| Withering is an important process in the processing of black tea,which not only affects the appearance of the tea but also the internal quality of tea.In this research,sensory evaluation and physicochemical analysis methods were used to study the effects of different withering time on the sensory quality,chemical changes and biological activity of black tea,in order to provide a theoretical basis for improving the quality of black tea.The main results are as follows:1.The effect of withering time on the sensory quality of black teaAnalyze the effect of different withering time 4±0.5h(WT4),6±0.5h(WT6),8±0.5h(WT8),10±0.5h(WT10),and 12±0.5h(WT12)on the sensory quality of black tea.The results show that the withering time mainly affects the aroma and taste quality of black tea.The withering time less than 8±0.5h especially at 4±0.5h-6±0.5h,the tea leaves were slightly green and the taste was greenish and astringent;at 8±0.5h-10±0.5h tea was sweet and full-bodied,and the taste was mellow;after more than 10±0.5h,the sweetness weakened and the taste decreased.The sensory score of each treatment was ordered as follows WT10(86.88)> WT8(86.74)> WT12(84.63)> WT6(83.27)> WT4(81.28).There was no significant(p < 0.05)difference between WT10 and WT8 treatments.According to the results of sensory evaluation,the recommended withering time is 8±0.5h-10±0.5h.2.The effect of withering time on the main compounds in black teaWith the increase of withering time,the content of tea polyphenols and flavonoids showed a downward trend;the content of tea polysaccharides and amino acids first increased and then decreased,with a peak value at 10±0.5h.The total soluble sugars showed an increasing trend;the content of the main pigment theaflavins showed a downward trend,but the decrease was not significant before 10±0.5h,and it decreased significantly after10±0.5h.The content of thearubigins increased but began to decrease after 10±0.5h;theabrownins increased significantly.UPLC-Q-TOF/MS identified 67 nonvolatile components,including 21 flavonoids/flavonoid glycosides,4 theaflavins,7 catechins,8glycoside-bound volatiles(GBV),and 17 amino acids,7 organic acids and 3 phenolic acids.With the increase of withering time flavonoid/flavonoid glycosides decreased significantly,organic acid content decreased but did not change significantly between 8±0.5h-12±0.5 h,alkaloid content decreased but did not change significantly between 4±0.5h-6±0.5h and10±0.5h-12±0.5h.The content of each component of theaflavins decreased but did not change significantly between 10±0.5h-12±0.5h,glycosidic bond volatiles(GBVs)did not change significantly at 4±0.5h-6±0.5h but decreased significantly after 6±0.5h.This shows that the withering time should not be too long otherwise the content of the substance will decrease which will affect the taste quality.A total of 59 volatile compounds were detected by GC-MS technology,including 16 kinds of alcohols,18 kinds of aldehydes,8 kinds of hydrocarbons,7 kinds of ketones,7 kinds of esters and 3 kinds of acids.The results show that alcohols are the main aroma category,accounting for more than 45% of the total.With the increase of withering time,the content of aromatic substances showed a trend of increasing first and then decreasing.The peaks of alcohols aldehydes and acids appeared at 10±0.5h,10±0.5h and 8±0.5h respectively.The content of esters,ketones and hydrocarbons showed a downward trend with the increase of withering time but did not change significantly between 6±0.5h-12±0.5h.Aroma analysis shows that the withering time will not exceed 10±0.5h otherwise the aroma content will decrease which will affect the aroma quality.3.The effect of withering time on the biological activity of black teaWith an increase of withering time,the ability of tea to scavenge DPPH and inhibitα-glucosidase and α-amylase activity decreased significantly but the effects of different treatments were not the same.Among them,the effect of tea to scavenge DPPH was significantly different among the treatments,the ability to inhibit α-glucosidase activity had no significant difference between 4±0.5h and 6±0.5h,8±0.5h and 10±0.5h treatments.The ability to inhibit α-amylase activity had no significant difference before 10±0.5h and it was decreased significantly after 10±0.5h.It shows that shortening the withering time is beneficial to maintain the biological activity of black tea.Comprehensive tea sensory quality and internal quality analysis,considering the biological activity of tea,the withering time of black tea will not exceed 10±0.5h but it will not be less than 6±0.5h,8±0.5h-10±0.5h is appropriate range and the best withering time is 8±0.5h.Under this withering condition black tea has sweet,rich,flavorful sensory qualities and good biological activity. |
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