| Green tea is the most widely produced tea in China.The processing procedure is fresh leaf-spreading-killing green-rolling-drying.Frying is one of the key steps for the unique quality of green tea.During frying,the physical and chemical changes of green tea are drastic.However,the previous research on this part is less.Due to the disadvantages of traditional frying machine,the color of the green tea made by traditional frying machine is gray,and the shape is not tight,we designed a continuous shape-frying machine which was optimized by orthogonal experiments.The shape,color,contained substance,and aroma components of green tea made by traditional frying machine and continuous shape-frying machine were compared.At the same time,the physical and chemical changes and differential metabolites during the frying process were studied.The results are as follows:1.The optimal process of continuous shape-frying machine was which set temperature of the drum was(290 ℃,240 ℃),the rotation speed was 26 RPM,and the tilt angle was 1.5 °.According to the optimized process of the continuous shape-frying machine,the process parameters in actual production were formulated,and compared with the traditional cycle frying machine process,the new process green tea and the traditional process green tea was obtained.The sensory evaluation results showed that the shape,soup color,aroma,flavor and the total score of the new process green tea were higher than that of traditional process green tea.The R,G,B,H,V,CAF,ECG,C,GCG,and CG values of the green tea fried by the new process were higher than those of the traditional frying,while the curvature radius value,S,GA,EGCG,EGC,GC value and free amino acids were in the opposite trend;the types of volatile substances in traditional frying green tea were lower than those in the new process green tea,but most of the volatile substances of traditional frying green tea,including those that exhibit chestnut aroma,were higher than those in the new process green tea.2.As the frying process progressed,the radius of curvature of unfinished tea gradually decreased,and the color texture parameters R,V,G,B,average gray value and gray standard deviation decreased first and then increased,the consistency value increased first and then decreased,H value increased significantly(p <0.05),S value decreased significantly(p <0.05),EGCG,EGC,chlorophyll a,chlorophyll b,amino acid and carotenoid content decreased significantly(p <0.05),GCG content increased significantly(p <0.05).The types of volatile substances decreased first and then increased,the alcohols aroma decreased,the aldehydes aroma increased first and then decreased,the aromatic hydrocarbons increased gradually,and the total volatile compound content decreased first and then increased.3.Correlation analysis and modeling of physical and chemical changes of unfinished tea during the frying process.The results showed that the water content and the radius of curvature had a very significant positive correlation(p <0.01),the leaf temperature and the radius of curvature had a very significant negative correlation(p <0.01);the H value had a very significant correlation with chlorophyll a,chlorophyll b,and carotenoids(p <0.01),S value was extremely significantly correlated with chlorophyll a,carotenoids,and ECG content(p <0.01).A linear fit was performed on the EGCG,chlorophyll a,and carotenoid contents of unfinished tea during the frying process,the results showed that the linearity of H value with EGCG and carotenoid content were all more than 0.9,it was feasible to predict the changes of the contained substance through the physical changes of the unfinished tea.4.Based on non-targeted metabolomics,metabolites of unfinished tea were researched during frying process,which identified 101 non-volatile metabolites of fried green tea,including 27 labeled metabolites,which were 4 amino acids,4 catechins Monomers,3 catechin dimers,2 phenolic acids,2 nucleotides,1 lipid,1 ester,5 flavonol / flavonoid glycosides and 5 other compounds.With the frying time increased,the changes of the 27 marker metabolites were as follows:(1)C,CG,GCG,theasinensin B and GC increased.Theaflavin 3’-gallate showed an overall upward trend,and its maximum content appeared at the 30 th minute.Proanthocyanidin C1 increased first and then decreased,reaching its maximum content within 10 minutes.(2)The content of piperonic acid decreased significantly,the content of serine,glutamic acid and phenylalanine increased gradually,which reached the maximum value at 10 minutes,and then gradually decreased.(3)The content of flavonoid C-glycoside increased gradually.(4)1-O-galactose glucose and 4-coumarinylquinic acid increased by 40.22% and 53.47%,respectively.(5)The content of dihydroactinidiolide decreased gradually.N-(1-deoxy-1-fructosyl)phenylalanine,N-(1-deoxy-1-fructosyl)leucine and theanine glucoside increased significantly.5.The metabolites of roasted green tea and backed green tea were compared,and 22 kinds of labeled metabolites were found.Some labeled metabolites of roasted green tea,including arginine,asparagine,lysine,histidine,piperic acid,and proanthocyanidins C1,were more than that of backed green tea.but the other 16 labeled metabolites were opposite. |
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