FREEZE DRYING OF YOGHURT WITH CANDIED CHESTNUT PUREE: SURVIVAL OF LACTIC ACID BACTERIA AND DETERMINATION OF PHYSICAL PROPERTIES

Abstract

Yoghurts with varying candied chestnut puree contents were freeze dried to produce a novel product: yoghurt powder containing candied chestnut puree. The amount of surviving lactic acid bacteria in the products was determined. The results showed that increasing the percentage of candied chestnut puree resulted in a decrease of moisture content, water activity, ash content, and L* values of the powder. Yoghurt with candied chestnut puree could be satisfactorily freeze dried with a minimum level of 8.93 log cfu/g dry matter survival rates for the lactic acid bacteria. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

Yoghurts with varying candied chestnut puree contents were freeze dried to produce a novel product: yoghurt powder containing candied chestnut puree. The amount of surviving lactic acid bacteria in the products was determined.

The results showed that increasing the percentage of candied chestnut puree resulted in a decrease of moisture content, water activity, ash content, and L* values of the powder. Yoghurt with candied chestnut puree could be satisfactorily freeze dried with a minimum level of 8.93 log cfu/g dry matter survival rates for the lactic acid bacteria.

- Keywords: lactic acid bacteria, yoghurt powder, candied chestnut puree, freeze drying -

(ProQuest: ... denotes formulae omitted.)

INTRODUCTION

Yoghurt is a smooth, semisolid fermented milk product produced as a result of the fermentation of milk by the action of symbiotic cultures of Streptococcus saliuarus subsp. thermophilus and Lactobacillus delbruecki subsp. bulgaricus. The starter microorganisms should be viable, active, and abundant in the product up to the date of minimum durability. The shelf life of yogurt is one day when stored at ambient condition (25°-30°C) and around 5 days at 7°C (KUMAR and MISHRA, 2004). Improvements in the shelf life of yoghurt can be brought about by dehydrating and converting it into a shelf-stable powder. Yoghurt can be dried by freeze, spray, microwave or convective drying methods, and yoghurt powder can be used as an ingredient for the manufacturing of many food products such as confectioneries, bakery foods, yoghurt drink mixes with fruits or vegetables, instant drink mixes, soup bases, dips, and sauces. It can also be consumed directly after reconstitution (KOÇ et al, 2010). Freeze dried yoghurt can be stored for 1-2 years at 4°C, while spray dried yoghurt cultures, when stored under dry and cool conditions, are guaranteed to maintain activity up to 1 year (KOÇ et al., 2009). The quality of yoghurt powder is mainly affected by the viable yoghurt starter bacteria count. Although freeze drying is the best method for drying yoghurt in terms of survival of yoghurt starter bacteria, the high cost of the process is a disadvantage (KOÇ et al, 2009; TAMIME, 1989; KUMAR and MÍSHRA, 2004).

The chestnut is one of the most popular nuts in the world. Unlike most other tree nuts, chestnuts are low in protein (2-4%) and fat (2-5%), but high in carbohydrates (up to 70%). Chestnuts also have fibrous substances, minerals (potassium and phosphorus) and vitamins (B and C) (RIBEIRO et al., 2007).

Chestnuts are typical seasonal fruits that maintain their optimum commercial quality for a comparatively limited period because of thenhigh water activity and sugar content (ATTANASIO et al., 2004).

There are different methods of consuming and processing chestnuts. They are commonly roasted, boiled, and fried. However, new products such as flours, creams, purees, canning, and pastries are also gaining importance. Chestnuts can be incorporated into a wide range of dishes such as soups, poultry stuffing, pancakes, muffins, and pastries. Turkey has a large share of the world's chestnut production. Most of the harvested produce is consumed fresh, but because chestnuts are highly perishable due to molding and rotting caused by fungi and the larval development of insects, the remaining crop must be preserved. For this reason, production and consumption of candied chestnuts is very common in Turkey. Candied chestnuts are a sweet product produced by soaking the chestnut shell and thin skin, then adding saccharose, glucose, glucose syrup, or invert sugar syrup, along with other additives according to the production technique. This product protects the nutritional value of fresh chestnuts and adds energy value due to the addition of sugar. The broken kernels are also marketed as puree. Chestnuts having a high content of nondigestable tissue, and health benefits include the development of the intestinal flora, the expulsion of harmful substances from the body, and effectiveness in lowering blood cholesterol levels (PARLAR and BILISLI, 2004).

