| Aroma of green tea is not stable.It is susceptible to environmental factors.During storage,green tea gradually lost its primary freshness,and developed characteristic aroma called stale odor.At present,there are few reports on the key aroma components that can give people a sense of stale odor in green tea.Gas chromatography-olfactory-mass spectrometry(GC-O-MS)technology combins with olfactory sensory analysis to assess the contribution of volatile components in the sample to its aroma.To find compounds that contributing to the stale odor,fresh green teas and stored green teas were analyzed by GC-O-MS in this study,and provide data support for the ageing degree of green tea.The main results of the study during process were as follow:1.Headspace components of green teas were concentrated using a solid-phase microextraction fiber(HS-SPME).Through optimization of the extraction fiber,extraction temperature and time parameters,it was found that a 65 μm PDMS/DVB type extraction fiber was selected,the extraction temperature was 70℃.and the time was 50 min.When conditions are met,the extraction efficiency of aged green tea is higher.2.The volatile compounds in four types of green tea stored in different temperatures(-20℃,4℃,room temperature,35℃):Roasted green tea,Lu’an Guapian,Huangshan Maofeng and Huoshan Huangya were analyzed by Gas chromatography-mass spectrometry(GC-MS).A total of 96 volatile compounds were identified,in which esters and alcohols were the major chemical groups related to fresh green tea,and ketones was the major chemical group for aged green tea.Four kinds of green tea showed increased relative levels of ketones,lactones and aldehydes after storage.3.PCA analysis was performed using 96 compounds as variables.It was found that the aging of green tea was mainly related to the storage temperature.Based on this,OPLS-DA analysis was performed.The principal component regression coefficients of the model were:R2=0.984,Q2=0.966.There were 43 kinds of volatile substances that could be used as different temperature storage sample groups,among which 21 compounds appeared just in the aged green teas.Fifty-four odor active compounds were perceived by GC-O panelists,including 13 alcohols,6 aldehydes,8 ketones,and 7 esters,10 olefins and some other substances.Combining the OPLS-DA analysis,there were 17 kinds of aroma components that made outstanding contributions to the stale odor of green tea.4.The organoleptic quantitative description was performed for the stale odor of green teas.Correlation analysis revealed that 17 compounds were positively correlated with the aging degree,among them α-ionone,Nonanoic acid,methyl ester and Hexanedioic acid,dimethyl ester were significantly correlated at the 0.05 level,β-cyclocitral,(E,E)-3,5-octadien-2-one(Z,E)-3,5-octadien-2-one,β-ionone and dihydroactinidiolide are significantly related at the 0.01 level.5.Try to evaluate the aging degree of green tea with β-ionone and dihydroactinidiolide,which established with extremely significant correlation.The quadratic fitting models are:Y=0.037+0.333X-0.003X2,R2=0.669 and Y=1.241+3.08X-0.28X2,R2=0.816(X≥0).The use of dihydroactinidiolide as a judgement material for the aging degree is superior toβ-ionone.It is still necessary to further study and analyze the substances for stale odor and introduce other compounds to reconstruct the aroma profile. |
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