Study On Fermentation Characteristics Of Probiotic Lactobacillus Plantarum P8 In Soymilk And Milk

The probiotic L. plantarum P8, mixed with different S. thermophilus respectively, were used as starter cultures for the soymilk and milk fermentation. The main conclusions were as follows:(1) L. plantarum P8 was mixed with S. thermophilus S21-2 and L01-2 and conducted in fermentation the soy milk. All fermentation of groups stopped at 6h when the pH reached 4.5. While the combination of L. plantarum P8 and S. thermophilus L01-2 showed better characteristics: the higher viscosity, the moderate sweet, the smooth and delicate taste and no whey separation. And the viable counts of L. plantarum P8 and S. thermophilus L01-2 were 5.5×10~7CFU/mL and 2.6×10~8 CFU/mL respectively. This combination not only can shorten the fermentation time, but also improve the bioavailability of soy milk. It was good candidate for applying to the probiotic fermented set soymilk.(2) The soymilk supplemented with skim milk(GroupⅠ) , WPC (GroupⅠ) or soy concentrated protein (GroupⅢ) respectively, was fermented with the starter of L. plantarum P8 or/and S. thermophilus L01-2 (single or mixed according to certain proportion). Among the products, the viable counts of L. plantarum P8 were more than 1×10~7 CFU/mL, and S. thermophilus L01-2 were more than 1×10~7 CFU/mL. The fermentation of GroupⅠwith single L. plantarum P8 cost the longest time for 15h, while the fermentation with combined strains or single S. thermophilus L01-2 cost the shortest time for only 5h. During fermentation time of GroupⅠ, the viable cells of S. thermophilus L01-2 can be significantly increased (p<0.01) and reach to 3×10~8CFU/mL at the end of fermentation. During storage time, the acidity of products, the contents of free amino nitrogen and the counts of viable cells was not significantly changed, while the viscosity was increased slowly and the capacity of holding water was strengthened. The sensory evaluation scores showed that the fermerntaition of GroupⅠshowed the best characteristics with no whey separated, no smell, no cooking taste, moderate sweet and the pleasing aroma of beans when L. plantarum P8 and S. thermophilus L01-2 was mixed according to the proportion of 1:1.(3) L. plantarum P8 was mixed respectively with S. thermophillus ND03, ND05 and ND07 with different proportion to ferment whole milk with single S. thermophillus as the control. The products would be the best when the combination ratio was 1:1 and the inoculum was 5×10~6 CFU/mL. Compared to other fermentation groups of L. plantarum P8 and S. thermophillus, the group of L. plantarum P8 mixed with S. thermophilus ND05 showed the shorter fermentation time, the higher number of viable counts of S. thermophilus ND05 and the products showed the best characteristics including the higher viscosity, the moderate sweet, the suitable acidity, no whey separated and the favourable stretchability. This combination showed their potential application to the yogurt products.