Effects of Solid Fermentation of Aspergillus niger on Release of Bound Phenols and Antioxidant Activity of By-products of Pueraria thomsonii

In order to improve the utilization value of the by-products from the Pueraria thomsonii and clarifie the release law of bound phenols, Aspergillus niger was used for solid state fermentation of kudzu peel and kudzu dregs. The contents of bound phenols, activities of cellulase and β-glucosidase were measured during fermentation. The types and contents of bound phenols released after fermentation were investigated by high performance liquid chromatography (HPLC). The antioxidant activities of two by-products extracting solution of Pueraria thomsonii were measured during fermentation. The results showed that the fermentation of Aspergillus niger could effectively release the bound phenols in the by-products of Pueraria thomsonii, and the content of the released bound phenolic substances increased significantly with the increase of fermentation time (P<0.05). After fermentation for 7 days, the bound phenols content in the kudzu peel and kudzu dregs was 1.63±0.11 mg/g and 0.93±0.05 mg/g respectively. The maximum cellulase activity of kudzu peel was 662.74±17.06 U/g on the 6th day of fermentation and the highest β-glucosidase activity was 332.64±26.52 U/g on the 7th day of fermentation. The maximum cellulase activity of kudzu dregs was 885.79±66.06 U/g on the 7th day of fermentation and the highest β-glucosidase activity was 354.63±9.45 U/g on the 3rd day of fermentation. There was a positive correlation between the release of phenols and the activities of cellulase and β-glucosidase during fermentation. The liquid phase results showed that 3'-hydroxypuerarin, p-hydroxybenzoic acid, puerarin and daidzein were contained in the fermentation product extract solution. The scavenging ability of fermentation product extract solution for DPPH· and ABTS+· increased with the increase of fermentation time. The results showed that the by-products of Pueraria thomsonii solid fermented by Aspergillus niger could promote the release of bound phenols and improve the antioxidant activity of fermentation solution.