Black Tea Phenolics Enhance Aerobic Growth of Lactobacillus Delbrueckii subsp. lactis under Oxidative Conditions

Black tea is rich in phenolic compounds with known antioxidant properties, yet their protective effects on lactic acid bacteria under oxidative conditions are not fully understood. In this study, the antioxidant action of phenolic compounds present in black tea infusion (BTI) was evaluated in relation to the aerobic growth of Lactobacillus delbrueckii subsp. lactis. Aqueous BTI was prepared from black tea leaves and characterised for total phenolic content (TPC) and radical scavenging activity. A BTI concentration of 40% (v/v) was selected for bioassays to exclude bactericidal or nutritive effects. The 40% (v/v) BTI exhibited a total phenolic content of 0.328 mg mL⁻¹ gallic acid equivalents and a DPPH radical scavenging activity of 3.099 mg mL⁻¹ ascorbic acid equivalents. Under anaerobic conditions, BTI did not significantly influence the bacterial growth. In contrast, under aerobic conditions, colony-forming unit counts were significantly higher in BTI-incorporated medium compared with BTI-free control. These findings indicated that black tea phenolics enhance the aerobic growth of L. delbrueckii subsp. lactis, most likely by mitigating oxidative stress through extracellular antioxidant mechanisms. The study highlights the potential of black tea phenolics to improve the aerobic tolerance of lactic acid bacteria. These results highlight the potential application of black tea phenolics in improving the aerobic tolerance of lactic acid bacteria in food and fermentation systems.