| Yellow tea is one of the six major tea categories in China,with rich health care effects such as antioxidant,anti-tumor,hypoglycemic,hypolipidemic and liver protection.Yunnan tea plant germplasm resources are abundant,but there are no relevant reports on the systematic study of Yunnan large-leaf yellow tea,and the processing technology of Yunnan yellow tea lacks guidance,let alone theoretical and technical support.In this study,Yunkang No.10,a large-leaf species from Yunnan,was selected as the fresh leaf raw material,and high performance liquid chromatography(HPLC),headspace solid phase microextraction(HS-SPME)and gas chromatography-mass spectrometry(GC-MS)were used to compare the effects of different anaerobic methods and different yellowing time on the quality of Yunkang 10 yellow tea,in order to form the optimal process and parameters of Yunkang No.10 yellow tea processing technology,which not only provides theoretical reference for the research of Yunnan yellow tea.At the same time,a new process of yellow tea is developed to enrich Yunnan tea,promote diversified consumption,and provide effective theoretical and technical support for the high-quality development of Yunnan tea industry.The main findings were as follows:1.The results of the study of sensory quality showed that N6-6 sensory evaluation score was the highest,yellow tea made of nitrogen-filled anaerobic for 6 h and yellowing for 6 h had the best sensory quality,the shape was tighter,golden with brown,moist,the soup color was tender yellow and bright,the aroma was rich and long-lasting,the tender fragrance,floral(rose),the sweet aroma was outstanding,the taste was sweet and mellow and fresh,and the brewed tea leaves were green and yellow,soft and bright.Secondly,the highest score was D-6,indicating that Yunnan large-leaf yellow tea represented by Yunkang No.10 should be yellowed for 6 h without anaerobic treatment,the shape was tight green and yellow,the soup color was bright yellow,the aroma was rich and long-lasting,the tender aroma and chestnut aroma were prominent with sweet aroma,the taste was mellow and fresh,and the brewed tea leaves were yellow and green soft and bright.2.The results of the study of flavored substances showed that there were significant differences in the content of water extract,total flavonoids,tea polyphenols,free amino acids,caffeine,gallic acid,total catechins and their components in different processes.The PLS-DA results showed that amino acids were the key flavor substances to distinguish yellow tea from different processing processes,and the content of amino acids could be significantly increased by nitrogen filling and vacuum anaerobic treatment of fresh leaves.The results of cluster heat map showed that without anaerobic treatment,yellowing for 6 h could reduce the contents of tea polyphenols,phenol ammonia ratio and flavonoids,and the suitable yellowing time of Yunnan large-leaf yellow tea represented by Yunkang 10 was 6 h.After anaerobic nitrogen filling treatment for 6 h and yellowing for 6 h,the content of flavonoids could be further reduced,the content of free amino acids and the content of water extract could be increased,and the content of C and GA could be increased at the same time,which could further improve the freshness of the taste of the tea soup,and be sweeter and more alcoholic,which could make the obtained large-leaf yellow tea of the best quality.The taste quality of yellow tea in this processing process was mainly manifested as the highest content of water extract,high content of tea soup water extract,rich in tea soup substances,strong taste,low total amount of flavonoids and tea polyphenol content,high content of free amino acids,low phenol-ammonia ratio,ester catechin EGCG and ECG content and non-ester catechin EGC and EC content was high,tea soup taste was rich,fresh and sweet.3.The results of aroma quality research showed that HS-SPME/GC-MS detected the volatile components of yellow tea in different processes,and a total of 72 known volatile components were qualitatively identified.The results showed that the number of volatile substances in yellow tea without anaerobic treatment was large,while the number of types generally decreased after anaerobic treatment,and the content was mainly terpenes and alcohols,and the processing technologies such as vacuum and nitrogen-filled anaerobic treatment helped to increase the content of volatile substances,especially alcohols.D-limonene and δ-cadinene were present in the volatile substances of Yunnan large-leaf yellow tea,which had important contributions to the sweet,fruity and woody aroma of the tea.A total of 10 different volatile substances were screened through PLS-DA,which could be used to identify different processes of yellow tea,mainly including linalool,β-myrcene,4-carene,β-caryophyllene,3-naponene,γ-terpinene,δ-cadinene,indole,etc.The clustering heat map showed that Yunnan large-leaf yellow tea with nitrogen-filled anaerobic treatment for 6 h and yellowing for 6 h had the best aroma quality,while the aroma quality of yellow tea without anaerobic treatment and yellowing for 6 hours was poor.The key volatile substances of yellow tea without anaerobic treatment and other processes were β-myrcene and 4-carene,and the key volatile substances of nitrogen-filled anaerobic yellow tea and other processing processes were linalool and indole,and the fresh and tender flowers and fruits were outstanding.On the whole,the aroma quality of N6-6 was the best,that is,the aroma quality of Yunnan large-leaf yellow tea treated with nitrogen-filled anaerobic treatment for 6 h and yellowing for 6 h was the best,containing indole,trans-β-ocimene,β-ocimene,linalool,β-myrcene,cis-linalool oxide,α-terpinene,δ-cadinene and other aroma substances,with many types and high content,mainly manifested as rich aroma,with sweet tender fresh floral aroma,sweet aroma.4.Studies have shown that Yunnan large-leaf yellow tea represented by Yunkang No.10 has a better processing technology: fresh leaves are spread out to dry→ nitrogen-filled anaerobic treatment(6 h)→ fixation(5 min)→ rolling(15 min)→ yellowing(26℃,6 h)→ drying(80℃,5 h)... |
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