Quantification of ascorbyl adducts of epigallocatechin gallate and gallocatechin gallate in bottled tea beverages

Although tea catechins in green tea and green tea beverages must be stable to deliver good sensory quality and healthy benefits, they are always unstable during processing and storage. Ascorbic acid (AA) is often used to protect catechins in green tea beverages, and AA is easily oxidized to form dehydroascorbic acid (DHAA). However, the function of DHAA on the stability of catechins is not clear. The objective of this study was to determine the effects of DHAA on the stability of catechins and clarify the mechanism of effects by conducting a series of experiments that incubate DHAA with epigallocatechin gallate (EGCG) or catechins. Results showed that DHAA had a dual function on EGCG stability, protecting its stability by inhibiting hydrolysis and promoting EGCG consumption by forming ascorbyl adducts. DHAA also reacted with (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), and (−)-epigallocatechin (EGC) to form ascorbyl adducts, which destabilized them. After 9 h of reaction with DHAA, the depletion rates of EGCG, ECG, EC, and EGC were 30.08%, 22.78%, 21.45%, and 13.55%, respectively. The ability of DHAA to promote catechins depletion went from high to low: EGCG, ECG, EGC, and EC. The results are important for the processing and storage of tea and tea beverages, as well as the general exploration of synergistic functions of AA and catechins.

Dark teas are prepared by a microbial fermentation process. Flavan-3-ol B-ring fission analogues (FBRFAs) are some of the key bioactive constituents that characterise dark teas. The precursors and the synthetic mechanism involved in the formation of FBRFAs are not known. Using a unique solid-state fermentation system with <i>β</i>-cyclodextrin inclusion complexation, as well as targeted chromatographic isolation, spectroscopic identification, and Feature-based Molecular Networking (FBMN) on the Global Natural Products Social Molecular Networking (GNPS) web-platform, we reveal that dihydromyricetin and the FBRFAs, including teadenol A and fuzhuanin A, are derived from epigallocatechin gallate (EGCG) upon exposure to fungal strains isolated from Fuzhuan brick tea. In particular the strains from subphylum Pezizomycotina were key drivers for these B-/C-ring oxidation transformations. These are the same transformations seen during the fermentation process of dark teas. These discoveries set the stage to enrich dark teas and other food products for these health promoting constituents.

This work describes a terbium luminescencebased protocol to selectively detect gallate-derived green tea polyphenols on a supramolecular gel immobilised paper platform for the first time. This user-friendly, inexpensive (E 0.0015) approach requires very low sample volumes for the analysis. The developed strategy enables simultaneous detection of gallate polyphenols in multiple tea samples with the potential for practical applications. Antioxidants play important roles by reducing oxidative stress and improving metabolic functions of living beings. [1] Gallic acid (GA) is one such important naturally occurring antioxidant present in several foods [2] and has been reported to have health benefits with anti-inflammatory, anti-cancer, antimicrobial, antiradical, anti-aging properties and also provides protection from cardiovascular and neurodegenerative diseases. [3-5] In this respect, green tea, a rich source of antioxidants is becoming one of the most popular beverages in the world market with increased awareness about its multiple health benefits. [6] Research has revealed that it contains a number of polyphenols that are powerful antioxidants and are responsible for the beneficial effects attributed to green tea. These polyphenols constitute up to 30% of the total dry weight of green tea. [7] Out of the eight different polyphenols present in green tea, four are gallate polyphenols: catechin gallate (CG), epicatechin gallate (ECG), gallocatechin gallate (GCG) and epigallocatechin gallate (EGCG). The non-gallate polyphenols are catechin (C), epicatechin (EC), gallocatechin (GC) and epigallocatechin (EGC) (Figure S1). [8] Generally, the gallate polyphenols are known to have more beneficial effects than other polyphenols as the galloyl moiety is known to play important roles in the health benefits credited to green tea. [9,10] EGCG, a gallate ester, is the most abundant and potent polyphenol present in green tea, [a