Effect Of Red Light On The Metabolites Of Fresh Tea Leaves Withering

Red light withering can significantly improve the flavor quality of tea.The current research mainly focuses on the aroma and taste of the finished tea made by light withering,ignoring the influence of red light on the long-term withering process.In this study,natural light withering/spreading and dark withering/spreading were used as controls.Two light withering/spreading treatments of red light 1000 lx and red light 3000 lx were set up.The color,pigment,non-volatile and volatile components of the tea leaves were systematically analyzed.The main research and content are as follows:1.In this study,the color and pigment of fresh tea leaves were analyzed through image acquisition and ultra performance liquid chromatography.The results showed that the tea leaves in the red light 3000 lx group were darker and greener than those in the natural light group during the spreading of fresh tea leaves.The G,V and S values of fresh tea leaves in the natural light group,the red light 1000 lx group and the red light 3000 lx group were significantly reduced during the spreading.Among them,the G and V values of the red light 3000 lx group were significantly lower than those of the natural light group,while the G and V values of the lower light intensity red light 1000 lx group were significantly higher than those of the natural light group.This indicates that the presence of light will lead to the obvious green loss and brightness reduction of tea leaves in the spreading process.2.This study detected six fat-soluble pigment components in spread leaves: chlorophyll a/b,pheophytin a/b,?-carotene and lutein.During the spreading process,the content of chlorophyll a and b showed a "decreasing-increasing-decreasing" trend.After 12 hours of spreading,the chlorophyll a/b content of each treatment is higher than that of the natural light group,indicating that red light and dark are beneficial to maintain the chlorophyll content of post-harvest tea.The content of lutein was higher in the dark group and the red light 3000 lx group,and it increased firstly and then decreased,while it decreased in the red light 1000 lx group and the natural light group.The content of ?-carotene showed an overall upward trend.The content of ?-carotene in the dark group and the red light 3000 lx group was significantly higher than that in the red light 1000 lx group and the natural light group.The higher content of ?-carotene provides rich aroma precursor substances for subsequent tea processing,which is beneficial to the formation of good quality tea aroma.3.This study is based on the comprehensive analysis of ultra performance liquid chromatographyhigh resolution mass spectrometry of withered leaves(red light 630 nm and dark conditions)at different times(0,2,4,6,8,10 and 12 h)changes in metabolites.The results showed that 94 non-volatile compounds were identified and relatively quantified,including 19 amino acids,10 catechins,12 dimeric catechins,20 flavonoid(alcohol)glycosides,9 phenolic acids,5 bases,nucleosides,and nucleotides,5alkaloids,3 organic acids,2 glycosidically bound volatiles,1 lipid and 8 other substances.Partial least squares discriminant analysis showed that the phenotypes of compounds treated with red light withering and dark withering showed two different trends.Hierarchical clustering heat map analysis found that amino acids and catechin monomers and dimers were most affected by red light.Among them,the level of 10 amino acids increased significantly after being irradiated with red light.The levels of epigallocatechin gallate and catechin in the catechin monomers were significantly reduced,the levels of theaflavins and Theasinensin A in catechin dimers had increased significantly,the transcriptional expression of Cs PPO1 and Cs PPO2 were significantly enhanced,which resulted in significant accumulation of theaflavins.4.In this study,headspace solid phase micro extraction-gas chromatography-mass spectrometry was used to detect and analyze the volatile components of withered leaves under different light treatments such as dark,red light(630 nm,1000 lx,3000 lx),natural light(260-325 lx),and the dynamic changes of the volatile components of withered leaves and red light withered differential volatile substances under different light treatments were studied.The results show that a total of 130 volatile components were detected in withered leaves at different time periods,including 26 alcohols,33 esters,29 hydrocarbons,12 aldehydes,13 ketones,and 17 others.Comparing different light withering methods,it was found that the total content of volatile components in the red light 3000 lx group pre-mid withering period(The first8 h)were significantly higher than that in other groups.With the increase of red light intensity,the total content of esters increased significantly(P<0.05),while the total content of ketones decreased significantly(P<0.05).Through orthogonal partial least squares discriminant analysis,the variable projection importance factor was greater than 1 and the coefficient of variation was greater than 50%,5volatile components were screened out with the greater response to red light,including 1,2-dimethylpropyl-2-methyl-butanoic acid ester,1-isocyano-3-methyl-benzene,decanal,2-methyl-2-decanol,linoleic acid ethyl ester.Among them,the coefficient of variation of decanal was as high as133.34% under red light 1000 lx.