| As a special type of tea in China,Oolong tea is popular among consumers for its unique floral and sweet taste.At present,China's oolong tea is mainly produced in the Fujian,Taiwan and Guangdong province,but for non-oolong tea producing areas such as Hunan province,appropriate varieties and processing techniques are needed to develop local oolong tea products better.As one of the main varieties of tea plants in Hunan province,Zhuyeqi cultivar has excellent quality characteristics such as high yield and wide adaptability,utilizing these characteristics for developing summer oolong tea,on the one hand,the utilization rate of summer tea resources can be improved,on the one hand,the categories of Hunan tea products can be enriched,which can not only promote the development of tea varieties in Hunan local tea varieties,but also improve economic benefits.This subject takes Zhuyeqi cultivar as material,through the analysis of the natural quality characteristics of the fresh leaves,the optimization of the processing technology of summer oolong tea,the main intrinsic quality components,aroma components and enzyme activity changes during the processing,to investigate the formation mechanism of the quality of the tea aroma and taste,and finally obtain a set of optimal processing techniques and parameters suitable for Zhuyeqi summer oolong tea.The main results are as follows:1.The natural quality characteristics of fresh leaves of Zhuyeqi cultivar: in terms of physical properties of fresh leaves,the leaf width was wide(3.36±0.35cm),the ratio of leaf length/leaf width was small(2.58±0.21),internode length was short(2.29±0.40cm),and the ratio of stem diameter/ internode length was large(0.84±0.19),the stratum corneum(2.52±0.29?m)and epicuticular(18.12±1.22?m)was thick,Zhuyeqi variety also has two layers of thick and closely arranged palisade tissue(53.49±1.84?m);In terms of the content of fresh leaves,the content of tea polyphenols in the leaves of the leaves was 21.39%,the total amount of flavonoids was 5.97 mg/g,the total amount of soluble sugars was 10.18%,the content of caffeine was 3.40%,and the content of water extracts was 44.03 %,the total amount of free amino acids was 2.86%,So Zhuyeqi variety has a significantly higher content of soluble sugar,water extract and tea polyphenol.Compared with the two local Hunan tea varieties of Bixiangzao and Huangjincha,the physical properties and contents of the fresh leaves of Zhuyeqi variety has the potential to meet the quality requirements of fresh leaves in the oolong tea rotating process and has the potential to make high quality oolong tea.2.The optimal processing route suitable for the processing of Zhuyeqi summer oolong tea was: fresh leaves?withering(weight loss was 10%)?rotating for 5 times?pan-fixing?rolling?first drying?second drying?raising fragrant.The three-factor and three-level orthogonal test and verification test results showed that the main order of the factors affecting the overall sensory quality of Zhuyeqi summer oolong tea was: withering degree>rotating times>stacking times.The superior comprehensive quality of Zhuyeqi summer oolong tea treatment was made by the withering weight loss rate of 10%,shaking for 5 times and non-stacking.3.The changes of quality components during Zhuyeqi summer oolong tea processing: during the withering,the content of tea polyphenols,catechins,flavonoids,caffeine and soluble sugar were decreased,the content of free amino acids and water extracts were increased,which laid the foundation for the subsequent rotating process;during the rotating,the biochemical components of the products are generally reduced.Under the action of enzymes and influence of heat,various quality components are decomposed and transformed,which is beneficial to reduce the bitterness and astringency of the tea soup and improve the sweetness of the tea,which is the key to the formation of sweet and mellow taste and fresh floral aroma of Zhuyeqi summer oolong tea.In the stage of the fixing and drying,the content of free amino acids increased,and the content of tea polyphenols,caffeine,flavonoids and other substances decreased,which further improved the taste quality of Zhuyeqi summer oolong tea.4.The changes in aroma components during the processing of Zhuyeqi summer oolong tea: a total of 122 kinds of aroma components were detected during the processing,it mainly includes alcohols,esters,hydrocarbons,ketones,aldehydes and other compounds for 6 kinds in total.There were 38 kinds of alcohol components,3 kinds of aldehydes,34 kinds of hydrocarbons,6 kinds of ketones,34 kinds of esters,7 kinds of other aroma components,the alcohol aroma,ester aroma and hydrocarbon aroma account for a high proportion,which is the main aroma category of Zhuyeqi summer oolong tea.During the processing,the total number of aroma components showed a fluctuating rise change trend,and the total number of aromas in the withering stage and the rotating stage increased significantly,and the total number of aromas in the rotating stage showed a “rise-low-rise” trend;the total peak area and total content of aroma substances showed an "M" type change trend,which increased during withering and rotating,and decreased during killing and drying.Overall,the proportion order of the aroma types of Zhuyeqi summer oolong tea was : alcohol=ester>carbohydrocarbon>other types>aldehyde=ketone.The main aroma components with higher content are mainly as the following: trans-nerolidol,(Z)-hexanoic acid-3-hexenyl ester,alpha-farnesene,hexyl hexanoate,trans-2-hexene hexanoate and linalool.Among them,the content of ?-farnesene and trans-nerolidol is up to 40% in the tea,which is the main component of the aroma of the tea.5.The main enzyme activity changes during the processing of Zhuyeqi summer oolong tea: the activity of polyphenol oxidase showed a wave-like trend,the overall performance was increased first and then decreased.(1)PPO activity increased during the withering period,who was increased first and then decreased during the rotating period.(2)Peroxidase activity generally showed an upward trend during processing.during the withering period,the growth rate was small,then it was larger during the rotating period,and reached the peak value during the five-shake period.(3)The activity of ?-glucosidase showed an “M”-type increasing trend during the processing,during the withering stage,the activity decreased slightly,but in the early stage of rotating,the activity of the enzyme showed a wave-like rising trend,reaching the peak during the three-shake period,and gradually decreasing in the late stage of rotating.(4)The cellulase activity showed “M” type double-peak change during processing,the overall trend was upward.The enzyme activity was higher in the early rotating period and reached the highest value in the second shaking.(5)The pectinase activity generally showed an upward trend during the processing,the enzyme activity increased significantly during the withering,but showed a “rising-lowering-rising” trend during rotating,the enzyme activity is stronger in the early rotating period and reached the highest value in the first shaking.6.The quality characteristics of Zhuyeqi summer oolong tea:the color of tea soup was orange and bright,the fragrance was clean and refreshing with fruity aroma,the taste was mellow and thick,and the infused leaves was yellowish green with red edge. |
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