Abstract
Numerous epidemiological and interventional clinical studies have consistently reported that black tea is good for human health. The polyphenolic compound, theaflavin, and its galloyl esters (theaflavins) are the primary red pigments in black tea that possess several health benefits, including fat-reducing and glucose-lowering capabilities and lifestyle-related disease prevention related to anti-obesity, anticancer, anti-atherosclerotic, anti-inflammatory, antiviral, antibacterial, anti-osteoporotic, and anti-dental caries properties. These compounds are produced by key enzymes, such as polyphenol oxidase and peroxidase, from parent green tea catechins present in fresh green tea leaves during the production of black tea leaves or the fermentation of green tea. However, theaflavins are only present in low concentrations in black tea; thus, their extraction from black tea leaves at sufficient levels for use in medical studies has been difficult. To circumvent this issue, different procedures for the synthesis of theaflavins using chemical oxidizing reagents or enzymes have been studied; however, low yields have limited their utility. Recently, however, several biosynthetic methods have been developed for the mass production of theaflavins. Using these methods, the physiological functions of theaflavins in lifestyle-related diseases in mice and humans have also been studied. In this review, we present the synthesis of theaflavins and their health benefits.
Highlights
During tea production, tea is largely separated into non-fermented tea and fermented tea.Enzymes such as polyphenol oxidase and peroxidase are present in tea plant leaves, which, for non-fermented tea, are either steamed, boiled, microwaved or electrically heated to inactivate endogenous oxidases
Black tea leaves are tea leaves in which green tea catechins are oxidized by endogenous polyphenol oxidase or peroxidase during the fermentation process [1,2,3,4]
TFs possess a benzotropolone skeleton. These compounds are produced from their parent catechins (Figure 2) [epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)] by polyphenol oxidase (PPO) or peroxidase (POD) in fresh green tea leaves during the production of black tea leaves or green tea fermentation [1,2,3,4]
Summary
Tea is largely separated into non-fermented tea and fermented tea. TF1 inhibits tube formation via reducing the secretion of vascular endothelial growth factor in a hypoxia-inducible factor 1α-independent manner, whereas the other theaflavins appear to work in a hypoxia-inducible factor 1α-dependent manner [5] Both epidemiological studies and interventional clinical studies have examined the relationship between drinking tea, such as green tea, oolong tea, black tea, and plasma cholesterol concentration, one of the major risk factors for arteriosclerosis. Several biosynthetic methods of TFs suitable for mass production have been reported [26,28,29,30,32,36,37] Using these methods, the physiological functions of TFs in mice [26,28,35] and humans [26] for the prevention of lifestyle-related diseases have recently been studied. We introduce the synthesis of TFs and the functionality of theaflavins (antimetabolic syndrome, anti-periodontitis, anti-norovirus, anti-osteoporosis)
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