Food powders have an increasing importance in food processing due to their ease of storage and transportation, and their suitability for use in innovative formulations. For these reasons, there have been several studies to determine powder properties of dried products (HOGERAMP and SCHUBERT, 2003; NI J DAM and LANGRISH, 2006; CHEN and PATEL, 2008; FANG et al, 2008; GONG et al., 2008; JINAPONG et al., 2008; JANGAM and THORAT, 2010; ROÇ et al, 2011).

The physical and biochemical properties of food powders determine their functionality and quality as food products. Flowability, which determines a product's handling properties, is an important characteristic of powdered products. Poor flowability is typically explained by the idea that small-particle sizes have more surface contact area and thus more frictional forces resistant to flow (JINAPONG et al., 2008). The flowing behavior of a powder not only depends on its physical properties, but also on a combination of parameters inherent in the powder, and on the ambient conditions and equipment used (TURCHIUU etal, 2005). Powder products are reconstituted before use. In the case of dried powdered foods, a number of properties influence the overall reconstitution characteristics (ROÇ et al., in press). Reconstitution of food powders follows the following steps: wetting of particles, sinking of particles into solution, dispersion of particles in solution, and complete dissolution of particles (CHEN and PATEL, 2008).

Compared to spray drying methods, freeze drying generally results in better survival of starter culture and improved reconstitution properties (KUMAR and MISHRA, 2004). The reconstituted freeze dried yoghurt has a high content of microorganisms, and the Lactobacillistreptococd ratio is no different than the original yoghurt (KUMAR and MISHRA, 2004). Yoghurt powder used as a functional food can also be mixed with dried fruit particles to formulate a novel product and improve the reconstitution properties of the yoghurt.

In this study, yoghurt and candied chestnuts, which are individually considered healthy products, were combined to obtain a novel product with beneficial properties of both. The aim of the study was to determine physical properties such as moisture content, water activity, ash content, color [L*, a*, b* values) and color change (AE) , handling properties such as bulk density and flowability, and reconstitution properties such as wettability and solubility, along with determining of the survival of lactic acid bacteria in yoghurt powder.

MATERIALS AND METHODS

White, plain yoghurt was purchased from a local producer (Pinar Dairy Products Inc., Turkey) and kept at 4°C until used on the day of purchase. Though the company makes other yoghurts, the white, plain variety, because of 14.2% (wb) total solids and 1.5% fat was selected as the test material. Candied chestnut puree containing 46.8% total sugar, 0.3% fat, 24.8% starch, and 0.9% protein was purchased in a local supermarket (Kardelen Inc., Turkey).

Preparation of yogurt mix

Yoghurts both plain and mixed with candied chestnut puree at 5, 10, and 20% by weight were prepared by mixing the ingredients and poured on metal Petri plates. Sample thickness was kept at a constant 3 mm by measuring with a digital caliper.

Freezing and freeze drying

The samples were frozen in an air-blast freezer (Frigoscandia, Helsinborg, Sweden) at -18°C for 2 hours, and freeze dried for 8 hours in laboratory scale equipment (Armfleld Model-FT33 Vacuum Freeze Drier, England) at 13.3 Pa absolute pressure with a condenser temperature of -45°C. Samples were dried to constant weight. All freeze dlying experiments were replicated twice.

