Lactic acid bacterial fermentation modified phenolic composition in tea extracts and enhanced their antioxidant activity and cellular uptake of phenolic compounds following in vitro digestion

This study examined the ability of lactic acid bacteria (LAB) to metabolise tea phenolics and to enhance their cellular uptake following in vitro digestion. Tea extracts (TEs) or tea catechin cocktail were fermented and/or digested before determining their antioxidant capacity in vitro. Fermented TEs and cell metabolites were characterised by LC-MS/MS. Results showed increase in DPPH radical scavenging activity and cellular antioxidant activity of tea samples after fermentation, particularly evident for BTE, which was in alignment with the bacterial modified phenolic composition and elevated total phenolic content. Phenolics were degraded after digestion, which led to reduction in antioxidant activity with fermented tea samples, although this was less obvious than that of non-fermented counterparts. In addition, more phenolics were taken up by Caco-2 cells following fermentation, with the major constituents being catechins, gallic acid and quercetins. Our findings showed that LAB fermentation may be an efficient approach to enhance phenolic bioavailability and to protect cells against oxidative stress.