Effect Of Amino Acids And Sugars On The Quality Of Pu-er Tea

Modern research revealed that Maillaid reaction can greatly improve the aroma and teasoup of puer tea. Amino acids and sugars could improve the tea quality through Maillaidreaction. However, reports on this field of research are limited in numbers. In this study, basedon spectrophotometric method and chromatism analysis, the effect of exogenous amino acidsand simple sugars, as well as their complex on the quality of the scattered pu-erh tea has beenstudied. The exogenous amino acids and simple sugars which can greatly improved the puerteas quality have been optimized, the aroma characteristics, the antioxidant activity and thecatechin composition of the optimized samples have also been analyzed.Contents of tea polyphenols (TP), catechin, free amino acid (FAA), caffeine, solublesugar, TR, TF and TB were determined and analyzed. The results showed that exogenoussugars could significantly reduce contents of FAA in tea, which demonstrated the occurrenceof Maillaid reaction. Exogenous sugars also reduced the ratio of TP and tea polysaccharide(TP/TPS), improved the quality of samples. Among all the treatments of exogenous sugars,sample treated by0.8%xylose was best. Sample treated by1.2g xylose and0.4g glucose wasproved to be optimal among samples treated by different xylose and glucose blendings.Samples treated by Arg, Gly, Ala, Val, His, Ile, Leu, Glu could reduce the ratio of TP and FAA,ratio of TB and TF，improve the organoleptic quality of sampls. Treatments of0.9g Histogether with0.3g Gly, and0.9g His togther with0.3g Glu reduced content of catechin, ratioof TP/FAA，increased ratio of （TF+TR）/TB. The addition of cystine, fructose, xylose andgalactose could decrease sharply content of caffeine.(TF+TR)/TB of samples treated by0.9gglucose together with0.3gGlu,0.3g glucose together with0.9gGlu,0.9g xylose togther with0.3gGly,0.3g xylose togther with0.9gGlu increased notably，TP/TPS of these samplesdecreased from9.10to3.29and3.26respectively, TP/FAA decreased from10.35to2.92and2.59respectively. Samples treated by0.3g xylose togther with0.9gGlu, and0.6g xylosetogther with0.6gGlu get higher scores in sensory evaluation.The color of tea immersions was quantitatively analyzed by L*a*b*system. Resultsshow that exogenous amino acids and sugars can significantly change brightness, red andyellow degrees of puer tea. L*, a*, b*are closely related to TB、TR、TF. Furthermore,exogenous amino acids and sugars can change catechins components and contents in puer tea.The simultaneous distillation and extraction method (SDE) and gaschromatography-mass spectrometry (GC-MS) were used to determine the volatiles of samples. 76components were totally identified. Ester, Terpenes and nitrogen-containing organiccompounds are the main aroma composition in samples. The result showed that tea samples ofdifferent treatments are abund in terpenes and its oxides (sweet aroma), alcohols and esters(fresh fruital aroma), indicating that the convertion from the raw puer tea to aged teas.The results of antioxidant activity of water immersions of samples indicated that IC50ofthe free radical scavenging abilities against DPPH of the water immersions of samples rangedfrom0.004μg/mL~0.206μg/mL. Compared with the black, treatements of0.6%Glu,0.8%xylose,0.6g xylose together with0.6Glu,0.6%His,0.6%Gly,0.3g xylose together with0.9g Gly,1.2g xylose together with0.4g glucose could significantly increased the antioxidantactivity. Of samples.The present results could offer some beneficial help for the research onthe improvement of tea quality without any lose of their antioxidant activity.