Optimisation of antioxidants extraction from soybeans fermented by Aspergillus oryzae

The extraction of antioxidant compounds from soybeans fermented with Aspergillus oryzae was optimised using a factorial design. A kinetic study of the total phenolic production and DPPH radical scavenging activity was first performed at the points selected in the factorial design. In both cases, the experimental profiles were fitted to a modified first-order kinetic model. To investigate the combined effects of temperature and solvent concentration on the extraction, the parameters obtained from the fitted kinetic models were used as response variables in a rotatable second-order design with quintuple replications in the centre of the experimental domain. The results obtained indicate that temperature had the most significant effect. The response surfaces show a maximum in the experimental domain studied. The optimum conditions for the extraction of total phenolic content were 65.3 °C and 73.1% ethanol, in which 56.2 mg of GAE/g were predicted. A scavenging activity of 81.6% DPPH radical was predicted at the optimum conditions of 61.6 °C and 60% ethanol.