Okara, a natural food ingredient for new product development of foodstuffs

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1 Focus on Dietary fibres & Pre/probiotics 46 Okara, a natural food ingredient for new product development of foodstuffs FERNANDO SCHVED*, BATIA HASSIDOV *Corresponding Author Galam group, Mobile Post Menashe, 37855, Israel Fernando Schved ABSTRACT: Okara is the solid non-soluble fraction obtained during soymilk manufacturing. Okara is a natural rich source of dietary fibre and protein, which can be processed to industrial useful forms such as powders, extrudates or pregelatinized powders. Based on its characteristics, Okara can assist in new product development (NPD) of foods by providing nutritious protein and fibre, while simultaneously reducing calorie contents and glycaemic loads. Inclusion rates into products may reach levels as high as percent. Moreover, Okara also contributes to the texture, water-holding and emulsifying capacity, and may also help in the development of "gluten-free" food products. Soy-derived products have long been in use in most of the food supply chain around the globe. However, in the production of isolated soy ingredients the use of extracting organic solvents is quite common. In view of the above, the soymilk production industry is a welcomed exception since it does not employ such extractive chemical aids (i.e. the extraction of soymilk only involves the separation of the liquid fraction after a hot water treatment and mechanical means). Thus, from an industrial point of view, Okara is a major processing stream obtained in soymilk manufacturing, just as milk whey is obtained from cheese-making in dairy industries. To describe it simply, Okara can be defined as the solid residue collected following to the extraction of the water extractable fraction resulting in traditional or industrial production of soymilk or tofu. Typically, 250 kg of okara are produced for every 1,000 litres of soy beverage (1). Okara is a food particulate constituent fraction of soybeans, and is obtained as a white/ off-white material. At present, Okara is generally used as animal feed for livestock in close proximity to soy beverage production facilities, sold as a wet product containing ~ percent water (data obtained from commercial interviews with feed producers). The main reason behind the limited use of Okara as a food ingredient is its deterioration if not dehydrated or frozen rapidly (i.e. due to bacterial fermentation and lipid oxidation). While the present use of Okara in the western food and beverage industry has been limited, Okara s high content of healthy protein and fibre provides food formulators with an additional natural unique ingredient for the market. In order to secure a high quality and stable product, modern and hygienic large-scale production expertise needs to be successfully implemented (i.e. rapid water removal to produce a >94 percent dry solids product with a low water activity (Aw) assuring its stability and shelf life). According to Wang and Cavins (2) 30 percent of soybean solids, 20 percent of soybean protein, and 11 percent of soybean oil ends up in the Okara. In fact, the proximate composition of the Okara will depend on the amount of water phase extracted from the ground soybeans, and whether further water is added to extract residual extractable components (3). Okara is rich in proteins ( g/100 g of dry matter), lipids ( g/100 g of dry matter), and dietary fibre (DF, g/100 g of dry matter) (3, 5-7). An excellent reviewing reference for an overall understanding of Okara composition is that of O Toole from 1999 (3). The fibre component was also reported by Guermani et al. (4) and consists of hemicelluloses, cellulose and lignin at the approximately following ratios: 41 percent, 19 percent and 38 percent, respectively. According to Kugimiya (8), the main component of the dietary fibre in Okara is ruptured cotyledon cells, and the seed coat does not behave the same way as the cotyledon cells when being macerated by various means (8). In O toole s review, Liu (9) is mentioned as reporting on work done by Hackler and others in the 1960 s, claiming that the protein in Okara is of better quality than that from other soy products; e.g., the protein efficiency ratio of okara was 2.71 while that of soymilk was only Wang and Cavins (2) also reported that the ratio of essential to total amino acids in Okara is similar to tofu and soymilk. Ma et al. (10) worked on the essential amino acid composition and protein digestibility of Okara. The essential amino acid contents of the two tested Okara- protein isolates were generally similar, and comparable to a commercial soy protein isolate (see table #3; ref. 10). Cysteine and methionine contents were significantly decreased in the Okara protein but increased with the temperature of preparation. Both, the essential amino acid profiles and total essential amino acid contents of the soy protein products, were comparable to the FAO/WHO standard, with the exception of the sulfur-containing amino acids (cysteine, methionine) and tyrosine, which were lower in the soy proteins. The in vitro digestibility of the Okara protein isolates was high compared with a value of 77.1 percent for the defatted soy flour, and was not significantly different from that of the commercial protein isolate. Ma et al. (10) also demonstrated that the fat binding capacity of Okara