Methods of analyses for powder properties

Moisture content of both fresh yoghurt and dried powders were determined gravimetrically with a modified method in an oven (Ecocell 222, Germany) at 105°C for 4 hours (PARLAR and BILI §LI, 2004). The water activity (aw) values of yoghurt powders were measured using a water activity measurement device (Testo AG 400, Lenzkirch, Germany) with a ±0.001 sensitivity. Ash contents were determined by dry ashing in a muffle furnace at 550° C for 8 hours (GÜLER and PARK, 2009). Analysis of powder properties for the products was made according to following methods: Flowability: 2 g of powder was transferred to a 50 mL graduated cylinder. The bulk density was calculated by dividing the mass of the powder by the volume occupied in the cylinder. The samples were dropped 50 times in order to evaluate their tapped densities. Then Carr Index and Hausner Ratio values were calculated by using Equation (1) and (2) respectively (JINAPONG et al., 2008; KOÇ et al., 2011).

...(1)

...(2)

Wettability: A measured amount of distilled water (100 mL) at 25°±1°C was poured into a 250 mL beaker. The powder sample (10 g) was placed in the beaker and the time it took for it to become completely wetted was recorded. Solubility: 2 g of yoghurt powder was added to 50 mL of distilled water at 25°±1°C. The mixture was agitated vigorously with a magnetic stirrer (Heidolph MR Hei-Standard, Germany) at 500 rpm. The time required for the material to dissolve completely was recorded (GOULA and ADAMOPOULOS, 2005; KOÇ eta I, 2010). Color: The color values of plain yogurt, prepared frozen-yoghurt samples, freeze dried yoghurt powders, and reconstituted yoghurt samples (L*, a*, and b* values) were measured with a Minolta Chroma Meter CR-400 (Minolta Co., Ltd, Japan). The total color change of reconstituted yogurt powders, with respect to fresh yoghurt samples, was calculated by using Equation 3 (HUNTER, 1975).

...(3)

All experiments on powder properties were replicated twice.

Enumeration of lactic acid bacteria

For the enumeration of lactic acid bacteria, 1 g of yoghurt for the initial load, or yogurt powder, was diluted with 9 mL of 0.1% peptone water and mixed uniformly with a vortex mixer (Elektro-M17, Turkey). Subsequent serial dilutions were prepared and viable numbers were enumerated using a pour-plate technique (DAVE and SHAH, 1997). MRS Agar (de Man Rogosa Sharpe Agar, pH 5.4, Oxoid, Hampshire, UK) in a double layer was used for L. bulgaricus and incubated at 37°C for 72 hours. Ml7 Agar (pH 7.2, Oxoid, Hampshire, UK) was used for the enumeration of S. thermophilus under aerobic incubation at 37°C for 48 hours. The average counts from the plates were calculated and the results were expressed in log cfu/g dry matter. Experiments on enumeration of lactic acid bacteria were performed in triplicate.

Statistical analysis

The data were analyzed by using a statisticalpackage program (SPSS 14.0 for Windows evaluation version; SPSS Inc., Chicago, 111) with a general linear model procedure. Differences were considered significant at p < 0.05. All analyses were carried out with parallels.

RESULTS AND DISCUSSION

Powder properties

The results of the analysis for physical, handling, and reconstitution properties of the powders are shown in Table 1. The moisture and water activity values of all yoghurt powders decreased with increased amounts of chestnut puree due to the increased amount of carbohydrates. Therefore, both the lowest moisture content and water activity values were found for yoghurt with 20% by weight chestnut puree. In another part of this study, in which rheological behavior and sensory analysis of the candied chestnut yoghurt at the same compositions were investigated, the most acceptable products were determined to be yoghurt with 10% by weight chestnut puree (SAKIN-YILMAZER et aL, in press). Ash content (%) values of yoghurt powder were found between 6.85 and 2.60 in wet basis. Ash content decreased with the addition of chestnut puree (46.8% total sugar) due to the increased amount of carbohydrates that leave no ash upon burning.

