In this study, the fungal community structure, metabolites, antioxidant ability, and taste characteristics of five Fu brick tea (FBT) from different regions of China were determined and compared. A total of 69 operational taxonomic units (OTUs) were identified and assigned into 5 phyla and 27 genera, with Eurotium as the predominant genus in all samples. Hunan (HN) sample had the strongest fungal diversity and richness, followed by Guangxi (GX) sample, and Zhejiang (ZJ) sample had the lowest. GX sample had higher amounts of gallic acid (GA), total catechins, gallocatechin (GC), and epicatechin gallate (ECG) as well as antioxidant activity than the other samples. The levels of total phenolics, total flavonoids, epigallocatechin (EGC), catechin, epicatechin (EC), thearubigins (TRs), and theaflavins (TFs) were the highest in the ZJ sample. Guizhou (GZ) and Shaanxi (SX) samples contained the highest contents of epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG), respectively. Total phenolics, GA, EC, CG, and TFs were positively associated with most of fungal genera. Total phenolic content (TPC), total flavonoid content (TFC), and most of catechins contributed to the antioxidant activities of FBT. HN sample had the strongest sourness and sweetness, ZJ sample had the strongest saltiness, SX sample had the strongest umami, and GZ sample had the strongest astringency, which was ascribed to the varied metabolites. This work reveals that FBT in different regions vary greatly in fungal community, metabolites, antioxidant activity, and taste characteristics, and provides new insight into the quality characteristics formation of FBT in different regions.

In this study, black soybean was firstly processed by solid-state fermentation (SSF) with a probiotic fungus Eurotium cristatum YL-1. The effect of SSF on the nutritional components (including proximate, amino acids, minerals, and fatty acids), total phenolics, isoflavones, antioxidant activity, and volatile organic compounds of black soybeans were revealed. Results of this work demonstrated that black soybean processed by SSF with E. cristatum greatly increased the contents of protein, essential amino acids, and some minerals (e.g., calcium, phosphorus, and magnesium). GC results revealed that more than 80% of the total lipids from both fermented and non-fermented black soybeans were unsaturated fatty acids, and SSF influenced the fatty acids composition. Higher contents of total phenolics and aglycone isoflavones (i.e., genistein, daidzein, and glycitein) of fermented black soybeans were achieved by SSF. Furthermore, SSF with E. cristatum considerably augmented the ferric reducing antioxidant power, scavenging effects against ABTS·+ and DPPH radical, reducing power, and chelating ability of black soybeans, which evaluated with various polarity solvent extracts. HS-GC-IMS analysis detected a total of 66 volatile compounds in FBS and BS, and 56 volatile organic compounds were successfully identified. The intensities of main volatile compounds (i.e., 10 esters, 11 alcohols, and 19 aldehydes) differed remarkably by fermentation with E. cristatum. The intensities of seven alcohols and nine aldehydes considerably decreased, whereas higher levels of esters were achieved by SFF. Thus, our results confirmed that black soybeans processed by SSF with E. cristatum is a promising approach to substantially improve its nutritional value, flavor characteristics, and biological effect, and might have great potential in the development of new functional foods or be used as a new nutritional ingredient applied in food design.