| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 91 === Abstract
The study was conducted to investigate the fermentation of soymilk with five commercial probiotics such as Streptococcus thermophilus, Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus helveticus, Lactococcus lactis. Results indicated that these five probiotics could grow in soymilk medium and their final viable cells number could reach to 107∼108 CFU/ml. Probiotic soymilk was prepared by fermenting soymilk product to pH 4.6, and then evaluated its sensory preference. It showed that soymilk fermented with L. helveticus and L. lactis were the most popular. Therefore, probiotic soymilk fermented with these two strains was tested in the follow-up experiments. In acid tolerance test, these two strains were able to maintain viable cells more than 108 CFU/ml at pH 3 for 4 h. Cells number of L. helveticus decreased 5.7 log after treatment at pH 2.5 for 3 h. On the other hand, L. helveticus in fermented soymilk decreased 1.3 log after treatment at pH 2.5 for 4 h. L. lactis decreased 3.7 log after treatment at pH 2.5 for 4 h; while in soymilk under the same treatment L. lactis could survive for 4 h without any loss of cell viability. L. helveticus could not survive at pH 2, while in fermented soymilk this strain could survive for 3 h and decrease 6.8 log. L. lactis could survive at pH 2 for 1 h and decrease 1.7 log. In fermented soymilk this strain could survive for 3 h and decrease 6.7 log. In bile tolerance tests, these two strains could survive in MRS broth contain 1-2% bile, their final cells numbers were more than 109 CFU/ml. Antimutagenic activity of soymilk fermented with L. helveticus and L. lactis against 4-nitroquinoline N-oxide (4-NQO) was 58% and 75%, respectively.
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