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The effects of tea polyphenols (TP) and different types of teas (green, black and oolong tea) processed from the same fresh leaves on pancreatic α-amylase activity were studied using potato starch and cooked potato as substrates. The results showed that, with the both substrates, low concentration of TP significantly increased α-amylase activity while high concentration inhibited it by non-competitive fashion. In addition, the extents of enzymatic activation and inhibition were different when TP was pre-incubated with α-amylase or starch, respectively. The interaction of TP with enzyme/starch led to decreased antioxidant capacity. Results also showed that all the three types of teas significantly enhanced α-amylase activity for a wide range of concentrations (0.34–27.14 mg/mL), and green tea showed the highest activation effect. It is concluded that high concentration of TP exhibits mild inhibitory effect against α-amylase, while green tea, black tea and oolong tea enhance α-amylase activity, which may be due to other constituents in the tea, enhancing α-amylase activity that counteracts the inhibitory effect of TP. [ABSTRACT FROM AUTHOR]

This study intends to produce a black tea vinegar (BTV) from low-quality bulk black tea in order to increase its consumption and added value, and to benefit from its functional characteristics. Three strains (Acetobacter sp. GDMCC1.152, Acetobacter pasteurianus GDMCC1.67, and Acetobacter aceti ATCC15973) of acetic acid bacteria (AAB) were inoculated into black tea infusion (BTI) with ethanol to produce BTV, and their effects on bioactive compounds, antioxidant activity, and volatile compounds in the vinegars were revealed. The results showed that the three strains were suitable for the production of BTV, and the vinegar quality was the best after acetic acid fermentation for 6 days. Compared with BTI, the contents of organic acids and volatile compounds and the antioxidant activity of the vinegars increased significantly. Among them, the vinegar produced by GDMCC1.152 strain had the highest content of organic acids, tea polyphenols (TPs), thearubigins (TRs), theabrownines (TBs), and volatile compounds. It also possessed the strongest antioxidant activity and a rich taste with an apple-like aroma. In summary, AAB fermentation can effectively improve the flavor and quality of BTI and produce a new healthy product with high activity, and Acetobacter sp. GDMCC1.152 is the most suitable strain for the production of BTV. • A black tea vinegar was prepared from low-quality bulk black tea. • Acetobacter sp. GDMCC1.152 was the most suitable strain for the production of black tea vinegar. • AAB fermentation improved the quality and antioxidant activity of black tea infusion. • Black tea vinegar is a healthy product. [ABSTRACT FROM AUTHOR]

The zinc-complexes of tea polyphenols (TP), including (−)-epigallocatechin gallate (EGCG), were prepared with zinc chloride at pH 6.5 in the absence of oxygen. The complexes were characterized with field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), ultraviolet–visible (UV–vis), fourier transform infrared (FTIR), 1H nuclear magnetic resonance (1H NMR) spectroscopy and thermogravimetric analysis (TGA), and their antioxidant and antibacterial activities were studied. The results showed that TP/EGCG complexed with zinc ion in the B-ring at 1:1, and the thermal stability of the complexes was better than that of TP/EGCG, and the scavenging activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide radicals and the antibacterial activities against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) were significantly stronger than those of EGCG/TP. We speculated that the complexation with zinc ion might enhance the thermal stability, the antioxidant activity and the antibacterial activity of TP/EGCG. It can be expected that the zinc-complexes of TP/EGCG will have a bright prospect for their potent biological activity. • TP-Zn complex was prepared and characterized. • The thermal stability of the complex was high. • The antioxidant and antibacterial activities of the complex were stronger than those of TP. [ABSTRACT FROM AUTHOR]