The bulk and tapped densities of yoghurt powders are also given in Table 1. The results of this study show that the addition of chestnut puree increased the bulk and tapped densities of the powders. KOÇ et cd. (in press) reported values of 538 and 746 kg/m3 respectively for plain yoghurt dried with spray drying, compared to bulk and tapped densities of 210 and 220 kg/ m3 for plain yoghurt dried by freeze drying in this study. The bulk densities of milk and whey were also reported to be 400 and 530 kg/m3, respectively. JINAPONG et al (2008) studied the spray drying of soymilk and reported the bulk and tapped densities at 210 and 350 kg/m3. For the determination of the flowability behavior of the powdered samples, Carr Index (Cl) and Hausner Ratio (HR) values were calculated and the results are shown in Table 1. These results show the candied chestnut yoghurt powders have very good flowability behavior (JINAPONG et cd., 2008). A Cl value of 27.93% was observed for spray dried yoghurt powders, indicating fair flowability (KOÇ et cd., in press). In a study by JINAPONG et cd. (2008), the Cl value was reported at 40% (bad flowability). The reason for this flowability was the small-particle size and large surface-area-per-unit mass of the powder, leading to more contact surface between powder particles and increased frictional forces that resisted flow. For the yoghurt powders cohesiveness values based on HR were low. The cohesiveness was observed to be in the intermediate level for the spray dried plain yoghurt powder (KOÇ et cd., in press).

The reconstitution properties of solubility and wettability are also given in Table 1. The increase in content of chestnut puree resulted in reduced times for solubility and wettability of the powders. At 31.8 s, the wettability value of plain yoghurt is very good, compared to 374 s for the spray dried yoghurt powders (KOÇ et cd., in press).

Color is important for marketability of the products and consumer acceptance. Even though a functional food could provide several health benefits to consumers, without being visually attractive it would not be marketable. Thus, the color of the supplemented products should, ideally, remain unchanged after production and during storage (ZARE et cd., 2011). The L*, a*, and b* values of the yoghurt powders at different chestnut puree concentrations are shown in Table 2. The addition of chestnut puree decreased the L*, and increased the a* and b*, values of the powders, except for a slight decrease in b* values of the powders with 5% and 10% of addition. The values of color changes, determined as the change in L*, a*, and b* values between reconstituted yogurt powder and fresh yoghurt samples by using Equation 3, are also given in Table 2. KOÇ et cd. (2010) reported that the total color change increased with increasing outlet air temperature in spray drying, ranging from 3.06 to 30.36. In a study by KUMAR and MISHRA (2005), mango- and soyfortified yoghurt was dried in a recirculatory convective dryer in 4 mm-thick forms using hot air at 50° C and an air velocity of 2.5 m/s with 80% air recirculation. The value of color change was calculated as 8.02.

Survival of lactic acid bacteria

Survival ratios of lactic acid bacteria in both plain and candied chestnut yoghurt samples are given in Table 3. All of the results are given in dry basis in order to compare the number of bacteria in yoghurt and yoghurt powder. The numbers of S. thermophdus (9.93 - 9.59 log cfu/g) were significantly higher than the numbers of L. bulgaricus (8.23 - 7.69 log cfu/g) in yoghurt samples with or without candied chestnut puree (p<0.05). Similar to our observations, ZARE et cd. (2011) reported the numbers of S. thermophilus as 8.39 log cfu/mL, and L. bulgaricus as 7.69 log cfu/mL in plain yogurt.

Freeze drying of candied chestnut yoghurt significantly reduced the number of S. thermophilus and L. bulgaricus, about 0.27-0.66 log and 1.101.78 log cfu/g dry matter, respectively. The survival ratio of lactic acid bacteria is shown in Fig. 1. VENIR et al. (2007) indicated that the freeze drying process of yoghurt samples with added sucroseblueberry reduced the numbers of S. thermophilus and L. bulgaricus about 1.52 and 2.33 log, respectively. According to the Turkish Food Codex Communique on Fermented Milk (No: 2009/25), yoghurt must contain at least a minimum of 7 log cfu/g total specific microorganisms (ANONYMOUS, 2009). In our study, yoghurt powder with or without chestnut-candy puree meet this criteria, with a minimum total lactic acid bacteria count of about 8.93 log cfu/g dry matter.

