Abstract: In order to promote the resource utilization of herbal tea residue,the solid-state fermention using Aspergillus niger was adopted in this study.The effects of six single factors,including time,temperature,water content,initial pH,nitrogen source,and carbon source,on the degradation rate of herbal tea residue and product pH after fermentation were investigated.According to the single factor experimental results and the actual situation of large-scale production,4% ammonium sulfate was used as nitrogen source,2% glucose as carbon source,through orthogonal experiments,the fermentation process was optimized with the degradation rate as the index.The antioxidant activity of herbal tea residue before and after fermentation was evaluated by measuring superoxide radical scavenging rate,hydroxyl radical scavenging rate and DPPH radical scavenging rate.It was found that the optimal parameters of fermentation were water content 60%,pH 9.0,31 ℃ for 168 h.Under the optimum conditions,degradation rate of herbal tea residue was 25.23%,products pH was 4.53.As the concentration of water-extract of herbal tea residue before fermentation was 24 mg/mL,the scavenging rates of superoxide radical,hydroxyl radical and DPPH radical were 43.56%,47.06% and 90.71%,respectively.When the water-extract concentration of product was 24 mg/mL,the scavenging rates of superoxide radical,hydroxyl radical and DPPH radical were 30.77%,95.63% and 87.36%,respectively.The results showed that Aspergillus niger was suitable for fermentation of herbal tea residue,and herbal tea residue had good antioxidant activity after fermentation by Aspergillus niger.

Key words: herbal tea residue; Aspergillus niger; orthogonal experiment; degradation rate; antioxidative activity