Effect of hydrophobic property on antibacterial activities of green tea polysaccharide conjugates against Escherichia coli

We previously found that green tea polysaccharide conjugates (gTPCs) have antibacterial activity against Escherichia coli. In this study, the effect of hydrophobic property on the antibacterial activities of gTPCs was evaluated to elucidate their property-activity relationship. Three gTPCs (gTPCs-5 h, gTPCs-12 h and gTPCs-24 h) were extracted from green tea with the ethanol precipitation time of 5 h, 12 h and 24 h, respectively. These three gTPCs did not differ significantly in terms of molecular weight distribution, amino acids composition and zeta potentials. Fourier transform infrared spectroscopy results revealed that gTPCs-5 h and gTPCs-12 h processed more hydrogen bonds than gTPCs-24 h. The surface hydrophobicity and contact angle of gTPCs-5 h were larger than that of gTPCs-12 h and gTPCs-24 h. The antibacterial activity of gTPCs against E. coli decreased in the order of gTPCs-5 h > gTPCs-12 h > gTPCs-24 h. There wasn't significant difference among the zeta potentials of E. coli treated by gTPCs-5 h, gTPCs-12 h and gTPCs-24 h, but the bacterial contact angles of E. coli treated by gTPCs-5 h were higher compared with those of the other two gTPCs. Furthermore, gTPCs-5 h exhibited higher activity to decrease bacterial membrane proteins, and increase bacterial membrane permeability than the other two gTPCs. In conclusion, gTPCs with higher hydrophobicity property exhibited stronger antibacterial activity against E. coli.