| Summary: | 碩士 === 實踐大學 === 食品營養與保健生技學系碩士班 === 103 === Soybean derived products are oriental traditional foods and a lot of people are used to taking them as convenient and instant protein supplements especially in the form of soymilk. In order to cut the production cost, most packaged soymilk producers may add artificial thickeners in their products to enhance texture qualities. This study is thus conducted to investigate the feasibility of using natural exoplysaccharides (EPS) produced by lactobacilli strains as texturing agents to substitute artificial thickeners. Lactic acid bacterial strains having the high yield of EPS production were screened and the effects of different carbon sources on their EPS production were also explored. The domestic soybean harvested from a Kaohsiung 10 soybean strain was used to make soymilk for fermentation. Several screened lactobacilli strains were then used to ferment soymilk additionally spiked with 0%, 2%, and 4% of glucose respectively for 8 hours at 37℃, followed by storage at 4% for 7 days. The bacterial counts, pH, EPS concentration, viscosity, and titratable acidity were analyzed. The results showed that 22 trains screened from more than 100 strains of lactic acid bacteria gave high yields of EPS with concentrations more than 200 mg/L. Among them, 4 potential probiotic strains, ST74, ST85, ST88, and ST94, were selected for further studies based on their acceptable resistance of acids, tolerance of bile salts, and meeting of gastrointestinal tract simulation test. Strain identification of three strains by API 50 kits indicated that they are Lactobacillus fermentum ST74, Lactobacillus fermentum ST85, and Lactobacillus buchneri ST88 respectively. Glucose was a better carbon source in exopolysaccharide production, showing a positively direct correlation of increasing EPS yields with increasing glucose addition, compared to fructose with a negative correlation. At a concentration of 4% glucose, strain ST85 exhibited the highest production of EPS, resulting in a concentration of 350 mg/L.
The increasing viscosity of fermented soymilk by L. fermentum ST85 was correlated with increasing EPS production, suggesting that this strain may have the potential as a fermentative probiotics in soymilk fermentation, but still requiring a further study on the feasibility of its
|
|---|
