| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系 === 96 === Various kinds of rice products (polished rice, brown rice, and purple rice) were hydrolyzed by a rice koji Aspergillus oryzae BCRC32279, which has high enzymatic activities of α-amylase and protease, to obtain rice hydrolysates. The hydrolysates were then inoculated by a lactic acid bacterium Lactobacillus kefiranofaciens and cultivated. The optimal medium composition and cultivation conditions were studied and contents of some functional components including exopolysaccharide were studied during lactic acid fermentation. Results showed that the highest amylase activity of rice koji was 65.47 U/g and acid protease activity was 132.87 U/g after two days of cultivation. The optimum condition for preparing rice hydrolysate was rice koji, rice powder, and water in a ratio of 1:1:6, and the hydrolysis was performed at 55℃ for ten hours. The total soluble solid content of the rice hydrolysate was about 14 oBrix under this condition.
The rice hydrolysate was diluted 4-fold, and supplemented with 1 % peptone, 1 % beef extract and 1 % yeast extract as nitrogen source, and some mineral salts. Finally pH value was adjusted to 5.5. The medium was named as modified rice hydrolysate which can be used for cultivating L. kefiranofaciens. Addition of 1 % lactose enhanced further the production of exopolysaccharide. The highest exopolysaccharide production of L. kefiranofaciens with the modified rice hydrolysate was obtained at initial pH 5.5 and cultivated at 33℃ for 6 days. The content of exopolysaccharide was about 0.3 mg/mL, lactic acid was about 30 mg/mL, and γ-aminobutyric acid (GABA) content was about 0.1 mg/mL in the culture broth. Furthermore, the production or content of these functional components were not affected by the rice hydrolysates prepared by different rice products. Co-culture of L. kefiranofaciens with Saccharomyces cerevisiae didn’t promote exopolysaccharide production, either.
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