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Studies On The Biotransformation Of Tea-catechin Using The Tannase From Aspergillus Niger By Solid-state Fermentation Of Tea Stem

Posted on:2013-04-08Degree:MasterType:Thesis
Country:ChinaCandidate:M Y CaiFull Text:PDF
GTID:2231330374994585Subject:Microbiology
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Tannase (E.C3.1.1.20) which is also named tannin acyl hydrolase, specifically breakdownsester and depside bonds in hydrolysable tannins to release glucose and gallic acid. It hasimportant applictaions in food, cosmetic and leather industries. Researchers have studied thestrain breeding and exploited the applications, but seldom investigated the low-cost fermentationtechniques. In this study, a tannase-producting strain JMU-TS528was identified, and wassubmitted to solid-state fermentation of tea stalk. The tannase was purified, characterized andapplied to biotranform the catechin in oolong tea and green tea. The main results were shown asfollows:1) JMU-TS528strain was identified to be Aspergillus niger through the methods ofmolecular identification and morphological observation; the tannase was prepared usingsolid-state fermentation of tea stem followed by ammonium sulphate precipitation,DEAE-Sepharose ion exchange chromatography and Sephacry S-200HR chromatography.2) The tannase showed optimum activity at pH5.5and50oC; it was stable within pH3.0-7.0and4-60°C. This enzyme was significantly inhibited by Al3+, EDTA and DTT; it wasactivated by Fe2+, Fe3+, Ag+, SDS, Urea, Tween80and Triton X-100. Tannase could hydrolyzepropyl gallate (PG), epicatechin gallate (ECG), epigallocatechin gallate (EGCG), gallocatechingallate (GCG), tannin acid (TA) and digallate (DG), among which it showed the highest affinityto TA, and the biggest Vmaxand Kcattowords GCG.3) The tannase was effective to catalyze the transformation of catechin ester (EGCG, GCGand ECG) in Oolong tea and green tea infusions to deestered catechins epigallocatechin (EGC),gallocatechin (GC), epicatechin (EC) and gallate acid (GA); it catalyzed the hydrolysis of EGCGwith higher reaction velocity than GCG and ECG in the tea infusion. The tannase-treated Oolongtea infusion showed higer DPPH·, ABTS·and OH·cavenging activities of14.5%,15.4%and44.5%, respectively. The tannase treatment increased the DPPH, ABTS·and OH·cavengingactivities of the green tea infusion by24.5%,24.5%and61.7%, respectively. Moreover, theaddition of tannase could reduce the tea-cream and improve stability of the tea infusion.In conclusion, a tannase-producing Aspergillus niger was identified, and the tannase wasprepared by using solid-state fermentation of tea stem. Meanwhile, the porperty and theeffectiveness in transforming the tea-catechin were illustrated, which increased the antioxidantactivity and improved the clarity. These results provide a foundation for the tannase production and application.
Keywords/Search Tags:Aspergillus niger, Tannase, Solid-state fermentation, Characterization, Catechins, Transformation
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