Effects Of Roasting Treatment On Nutrition And Flavor Characteristics Of Tea

There are common problems on flavor such as bitter and astringent taste and lacking of outstanding aroma in summer and autumn teas.The major aim of this study was dealed with the above flavor problems in green tea and Huangda tea associated with roasting process and analyzed the change of catechins,alkaloids and amino acids by HPLC.The volatile compositions of tea were extracted by using solid phase micro extraction and analyzed by GC-MS as well as investigating the main biochemical components in tea for qualitative identification by UPLC-MS/MS to analyze the effects of roasting on the chemical quality of tea.The sensory evaluation was used to analyze the effects of roasting on flavor quality,achieve to explore the optimum process parameters and improving flavor quality.In order to explore the best process for improving its flavor quality,it provides a theoretical basis for improvement and quality improvement of tea processing technology.The main findings are as follows:(1)Roasting treament has a significant effect on improving the flavor quality of tea.After the roasting of green tea,the oldy flavor faded and chestnut-like odors appeared,and the taste changed from bitter to mellow.The aroma of Huangda tea,which of grassy flavor disappeared and caramelic oder appeared,on taste showed that astringency taste decreased and become mellow.The optimum roasting process of green tea was 100 ° C for 90 min,120 ° C for 60 min and 140 ° C for 30 min.The best roasting technique for Huangda tea is low temperature roasting(130-140 ° C).(2)With the increase of roasting temperature,the content of water extracts in green tea and Huangda tea increased,the total amount of tea polyphenols and free amino acids decreased.And soluble sugars showed an upward trend in green tea.In Huangda tea,the trend was opposite.The content of trans-catechins in green tea decreased significantly,the content of cis-catechins and GA increased,the content of caffeine did not change significantly,sweet taste amino acid content increased slightly,and umami taste and bitter taste amino acid content decreased significantly.The content of tran-catechins in Huangda tea was significantly decreased,while the content of cis-catechins increased primarily and then decreased,the content of gallic acid increased significantly,there was no significant difference in the change of caffeine content(P>0.05),the content of umami taste and sweet taste and bitter taste amino acid decreased significantly(P<0.05).(3)A total of ninety-three volatile compounds were identified in roasting green tea,and the relative content of volatile odor of oldy flavor was reduced including 1-Octen-3-ol,Heptanal,5,6-expoxy-?-ionone.The relative content of geranylacetone,phenylethyl alcohol and beta ring citral with floral and fruity odor substance increased significantly.Eighty-six volatile compounds were detected in roasting Huangda tea,and the content of major volatile substances with floral flavor as nerolidol,geraniol,2-Heptenal,Phenylethyl Alcohol decreased dramatically,while the relative content of caramelic-like substances including 2,5-dimethyl pyrazine,2-acetyl pyrrole,2-ethyl-3,5-dimethyl pyrazine increased.(4)The UPLC-MS/MS technology was used to qualitatively analyze the main chemical constituents of green tea and Huangda tea before and after roasting.Twenty-six common compounds such as Gallic acid,Theanine and Catechin were identified.