Amino acids are important flavoring substances in tea. During the processing of tea processing machinery, various enzymatic or non-enzymatic reactions will also occur and be converted into important components of tea aroma and pigments. Currently, 26 amino acids have been found in tea, including 20 protein-derived amino acids and 6 non-protein-derived amino acids.
1. Effects of tea germplasm resources on the synthesis, metabolism and transformation of tea amino acids
The content of amino acids, especially theanine, varies among different tea tree varieties. The amount of green leaf varieties increases with the leaf position of one leaf, two leaves, and three leaves, and the content of theanine in young shoots is the highest.
2. The influence of the production environment on the synthesis, metabolism and transformation of tea amino acids
In spring, you can use a tea harvester to quickly pick tea leaves. The amino acid content of spring tea is significantly higher than that of summer tea. The reason is that strong light and high temperature in summer will lead to lower tea tree nitrogen metabolism and strong theanine hydrolysis and transformation capabilities, resulting in lower amino acid content in young shoots in summer.
3. Effects of processing technology and storage on the synthesis, metabolism and transformation of tea amino acids
The changes in the amino acid content of tea during the processing are mainly affected by two aspects. On the one hand, some small molecule proteins or polypeptides undergo local hydrolysis and pyrolysis under the action of moisture and heat, causing the accumulation of amino acids; on the other hand, the amino acids are It is reduced through oxidation, hydrolysis, transformation, and combination with sugar and polyphenols to form color, aroma and taste substances.
(1) Spreading and withering
During the spreading and tea withering machine stages, free amino acids are formed by protein hydrolysis, so the total amino acid content generally shows an upward trend. However, the theanine content activates the expression of theanine hydrolase due to water loss, causing theanine to be hydrolyzed, showing Downtrend.
(2) Fermentation stage
Fermentation is mainly divided into polyphenol oxidase fermentation and microbial fermentation. During the fermentation process of tea, the cells are damaged after being passed through the tea rolling machine, and the phenolic substances in the cells are oxidized by polyphenol oxidase. The resulting quinone compounds undergo some reversible or irreversible chemical reactions with amino acids, which has a certain effect on the aroma of black tea. important role.
(3) Fixing and drying
During the fixing and drying stages, high temperature plays a dominant role. Amino acids often undergo oxidative polymerization with o-quinones or undergo Maillard reactions with carbonyl compounds. The higher the temperature of the tea fixing machine, the higher the temperature of the tea fixing machine, the more hydrolyzed the amino acids will be while promoting the hydrolysis of proteins. and transformation.
(4)Storage
During the storage process of tea, amino acids will be further degraded and transformed due to changes in environment and time. The higher the temperature and the greater the humidity, the greater the amount of degradation.