ria in the intestines, 8 pre- vention of cancer, 9 lowering the levels of blood choles- terol and reducing the risk of coronary heart disease, 2 modulating the immune re- sponse, 10 and stimulation of minerals absorption. 11 With the progress of oligosaccharides re- searches, it was found that soybean oligosaccharides are not the direct causes of flatulence. Modern safety tests have proven that oligosaccharides are safe for human consumption. 12 Soybean consumption in Asian countries has a history of several thousand years and many forms of soybean prod - several thousand years and many forms of soybean prod ucts were evolved. Some of the examples are non-fermented soybean foods such as tofu, soybean sprouts, dried tofu, soybean sheet (in Chinese) or Yuba (in American), and fer- mented soybean foods, such as soy sauce, sufu, tempeh, natto and miso. Soybean sheet formed on the surface of heated soymilk with the evaporation of surface va- por is a traditional dried soybean food in the far East. 13 It is an edible coat- ing or film of soybean pro- teins. As a vegetarian food ingredient, it has consider- able potential in western markets. During the preparation of soybean food, processing methods have great impact on the nutritional composi- tions of the final products. In case of production of tofu, large quantity of wa- ter-soluble protein, saccha- rides and isoflavones were lost in whey waste water. 14 In some practical produc- tion steps the oligosaccha- ride contents usually de- creased to various extent with different processing methods. 15-17 Processing unit opera- tions, such as soaking, de- hulling, grinding, washing and heat treatment alter the distribution and content of oligosaccharides, which caused much of Corresponding Author: Pro- fessor Tiejin Ying, Department of Food Science and Nutrition, School of Biosystems Engi- neering and Food Science, De - partment of Food Science and Nutrition, Zhejiang University, 268 Kaixuan Road, Hangzhou, Zhejiang, China 310029 Tel: 86 571 86971162; Fax: 86 571 86032848 Email: [email protected]
Q Wang, L Ke, D Yang, B Bao, J Jiang and T Ying 90 o lig o saccharide losses in soybean sheet production raffinose and stachyose loss in final soybean products. 7 Fermentation with R. oligosporus for production of tem- peh resulted in reduction of more than 80% stachyose and 50% raffinose respectively. 7 Decrease of stachyose and raffinose by hydrolysis with α-galactosidase enzyme, ger- mination and irradiation is also well-documented. 18 These researches emphasized the effect and importance of pro- cessing techniques on the oligosaccharides changes. Many similar researches have been done in tempeh fer- mentation. 7,17 However no report is available about oligosaccharides changes in soybean sheet production. The aim of this study is to investigate the changes of oligosaccharides during the preparation of soybean sheet and provide a basic loss profile for further study.
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