Study On The Key Flavor Compounds And Bioactive Substances Of Citrus Pu-erh Tea

The research object of this paper is three parts of Citrus Pu-erh tea: whole fruit,inner tea and outer fruit.The main contents of this paper are:(1)Analysis of aroma components of three samples of Citrus Pu-erh tea.(2)Analysis of the components related with taste of Citrus Pu-erh tea.The first and second parts are interlinked,and the conclusion can be shown through the final flavor wheel,which realizes the comprehensive flavor analysis of the Citrus Pu-erh tea.(3)Based on the contents of total polyphenols and flavonoids,the antioxidant capacity and hypoglycemic ability of the sample were further determined.The specific research conclusions are as follows:(1)The three samples(CP,IT,OF)had strong significance in the sensory evaluation results(P ≤ 0.01 or P ≤ 0.001).And verified by E-nose.Among them,CP sample is more prominent in the aroma characteristics of phenolic,fatty and minty,IT sample is more prominent in the aroma characteristics of roasted,musty and herbal,and OF sample is better than the other two samples in the aroma properties of woody,fruity and floral.A total of 47 volatile compounds were identified.The FD factors obtained by aroma dilution analysis(AEDA)showed that the FD factors of the same compound varied greatly from sample to sample.The contribution of one particular key aroma active compounds to the overall aroma was quantitatively assessed by calculating odor activity value(OAV)and odor characteristic influence value(ACI).The key aroma substances in CP samples were linalool,methyl aminobenzoate,p-cresol,(+)-carvone,methyl methanthranilate,vanillin,(+)-limonene,2,4-di-tert-butylphenol.Aroma omission showed that the volatiles that significantly affected the overall aroma of CP samples were methyl methanthranilate,methyl anthranilate,(+)-carvone,vanillin,z-carvol,2,4-dimethyl styrene,(+)-limonene,(-)-carvol,terpine-4-ol,2,4-di-tert-butylphenol and thymol.The results of aroma omission experiment are consistent with the results calculated from OAV and ACI values.PLSR model classified the key aroma active compounds into the following categories:sweet aroma(vanillin);floral(β-ionone);fruity(methyl anthranilate,methyl methanthranilate,citronellal,(+)-carvone,Z-carvol);musty(p-cymene),woody(perillaldehyde);herbal(linalool,(+)-limonene,α-terpineol,2-ethylhexyl alcohol);phenolic(2,4-di-tert-butylphenol,p-cresol,2,4-dimethyl styrene);minty(dihydrocarvone);fatty(octanoic acid).(2)The taste characteristics of three parts of Citrus Pu-erh tea and the corresponding indicators were tested qualitatively and quantitatively.The results showed that the total sugar content in the outer peel of Citrus Pu-erh tea was the most,mainly sucrose and fructose,and their sweetness is OF > CP > IT.The results of organic acid content in three parts of Citrus Puerh tea showed that the organic acid content in CP was the highest,followed by that in OF,and the organic acid content in IT sample was the least.The results of free amino acids in three parts of Citrus Pu-erh tea showed that the content of free amino acids in the OF was the highest,followed by the CP,and the total amount of free amino acids in the IT was the least.The TAV values of umami,sweet and bitter taste were mainly measured.The nucleotide results of three parts of Citrus Pu-erh tea showed that there was little difference of each nucleotide content in the sample.According to data from E-tongue,the taste properties of the three Citrus Pu-erh tea samples were significantly different(P ≤ 0.01).Except for sweetness and sourness,the other seven attributes showed the highest score in IT sample and the lowest score in OF sample.These results indicated that the intensity of taste properties of CP samples was regulated by IT and OF.There seems to be a synergistic effect between OF and IT on sweetness attribute scores,which results in the highest sweetness scores for CP samples.Overall,the aroma and taste attributes of the three Citrus Pu-erh tea samples were significantly different,even after years of co-fermentation.Untargeted metabolomics results showed that 29 compounds were involved in two important metabolic pathways,glucosinolates and flavonoids biosynthesis.14 of the compounds were related to taste.The 47 flavor substances in the CP sample and their flavor descriptions(35 aromatic active compounds and 12 flavor-related compounds)were plotted on the flavor wheel.These findings reveal the relationship between the structure and aroma characteristics of CP samples and identify the main source of flavor compounds in CP samples.The aroma substances of the CP samples were mostly found in the samples of IT and OF,which can be considered as the joint action of Pu-erh tea and citrus peel.The detected components can initially explain the composition-component relationship and provide support for food pairing and derived flavor pairing.(3)The contents of total polyphenols and flavonoids in CP samples were higher than those in inner tea and outer fruit.The DPPH、ABTS and ·OH radical scavenging capacity and total antioxidant capacity of CP samples were the strongest,followed by the inner tea,while the outer fruit had the weakest antioxidant capacity.The trend of the determination results of all antioxidant capacity indexes was consistent with the difference results of total polyphenols and total flavonoids content measured.The inhibition rate of α-glucosidase and α-amylase of CP samples was higher than that of positive control.In conclusion,the combination of Pu ’er tea and citrus peel in Citrus Pu-erh tea can indeed improve the inhibition ability of α-glucosidase and α-amylase,which is conducive to the regulation of blood glucose balance.These conclusions can provide a certain theoretical basis for the regulation of Citrus Puerh tea flavor and the development of active substances,and provide a certain theoretical guidance for the future research and development of Citrus Pu-erh tea.