Abstract
Teas can be classified according to their degree of fermentation, which has been reported to affect both the bioactive components in the teas and their antioxidative activity. In this study, four kinds of commercial Taiwanese tea at different degrees of fermentation, which include green (non-fermented), oolong (semi-fermented), black (fully fermented), and Pu-erh (post-fermented) tea, were profiled for catechin levels by using high performance liquid chromatography (HPLC). The result indicated that the gallic acid content in tea was directly proportional to the degree of fermentation in which the lowest and highest gallic acid content were 1.67 and 21.98 mg/g from green and Pu-erh tea, respectively. The antioxidative mechanism of the gallic acid was further determined by in vitro and in silico analyses. In vitro assays included the use of phorbol ester-induced macrophage RAW264.7 cell model for determining the inhibition of reactive oxygen species (ROS) production, and PKCδ and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit (p47) activations. The results showed that only at a concentration of 5.00 μM could gallic acid significantly (p < 0.05) reduce ROS levels in phorbol ester-activated macrophages. Moreover, protein immunoblotting expressed similar results in which activations of PKCδ and p47 were only significantly (p < 0.05) attenuated by 5.00 μM treatment. Lastly, in silico experiments further revealed that gallic acid could block PKCδ activation by occupying the phorbol ester binding sites of the protein.
Highlights
One of the most oft-consumed drinks in the world, especially in Asian countries [1], is tea [2,3].Various beneficial health effects of teas, performed by bioactive components, were reported, such as lowering cholesterol [4] and low-density lipoprotein (LDL) content [5], reducing risk of type 2 diabetes [6,7], the risk of coronary artery disease [8], and strengthening immunity [4]
It was clear that the levels of gallic acid increased with the degree of fermentation, whereby the highest and lowest content were found in Pu-erh tea (21.98 mg/g) and green tea (1.67 mg/g), respectively
It was found that catechin derivatives containing galloyl groups, i.e., epicatechin gallate (ECG), epigallocatechin gallate (EGCG), and gallocatechin gallate (GCG), in fermented teas (Pu-erh and black tea) were relatively lower than non-fermented and semi-fermented teas
Summary
One of the most oft-consumed drinks in the world, especially in Asian countries [1], is tea [2,3]. Quantification of bioactive compounds in Pu-erh, green, oolong, and black teas were reported in which green tea had the highest amount of both total phenolics and catechins, whereas black tea and. Among other bioactive compounds in teas, the levels of gallic acid, which is a well-known catechin for its antioxidative activity, were found to vary in Chinese and Japanese commercial green, oolong, paochong, and Pu-erh teas. The highest gallic acid content was found in commercial Pu-erh tea (2.01 mg/100 mg) and the lowest amount in Chinese green tea (0.04 mg/100 mg) [13]. We reported the effect of the fermentation process on bioactive compound levels in tea in this study. Further an investigation of the antioxidative activity was conducted on gallic acid, the bioactive compound mainly affected by the fermentation process, by using our previously proposed model
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