Effects of different fixation methods on γ-aminobutyric acid content and quality components of Huangjinya green tea

【Objective】By studying the effects of different fixation methods on the γ-aminobutyric acid(GABA) content and main quality components in Huangjinya green tea treated by vacuum anaerobic treatment,the best way of fixation that could effectively retain GABA and improve tea quality was screened, which could provide theoretical basis for the production of high content GABA Huangjinya green tea and the deep processing of Huangjinya. 【Method】In this experiment,the tea samples treated with vacuum anaerobic treatment at room temperature for 6 h by four different fixation methods,namely microwave,roller,steam and pan frying. The GABA content of the tea was determined by high-performance liquid chromatography(HPLC). And according to the national standard method, the main quality components such as aqueous extract(AE), total free amino acids, caffeine(CAF), tea polyphenols, catechin components and flavonoids were determined, simultaneously using principal component analysis(PCA) and orthogonal partial least squares discriminant analysis(OPLS-DA) to analyze the characteristic components of Huangjinya green tea. 【Result】The microwave sterilization had the best retention effect on GABA content in Huangjinya green tea,at 1.66 mg/g,meeting the standard of GABA tea(≥1.50 mg/g). The total free amino acids content(3.88%),simple catechins content(50.92 mg/g), epigallocatechin(EGC) content(41.47 mg/g), epigallocatechin gallate(EGCG) content(64.48 mg/g), epigallocatechin gallate(ECG) content(2.45 mg/g), catechin gallate(CG) content(13.70 mg/g), total catechins content(134.20 mg/g) and total flavonoid content(11.54 mg/g) were significantly higher than those of the green tea processed by the other three fixation methods(P<0.05); the polyphenol content and phenol to ammonia ratio were significantly lower than those of the other tea samples,they were 16.03% and 4.13 respectively. The CAF content was 40.07 mg/g,which was lower than that of steam fixation tea samples,but it was already at a higher level in green tea. The PCA results show that the main quality components of tea samples processed by microwave fixation were significantly different from other fixation methods,and catechin(C),myricetin(Myr),GABA,gallic acid(GA),CAF,AE and epicatechin(EC) were the main marker components that caused the difference in the quality components of microwave fixation,drum fixation,steam fixation and pot fried fixation. 【Conclusion】The microwave fixation has the highest retention of GABA content and the lowest loss of quality components in Huangjinya green tea among the four fixation methods, the overall tea quality is excellent. So microwave fixation can be used as the best way to process Huangjinya GABA green tea.