isolates was significantly higher than that of commercial soy protein isolate. Fat absorption has been related to physical entrapment of oil by the protein matrix, and samples with larger surface area (lower bulk density) would bind more oil (11). Moreover, according to Ma et al. (10), Okara protein isolates had significantly higher percentage overrun, and foam stability than that of a commercial soy protein isolate. In their conclusions, Ma et al. (10 ) wrote: Although the okara protein isolates had poor solubility, other functional properties (emulsification, foaming and binding properties) were comparable to those of commercial soy isolate, suggesting the potential use of Okara protein as food ingredient. Recently, Préstamo et al. (7) reported on the effects of Okara diets using an animal rat model. According to their work, both control (regular rat chow) and Okara test

2 chow diets (standard rat chow plus Okara resulting in a final concentration of 10 percent (w/w) with 5 percent dietary fibre) had an equivalent caloric content. Both control and test diets had no effect on food intake, which on average was 10±0.1 g/day. Nevertheless, when compared to the control group for final weight, growth rate, and feeding efficiency results were lower in the group fed with Okara. One of the most interesting outcomes of the study above was that the Okara diet increased faecal excretion (daily stool weight was always higher for the Okara-fed group than for the control group). According to these researchers, the above results were attributed to a higher moisture content of faeces in the Okara-fed group, because of a higher intake of insoluble dietary fibre. In this context, similar patterns were also reported by Takahashi et al. (12). Moreover, an additional important outcome originating from this study was that total SCFA (short chain fatty acid) of caecal contents were higher in Okara-fed rats, than in controls. This observation was also previously reported by Tortuero et al. (13) and was in line with the work of Takahashi et al. from 1992, which tested also the effect of okara fibre on the rat gastrointestinal tract (12). Takahashi et al. concluded that the apparent degradability of Okara was twice that of wheat bran, and that there were also differences in the ph of the caecal contents. Moreover, according to Takahashi et al. (12) Okara fibre also reduces transit time in the intestine. The outcomes of the above reports i.e. reducing feeding rates, reducing intestine transit times, increased production of SCFA, lowering ph and increasing faecal wet weight are beneficial physiological outcomes, which may help to maintain a healthier gut performance. According to this report (7) Okara, a rich source of low-cost dietary fibre and protein, might be effective as a dietary weight-loss supplement with potential prebiotic effect. Recently, Jiménez-Escrig et al. (14) while working on a rat model with a defatted Okara preparation (dietary-fibre rich Okara) showed increased anti-oxidative gut protection, reduced weight gain, and improved calcium absorption. More recently, Espinosa-Martos & Rupérez (15) showed high swelling and water retention capacity of okara as compared to soybean seed. Western life-style societies and emerging eastern leading economies suffer from serious health related malconditions, which heavily affect overall health care expenditures and life quality. Among these health-treating related malconditions, one can mention (I) increased overweight and obesity rates, (II) increased rates of metabolic disorders related to blood glucose control, and (III) diabetes. From a nutritional point of view, these westerntype malconditions may result from a) lack of dietary fibre consumption which by itself is associated with increased cardiovascular disease (CVD) and cancer rates and by b) increased consumption of empty calories (mainly in the form of sweetened soft drinks), c) increased intake of surplus calories, and d) excess consumption of fatty foods. In view of the above, formulating food products with Okara may help food processors with their efforts aiming to develop healthier products. Moreover, among several mega-global food nutrition trends, food formulation with natural ingredients appears to be of higher priority. Since Okara is obtained without the use of chemical extraction aids, such as alcohols or organic solvents, it provides a natural tool to enrich food products with protein and fibre. Therefore, due to its high fibre and protein content, neutral-bland taste and natural characteristics, Okara has the potential to be used in the food industry as a functional ingredient (16). Based on its chemical characteristics, food products formulated with Okara, (common usage dose ~ 5-60 percent w/w basis) may enjoy from: 1) a lower calorie content, 2) lower glycaemic index and load, 3) a natural ingredient profile (if all other ingredients meet also this requirement), 4) a high quality protein content, and 5) a satiating effect due to both its DF and protein content. Okara can be processed to several textural forms in addition to its simple powder form, i.e. Okara can be extruded to produce products which may be incorporated into breakfast cereals, nutritional bars, healthy snacks, coated products, top-cups (for dairy products) or granola-type finished goods. Moreover, Okara may also be formulated while combining with starch to pregelatinized soluble