The Basic Research On Respiration And Physicochemical Characteristics Of Tea Fresh Leaves In Congou Black Tea Witheirng Process

Taking the withering process of congou as the research object, setting different witheringparameters (temperature, relative humidity, light intensity, oxygen concentration, etc.) to research theeffect of different withering factors on dynamic change of physical characteristics, respirationcharacteristics, and the main biochemical components and enzymatic activity of tea fresh leaves, and theimpact on the subsequent processing steps and sensory quality of made tea were also studied. On thisbasis, consolidating the following three withering parameters: temperature, relative humidity, lightintensity, through the Box-Behnken design, using catechin content, the "TP+AA+SS" content inwithering final tea samples, and sensory quality of made tea as the investigation indicators, thecorresponding optimization withering parameters were proposed, and the regression models were built.The main research results were as follows:1. With the increasing of withering time, the respiration and physicochemical characteristics of teafresh leaves showed the following rules.(1) The moisture content of tea fresh leaves decreasedgradually, bulk destiny, flexibility and plasticity of leaves increased at first and then decreased duringwithering, and the variation of elasticity was opposite. The inflection point of bulk destiny andflexibility appeared when the moisture content was between64%and68%, and the inflection point ofplasticity and elasticity appeared when the moisture content was between68%and72%.(2) Theluminosity declined generally, which meant the brightness of withered leaves decreased, and the avalue(red and green degree) increased slowly.(3) The released amount of CO2decreased at first, thenincreased and decreased finally, and the inflection point was appeared when the water content ofwithered leaves was between68%and70%.(4) The conventional biochemical compositions, such aspolyphenols, soluble sugar, total soluble solids and water-soluble protein content showed a downwardtrend, and amino acids and caffeine content showed an upward trend; the polyphenol oxidase activitygradually decreased and the peroxidase activity increased gradually.2. Under different withering oxygen concentration(21%O2,40%O2,59%O2), with the increase ofoxygen concentration, bulk density, flexibility, elasticity, total catechin contents, and POD enzymaticactivity declined; the physical characteristics such as plasticity, luminosity, color a value, qualitybiochemical ingredients, PPO enzymatic activity, and sensory scores rose. In different oxygenconcentration treatment, the made tea under59%O2treatment got the most contents of theaflavins andthearubigins, and had the best sensory flavor.3. Among different withering light intensity(3000lx,6000lx,9000lx), under6000lx treatment, thephysical characteristics of withered leaves such as bulk density, flexibility, elasticity, and color a value,the quality biochemical ingredients(polyphenols, amino acids, tea pigment, etc.), the enzymaticactivity(PPO, POD) and sensory quality of made tea got the highest score. The released amount of CO2in different treatments showed the following rule:6000lx＞3000lx＞9000lx.4. Under different withering temperatures(20℃,28℃,36℃), the released amount of CO2increasedwith the rise of withering temperature. The physical characteristics of withered leaves such as density, flexibility, and plasticity, and the enzymatic activity(PPO, POD) got the highest point under28℃treatment. The biochemical ingredients, such as polyphenols, theaflavins, and thearubigins, and thesensory quality of made tea also were best under28℃treatment. Under different withering relativehumidity(RH50%, RH70%, RH90%), the physical characteristics of withered leaves such as density,flexibility, plasticity, and color a value were positively related to withering relative humidity, andflexibility and luminosity were negatively correlated to withering relative humidity. The70%treatmentowed the suitable withering time, provided the prefect condition for the suitable transforming ofquality substances, got the most amounts of polyphenols, amino acids, flavonoids, theaflavins,thearubigins, etc., and had the optimal sensory quality. Under90%treatment, the withering time last16hours; as excessive consumption of tea quality ingredients, amino acids content is only69%ofRH70%treatment, and theaflavins content of only62.5%of RH70%treatment; and the comprehensivequality declined.5. Under the Pearson statistical analysis, the tea polyphenols and soluble sugar content in finalwithering had a significant positive correlation with the sensory quality of made tea; total catechinscontent and the total contents of polyphenols, amino acids, and soluble sugar got an extremesignificant positive correlation with the sensory quality of fired tea. On this basis, the application ofBox-Behnken design was used to optimize the withering process: when the total amount of catechinswas an index, the total amount of catechins=13.04-0.60A+0.51B-0.25C+0.44AB-0.78AC-0.12BC-2.31A2-2.00B2-1.02C2, the F value of model was3.85(significant), and the optimal witheringparameters was27.18℃temperature,72.36%relative humidity, and5733.92lx light intensity; whenthe total content of "TP+AA+SS" was an indicator, the total content of "TP+AA+SS"=37.39+0.093A-0.015B+0.53C-0.55AB+1.05AC-0.33BC-2.26A2-1.25B2-2.64C2, the F value of model was35.02(extremely significant), and the optimal withering parameters was28.41℃temperature,69.37%relative humidity, and6335.03lx light intensity; when using the sensory evaluation score as an index,the sensory evaluation score=88.91-1.38A+1.70B+1.31C+2.25AB+7.92AC-0.10BC-3.82A2-8.07B2-4.56C2, the lack of fit was4.95(not significant), the optimal withering parameters was27.63℃temperature,71.98%relative humidity, and6307.82lx light intensity.