| After the leaves are plucked from tea tree,withering occurs immediately,during which the moisture of fresh tea leaves is continuously reduced,causing wrinkling on the upper and lower epidermis.Meanwhile,the complex compounds are resolved into simple compounds.Both the changes in the physical and chemical properties of tea leave have an important effect on tea quality.Thus,the effects of withering on these properties should were determined to improve tea quality during tea processing.In this study,we designed and fabricated a probe and cup match the CT3 25 texture analyzer to test the elasticity and flexibility of withered tea leaves of Fudingdabai comprising two leaves and a bud during withering and de-enzymed tea leaves during spreading,and the test parameters were also studied.Withered and de-enzymed tea leaves with different water contents of Zhongcha 108 comprising two leaves and a bud were used to process congou black tea and green tea,respectively.Computer vision technology was used to analyze the color and texture of tea leaves in processing,sensory quality evaluation of made tea was carried out.Dynamic changes in the major chemical components of green tea,including amino acids,catechins,tea polyphenols,soluble sugars,soluble proteins,caffeine(CAF),and gallic acid(GA)were investigated during withering with different times(ranging from 0 h to 21 h)and temperatures(15°C,20°C and 25 °C).One-way and two-way analyses of variance(ANOVA)with Duncan's test were used to analysis the changes in chemical components.The main findings were summarized as follows:(1)The probe and cup matched the CT3 25 texture analyzer well,and the elasticity and flexibility of manufactured tea leaves during withering and spreading were tested by a texture analyzer with the compression-load test mode and 3 kg load.(2)The “rise–decline” trend of the plasticity and flexibility and decline trend of the elasticity of the withered tea leaves were observed during the withering process.The good elasticity and peak values of plasticity and flexibility were observed when the water contents of withered tea leaves reached 65.51%(DW)to 61.48%(DW).The “increase-decrease” trend of the plasticity and flexibility and a stable elasticity of the de-enzymed tea leaves were observed during spreading.The good elasticity and peak values of plasticity and flexibility were observed when the water contents of the de-enzymed tea leaves reached 55.79%(DW)to 50.83%(DW).The elasticity,plasticity,and flexibility of the de-enzymed tea leaves declined significantly,and the physical basis for processing high-quality green tea was not available when the water contents decreased to 33.7%(DW)-22.27%(DW)during spreading.(3)The water contents of the withered and de-enzymed tea leaves significantly correlated with plasticity and flexibility.The percentage changes present the plasticity > flexibility > elasticity caused by the decline in water contents of the withered and de-enzymed tea leaves during withering and spreading.The increase in plasticity of the tea leaves was greater than the increases in flexibility and the reduction in elasticity due to de-enzymimg.(4)Analysis of color and texture showed that with the decrease in water contents of the tea leaves during withering,the color of the tea leaves gradually changed from bright yellowish green to dark brownish green,and the uniformity and consistency of texture decreased.The color of made tea changed from bright and red with yellow to dark brown,and the color of tea soup changed from red to yellow and bright to dark red when the congou black tea was processed with tea leaves that underwent a long withering time.Good integrity,high strip rate,tight strips,and complex texture of made tea were also observed.Analysis of the color and texture showed that the brightness increased,the gray scale increased,the color faded gradually,the green color decreased gradually,the texture consistency increased,the smoothness improved,and the symmetry stabilized when the water contents of the de-enzymed tea leaves decreased during spreading.The water content showed no significant correlation with the color and texture of the de-enzymed tea leaves,which was different from the withered leaves.The hue value decreased,the color gradually darkened,the texture became complex,and the uniformity and symmetry of the de-enzymed tea leaves increased after rolling.The color of tea soup changed from yellow-green,light and bright to yellow-red,deep and dark gradually.High brightness,smooth texture,uniformity,and integrity were achieved after the de-enzymed tea leaves underwent a moderate spreading process to losing some water before being processed to green tea.(5)The aroma and taste of the congou black tea that did not undergo withering was strong,tender,and sweet,but the shape of made tea and the tea leaves residue were poor.The shape of made tea and tea leaves residue was good when the congou black tea was processed with the moderately withered tea leaves,but the tenderness and sweetness aroma and taste obviously decreased.The shape of the congou black tea processed with excessively withered tea leaves was acceptable,with a sultry,bitter,and astringent aroma and taste.A good shape and soup color was achieved when the tea leaves underwent moderate withering during black tea processing.The fresh tea leaves were handled in the de-enzyming process during any time of withering to obtain the de-enzymed tea leaves.The soup of green tea A,which was processed from de-enzymed tea leaves with high water content(i.e.,without withering)has a bright color and a strong refreshing taste.The soup of green tea C,which was processed from de-enzymed tea leaves with low water contents,has a slight scorching and bitter taste.Green tea B and C,which were processed from de-enzymed tea leaves with low water contents,obtained similar scores in the shape of made tea and on the tea leaf residue,and they were higher than that of green tea A.(6)Withering temperature can significantly affect the content of soluble protein in green tea.During withering,the content of soluble protein decreased significantly when the wither temperature was 25 °C.The content of soluble sugar initially decreased and then increased at 15 °C and 20 °C.Both withering temperature and time exerted significant effects on the total content of free amino acids,but their interaction effects did not affect the total contents of free amino acids.The contents of most free amino acids increased with increasing withering time and temperature.Theanine contents decreased slightly with fluctuations during withering.Both withering temperature and time significantly affected the contents of sweet-and bitter-tasting amino acids and protein amino acids,but their interaction effects did not affect their contents.The contents of sweet-and bitter-tasting amino acids increased with increased withering temperature and prolonged withering time.The content of protein amino acids increased with increased withering temperature and prolonged withering time.The content of protein amino acids did not significantly differ under the different temperatures.The contents of catechins and ester catechins initially increased and then decreased,and the content of simple catechins decreased slightly during withering.A significant increase of caffeine content significantly increased with prolonged withering time at different withering temperatures.The content of GA increased during withering. |
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