LED红光萎凋对红茶关键酶活性、理化性质及挥发性物质的影响OA

[Objective]The study aimed to explore the role of LED red light in regulating the dynamic changes of key enzyme activities,physicochemical properties and volatile compounds during the withering pro-cess of black tea,providing a reference for the withering processing of high-quality black tea.[Method]Natural indoor withering was used as the control(CK),with an LED red light(650 nm,2 000 lx)withering treatment group(RL)established for comparison.Samples were collected at 0,2,4,6,8,and 10 h,respectively,to deter-mine the activities of polyphenol oxidase(PPO),peroxidase(POD),and β-glucosidase(β-GC),along with the contents of tea polyphenols,free amino acids,soluble sugars,and flavonoids.Volatile compounds were analyzed using the GC-IMS technology,and principal component analysis was performed to clarify the quality differences between different withering stages.[Result]During red-light withering,PPO activity in tea leaves peaked at 8 h,reaching 15.65 U/g,an 8.70％ increase compared to CK.POD activity reached its maximum at 10 h,reach-ing 16.26 U/g,a 25.08％ increase of compared to CK.β-GC activity in tea leaves reached its peak of 4.58 U/g at 4 h.Under red light withering,tea polyphenols content decreased significantly at 2,4,and 8 h(P＜0.01).Flavonoid content decreased significantly at 8 and 10 h(P＜0.01).Soluble sugar and free amino acid contents significantly increased at 10 h and 8-10 h of red light withering(P＜0.01).After 10 h of red light withering treatment,free amino acid content rose to 3.58％,representing a 20.95％ increase compared to CK.GC-IMS identified 85 volatile compounds.At 4 h of red light withering,the reduction of green-tasting sub-stances(e.g.,methyl salicylate and(Z)-4-heptenol)accelerated,while fruit-scented substances(such as limo-nene and α-pinene)increased,completing the process 2 hours earlier than CK.During the late withering stage(6 to 10 h),fruit and wine-like substances(e.g.,2-hexanone and 3-methylbutanol)significantly increased,whereas acidic substances(ethylene glycol monobutyl ether)decreased.The content and variety of constituents and aromas were most abundant at 10 h.Principal component analysis(PCA)showed that there were significant differences in the principal components of the samples at 8 h and 10 h,with a cumulative explanatory power of 68.9％.[Conclusion]LED red light withering significantly promoted glycosidic precursor hydrolysis and the generation of fruity aroma compounds by activating β-glucosidase and modulating oxidative enzymes,with the 4 h identified as the key node for aroma transformation.At 10 h of red light withering,the variety and content of free amino acids,soluble sugars,other constituents,and volatile compounds were most abundant.