Study On Effect Of Whey Protein Hydrolysate On Fermentation And Storage Property Of Yogurt

Yogurt is a kind of food with multiple functions, such as nutrition, health and beauty. Besides, it can be easily digested by human. So during the last two years, the production and consumption of yogurt have gained rapid development. For the dairy processing enterprises, how to shorten fermentation time, improve production efficiency, and reduce dosage of starter as well as maintain high product quality is an important research direction. This topic is to study the effect of whey protein hydrolysates on yogurt fermentation, biological activity of lactic acid bacteria and rheological properties. We hope to provide new methods and theoretical guidance for the dairy industry in producing high quality, multiple physiological functions, nutrient-rich fermented dairy products.In this study, Papain, Alcalase, Neutrase, Flavourzyme and Protamex were used in whey protein hydrolysing. For each enzyme, low, medium and high degree of whey protein hydrolyzates(WPH) were choosed to add to milkbase to study the effect of degree of hydrolysis(DH) and different enzymes on fermentation characteristics and biological activity of lactic acid bacteria. The results showed that, within a certain degree of hydrolysis (DH 4.08 ~ 9.88%), the higher the DH, the higher the fermentation-promoting capacity of the hydrolysates, and with an addition amount of 3%(w/w), the fermentation time can be shortened by 6~12% ; Among the enzymes, Alcalase and Flavourzyme promoted the fermentation most significantly(with an addition amount of 3%, they can shorten the fermentation time by 12% respectively), followed by Neutrase; WPH can increase the acid-producing ability and viability of lactic acid bacteria during fermentation; Based on the consideration of fermentation-promoting ability, flavor of yogurt and production cost, the appropriate additive amount of WPH was 4~6%.Study on the storage characteristics showed that, 4%(w/w) Alcalase hydrolysate had little impact on the sensory quality of yoghurt, while it properly raised the apparent viscosity of yogurt and slowed down the post-acidification during storage; WPH can reduce the overall mortality rate of lactic acid bacteria, and in particular, it can improve the stability of Streptococcus thermophilus during storage. After storage, for sample and control, the ratio of Streptococcus thermophilus to Lactobacillus bulgaricus was129.09 and 11.48 respectively; 4% WPH improved yoghurt texture, giving more abundant taste and increased the stability of yogurt.Hydrolysates from Alcalase and Neutrase were fractioned into 10 kDa, 5 kDa, 3 kDa and P fractions by plate membrane with different molecular weight cut-off(MWCO) ane each fraction was added to milkbase to produce yogurt. The results showed that, P fractions of the two enzymes promoted fermentation the most significantly.That is, fraction with average MW less than 3 kDa played the most important role in promoting yogurt fermentation; compared to the corresponding amino acid mixture, WPH increased the acid-producing ability of lactic acid bacteria much higher . So, we can conclude that, micromolecule peptides played the most important role in promoting yogurt fermentation.