| Summary: | 碩士 === 國立宜蘭大學 === 食品科學系碩士班 === 106 === Soybean residue and rice bran are rich in nutrients and active components, but high moisture content of extracted residue or high lipase activity could cause rapidly decaying and hard to be application except for animal feed or fertilizer. Radio frequency (RF) can rapidly heat up water molecules or ions in food by rapid conversion of electric field; therefore, RF drying can overcome the heat and mass transfer resistances to accelerate drying processing. The objectives of this study were to dry the soybean residue and to inactive lipase of rice bran by RF heating. Then the soybean residue and rice bran were the media for Poria cocos solid-state fermentation to increase bioactive components and improve antioxidant activities. The results showed that they required 14, 22 and 30 min for reducing moisture content from 80% to 15% to dry 1, 1.5 and 2 kg of soybean residue by RF, respectively. RF drying rate was 25 times of 45℃ cold air drying, and the total energy consumption was reduced to 1/9. The total polyphenols content and DPPH free radical scavenging ability in RF soybean residue were higher than cold air dried soybean residue, but there was no significant difference in color between two different drying methods of soybean residue. RF dried soy residue contains 54.5% of carbohydrates, 27.6% of crude protein and 10.6% of crude fat. On the other hand, 1 kg rice bran was stabilized by RF with gap of 6 cm heating 2 min to inhibit lipase activity without affecting color and antioxidant activity. RF stabilized rice bran contains 48.3% of carbohydrates, 15.4% of crude protein and 19.1% of crude fat. RF really stabilized rice bran during 8 weeks storage at 4, 25, and 37℃. Finally, Poria cocos solid-state fermentation was carried out with different fermentation time periods (0, 30 and 60 days) with 500 g mixed medium (40% moisture content) with different ratios of soybean residue and rice bran (1:0, 2:1, 1:1, 1:2 and 0:1). All the contents of crude polysaccharide, crude triterpenoids, total polyphenols and flavonoids in Poria cocos solid-state fermentation product increased with the increase of the proportion of rice bran in the mixed media and fermentation time. However, considering the time cost and other factors, the suitable Poria cocos solid-state fermentation conditions: 40% of the moisture content, soybean residue and rice bran = 1:1, at 25℃ for 30 days. It took only 30, 200 sec at the RF electrode gap of 15 cm to pasteurize and reduce the moisture content below 15%; therefore, it could replace the traditional sterilization 60 min in an autoclave and cold air drying 100 min at 45℃. RF heating greatly shorten pasteurization and drying time of Poria cocos solid-state fermentation product in 3 min to complete, but also retain the appearance of Poria cocos white mycelium color, to avoid browning. The Poria cocos fermentation product after RF treatment contained 5.03% of mycelium, 9.83% of crude polysaccharide, 4.43% of crude triterpenoids, 3.54 mg gallic acid equivalent/g DW of total polyphenols, 0.38 mg quercetin equivalent/g DW of flavonoid content and good antioxidant capacity. Zebrafish animal experiments confirmed the 200 mg/L extracts from the Poria cocos solid-state fermentation product to have antioxidant activity.
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