| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 100 === Rice bran is a common underutilized milling by-product of brown rice. It is well-known that rice bran contains amounts of protein, oil, crude fiber, vitamin E, vitamin B complex and minerals. In addition, rice bran also contains some functional and bioactive compounds which are beneficial as an antioxidative agent, hypolipidemic agent and liver protection agent. Moreover, rice bran protein has unique nutritional values and nutraceutical properties which are suitable as a hypoallergenic protein in infant food ingredients. However, the application of rice bran protein in the food industry is still limited due to rapid oxidative rancidity by the formation of free fatty acids by lipase, amounts of starches that are extensively bound to proteins and make it very difficult to separate the protein bodies from these components, and difficulty in protein extraction due to strong aggregation tendency caused by extensive disulfide bonding.
In this study, microwave stabilization treatment (800 W) for fresh rice bran from several initial moisture contents (from moisture content of 7.3% adjusted to 15.0%, 21.0%, 25.0%, and 30.0%) with different period of heating time (0 s to 30 s, 60 s, 90 s, 120 s, 150 s, and 180 s) have been used for extending rice bran shelf-life by lipase inactivation. Effect of intermittently microwave heating treatment (60 s and 150 s) of rice bran stabilization on lipase inactivation and acid value of rice bran samples were investigated. Results showed that lipase activity of rice bran with initial moisture content of 25.0%, heated for 150 s reduced from 3.49 ± 0.22 U/g to 0.96 ± 0.03 U/g, the lipase inactivation was about 72.53 ± 0.86%. Intermittently microwave heating of rice bran with initial moisture content of 25.0%, heated for 150 s could reduce lipase activity. However, the color appearances of rice bran sample had changed and rice bran quality was decreased for further food uses. For acid value level determination, rice bran with initial moisture content of 25.0%, heated for 150 s could be store at 4°C, 25°C, and 40°C for 12 weeks.
For biotransformation by 0.6% of α-amylase enzymatic treatment at 55°C with pH 6.5 for 30 minutes, starch removal rate were 67.92 ± 0.48%, 68.56 ± 1.84%, and 64.12 ± 1.93% for raw rice bran, microwave stabilized rice bran with initial moisture content of 25.0%, heated for 150 s, and defatted microwave stabilized rice bran with initial moisture content of 25.0%, heated for 150 s, respectively. Protein recovery reached above 90.0%.
For SDS-PAGE patterns of raw rice bran, microwave stabilized rice bran with initial moisture content of 25.0%, heated for 150 s and defatted microwave stabilized rice bran with initial moisture content of 25.0%, heated for 150 s with/without α-amylase enzymatic treatments showed no smeared bands of polypeptides for the protein. It might prove that α-amylase enzymatic treatments at 55°C with pH 6.5 for 30 minutes did not cause any substantial damage to protein.
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