Investigating The Influence Of Aspergillus Niger Extracellular Enzyme On The Volatiles And Aroma Of Instant Green Tea

Tea is one of the most traditional economical crops in China.Instant tea is an important tea deep processing product.The flavor of instant tea greatly changes during the processing,which affect its quality and application.Aspergillus niger is an important scource of food enzyme preparation,and it is important to study the enzyme resources of Aspergillus niger to improve the instant tea flavor.It is of great significance to explore the enzymatic resources of A.niger for improving the flavor of instant tea powder.In this study,instant green tea was applied to investigate the effects of crude enzymes fermented by A.niger on the volatiles and aroma of instant green tea via GC-MS analysis and sensory evaluation,and the preliminary separation of volatile components precursor was further explored.The main results were as follows:(1)In this paper,the crude enzymes that were extracted from the fermented broth of tea stalk and potato dextrose medium named ETS and EPD,respectively.39 volatiles were detected in original instant green tea,ETS-treated instant green tea and EPD-treated instant green tea by GC-MS,including 7 kinds of terpenes,4 kinds of alcohols,7 kinds of aldehydes,5 kinds of kentons,6 kinds of esters,10 kind of others.In these 3 samples,30 kinds of volatiles were identified in original instant green tea,33 kinds of volatiles were identified in ETS-treated instant green tea and EPD-treated instant green tea,respectively.(2)The quantitative analysis showed that,the main volatiles in original instant green tea were hexanal,2-ethylfuran,decanal,octanal,linalool,trans-limonone oxide and trans-nerolidol.Compared with the original instant green tea,the treatment of ETS increased the content of 2-ethylfuran,ethyl 2-methylbutyrate and decanal and decreased the content of trans-limonene oxide and 2-heptanone;the treatment of EPD increased the concentrations of 2-ethylfuran and ethyl 2-methylbutyrate and decreased the concentrations of octanal,methyl salicylate and trans-limonene oxide.The results of sensory evaluation showed that: After ETS treatment,the floral and fermented notes increased,while green,woody and sweet notes decreased;and the treatment of EPD decreased green and floral notes.(3)A preliminary separation and verification of aroma precursors in instant green tea have been performed.The results showed that the aroma precursors were mainly existed in 20% methano elution site.After ETS treatment,when the crude extract separated by the solvent systems of ethyl acetate-butanol-water(2:1:3)in HSCCC,11 volatiles were identified.Among these volatiles,the main volatiles were methyl salicylate,cis-3-hexenol and hexanal,which content mainly concentrated in 60-110 min period.After ETS treatment,when the crude extract separated by the solvent systems of ethyl acetate-butanol-water(2:1:1)in HSCCC,12 volatiles were identified,which contents were also mainly concentrated in the 60-110 min period.The content of each components were significantly higher than that of the crude extract separated by the solvent systems of ethyl acetate-butanol-water(2:1:3).These results indicate that both ETS and EPD contain novel enzymes for modulating the aroma of instant green tea.There are many volatiles precursors in instant green tea.The initial separation of these precursor components may provide a basis for subsequent identification of the precursors of specific enzymes and identification of enzyme composition,and also have an important reference value.