Effect of Red and Blue Light Exposure During Withering on Amino Acid and Catechin Contents of Congou Black Tea

Effect of light-exposure(i.e.,red,blue or no light)during the withering process of Congou black tea was studied.Contents of amino acids and catechins of the tea leaves were monitored,and the sensory evaluation on the steeped tea performed.The results showed that the total and most amino acids,except Asp and Thea,in the leaves increased gradually during the withering process.Exposed under the red light,Asp and Thea in the leaves decreased,while Ile,Leu,Tyr,Lys and His increased in greater extents than other amino acids.When no light was applied,Ser,Val and Phe in the leaves increased most significantly.Withering under the blue light,the tea leaves contained significantly greater amounts of the rest of amino acids than under either the red light or no light.The contents of GC,EGC,ECG,EGCG,total esters type catechins and total catechins in the leaves decreased gradually upon withering,while those of C,GCG and CG increased at the beginning and then decreased afterward.During the spreading of the leaves for withering,EG decreased initially and then increased.Exposed under the red light,the tea leaves contain less of GC,EGC,EGCG,total esters type catechins and total catechins than other lighting conditions.Either the blue or red light exposure reduced more ECG than total darkness.The sensory evaluation on the brewed tea showed that the Congou black tea withered under the red light had the highest score on aroma,and that withered under the blue light had the highest score on taste.It appeared that the light-exposure during withering could affect the amino acid and catechins contents of the teas.Congou black tea withered under the red light seemed to have the best quality among all samples.