Production Of Tannase From Aspergillus Niger By Solid-state Fermentation Of Tea Stalks And Its Application In Tea Processing

In the present paper,the agricultural byproduct,tea stalks,were thoroughly used to prepare tannase by solid-state fermentation?SSF?.First of all,the fermentation parameters were optimized through a sequential statistical strategy.Then,the tannase from Aspergillus niger by SSF was used to treat tea stalks and inferior Tie Guanyin tea.And the effects of tannase-aided treatment on catechin contents and bioactivitives were investigated.The results were showed as follows.Among the seven tested variables,inoculum size and incubation time were identified as the most significant factors for tannase production via a Plackett-Burman design?PBD?.Then,the levels of the two significant variables were further optimized through a single steepest ascend experiment and central composite design?CCD?with response surface analysis.The ANOVA results demonstrated that the model was highly significant,so it can be used to navigate the design space.The optimal conditions were:5 g tea stalks power in a 250 m L Erlenmeyer flask,accompanied 5%?w/w?NH₄Cl and?-lactose,a basal salt solution at initial pH 6.0,liquid-to-substrate ratio?v/w?2,culture temperature 28oC,inoculum size 4.35 mL?1×10⁸spores/mL?.Under the optimal conditions,the experimental value of tannase activity reached84.24 U/gds,which was closely matched the predicted value?87.26 U/gds?.Optimization process resulted in an increased yield of tannase activity by two-fold?from 40.22 to 84.24 U/gds?over the basal medium.With the help of tannase,catechins in the tea and 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 production of gallic acid.Compared to untreated tea stalk infusion,total catechins in tannase-treated analog increased by 11.5%,and ester catechins decreased by 94%,along with the increased contents of non-ester catechins and gallic acid?156%and 684%,respectively?.However,after treated by tannase,the total catechins in inferior Tie Guanyin did not change much,but ester catechins decreased by 23.5%,and non-ester catechins and gallic acid increased by 15.3%and 182%,respectively.The tannase-treated infusion had a relatively lower binding ability with protein and less tea cream formation,which is good to increase clarity and stability of tea and tea stalk infusion.These compositional changes had a positive meaning to improve the taste of defective tea and tea stalk extracts.After treated with tannase,the antioxidant activity of tea and tea stalk 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.And the IC₅₀ of tannase-treated tea infusion were only 43.3%and 86.4%of the control group.Assays of pancreatic?-amylase and lipase activities were used to evaluate the effects of tannase treatment on hypoglycemic and hypolipidemic activities in tea and tea stalk infusion.With or without tannase treatment,Tie Guanyin and tea stalk had some inhibition rate of pancreatic?-amylase and lipase activities.However,the inhibition rate of tannase-aid tea stalk infusion increased,and that of tannase-treated tea decreased on the contrary.The results demonstrated that tea and tea stalks with tannase treatment can obtain better quality attributes.In conclusion,tannase from Aspergillus niger by solid-state fermentation of tea stalks was used to treat tea stalks and inferior Tie Guanyin in order to taking advantage of agricultural byproduct,tea stalks.Meanwhile,the property and effectiveness of tannase on tea catechins were illustrated,which increased the clarity and antioxidant capacity of tea extracts,along with some hypoglycemic and hypolipidemic activities.These results provide a theoretic foundation for tannase production as well as its application in tea and tea stalk processing.