| Aroma was an important indicator that affected the grade evaluation,price and quality of tea products.The aroma of tea products was affected by harvest season,processing technology and exogenous enzymes.Baiyaqilan tea was a new variety of oolong tea with unique orchid flavor,and the research on its aroma quality and improvement was still insufficient.In this paper,in order to study the aroma quality of baiyaqilan spring tea and autumn tea,freeze-dried and spray-dried baiyaqilan instant tea.Baiyaqilan tea and its instant tea were studied by quantitative descriptive analysis(QDA),headspace solid phase microextraction(HS-SPME),gas chromatography-mass spectrometry(GC-MS),odour activity value(OAV)analysis and gas chromatography-mass spectrometry-olfactometry(GC-MS-O)analysis,and further analyzed the effects of common glycosidases on the aroma quality of baiyaqilan instant tea.The results were as follows:(1)The results of QDA showed that different aroma attributes of baiyaqilan spring tea and autumn tea had different aroma intensities.The main aroma profiles of spring tea were grassy,woody and roasted notes,while that of autumn tea were floral and sweet notes.The overall acceptability of autumn tea was significantly higher than that of spring tea(P ? 0.05).And the results of multiple stepwise regression analysis showed that the intensity of floral,grassy and sweet notes was positively correlated with the acceptability.GC-MS analysis showed that the volatile compounds of spring tea and autumn tea were basically similar in composition,but the content of spring tea was lower than that of autumn tea,with the total content of 4419.0 ?g/L and 5714.4 ?g/L,respectively.OAV combined with GC-MS-O analysis showed that the key aroma compounds of baiyaqilan tea mainly included 16 compounds,including 6-methyl-5-hepten-2-one,benzeneacetaldehyde,(E,E)-3,5-octadien-2-one,3-ethyl-2,5-dimethyl-pyrazine,trans-linalool oxide,hotrienol,safranal,geraniol,indole,(E,E)-2,4-decadienal,(E)-?-damascenone,(Z)-3-hexenyl hexanoate,(E)-?-Ionone,cis-geranylacetone,(E)-?-ionone and cis-jasmin lactone.Among them,cis-jasmin lactone,(E)-?-ionone and cis-geranylacetone were the main contributors to the unique orchid flavor of baiyaqilan tea.(2)The results of QDA showed that freeze-dried instant tea mainly presented caramel,roasted and floral notes,while spray-dried instant tea mainly presented caramel,roasted and sweet notes.The acceptability of spring tea and freeze-dried instant tea was similar and significantly higher than that of spray-dried instant tea(P ? 0.05).The results of GC-MS analysis showed that freeze-drying was more conducive to the retention of volatile compounds in tea.The total contents of volatile compounds in freeze-dried and spray-dried instant tea were 36356.1 ?g/L and 16330.5 ?g/L,respectively,and the loss of aldehydes was relatively serious.OAV combined with GC-MS-O analysis showed that the key aroma compounds of instant tea mainly included 12 compounds,including cis-linalool oxide,3-ethyl-2,5-dimethyl-pyrazine,trans-linalool oxide,hotrienol,phenylethyl alcohol,decanal,geraniol,indole,(E)-?-damascenone,cis-geranylacetone,(E)-?-ionone and cis-jasmin lactone.The three compounds that contributed to the unique orchid flavor of baiyaqilan products were also among them.(3)Taking the non-enzyme-treated spray-dried instant tea(NSIT)as a control,spray-dried instant tea was treated with ?-D-glucosidase,?-D-glucosidase and ?-D-xylosidase complex enzyme,?-D-glucosidase and ?-L-arabinosidase complex enzymes(GSIT,GXSIT,GASIT),respectively.The results of QDA showed that NSIT mainly presented caramel,roasted and sweet notes;GSIT,GXSIT and GASIT mainly presented floral,grassy,sweet and caramel notes.After treated with glucosidase,the floral and grassy notes intensity of spray-dried instant tea were significantly enhanced(P ? 0.05),and the intensity of roasted and caramel notes were significantly decreased(P ? 0.05),and there was no significant differences in the intensity of aroma attributes of GSIT,GXSIT and GASIT.GC-MS analysis showed that after glycosidase treatment,the total volatile compounds of GSIT,GXSIT and GASIT increased by 531.5%,138.5% and 168.3%,respectively.Volatile compounds with a large increased in content included(Z)-3-hexenol,benzyl alcohol,phenylethyl alcohol,geraniol,decanol,benzaldehyde,(E)-?-damascenone,methyl salicylate and cis-geranylacetone.OAV analysis showed that the intensity of grassy,floral and sweet notes of GSIT increased due to the increase of OAV values of(Z)-3-hexenol,benzyl alcohol,3-ethyl-2,5-dimethyl-pyrazine,methyl salicylate,geraniol and(E)-?-damascenone;the intensity of the grassy,floral and sweet notes of GXSIT and GASIT increased due to the increase of OAV values of(Z)-3-hexenol,geraniol and(E)-?-damascenone.GC-MS-O analysis showed that the aroma intensity values of benzeneacetaldehyde,3-ethyl-2,5-dimethyl-pyrazine,phenylethyl alcohol,cis-linalool oxide(pyranoid),2,5-dimethyl-1-propylpyrrole,methyl salicylate,geraniol,(E)-?-damascenone,cis-geranylacetone and cis-jasmin lactone were increased after treated with glucosidase.In addition,the OAV value and aroma intensity of cis-geranylacetone and cis-jasmin lactone,which contributed to the orchid flavor of baiyaqilan tea products,were also increased after treated with glucosidase.In short,the results showed that the orchid flavor of baiyaqilan tea products was mainly contributed by cis-jasmin lactone,(E)-?-ionone and cis-geranylacetone.The aroma quality of baiyaqilan tea picked in different seasons and instant tea prepared by different drying methods were different.The aroma quality of autumn tea and instant tea prepared by freeze-drying was better.?-D-glucosidase and its complex enzymes with ?-D-xylosidase and ?-L-arabinosidase could significantly improved the overall aroma quality of baiyaqilan instant tea.This study provided a theoretical basis for the classification and flavor improvement of baiyaqilan tea and its instant tea,and had extensive reference value for the quality classification and improvement of oolong tea. |
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