Effects of Meteorological Factors on Content of Free Amino Acids and Caffeine in Green Tea

Green tea, the most significant type of tea in China, is greatly influenced by meteorological factors in its quality development. However, the report about the relationship between quality components of green tea and meteorological factors is insufficient. In this study, data on the content of 144 free amino acids from 10 provinces and 220 caffeine content measurements from 12 provinces are collected through a literature review, covering the period from 2018 to 2023. Meta-analysis and correlation analysis are employed to identify key meteorological factors influencing the content and impact of tea quality components. Results indicate that the concentration of free amino acids exhibits an increasing trend from southwest to northeast. Specifically, levels of free amino acids in Yunnan, Guizhou, and Sichuan are lower, whereas those in Zhejiang and Anhui are the highest. The temperature in Guangdong and Jiangxi is higher than that in other provinces during 30 d prior to tea picking. Additionally, Jiangxi records the highest levels of rainfall, while Yunnan experiences the most sunshine hours. With the increasing number of limited sunshine days in 30 d prior tea picking, the content of free amino acids gradually decreases, and the content of free amino acids decreases by 4.68 % on average for each day of limited sunshine hours, and the maximum could be reduced by 30.39%. The caffeine content exhibits an increasing trend from the southeast to the northwest. Higher levels of caffeine are found in Henan, Hubei, and northeastern Sichuan, while lower levels are observed in Zhejiang, Fujian, and northeastern Guangdong. Compared to other provinces, Guangdong and Fujian experience higher temperature, while Jiangxi receives the highest levels of rainfall, and Yunnan enjoys the longest sunshine hours. With an increase in the number of moderate rain days during 30 d prior to harvesting, the average caffeine content decreases by 4.43%, with a maximum reduction of 25.58% for each additional day of moderate rainfall. In general, free amino acids and caffeine exhibit a significant negative correlation with limited sunshine hours and moderate rainfall days. Numbers of limited sunshine days and days of heavy rainfall and below may be the primary meteorological factors influencing free amino acids and caffeine levels.