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微波乾燥黃豆渣和其抗氧化性的研究
Study on Microwave Drying of Soybean Residue and its Antioxidant
摘要
黃豆經研磨成豆漿的製程中會產生約1.2倍的濕黃豆渣，因其產量大、水分含量高易快速腐敗，需乾燥以增加其應用性和經濟價值，事實上，微波乾燥可使食品內的極性水分子快速震動和離子移動而產生熱，使水分蒸發以達到快速乾燥之效果。故本研究之試圖根據熱風乾燥和冷凍乾燥的黃豆殘渣的最終特性（例如:抗氧化活性）提出有希望的微波乾燥方法。由1、2和3 kg的黃豆渣在不同微波功率（1、2和3 kW）之乾燥動力學，以3 kW微波乾燥黃豆渣有較快的乾燥速率，在1、2和3 kg黃豆渣的乾燥速率分別為36.917、41.004和44.107 g H2O/min，且分別需22.70、39.25和53.80 min，然而使用80℃熱風乾燥和傳統冷凍乾燥分別需要5.5hr及24hr。再將乾燥黃豆渣進行一次95%乙醇微波萃取，後以50mg/mL萃取液進行抗氧化成分及抗氧化性質測定。結果顯示三種乾燥方式的類黃酮含量並無明顯差異，皆為0.045mg/g，在多酚含量和DPPH清除自由基能力分別為0.97-1.35 mg/g和10-15%。而微波乾燥和冷凍乾燥的黃豆渣在明亮度（L*）為82，二者無明顯差異，不過高於熱風乾燥黃豆渣，故微波乾燥黃豆渣可保有良好抗氧化能力與明亮度，又可大幅縮短乾燥時間。
並列摘要
Soybean milk could generate about 1.2 fold of wet soybean residue in the soybean grinding processes. Due to large output, high moisture content and high elevated rate of decaying of such residues, drying processes inevitably required to be applied with consideration of economic feasibility. In fact, microwave drying caused substantial binding vibration and movement of polar water molecules in food to generate heat; therefore, water could be effectively evaporated for fast drying. This study tended to suggest a promising microwave drying process according to resultant characteristics ( e.g., antioxidant activity) of hot air dried and freeze dried soybean residue. As transient drying dynamics of 1, 2, and 3 kg of soybean residue and different microwave powers (1, 2, and 3 kW) indicated, drying rate of the soybean residue seemed to be more favorable at 3000 W. The drying rates of 1, 2, and 3 kg of soybean residue were 36.917, 41.004, and 44.107 g H2O/min, and they required 22.70, 39.25, and 53.80 min, respectively. However, they required 5.5 and 24 hr were demanded for 80°C hot air drying and conventional freeze drying, respectively. The dried soybean residue was first microwave extracted through 95% ethanol. The resulting antioxidant chemical species and antioxidant activities of the extracts revealed that there were no significant differences in flavonoid content (0.045 mg/g) of the three dried products. The polyphenolic content and DPPH radical-scavenging activity were 0.97-1.35 mg/g and ca. 10-15%, respectively. Apparently, microwave dried and freeze dried soybean residues showed no significant difference in the brightness (L*) (ca. 82) still higher than hot air dried product. Therefore, microwave drying could maintain antioxidant activity and owned brightness like the freeze-drying method. Of course, microwave drying could significantly decrease the drying time.