Studies On The Application Of Lactobacillus Helveticus And Lactobacillus Casei In Soy-based Yogurt Preparation

Lactobacillus helveticus LH-B02 and Lactobacillus casei L.casei-01 were proved growing well in soy milk to produce soy cheese, so we studied them combination of Lactobacillus bulgaricus and Streptococcus thermophilus in soy milk.The growth of different combinations of Lactic acid bacteria in soymilk under fermentation were sdudied. The pH value, acidity, sensory characteristics and texture properties of soy-based yogurt fermented by the starter combination of Lactobacillus casei L.casei-01, Streptococcus thermophilus IFFI 6038, Lactobacillus bulgaricus AS1.1482 and the starter combination of Lactobacillus helveticus LH-B02 Streptococcus thermophilus IFFI 6038, Lactobacillus bulgaricus AS1.1482 were studied. The results indicated that the optimal soy-based yogurt was able to be obtained when a mixture of soymilk and reconstituted skim milk (7:3) was made and fermented by the starter combination of Lactobacillus helveticus LH-B02 Streptococcus thermophilus IFFI 6038, Lactobacillus bulgaricus AS1.1482 in this study.The effect of addition of reconstituted milk and ratio of soy with water on texture was studied. The four kinds of soy milk were made by water at ratios of 1:6, 1:8, 1:10, and 1:12. These four kinds of soy milk were fermented by Lactobacillus helveticus LH-B02 Streptococcus thermophilus IFFI 6038, Lactobacillus bulgaricus AS1.1482, and the pH value, titratable acidity and texture properties were studied. The soy milk made by water at ratio of 1:10 added 10%, 20%, and 30% milk were also studied; and the four kinds of soy-based yogurt were stored 1day at 4℃prior to microstructure analysis. Finally, we choose the ratio with water and soy 1:10 and the addition of reconstituted milk 30%.Fermentation process of Lactobacillus helveticus, Lactobacillus casei and the combinations of other different LAB were also studied. The pH values and titratable acidity of fermented reconstituted skim milk (RSM), pure soymilk (PSM) and mixed milk (MM) by single Lactobacillus helveticus LH-B02, Lactobacillus casei L.casei-01, and the combination of Streptococcus thermophilus IFFI 6038 and Lactobacillus bulgaricusAS1.1482 were determined. The single Lactobacillus helveticus LH-B02 grew well in RSM, the production of acidity was higher than Lactobacillus casei L.casei-01, but Lactobacillus helveticus LH-B02 grew not so well in PSM. Comparing to Lactobacillus helveticus LH-B02, Lactobacillus casei L.casei-01 grew well in PSM. The combination of Lactobacillus helveticus LH-B02 and Lactobacillus casei L.casei-01, the respective combination of Streptococcus thermophilus IFFI 6038 and Lactobacillus bulgaricusAS1.1482 can grow well in PSM. The SDS-PAGE analysis proved that the protein depredated by lactic acid bacteria was almost unchanged but for lipase. Furthermore, the L-lactic acid and D-lactic acid of soy-based yogurt fermented by 6038+1482+L.casei-01,6038+1482+LH-B02 and L.casei-01+LH-B02 were determined by HPLC. The result showed that the highest ratio of L-lactic acid was soy-based yogurt fermented by L.casei-01+LH-B02.The trypsin inhibitor (TI) activities of soy products were studied in the producing of soy-based yogurt. The results showed that soy soaking by 0.5% sodium bicarbonate solution for 12 hours can't increase the activity of soy TI. It showed that the effect of temperature and time were obvious. The soy TI can decrease to the aim of our need under 100℃for 15min. The effects of fermentation by lactic acid bacteria (LAB) and addition of milk were also studied. We can conclude that the activities of TI can be decreased by LAB, but there was no more different among different combination of LAB, and the addition of milk can also reduce the activity of TI.