Abstract: By determining the content of glutathione (GSH),SOD enzyme activity,and hydroxyl free radical scavenging ability of 12 yeast strains and total reducing capacity,and superoxide anion free radical scavenging ability of 8 lactic acid bacteria,Y1 (Candida utilis) and L8 (Lactobacillus casei) with high antioxidant activity were screened.The changes of tyrosinase inhibition rate and total reducing capacity of 14 kinds of Chinese traditional herb medicine with mixed bacteria (Y1 and L8) were compared before and after fermentation.Based upon test results,it is suggested that Rhodiola rosea (after fermentation) is the best Chinese traditional herb medicine to be used.Rhodiola rosea as the starting material is to be hydrolyzed by cellulase-pectinase complex enzyme;with tyrosinase inhibition rate as the index;the conditions for fermentation of Rhodiola rosea with mixed bacteria were optimized by using response surface methodology.Results indicate that the conditions of Rhodiola rosea fermented by mixed bacteria can be recommended as follows:glucose mass fraction,12.35%;liquid-solid ratio,18.67∶1 (mL∶g);fermentation time,5.25 d.Under such conditions,the tyrosinase inhibition rate achieves 73.21%,which is 67.72% higher than that before the fermentation.

Key words: skin-whitening agent, antioxidation, mixed bacteria fermentation, Rhodiola rosea, response surface methodology