Abstract: Acidity change and apparent viscidity change of yogurt mixed with different amount and different hydrolytic degreepea-protein hydrolysate by neutral protease As1.398 were studied in this paper. Rheological shear stress, parameter andviscosity index in different shear rate were studied in yogurt.The result showed that to mix enzymatic soy-protein hydrolysatewith milk would contributed to acidic forming in yogurt. It took shortest time to be the fermentive end for yogurt when milkwas mixed with 7.5%～10% enzymatic soy-protein hydrolysate which hydrolytic degree was 5.61%. The apparent viscidityof fermented yogurt was increased when milk was mixed with 7.5% DH3.76% enzymatic soy-protein hydrolysate. Flexibilityof yogurt was reduced when milk mixed with soybean hydrolysate and the yogurt was non-newtonian fluid. Shear stress ofyogurt in high shear rate was far higher than CK when milk was mixed with DH8.89% enzymatic soy-protein hydrolysate.

Key words: yogurt, soy protein, enzymatic hydrolysis, rheological behavior