Enhanced bioaccessibility of green tea polyphenols and lipophilic activity of EGCG octaacetate on gram-negative bacteria

The polyphenol acetates derived from green tea (Camellia sinensis. L) catechins, effectively increases the bioaccessibility as evaluated by simulated invitro enzymatic digestion method. The acetylated polyphenols showed significantly higher bioaccessibility (60.13 +/- 0.3%) with respect to their precursors (31.80 +/- 0.7%). The antibacterial activity of major catechins and their acetates on food-borne pathogens indicated the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) respectively for gram-positive bacteria (GPB)- Bacillus subtilis (EGCG, 130 mu g/mL and 150 mu g/mL; EGCG octaacetate 100 mu g/mL and 120 mu g/mL), Staphylococcus aureus (EGCG, 200 mu g/mL and 250 mu g/mL; EGCG octaacetate 150 mu g/mL and 200 mu g/mL) and the gram-negative bacteria (GNB). Escherichia coli (EGCG, 580 mu g/mL and 700 mu g/mL; EGCG octaacetate 250 mu g/mL and 300 mu g/mL) and Yersinia enterocolitica (EGCG, 620 mu g/mL and 740 mu g/mL; EGCG octaacetate 280 mu g/mL and 330 mu g/mL). The prepared EGCG octaacetate had higher inhibitory effect against both GNB and GPB, than EGCG, which showed moderate activity on GPB and less effect on GNB. This is attributed to its lipophilic nature, a distinctive property, as evaluated by lipophilicity test. It is further substantiated with membrane permeability assay using fluorescent microscopy and the morphological alterations on E. coli cells by scanning electron microscopy (SEM) studies.