Study Of No-sugar Instant Soy-curd

The objective of this research was to prepare a powder product, which contains rich soyprotein. The product has good instant dispersion and gelation properties. It could be dispersedinstantly in hot water, then coagulated in few minutes, and we could get fresh delicioussoy-curd.Firstly, the effects of coagulators and gelation conditions on gelation properties of soyprotein were tested. Gel strength,water-holding capacity (WHC) and coagulating rate areimportant gelation properties of soy protein. Major effect factors on these properties includeprotein concentration of SPI solution,temperature and time of thermal treatment,type andconcentration of coagulant,pH,ion strength. According to experiments,optimal coagulantand gelation condition for actual system can be obtained as follows:protein concentration 4%,95℃ heating 15 min, 0.33% GDL, duration at 80℃ for 30 minutes, ion strength 0.01M(NaCl), final pH 5.0.Secondly, three methods to improve the solubility of product were compared, includedadding reducing agents(Na2SO3, NaHSO3 and L-Cys-HCl), limited enzymatichydrolysis(Alcalase and As 1.398) and alkaline and acid treatment. At the same time, theeffect of these three methods on gelation properties of soy protein was stuied. Then we foundadding L-Cys-HCl within a certain concentration could improve the solubility of soy proteinin soy milk, also gelation properties. The best concentration of L-Cys-HCl is 10μmol/g soyprotein. At this level of L-Cys-HCl, protein dispersibility index(PDI) of soy milk powder weprepared was 50.12%. It was 5.45% higher than that of blank sample.Thirdly, the optimal processing technology was obtained. A suitable water/bean ratio wasselected as 7:1 by testing the yield of protein and total solid. Proper emulsifiers for soy slurrywere SE-15 and Tween60(SE-15:Tween60=3:2). Use this compound emulsifier, soy milkpowder with high instant solubility and dispersibility was obtained. Optimal formula with fullfat milk powder, NaCl and soy oil at the ratio of 3%:2%:0.3% (additive: soy slurry , w:w) wasgot by sensory evaluation experiment. The influence of spray-drying condition on instantsolubility of soy milk powder was discussed. After these, the solubility of product wasimproved more. PDI of soy protein was 63.82% and dispersibility of soy protein was 45.9seconds.Finally, formula of instant coagulator and gelation condition were obtained. The mixtureof GDL and papain*(papain sprinkled by low DE maltodextrin) was used as compoundinstant coagulator(GDL: Papain=9:11). 10 gram Spray-dried soy milk powder mixed withcompound instant coagulator(10:1) was added in 90ml 90-95℃ hot water, then stirredquickly for 10 seconds. After 5 minutes, soy-curd could be obtained.