Abstract: Tea saponin tertiary amine intermediate was formed by reaction between tea saponin and 3-dimethylamino propylamine.Then the intermediate further quaterized with bromoethane to produce tea saponin quaternary ammonium salt.Suitable conditions for preparation of the intermediate were identified as:using triglycol as solvent;molar ratio n(tea saponin)∶n(3-dimethylamino propylamine)=1∶2.5;reaction temperature 130 ℃ for 8 h.The yield of the intermediate achieves 85.7%.Surface activity of the tea saponin quaternary ammonium salt product was measured as cmc 0.398 g/L,and γ_cmc 40.82 mN/m.Foaming power of the product is good but its foam stability is poor.Its resistance to oxidation were measured as,at a mass concentration of 1.0 g/L,the ion ·OH and ·O₂^- scavenging rate reaches 55.4% and 66.3% respectively.Meanwhile,the bacteria inhibitory effect of the product against E.coli,Bacillus subtilis and Staphylococcus aureus is better than that of tea saponin.

Key words: quaternary ammonium salt, tea saponin, modification, surface activity, bacteriostatic capacity, resistance to oxidation