No significant differences in the number of lactic acid bacteria were obtained in the different concentrations of chestnut candy (p>0.05). VENIR et al (2007) observed that freeze drying resistance appeared to be similar for S. thermophilus and L. bulgaricus in plain yoghurt; on the other hand, they observed that the addition of sucrose-blueberry to yoghurt increased the survival of S. thermophilus and L. bulgaricus.

Freeze drying is considered a suitable dehydration process for bacteria when the ultimate goal is achieving a solid and stable final formulation (CARVALHO etal, 2004). CAPELA et al. (2006) pointed out that different species of Bifidobacterium and Lactobacillus survived in the freeze drying process at about 52.21 (84.99%) and 40.93 (85.73%), respectively. In this study, it was observed that S. thermophilus was more resistant than L. bulgaricus in the freeze diying process. The survival of S. thermophilus was greater after the freeze diying process compared to Lactococcus lactis subsp. cremoris and Lactobacillus casei subsp. pseudoplantarum (TO and ETZEL, 1997). KIM and BHOWMIK (1990) observed that S. thermophilus was also more resistant to spray- and freeze diying processes than L. bulgaricus. In another study, the survival rate of S. thermophilus was found to be higher than that of L. bulgaricus during spray diying of yoghurt samples (KOÇ et al., 2010). It is concluded that the freeze diying process can cause membrane injury of L. bulgaricus, which results increase in membrane permeability (CASTRO et al., 1997).

CONCLUSIONS

Yoghurt, plain or with candied chestnut puree, could be satisfactorily freeze dried with the determined physical, handling, and reconstitution properties. Increasing the percentage of candied chestnut puree resulted in a decrease of moisture content, water activity, ash content, and L* values of the powder product. Very good flowability and low cohesiveness were observed, considering the reconstitution properties of the powders. Total lactic acid bacteria survived at a minimum level of 8.93 log cfu/g dry matter in freeze dried, candied chestnut yoghurt samples, meaning that it meets Turkish Food Codex Communique on Fermented Milk criterion of higher than 7 log cfu/g. Further studies are needed for the survival of lactic acid bacteria in the storage conditions of yoghurt powder.

References

REFERENCES

Anonymous. 2009. Turkish Food Codex Communique on Fermented Milk; Resmi Gazete (No: 2009/25). Ankara (in Turkish).

Attanasio G., Cinquanta L., Albanese D. and Matteo M.D. 2004. Effects of diying temperatures on physico-chemical properties of dried and rehydrated chestnuts (Castanea sativa). Food Chem. 88:583.

Capela R, Hay T.K.C. and Shah N.R 2006. Effect of ciyoprotectants, prebiotics and microencapsulation on survival of probiotic organisms in yoghurt and freeze-dried yoghurt. Food Res. Int. 39:203.

Carvalho A.S., Silva J., Ho R, Teixeira R, Malcata F.X. and Gibbs R 2004. Relevant factors for the preparation of freeze-dried lactic acid bacteria. Int. Dairy J. 14:835.

Castro H.R, Teixeira RM. and Kirby R. 1997. Evidence of membrane damage in Lactobacillus bulgaricus following freeze diying. J. Appl. Microbiol. 82:87.

Chen X.D. and Patel K.C. 2008. Manufacturing better quality food powders from spray diying and subsequent treatments. Diying Technol. 26:1313.

Dave R.I. and Shah N.P. 1997. Viability of yoghurt and probiotic bacteria in yoghurts made from commercial starter cultures. Int. Dairy J. 7:31.

Fang Y., Selomulya C. and Chen X.D. 2008. On measurement of food powder reconstitution properties. Diying Technol. 26:3.

Gong Z., Zhang M., Mujumdar A.S. and Sun J. 2008. Spray diying and agglomeration of instant bayberry powder. Diying Technol. 26:116.

Goula A.M. and Adamopoulos K.G. 2005. Spray diying of tomato pulp in dehumidified air: II. The effect on powder properties. J. Food Eng. 66:35.

