Impact of cold atmospheric plasma treatment on black tea kombucha fermentation dynamics

• Cold plasma treatment accelerated bacterial activity in kombucha fermentation. • Corona discharge enhanced sucrose hydrolysis and acetic acid production. • Corona discharge increased the polyphenol content in tea infusion. • Corona discharge induced biodegradable activity during fermentation. Effect of cold pulsed corona discharge (CD) on the fermentation of black tea kombucha was studied. Kombucha samples were exposed to plasma in two 15-minute sequences, with a six-hour break between them. CD treatment slightly decreased the initial yeast viability (50.85 % vs. 73.62 % for control) but improved growth recovery, resulting in similar yeast number at the end of fermentation. Result showed CD enhanced sucrose hydrolysis and acetic acid production, indicating a bacterial activity acceleration. The pH gradually decreased in all samples during fermentation, from 4.2 to 3.4. Conversely, the conductivity increased from 0.8 to 1.1 mS/cm during the 10 days of fermentation due to changes in the components of the liquid. Two notable phenomena were observed with regard to the total polyphenol content (TPC) (i) an increase of around 62 % in the ethyl acetate (EtOAc) extract of unfermented tea and (ii) the consumption of polyphenols in the presence of bacteria regardless of the used solvent, indicating a biodegradable activity during fermentation. The results obtained for fermented tea closely correlated with antioxidant activity (the IC 50 increased from 7.6 to 16.3 µg/mL). HPLC-DAD revealed the presence of six phenolic compounds and GC–MS detected 24 volatile compounds in black tea exposed to plasma affecting both phenolic and volatile compound composition. A toxicity analysis of a human embryonic kidney cell line (HEK-293) revealed no toxic effects when kombucha was treated using CD process, this demonstrates that combining plasma discharge and fermentation creates a new process for producing bioactive compounds that preserves their functional properties.