Differences and distribution of quality components in Fu brick tea around fungal fermentation

The differences in and distributions of the quality components of Fu brick tea before and after flowering (also called fungal fermentation and known as "Fahua" in China) remain unclear, and the standard of judging quality by the number of golden flowers (GFs; yellow closed capsules of Eurotium cristatum spores) by consumers lacks a scientific foundation. In this study, Fu brick tea (AFT) was obtained from pre-flower raw dark tea (BFT) through the traditional processing of Fu brick tea. The AFT was then hand-selected and divided into pure tea (SFT) and GFs. It was found that the flavonoid, tea polyphenol, free amino acid, aqueous extract, and ester-type catechin content in the AFT were all significantly lower than in the BFT (p < 0.05); the content of 34 types of volatile compound was significantly higher (26 alkanes, 4 alkenes, 2 alcohols, 1 ester, 1 aldehyde) (p < 0.05), and the content of 14 types of volatile compound was significantly lower (6 alkanes, 4 alcohols, 2 esters, 1 ketone, 1 alkene) than in the BFT (p < 0.05). Furthermore, the content of 39 types of nonvolatile substances, including four carboxylic acids, three flavonoids, and D-Arabitol, amino acids and their derivatives, was significantly higher in the AFT (p < 0.05). The content of flavonoids and their derivatives, including 24 types of saturated alkanes and seven types of aldehydes and esters of volatile compounds (3 alkenes, 2 alcohols, 1 ester, and 1 aldehyde) (p < 0.05), was significantly higher in the SFT than in the GFs (p < 0.05). The GFs had significantly higher content of water-soluble leachate, maltose, glycosylated flavonoids, D-salicylose, and amino acids and their derivatives than the SFT (p < 0.05). Widdrol, linalool, N-octanal, and 25 other volatile compounds (9 alkenes, 9alcohols, s aldehydes, 1 ester, 1 alkane, 1 ketone, 1 Naphthalene) were detected only in the GFs.