Study On The Changes Of Main Chemical Components During The Processing Of Huoshan Large Yellow Tea

Huoshan Large Yellow Tea(HLYT),a product of national geographical indication protection,mainly produced in the administrative area of Huoshan County,Lu'an City,Anhui Province.It is made of coarse fresh tea leaves and is processed by traditional technologies,which is made of fixation,rolling,first drying,yellowing,second drying and high temperature roasting.HLYT have the characteristics of "bronze and baking aroma" and the tea soup mellow and sweet because of its special “yellowing” and “high temperature roasting” processing technologies.In the study,samples of fresh tea leaves and processing procedures for fixation,rolling,first drying,yellowing,second drying and high temperature roasting were taken as the research object for systematic study on the main quality components of HLYT.What's more,the change laws of the main quality components of HLYT during the processing were clarified.The results of the study are showed as follows:(1)Contents of water extract of all samples in this study within the range of 26%~31%,and the finished sample is about31%;During the processing of HLYT,the total amount of tea polyphenols in finished sample had a significant increase compared with fresh tea leaves,which was increased by about 15%;The amount of tea total polyphenols in finished sample had a significant decrease with respect to the yellowing leaves,which decreased by approximately 30%.Content of caffeine remained stabled during the processing.Compared to fresh leaves,the levels of epigallocatechin gallate(EGCG),epigallocatechin(EGC)and epicatechin gallate(ECG)decreased significantly by about 54%,68% and 50%,respectively.The contents of gallocatechin gallate(GCG)and gallocatechin(GC)in finished HLYT increased significantly,with five times and 11% increasing;The total amount of free amino acids during the processing was inclined to descend.Compared with tea fresh leaves,the content of glutamic acid in finished HLYT sample decreased by nearly 50%,and phenylalanine decreased by approximately 30%.The drop of histidine acid is about 80%,and theanine is almost undetectable.(2)The volatile aroma components of the yellowing sample during the processing of HLYT were dominated by phytol,linalool,methyl palmitate and cedar.The odor of phytolitol accounted for 41%,the floral scented linalool accounting for 6%,and the fragrance of methyl palmitate accounted for 3.0%.After the high temperature roasting,the phytol,a floral fragrant compound,was almost undetectable.The content of benzaldehyde with almond aroma increased significantly.The relative content of alcohol dropped to 4%.Meanwhile,the newly produced pyrazine derivatives,especially 2,5-dimethyl-and 2,6-dimethyl-pyrazine were the largest proportion,which might be the key contributors for the formation unique baking aroma of HLYT.Besides,3,7-dimethyl-1,5,7-octatrien-3-ol with a pleasant fruit aroma and ?-ionone with cedar raspberry aromas were also newly produced.(3)PCA analysis of the chemical composition of the sample compound during the processing of HLYT.The 30 compounds of the seven samples were isolated.Fresh tea leaves,fixation,rolling,first drying,yellowing,second drying and low temperature roasting have the similar chemical profiles,separated from the samples of high temperature roasting;the OPLS-DA model was used to analyze the polyphenols compositions of high temperature drying during the processing.The two groups of samples were used in this model and a good distinction was made.The chemical composition of the finished HLYT samples was significantly changed after the process of high-temperature roasting.Epi-catechins mainly underwent isomerization reactions and then nonepi-catechins increased significantly.