Illustrating The Effect Of Aspergillus Niger Extracellular Enzymes On The Aroma Of Instant Oolong Tea Using Sensory Evaluation,GC-MS And Proteomics Analysis

Tea is one of the most popular beverages over the world.As the value-added product of tea,instant tea that is processed via water extraction,concentration and drying becomes more and more attractive.During the processing such as extraction and drying,the aroma of tea extremely damaged,which makes instant tea has the aroma worse than than that of the non-instant tea.In this study,GC-MS,sensory evaluation and proteomics analyses were used to explore the effect of the extracellular enzyme from Aspergillus niger on the aroma of instant Oolong tea,which is very significant to improve the characteristic aroma of instant tea.The major content and results are shown below.(1)GC-MS was used to qualitative analysis Oolong tea,instant Oolong tea and enzyme-treated instant Oolong tea.Total 43 volatile compounds were detected in the three samples.Among these,there were 7 alcohols,9 aldehydes,10 terpenoid,6 lipid,3 furans,6ketone and 2 others.At the same time,28 and 23 volatile compounds were identified in Oolong tea and instant Oolong tea samples,respectively.(2)Volatile compounds were quantitatively analyzed using standard curves and internal references.The main compounds of enzyme-treated Oolong tea sample were cis-3-hexenol,benzaldehyde,2-penty-furan and 3,5-dimethy-phenol,and the content of all these compounds significantly increased compared with those of instant Oolong tea sample.The sensory analysis showed that the floral and grass notes of enzyme-treated instant Oolong tea greatly improved while the intensities of sweet and roasty notes decreased.In addition,the overall aromas profile became close to that of the Oolong tea;and the characteristics aroma of Oolong tea recovered in the enzyme-treated instant Oolong tea.(3)The proteomics analysis showed that there were 380 proteins in the crude enzymes from Aspergillus niger,among these,166 were characteristic proteins of the crude enzyme fermented in the tea stalk medium.In comparison to the crude enzymes fermented in the wheat bran medium,the crude enzyme sample from tea stalk medium has 107 up-regulated proteins and 88down-regulated proteins.Compared with the crude enzyme fermented in the czapek's medium,the crude enzyme extract showed 103 up-regulated proteins and 21 down-regulated proteins.These differential proteins mainly related to the metabolic process,cellular process and cellular component organization or biogenesis,and involved in binding and catalytic activity.These results indicated the crude enzymes from Aspergillus niger fermented in tea stalk medium have could significantly change the characteristic aroma of instant Oolong tea,and it contains some enzymes that differentially expressed in comparison to those fermented with other media,laying a new foundation for separating and identifying the enzymes to improve the aroma of instant tea.