widespread conviction that the effect of dietary fiber on plasma cholesterol concentration may be largely mediated by enhanced fecal excretion of bile acids. Many types of dietary fibers show hypocholesterolemic activity in human, increasing fecal bile acid output. However, increased bile output due to fiber is not always accompanied by a reduction in plasma cholesterol. Therefore, the mechanism by which fiber exerts its hypercholesterolemia effect remains an intriguing question (GALLAHER and SCHNEEMAN, 2001, CHAU et ed., 2004, MC PHERSON, 1992). Dietary fiber is also associated with glucose control and thus with diabetes (GALLAHER and SCHNEEMAN, 2001; IBAÑEZ-CAMACHO etal., 1983; GALATI etal, 2003) and may play a role in reducing the risk of certain types of cancer, particularly colon cancer, and reduce symptoms of chronic constipation, diverticular disease and hemorrhoids (MC PHERSON, 1992; ANDERSON et al., 1994).

There have been several studies on the possible uses of fresh young cactus cladodes ("nopalitos") in medicine (FRATI-MUNARI etal., 1992), as well as some studies directly related to the consumption of "nopal" powder capsules (FRATI-MUNARI et al, 1989). Studies on the use of cactus cladode powder in foods are very scarce. Nevertheless, this possibility is an interesting alternative for increasing fiber consumption, which is known to be frequently below the recommended dietary intake in most countries.

Other nutritional components in the cactus powder studied were ash and minerals (Table 3). The calcium content could be considered high and similar to that reported by RODRIGUEZ-GARCÍA et al. (2007), 3.30 mg/ 100 g in of 65day harvested cactus pads (200 g). However, the availability of this mineral is not clear; some authors report that calcium is in the form of calcium oxalate in the cladodes (PIMIENTA, 1990), which would limit its bioavailability. MCCONN and NAKATA (2004) suggested that although the cactus pear pads are enriched in a number of minerals, the calcium is not freely available because it is present as calcium oxalate crystals. RODRÍGUEZ-GARCÍA et al (2007) reported that when the maturity stage of cladodes increases, calcium oxalate content decreases and calcium increases. This would favor calcium absorption. On the other hand, in studies on the bioavailability of calcium salts cited by WEAVER (2003), it was reported that calcium does not need to be dissociated from low molecular salts, such as oxalates, to be absorbed.

The caloric value of the powder was 6.9 kJ/g. This value was less than that of wheat flour or legume flour 15.33 and 14.95 kJ/g, respectively (FAO/LATINFOODS, 2002). The caloric value of cladode powder was about 40.0% that of wheat flour and is in the range suggested by LARRAURI (1999) for commercial dietary fiber powder, close to 8.00 kJ/g.

The microbiological analysis showed that the total aerobic mesophylic count was 3.3 c.f.u./g and the total yeast and mold count was 4.6 c.f.u./g. These values are low. In addition, the "nopal" powder will not be consumed directly, but rather will be used as an ingrethent in foods that are generally thermally treated.

The viscosity behavior of cactus cladode powder suspensions and the effect of pH, concentration and temperature can be observed, respectively, in Figs, 1, 2 and 3, along with the corresponding regression equations. The property of certain types of dietary fiber (pectins, mucilages, gums, carrageenan, etc) to form highly viscous solutions is widely known (GALLAHER and SCHNEEMAN, 2001). Viscosity is an important characteristic for the formulation of foods and for their influence on intestinal bowel formation and transit. KENDALL and JENKINS (2004) recommended increasing consumption of viscous fibers to promote heart health. The viscosity of a nopal powder suspension, as in other types of polymer solutions, is affected significantly by temperature (Fig. 1). At higher temperatures the effect on viscosity is less affected by the concentration of the nopal powder, the slopes of the curves are less at higher temperatures (70°C) than at lower temperatures (10°C). The viscosity is also influenced by the concentration of the powder and the pH of the sample (Fig. 2). According to SAENZ et al (1992), the change observed at different pH values can be attributed to the ionization of carboxylic groups at high pH and the repulsion of negative charges, maintaining the mucilage molecule extended with the consequent increase in the viscosity. The slopes at pH 6 and 7 were similar (19,23 and 16.49, respectively) and greater than that at pH 4 (7.27). This behavior gives useful information for the potential addition of this kind of fiber to some foods because many foods have a pH close to 4.0. The effect of concentration on the viscosity (Fig. 3) shows that independent of temperature, the viscosity increased when the concentration increased. This behavior was also observed in cereal and legume flour suspensions (6.8 and 5.8%, respectively), where the viscosity ranged from 12 to 405 mPa s depending on whether the flours were uncooked or extruded. But when the concentration was increased from 7.5 to 12%, the viscosity values increased significantly, from 1,000 to 14,000 mPa s (REYES, 1984).

The temperature always affected the viscosity at all pH and concentrations assayed. As can be expected, the lower viscosity values are associated with higher temperatures. The nopal powder concentration influenced the viscosity at all the temperatures and pH values assayed, showing a direct relationship between concentration and viscosity.

At a constant pH, as the concentration increased, the viscosity also increased. In a 7% nopal powder water suspension, the viscosity reached a high value (1726. 1 mPa s at 20°C); a product with these characteristics could be difficult to manage. For this reason, the recommended concentration in fluid food formulations should be close to 5%. This amount will contribute only a proportion of the recommended daily dietary fiber intake, but it would help increase the low dietary fiber intake of many people. This study and those cited above suggest that a purified cladode powder, using cladodes without the epidermis, could be used as a food additive that would give a different final product having other physical characteristics such as viscosity, color and aroma, allowing for greater addition to foods.

In conclusion, the cactus powder obtained from mature cladodes is a low calorie food ingrethent with high fiber content, making it a good source of alternative dietary fiber. The IDF/SDF ratio suggests that the main physiological effect could be to regulate intestinal functioning, depending on other factors, such as the amount of intake. This aspect needs further study. The viscosity produced by this powder is an important property to be considered during the formulation and preparation of foods, especially liquids.

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Paper received April 3, 2009 Accepted May 24, 2010