| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 97 === Rice is one of the commonly consumed cereals for our country. It is also used for making traditional fermented food. Rice was used as substrate for preparing rice-koji by several strains of Aspergilius oryzae in this study. Results showed Aspergillus oryzae NCH K-2 was chosen as the best one. A. oryzae NCH K-2 with enzymatic activities such as α-amylase and protease was then used to hydrolyze rice powder(20 mesh). The rice hydrolysates were subsequently inoculated by a lactic acid bacterium Lactobacillus kefiranofaciens BCRC 16059 and cultivated. The optimal medium composition were studied using rice hydrolysate as major source of medium. Moreover, the antioxidant capacity and contents of some functional components including exopolysaccharide were investigated.
Results showed that, the optimum time for koji-making was 48 hours. The highest amylase activity of rice koji was 131.64 U/g and acid protease activity was 1035.3 U/g, respectively. 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. When brown rice powder was used as the substrate, the total soluble solid and amino nitrogen content of the rice hydrolysates were 10.5 oBrix and 0.0285 g/100mL under this condition, respectively. The rice hydrolysate was diluted 3 folds, and supplemented with 1.5 % rice bran as nitrogen source was named as modified rice hydrolysate which can be used for cultivating L. kefiranofaciens BCRC 16059.
The highest DPPH free radical scavenging activity, trolox equivalent antioxidant capacity, reducing power and hydrogen peroxide scavenging activity of the fermentation broth obtained by fermenting the modified rice hydrolysate with L. kefiranofaciens BCRC 16059 were enhanced. On the other hand, L. kefiranofaciens BCRC 16059 has the ability of production exopolysaccharide. Therefore, the highest polysaccharide production of L. kefiranofaciens BCRC 16059 with the modified rice hydrolysate was about 0.742 mg/mL, while the GABA content remained constant in the fermented broth. However, the modified rice hydrolysate which contained GABA in itself could ensure the functionality of fermented drink.
The consumer preference test was performed for four kinds of tested samples, including the modified rice hydrolysate before and after fermentation, and the sweetness of the fermented broth was adjusted to 5 oBrix and 10 oBrix. Results showed that, the fermented broth with the sweetness being 10 oBrix had the highest score on overall intensity, followed by the 5 oBrix and fermented broth, and the overall intensity of modified rice hydrolysate without fermentation was the lowest. This study proved that the fermented broth by lactic acid bacterium could be developed as a nutritious fermented drink with characteristic flavor.
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