ingredients. Combining and implementing Okara in food products is simple and relatively easy. For example Okara may be used to partially substitute flour in bread, pastry recipes and other food products containing flour such as pasta, crackers, bagels, snacks etc. In pastries such as cake mixes and cookies, replacing percent flour with Okara flour improves texture and mouth feel. In cakes, Okara may improve moisture retention and texture (contributing to a low A w ), and in cookies Okara helps improving crispiness and flavour. Exchanging 50 up to 100 percent flour with Okara improves the nutritional value of pastries, enriches it with both protein and fibre, and lowers the caloric value of the product. In pasta, it is possible to replace percent of the flour with Okara while improving the nutritional value, and reducing its caloric content. Okara may also be very useful in NPD s of gluten-free products. It is possible to replace all the flour with Okara flour to produce products for celiac consumers, while providing high levels of dietary fibre. In our food application laboratories, we have produced gluten-free pasta based on Okara combined with starch. In addition, gluten-free granolas were formulated in our labs, which may also be used in topcups for dairy products such as yogurts. Moreover, Okara is also suitable for producing a gluten-free substitute for bread crumbs, and coating preparations for schnitzels, meat, fish, and also as tempura-style coatings for fried meats and vegetables. Prebiotic coatings using Okara were developed as well and are in the scope of a Spanish patent application from 2004 (16). Thanks to Okara s neutral-bland flavour it can be successfully combined with different flavours and can be used as a substitute for ground nuts, almonds, marzipan, and as a filling for cookies, cakes and chocolates. Okara may be formulated both into sweet and salty-spicy finished goods. Okara also contributes to the emulsifying abilities thanks to its natural lecithin content, enabling the production of mayonnaise-style salad sauces without the need for egg addition or external emulsifiers. Thanks to Okara s high protein content, it delivers a good griping /sticking capacity for pasta or meat. Moreover, in our labs we have also formulated Okara in liquid products such as creamy soups resulting in improved fullness and creaminess sensations, while providing ~ 4 gram of dietary fibre per portion. Okara may also be extruded to obtain puffed structures (close to 100 percent Okara is puffed in an extruder) which can be Focus on Dietary fibres & Pre/probiotics 47

3 Focus on Dietary fibres & Pre/probiotics used to formulate healthier snacks and cereals. In extruded products Okara can improve crispiness and nutritional values. Okara may also contribute to formulate healthier snacks by providing both high protein and fibre contents, by lowering final caloric values, fat and salt. Finally, Okara can also be used as a coating ingredient to produce coated peanuts and other-like products by replacing flour, resulting in crispier and healthier products with improved taste. CONCLUSIONS Okara s nutritious protein and dietary fibre content, alongside with its many physical, textural properties and neutral flavour taste make it an excellent new proposition for NPD of foodstuffs. Furthermore, being a natural gluten-free food ingredient Okara could add even more value to the products formulated with it. REFERENCES AND NOTES 1. Okara: Overview of Current Utilization at 2. H.L. Wang, J.F. Cavins, Cereal Chemistry, 66, pp (1989). 3. D.K. O Toole, Journal of Agricultural and Food Chemistry, 47, pp (1999). 4. L. Guermani, C. Villaume et al., Science des Aliments, 12, pp (1992). 5. M. Fukuda, Y. Sugihara et al., Journal of the Japanese Society for Food Science and Technology, 53, pp (2006). 6. O. Surel, B. Couplet, Journal of the Science of Food and Agriculture, 85, pp (2005). 7. G. Préstamo, P. Rupérez et al., European Food Research and Technology, 225, pp (2007). 8. M. Kugimiya, Journal of the Japanese Society for Food, Science and Technology, 42, pp (1995). 9. K.S. Liu, Soybeans: Chemistry, Technology, and Utilization, Chapman & Hall, New York (1997). 10. C.Y. Ma, W.S. Liu et al., Food Research International, 29(8), pp (1997). 11. J.E. Kinsella, Critical Reviews in Food Science and Nutrition, 7, pp (1976). 12. T. Takahashi, Y. Egashira et al., Journal of the Japanese Society of Nutrition and Food Science, 45, pp (1992). 13. F. Tortuero, E. Fernandez et al., Nutrition Research, 17(1), pp (1997). 14. A. Jimenez-Escrig, M.D. Tenorio et al., Journal of Agricultural and Food Chemistry, 56, pp (2008). 15. I. Espinosa-Martos, P. Rupérez, European Food Research and Technology, 228, pp (2009). 16. G. Préstamo, P. Rupérez et al., Recubrimiento prebiótico a base de okara para fritos y precocinados (Okara based prebiotic covering for frying and pre-cooking of foods), Spanish application patent No. ES (2004). What s healthy today? What s new in food science? Will a short note today reveal as a straightforward innovation in our future diet? Ingredients as never seen before, healthy applications, novel methods of analysis, worth to know developments, all this is SCIENCE IN PILLS. Each week, we select those scientific news which hit our curiosity and publish them in our new SCIENCE IN PILLS section. Visit it at the address: 48

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