Effects of anaerobic fermentation time on γ-aminobutyric acid content and quality components of Huangjinya green tea

【Objective】To study the effects of different anaerobic fermentation time treatments on Huangjinya green tea γ-aminobutyric acid(GABA) content and quality components, the optimal anaerobic time for high quality and high GABA content Huangjinya green tea was clarified,which provided a theoretical basis for the product development of Huangjinya green tea and tea quality improvement. 【Method】Used one bud,two leaves and three leaves of Huangjinya as raw materials,after conventional spreading,vacuum sealing packaging was carried out using a food vacuum sealing machine. The samples were anaerobic at room temperature for 0(control),3,6,9,12,and 15 h,and prepared using green tea technology. High performance liquid chromatograph was used to detect the GABA content in tea samples,combined with sensory evaluation and quality component detection,to analyze the changes in the influence of anaerobic fermentation time on the GABA content and quality components of Huangjinya green tea. 【Result】After anaerobic treatment,the GABA content of the tea samples reached the GABA tea standard(1.50 mg/g),with the highest GABA content(2.50 mg/g) after 6 h of anaerobic treatment,which was as 12.5 times as the control sample(0.20 mg/g). Within 6 h of anaerobic treatment,the sensory quality of the tea sample was normal,with a complete and golden appearance,a bright green and yellow soup color,a pure aroma,a fresh and mellow taste,and a golden and bright leaf base. After more than 6 h of anaerobic treatment,the sensory quality decreased obviously,manifested as a complete and golden appearance,a bright yellow soup color,a ripe and stuffy aroma,a green and astringent taste,mixed leaf base color,and a red stem. After anaerobic treatment,the increase in amino acids was 0-9.43%,the decrease rates of caffeine and water extracts contents were 1.89%-14.83% and 2.26%-6.41%,respectively,there was no significant change in the contents of tea polyphenols and total flavonoids(P>0.05,the same below),with a polyphenols/amino acid ratio ranging from 0.16% to 4.06%,the total amount of catechin increased by 1.91%-7.93%,and the bitterness and astringency index of catechin did not change significantly,the total flavonoid glycosides increased by 132.15%-169.06%,the total amount of free amino acids decreased by 10.03%-27.64%. Among the control samples,the theanine(The) and phenylalanine(Phe) contents were the highest with 1.23 and 0.96 mg/g respectively,followed by aspartate(Asp) and glutamate(Glu) with 0.84 and 0.81 mg/g. Cysteine(Cys) content was the lowest(0.04 mg/g). Among anaerobic samples,GABA and The had the highest content,ranging from 1.60-2.50 mg/g and 1.12-2.30 mg/g respectively,followed by lysine(Lys),ranging from 0.72-0.82 mg/g. Glutamine(Gln),valine(Val),Cys,isoleucine(Ile) and leucine(Leu) had the low contents,ranging from 0.02 to 0.05 mg/g. while the content of fresh amino acids increased by 10.59%-45.29%,while the contents of aromatic,bitter flavour,sweet flavour,and sour flavour amino acids decreased by 28.79%-50.00%,51.85%-85.80%,68.72%-78.97% and 82.24%-96.26%,respectively. 【Conclusion】The tea samples treated with anaerobic fermentation for 6 h have the highest GABA content and excellent overall quality. It can be used as the optimal anaerobic fermentation time for processing Huangjinya GABA green tea.