Tannase treatment improves contents of catechins and bioactivity of tea stalk infusion

Abstract: Tea stalk, also known as tea stem, a residue obtained from the process of initial tea selection, is a very abundant and low-cost agricultural byproduct which is plentifully available in southern China, and its use has not been exploited and standardized. In this study, in order to use the agricultural byproduct, tea stalk, thoroughly, tea stalk infusion was prepared with the help of tannase preparation from Aspergillus niger JMU-TS528 by the solid state fermentation of tea stalks. Then, the property and effectiveness of a tannase-aided treatment on the contents of catechins and bioactivity changes in tea stalk infusion were illustrated, including their antioxidant activity and inhibitory potential against pancreatic α-amylase and lipase in vitro. Results showed that, with the help of tannase (2 U/mL) treatment at 50oC for 60 min, the contents of catechins in enzymatic hydrolysis tea stalk infusion changed a lot, much ester catechins (EGCG, GCG and ECG) were hydrolyzed into non-ester ones (EGC, GC and EC, respectively), accompanied by the production of gallic acid. Compared to untreated tea stalk infusion which was extracted by boiling water, th total catechin in a tannase-treated analog increased by 11.5%, and ester catechins decreased by 94%, along with the increases of non-ester catechins and gallic acid (156% and 684%, respectively). Meanwhile, the tannase-treated infusion had a relatively lower binding ability with protein and less tea cream formation, which were effective in improving the clarity and stability of tea stalk infusion. Furthermore, after being treated with tannase, the antioxidant activity of tea stalk infusion had a significant increase, as the tannase-treated tea stalk infusion had a greater OH· and DPPH· scavenging effects with their IC50 decreased by 74.1% and 25.9%, respectively. In addition, assays of pancreatic α-amylase and lipase activities were used to evaluate the effects of tannase treatment on pancreatic enzymes inhibitory activities of tea stalk infusion. And whether it was extracted with tannase solution or water, tea stalk had some inhibition rate on pancreatic α-amylase and lipase activities. However, the tannase-treated tea stalk infusion had a significantly higher inhibition rate of pancreatic α-amylase and lipase activities than the untreated analog (89% and 107%, respectively) at a concentration of 5000 mg/L. Results from this study demonstrate that tea stalk infusion with tannase treatment can obtain better quality attributes, which is promising for the economic utilization and value addition of some important agro residues.