Comparative in vitro biological characterization of black and green tea infusions fermented with brewer’s yeast and SCOBY with special emphasis on antioxidant activity

Abstract

This research work was designed for a detailed comparative in vitro biochemical characterization of different fermented tea infusions. Green tea, crush-tear-curl (CTC) black tea and orthodox black tea, along with brewer’s yeast (Saccharomyces cerevisiae) and traditional starter SCOBY (symbiotic colony of bacteria and yeast), were co-cultured for fermentation to produce different tea wines and kombuchas respectively. Primary investigations for qualitative characters on these fermented broths revealed the presence of total phenol, flavonoid, coumarin, tannin, protein, cardiac glycoside, glycerol, terpenoid, steroids and alkaloid. All the broths except kombuchas contained caffeine. Total phenol and flavonoid contents were also quantified, with fermented green tea samples showing a noticeable result. While all the fermented tea samples showed high free-radical scavenging activity, the best results were found in the green tea samples (before and after fermentation). However, fermented CTC samples had the highest fermentation-led increasing antioxidant properties. Physicochemical properties like acidity (pH), Brix, specific gravity and alcohol percentage (ABV) were considered as qualitative parameters to study the fermentation process and judge the acceptability of broths as edible beverages. Interestingly, when correlated with antioxidant property results, fermented CTC tea samples exhibited comparatively higher alterations in physicochemical properties due to fermentation. Comparatively, more glucose uptake capacity (in vitro antidiabetic activity) was found in fermented CTC broths, while inhibition of lipid peroxidation was substantive with yeast-fermented tea samples only. Unlike the yeast-fermented samples, the antibacterial properties exhibited by kombucha samples were promising. The presence of alcohol, biologically active groups of components, antioxidant and antibacterial activity etc. have added value to these fermented tea broths and established their acceptability as edible beverages. The production and in vitro biological characterization of different fermented tea broths have allowed a comparative analysis that is much needed for future research on and development of fermented teabased drinks.