Enhanced antioxidant activity of okara through solid state fermentation of GRAS Fungi

Abstract The enhancement of antioxidant activity of fermented okara was investigated using fungal solid-state fermentation. The initial fungal concentration and water activity were found to influence the enhanced antioxidant capacity of fermented okara. Extracellular enzymes, especially proteases and carbohydrases might facilitate the hydrolysis of okara protein that yielded antioxidative amino acids and peptides, as well as the release of isoflavones-derived components. Fermentation of okara with R. oligosporus with 1.04×10-3 gDCW/gokara as initial concentration, water activity of 0.931 was found to yield the highest antioxidant strength. Whereas for A. Oryzae, 1.6×10-3 gDCW/gokara was optimum as the initial concentration with water activity of 0.913. With these optimum conditions, solid-state fermentation of okara could enhance the antioxidant activity up to 2.6- and 5.5-fold, respectively for R. oligosporus and A. oryzae. Besides having an enhanced antioxidant activity, the fermented okara also had higher protein content, amino nitrogen content, and protein digestibility.

摘要 本研究采用真菌固态发酵（solid-state fermentation）技术，探究了提升豆渣（okara）抗氧化活性的效果。研究发现，初始真菌浓度与水分活度会显著影响发酵豆渣的抗氧化能力提升效果。胞外酶（extracellular enzymes），尤其是蛋白酶（proteases）与碳水化合物酶（carbohydrases），可促进豆渣蛋白水解，生成具有抗氧化活性的氨基酸与肽类，同时释放异黄酮（isoflavones）衍生物。采用少孢根霉（R. oligosporus）发酵豆渣时，当初始真菌浓度为1.04×10^-3 gDCW/g豆渣、水分活度为0.931时，所得发酵产物的抗氧化活性达到最高水平。而米曲霉（A. oryzae）的最优初始真菌浓度为1.6×10^-3 gDCW/g豆渣，最优水分活度为0.913。在上述最优条件下，固态发酵豆渣可分别使少孢根霉与米曲霉发酵产物的抗氧化活性提升至原始水平的2.6倍与5.5倍。此外，发酵后的豆渣不仅抗氧化活性得到增强，其蛋白质含量、氨基氮（amino nitrogen）含量与蛋白质消化率（protein digestibility）也均有显著提升。