| Summary: | 碩士 === 國立嘉義大學 === 食品科學系研究所 === 104 === Rice is one of the most important crops in Asia. Among the collected germplasms, some varieties bear various bran colors, called colored rice. It is commonly observed that deep-colored rice exhibit higher antioxidant activities and confer more health benefits than the white colored rice, mainly due to presence of anthocyanins and proanthocyanidins. Miso is generally produced by mixing and grinding cooked soybean with salt and rice koji into paste and sudjected to fermentation. During fermentation, various enzymes released form rice koji (Aspergillus oryzae) function extensive decomposition of the large molecules such as soybean proteins and rice starch. Miso bearing high contents of protein, vitamins, minerals and dietary fiber is one of the popular fermented foods. However, some consumers concern the generally high salt level in miso mainly based on the viewpoint of health consideration. Therefore, in this study, various colored rice (purple rice, red rice 10003, red rice 10005 and Red Indica) were collected and subjected to investigation of antioxidant activities. Accordingly, based on antioxidant performance, the purple rice was selected for preparation of rice koji and used in the followed salt-free miso fermentation. In HPLC analysis of the aqueous extracts of the purple rice and in reference of the reported literature, cyanidin-3-glucoside and peonidin-3glucoside were detected as the major pigments. During rice koji preparation by inoculation with Asp. oryzae conidiospores and incubation for 5 days, antioxidant activities of the aqueous rice extracts increased with an increase of incubation time. When the extracts were subjected to HPLC analysis and detection with 280 nm, a new flavonoid peak was be and the integrated peak areas increased with time of incubation. In further regression of the peak areas and the detected antioxidant activities, linear correlations between peak area with reducing powers (R2 = 0.8776) and trolox equivalent antioxidant capacity (R2 = 0.7603) were observed, respectively. After collection of the substance under the specific peak by repeated HPLC analyses of the 5-day-koji aqueous-extracts and subjected to LC/MS/MS analysis, based on the fragmented m/z values, a major m/z fragment with 384 was detected and assumptively identified as sinapoyl glucose which might be hydrolyzed from cyanidin + hexose + pentose + sinapoyl. In free-salt miso fermentation with ethanol and sugar in substitution of salt for 8 weeks, antioxidative activities of the 8 week-fermented miso aqueous extracts were higher than those of 0 and 4 week-fermented miso extracts. In HPLC analysis of the aqueous miso extracts monitored at 490 nm, contents of cyanidin-3-glucoside and peonidin-3-glucoside decreased significantly after 8-week fermentation. As subjection of miso to L, a and b determination and displayed by Hunter’s Lab system, miso color changed from bright purple to dark and yellow to red. During miso fermentation, pH values decreased and content of small molecular N-containting compounds increased. As generally concluded, in addition to the selected purple rice bearing potential antioxidant activities, enhanced antioxidant activities were demonstrated when the rice were subjected to rice koji preparation and salt-free miso fermentation. This is of virtue to merit use of the purple rice in development of low-salt fermented foods.
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