Güler Z. and Park Y.W. 2009. Evaluation of chemical and color index characteristics of goat milk, its yoghurt and salted yoghurt. Tropical and Subtropical Agroecosystems 11:37.

Hogekamp S. and Schubert H. 2003. Rehydration of food powders. Food Sei. Technol. Int. 9:223.

Hunter R.S. 1975. Scales for the measurements of color difference. In the measurement of appearance. New York: Wiley-Interscience. 133 p.

Jangam S.V. and Thorat B.N. 2010. Optimization of spray diying of ginger extract. Diying Technol. 28:1426.

Jinapong N., Suphantharika M. and Jamnong P. 2008. Production of instant soymilk powders by ultrafiltration, spray diying and fluidized bed agglomeration. J. Food Eng. 84:194.

Kim S.S. and Bhowmik S.R. 1990. Survival of lactic acid bacteria during spray diying of plain yoghurt. J. Food Sei. 55:1008.

Koç B., Sakin-Yilmazer M., Balkir P. and Kaymak-Ertekin F. 2009. Yogurt tozu i§leme teknolojisi, depolama ve kullanim alanlari. Gida 34:245 (in Turkish).

Koç B., Sakin-Yilmazer M., Balkir P. and Kaymak-Ertekin F. 2010. Spray drying of yoghurt: Optimization of process conditions for improving viability and other quality attributes. Diying Technol. 28:495.

Koç B., Sakin-Yilmazer M., Kaymak-Ertekin F. and Balkir P. Physical properties of yoghurt powder produced by spray diying. J. Food Sei. Technol. In press, DOI: 10.1007/ si 3197-012-0653-8.

Koç M., Koç B., Susyal G., Sakin-Yilmazer M., KaymakErtekin F. and Bagdatlioglu N. 2011. Functional and physicochemical properties of whole egg powder: effect of spray diying conditions. J. Food Sei. Technol. 48:141.

Kumar P. and Mishra H.N. 2004. Yoghurt powder-A review of process technology, storage and utilization. Food Bioprod. Process 82:133.

Kumar P. and Mishra H.N. 2005. Effect of stabilizer on diying characteristics and quality of mango soy fortified yoghurt. Eur. Food Res. Technol. 220.

NLjdam J.J. and Langrish TA.G. 2006. The effect of surface composition on the functional properties of milk powders. J. Food Eng. 77:919.

Parlak S.U. and Bili§li A. 2004. Kestane §ekerinin özellikleri ve besin degeii. Geleneksel Gidalar Sempozyumu, September 23-24, 2004, Van, Turkey, (in Turkish).

Ribeiro B., Rangel J., Valentáo P., Andrade P.B., Pereira J.A., Bölke H. and Seabra R.M. 2007. Organic acids in two Portuguese chestnut (Castanea sativa Miller) varieties. Food Chem. 100:504.

Sakin-Yilmazer M., Dirim S.N., Di Pinto D. and KaymakErtekin F. Yoghurt with candied chestnut: freeze drying, physical, and rheological behavior. J. Food Sei Technol. In press. DOI: 10.1007/sl3197-012-0890-x

TamimeA.Y. 1989. Microbiology of starter cultures. In: Robinson R.K., Editor. The microbiology of milk products. 2nd Ed. London: Elsevier Applied Science, p. 131.

To B.C.S. and Etzel M.R. 1997. Spray diying, freeze diying, or freezing of three different lactic acid bacteria species. J. Food Sei. 62:576.

Turchiuli C., Eloualia Z., Mansouri N.E. and Dumoulin E. 2005. Fluidised bed agglomeration: Agglomerates shape and end-use properties. Powder Technol. 157:168.

Venir E., Torre M.D., Stecchini M.L., Maltini E. and Nardo P.D. 2007. Preparation of freeze-dried yoghurt as a space food. J. Food Eng. 80:402.

Zare F., Boye J.I., Orsat V., Champagne C. and Simpson B.K. 2011. Microbial, physical and sensory properties of yoghurt supplemented with lentil flour. Food Res. Int. 44:2482.

Paper received March 24,2013 Accepted June 17, 2013