| Dark tea with a certain storage period is unique in both quality and taste.It is a high-end product with high collection value,good economic benefits and rapid market development.However,the processing technology of dark tea is unique,and there is a phenomenon of cross-regional processing and storage.The relative humidity in the storage environment is an important reason for the quality of dark tea.In this paper,the suitability and safety of environmental conditions for storage and transportation of dark tea under the background of transformation and upgrading of dark tea industry were studied.The chemical composition and microorganisms of dark tea under different relative air humidity storage conditions were systematically studied.UHPLC-Q-TOF-MS non-targeted metabolomics technique was used to qualitatively describe and quantitatively characterize the quality components of dark tea stored at different relative air humidity.A total of 144 metabolites were identified,including 21 monomeric catechins and their derivatives,31 polymeric catechins and their derivatives,38 flavonoids and their glycosides,24 phenolic acids,5 amino acids,6 organic acids,5 nucleosides and 14 carbohydrates and their derivatives.The differential metabolites were identified by univariate analysis.The results showed that there was a strong positive correlation between the six methylated catechins and high relative air humidity conditions,which may be the result of methoxytransferase produced by microorganisms.The potential biomarkers related to the storage of dark tea at different relative air humidity were screened by multivariate statistical analysis.The results showed that 7 FGs and 3 monomer catechin derivatives were up-regulated,indicating that the biomarkers of dark tea stored at high relative air humidity(88 ± 0.1%RH)included FGs and monomer catechin derivatives.Combined with the results of sensory evaluation,the main effect of air relative humidity on sensory evaluation during storage was studied.The results showed that group C(89.00 ± 1.13)>group B(85.70 ± 0.92)>group D(85.60 ± 1.15)>group E(82.55± 1.04)>group F(82.10 ± 1.65)>group G(81.50 ± 1.45)>group A(80.25 ± 1.25),indicating that dark tea was more suitable for storage at relative air humidity of(57 ±1.3)%RH.The results of differential multiple analysis and discriminant analysis showed that high levels of polymeric catechin derivatives and FGs were the main reasons for the good sensory quality of group C samples.The microbial flora of dark tea samples was analyzed by PacBio SMRT three-generation sequencing technology.A total of 12 fungal genera and 162 bacterial genera were identified.The relative abundance results showed that the dominant phylum in fungi was Ascomycota(91.90-99.97%),and the dominant phylum in bacteria was Proteobacteria(80.70-84.61%).The results of differential contribution analysis showed that biological functional microorganisms included 1 fungal genus(Aspergillus)and 7 bacterial genera(Cronobacter,Bacillus,Bacteroides,Pantoea agglomerans,Staphylococcus,Gluconobacter and Moraxella).VIPpre value≥1.0;the parameters with correlation coefficient | r |≥ 0.8 and P 1%were used for combined analysis of microbial and compound data.There were 4 genera of core functional microorganisms,including 1 fungal genus(Aspergillus)and 3 bacterial genera(Gluconobacter,Cronobacter,Pantoea). |
