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工艺，考察了发酵豆渣（okara）抗氧化活性的提升效果。研究表明，初始真菌接种浓度与水分活度（water activity）会显著影响发酵豆渣的抗氧化能力提升幅度。胞外酶（extracellular enzymes），尤其是蛋白酶（proteases）与碳水化合物酶（carbohydrases），可能促进豆渣蛋白水解，生成具有抗氧化活性的氨基酸与肽类，同时释放异黄酮类组分。研究发现，采用少孢根霉（R. oligosporus）发酵豆渣，当初始接种浓度为1.04×10^-3 gDCW/gokara、水分活度为0.931时，可获得最高的抗氧化活性水平。而米曲霉（A. oryzae）的最优初始接种浓度为1.6×10^-3 gDCW/gokara，对应最优水分活度为0.913。在上述最优条件下，固态发酵豆渣可使少孢根霉与米曲霉发酵产物的抗氧化活性分别提升至原水平的2.6倍与5.5倍。此外，发酵豆渣不仅抗氧化活性得到增强，其蛋白质含量、氨基氮含量与蛋白质消化率也均有所提升。