Abstract
The flowering process has been reported to play crucial roles in improving the flavor and efficacy of fermented tea. Hippophae rhamnoides leaves containing many beneficial ingredients are a suitable plant source for tea processing. In this study, we isolated a β-glucosidase-producing fungus Eurotium amstelodami BSX001 from the fermented tea and used Hippophae rhamnoides leaves (HRL) as a substrate to explore the detailed process of bioconversion of some important functional factors. The results show that the contents of total phenolic compounds and flavonoids increased significantly after seven days, especially flavonoid aglycones (e.g., quercetin, kaempferol, and isorhamnetin). Such compounds greatly enhance the antioxidative activity of fermented products. Metabolic analysis of the standard compounds (rutin, quercetin-3-glucoside, kaempferol-3-glucoside, quercetin, isorhamnetin-3-glucoside, isorhamnetin, and kaempferol) further confirmed the effective biotransformation by E. amstelodami. Mechanisms of the bioconversion could be involved in deglycosylation, dihydroxylation, and O-methylation. Our findings expand the understanding of tea fermentation process and provide further guidance for the fermented tea industry.
Highlights
Flavonoids are phenolic compounds that are widely found in nature
The content of total phenolic compounds was calculated as mg of gallic acid equivalent (GAE) on the basis of dry weight (DW) from the calibration curve of the standard gallic acid
The total content of flavonoids was calculated as milligrams of rutin equivalent (RTE) based on dry weight from the calibration curve of the standard rutin
Summary
Flavonoids are phenolic compounds that are widely found in nature. They are secondary plant phenolic compounds widely distributed in plant leaves, seeds, barks, and flowers. Hydroxyl groups are added, methylated, sulfated or glucuronidated [4] Based on their unique chemical structures, flavonoids show a variety of catalytic properties for scavenging reactive oxygen and nitrogen species. The presence of an ortho-hydroxylation on the B-ring of flavonoid molecule, a C2-C3 double bond on the C-ring, the number of free hydroxyl groups or the presence of a 3-hydroxyl group is usually essential for antioxidant and antiradical activities [5,6]. Due to these numerous properties, flavonoids have been found to be emerging natural compounds in a wide variety of industries.
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