| The mainly-planted tea cultivars in the north of Zhejiang yellow tea region were used as fresh leaves to process yellow tea.This study focus on the key factors effect on yellow tea quality: such as grade of maturity and cultivars of fresh leaves,processing method(rolling,drying,yellowing).Sensory evaluation and chemical analysis were applied to explore the quality of processing samples and finished products.Chromatic difference analysis and Dose-over-Threshold analysis were employed to investigate the color and taste of yellow tea infusion,the main results are as follows:(1)As the increase of fresh leaves tenderness,the quality of yellow tea declined.In sensory quality,the amount of pubescence and tender shoots decreased,the degree of yellow and bloom lowered,the diversity of aroma lossed while the astringent of taste enhanced.About the main chemical components,with the increase of fresh leaves tenderness,the contents of catechins,flavonol glycosides,alkaloids,GA and phenol ammonia gradually increase,the contents of amino acids gradually decrease.EGCG,ECG,EGC,Myricetin-3-O-glucoside,Myricetin-3-O-galactoside and Quercetin-3-O-galactoside have a large increase,Theanine,Glutamic acid and Arginine reduces rapidly.(2)Moganhuangya Tea manufacture by Yingshuang,Baiye 1 hao,Zhenong113,Zhongcha108 and Jiukeng own characteristic and its unique flavour properties.Which all accord with the general yellow tea feature "the yellow appearance and infusion,the sweet smell and mellow taste." Meanwhile,the special properties of cultivars kept,Zhenong113 has obvious pubescence,faint flowers smell and fresh and brisk taste;Yingshuang and Jiukeng have sweet and mellow taste.The yellow tea contain 1.62 mg/g?3.01 mg/g GA,145.51mg/g?195.96mg/g catechins,8.30mg/g?12.78mg/g flavonol glycosides,44.26 mg/g?53.1mg/g alkaloids,38.21?62.22mg/g amino acids,6.22?11.27 phenol ammonia,10.57%?14.39% soluble sugar.Based on sensory evaluation,consumer preference and taste components analysis,we suggested that Yingshuang,Baiye 1 hao,Zhenong113 and Jiukeng could be processed into high-quality Moganhuangya Tea,while Zhongcha108 need further processing experiment.(3)During the processing,dynamic changes of main taste components of yellow tea by Zhenong113 indicated that: the contents of tea polyphenols continuous reduce,especially ester catechins,GA which released from EGCG hold an increasing trend,flavonol glycosides slightly decrease.The contents of amino acids increase at the spreading and early yellowing stage and then decrease in later yellowing stage and drying process.Phenol ammonia decline with fluctuation.Caffeine and theophylline increase at first and then decrease,the change of theobromine inversely.(4)Rolling,drying and yellowing process have a vital effect on Moganhuangya Tea quality.Yellowing process plays an important role,which leads to dramatically change in taste components,especially catechins and amino acids.As a whole,the proper yellowing condition could rapidly drop the contents of catechins,slightly increase the contents of amino acids and slightly decrease the contents of flavonol glycosides.The optimum process of Moganhuangya Tea including: spreading,heating,rolling,first drying,yellowing,and drying.When the yellowing condition is that the tea leaves temperature in 45?,the yellowing humidity in 75%RH and change the air every ten minutes,the quality of Moganhuangya Tea is the best.(5)Tea concentration of 16 Moganhuangya Tea infusion range from 3.87?4.97mg/m L,flavonol glycosides in tea infusion was very little,however,it made a great contribution to the quality of tea infusion color and taste.Myr-gly,Que-gly and Kae-gly were significantly correlated with L,a,b value.The Dot value of flavonol glycosides were relatively high,them could be the main contributors to yellow tea taste.The Dot value of Quercetin-3-O-rutinoside was over 5000,which were 3?4 orders of magnitude greater than other components.In addition,catechins,amino acids,caffeine and gallic acids also contribute to yellow tea taste. |
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