| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系 === 95 === Although brown rice contains almost the complete nutrition of rice, it is hard to be utilized in the daily diet due to difficulty in cooking and digestibility. A new fermented beverage combining two functional food elements, nutritious brown rice and fermentation, was developed in this study.
Several strains of Aspergilius oryzae were inoculated to steamed rice to produce rice-koji. High enzymatic activities were obtained when rice-koji was incubated for 2 days. Finally, A. oryzae BCRC 32279 was chosen for subsequent experiment due to its balanced activities of both amylase and acidic protease at same time. The optimal saccharifying conditions for rice-koji to hydrolyze brown rice were performed at 50℃ for 10 h. The soluble solid and amino nitrogen content of the hydrolysates were about 20 oBrix and 0.04%, respectively. Moreover, higher soluble solid and amino nitrogen content were obtained if brown rice was pulverized. Saccharified mash of brown rice were thereafter fermented with yeasts (Saccharomyces cerevisiae K901 and C2109) or lactic acid bacteria (Lactobacillus casei BCRC 14080 and Lactobacillus plantarum BCRC 10069). For yeasts, the results showed, greater amount of metabolites were produced as fermentation temperature increased from 10℃ to 20℃. The alcohol fermentation was stopped once ethanol concentration reached 1% (w/w), then it took fermented at about 10 h, 25 h and 40 h for temperatures at 20℃, 15 ℃ and 10℃, respectively. As for lactic acid fermentation, the results showed soluble solids content, pH value and concentration of sugars were decreased while titratable acid, viable count and concentration of lactic acid were increased with fermentation time. The optimal fermentation time was 48 h.
Finally, the antioxidative activites of fermentation broth by yeast fermentation either at 10℃ or 15℃ was better than that at 20℃; and S. cerevisiae K901 was better than C2109. As for fermentation broth obtained with lactic acid bacteria for 48 h had the highest antioxidative activity, and L. plantarum was better than L. casei. Analyses of GABA content for fermentation broth obtained from alcohol fermentation by yeasts were from 0.282 to 0.377 mg/mL, while those from lactic acid bacteria ranged from 0.561 to 1.45 mg/mL. The results revealed that lactic acid bacteria, as compared to yeasts, were useful for the production of GABA.
Finally, results of the consumer preference test showed that the score of C2109+Lc was the highest. Briefly, the fermented drink made by mixed fermentation broth from yeast with lactic acid bacterium (1:1, v/v) was more popular than the fermented drink only by yeast or lactic acid bacterium alone.
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