Research On The Quality And Processing Of White Tea In Zhejiang Province

In this study, the tea cultivars in Zhejiang were used as fresh leaves to process the white tea, and chemical analysis and sensory evaluation were employed to explore the dynamic changes of chemical components, correlations between taste components and sensory characteristics, optimization of different processings and the influence of aging effects. The results obtained are as follows:(1) During the processing of white tea with Zhenong 117 and Chunyu 2, the biochemical contents changed tremendously. Take Chunyu 2 for instance, the content of the aqueous extracts increased by 13.98% after withering for 33 h, but slightly decreased by 5.66% in the later stage and after drying. The contents of polyphenols catechins continued to decrease by 14.12% and 47.82%, respectively. The contents of trans catechins increased at the initial stage of withering while four cis catechins continued to decrease. Caffeine showed an increasing trend by 18.51% during the withering, and lowered by 5.75% after dying. The contents of TB decreased by 68.36% after withering for 17 h and continue to decreasing but at lower speed, however, TP increased by 87.5% during processing. The contents of amino acids soared in the withering process by 43.57%, but reduced by 12.67% after drying.(2) The content of polyphenols, especially catechins, which mainly dominated by withering temperatures, changed in a greater magnitude (P<0.05) as the temperature went higher, leading to a lower contents of polyphenols and catechins. The contents of TB, caffeine and amino acids were mainly dominated by withering time, which varied more substantially (P<0.05) in longer withering time, resulting in lower content of TB and higher contents of caffeine and amino acids. Different drying temperatures 50℃,80℃ and 100℃ had little effect (P>0.05) on the contents of alkaloids, but the content of amino acids decreased (P<0.05) as the drying temperature rose. The content of polyphenols and catechins increased in Chunyu 2 as the drying temperature went higher, but opposite tender was found in Zhenong 117. According to the results of sensory evaluation, the white tea processed from withering indoors, withering in groove and withering under 28℃ exhibited green taste, resulting in poor quality. In the other hand,white tea processed from withering under sunlight and withering under 35℃, which could be used as two preferred withering process, showed good in quality. In addition, three different dying temperatures could all be applied while higher temperature could develop the sweetness of white tea.(3) Ingredients varied significantly (P<0.05) different among different cultivars. The contents of polyphenols ranged from 75.51 mg/g to 362.48 mg/g. The contents of catechins ranged from 61.31 mg/g to 121.70 mg/g. The contents of alkaloids ranged from 21.37 mg/g to 43.27 mg/g. The contents of amino acids ranged from 8.1 mg/g to 49.9 mg/g. Zhenong 113, Chunyu 1 and Chunyu 2 performed best quality as well as highest preferences according to sensory evaluation. Fudingdahao showed the strongest taste of umami (6 points), bitterness (7.1 points) and astringency (8.5 points) while Anjibaicha exhibited the highest sweetness (4.8 points). Catechins and ester catechins were significantly and positively correlated with bitterness (Pearson=0.97) and astringency (Pearson=0.92) while significantly and negatively correlated with sweetness (Pearson=-0.81). Amino acids was significantly and positively correlated with umami (Pearson=0.88). Based on the quality of ingredients and sensory evaluation, we suggested that Chunyu 1 could be processed into traditional white tea, while Zhenong 113 and Chunyu 2 could be used to develop characteristic products.(4) The contents of aqueous extracts dropped (P<0.05) after one year aging, but showed a minor rise in the first six months. The content of polyphenols and catechins decreased after aging, but increased in the second half year in Chunyu 1, Chunyu2 Yingshuang and Zhenong 117, which still lower than those before aging. The contents of non-ester catechins reduced after aging while the contents of ester catechins ascended.The contents of alkaloids changed little, but a significant (P<0.05) increase was found in TP in the first half year, as well as a significant decrease (P<0.05) in the second half year. The contents of amino acids increased in the first half year, but dropped in the second half year.