Optimization of the Conditions for Converting Hesperidin to Hesperetin by Aspergillus niger and Comparison of Their Antioxidant Activities
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Abstract:
In this study, microbial transformation method was used to prepare hesperetin by directed biotransformation using Aspergillus nigerstrain (A. niger CP-2) with hesperidin as the substrate. Single factor experiments were carried out on the inoculation amount of A. niger strain, pH, substrate concentration, reaction temperature, and speed of the constanttemperature shaker, then the three important influencing factors, inoculation amount, pH, and substrate concentration were selected for the Orthogonal experiments to investigate the optimal transformation conditions. The results showed that the product of A. niger CP-2 biotransformation was identified as hesperetin by high performance liquid chromatography (HPLC), and the optimal process was determined as follows: inoculum amount of A. niger was 10%, pH value was 7.5, the concentration of hesperidin substrate was 1.0 mmol/L, the temperature of the reaction was 37 ℃, and the speed of the shaking machine was 200 r/min. After 24 h of reaction in this reaction system, the yield of hesperetin was 63.90%. Moreover, the antioxidant activity of the transformed product, hesperetin, and its protective ability against H2O2-induced damage to HCK-8 cells were higher than those of the transformation substrate, hesperidin. Therefore, the biotransformation technology using A. niger can provide a theoretical basis for the high-value utilisation of the active substances in the citrus by-products of the genus Citrus.
