| Summary: | 碩士 === 國立嘉義大學 === 食品科學暨生物藥學研究所(Graduate Institute of F === 98 === The purpose of this study was to investigate the antioxidant activity of extracts obtained from buckwheat by different solvents extraction and further purified by the column fractionation. We also investigated the optimum roasting conditions of buckwheat and brewing conditions of roasted buckwheat tea, and storage stability of buckwheat tea can.
Result showed that the order of extraction yield was methanol＞ethanol＞acetone＞ethyl acetate＞n-hexane. The buckwheat crude methanol extract (BCME) had the highest total flavonoid content (TFC) and total phenolic content (TPC) which was 12.43 RE mg/g dm and 7.72 FAE mg/g dm, respectively. The result of antioxidant activity determination showed that BCME had the highest DPPH radical scavenging activity, ferrous ion chelating capacity, reducing power and inhibitory power of conjugated dienes among the samples. The fractionation of BCME by using Amberlite XAD-2 column, the BCME was further eluted with water, 20%, 40%, 60%, 80% and 100% methanol in sequence. After fractionating, results showed that the water fraction had the highest amount of eluate and the 60% methanol fraction had the highest TFC (786.06 RE mg/g dm) and TPC (707.64 FAE mg/g dm). In addition, the 60% methanol fraction also had the highest DPPH radical scavenging activity and reducing power and inhibitory power of conjugated dienes. The DPPH radical scavenging activity of 60% methanol fraction was similar to BHT and α-tocopherol at 50ppm and its reducing power was similar to BHT and α-tocopherol at 500ppm and its inhibitory power of conjugated dienes was similar to BHT and α-tocopherol at 1000ppm while the ferrous ion chelating capacity was low. The main antioxidant compounds of 60% methanol fraction were rutin, catechin, 4-hydroxybenzoic acid, chlorogenic acid, vanillic acid, p-coumaric acid and ferulic acid.
When buckwheat was roasted at 140℃ for 1hr, the antioxidants content and antioxidant activity and sensory evaluation was the best. In the brewing test of roasted buckwheat tea, the results showed that the optimum conditions were the ratio of buckwheat to water 1:10 (w/v) and hot water of 100℃ and brewing time of 5min due to a high antioxidants content and antioxidant activity. In the storage test of the roasted buckwheat tea drink (bottled), the results showed that the antioxidants content and antioxidant activity of the can no markedly decreased after storage for 2~6 months. After 6 months storage, the overall score of the can still high by sensory evaluation.
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