Antimicrobial Activity of ε-Poly-l-lysine after Forming a Water-Insoluble Complex with an Anionic Surfactant

ε-Poly-l-lysine (ε-PL) is one of the few homopoly(amino-acid)s occurring in nature. ε-PL, which possesses multiple amino groups, is highly soluble in water, where it forms the antimicrobial polycationic chain (PLⁿ⁺). Although the high water-solubility is advantageous for the use of ε-PL as a food preservative, it has limited the applicability of ε-PL as a biopolymer plastic. Here, we report on the preparation and availability of a water-insoluble complex formed with PLⁿ⁺ and an anionic surfactant, bis(2-ethylhexyl) sulfosuccinate (BEHS^-, is also commercialized as AOT) anion. The PLⁿ⁺/BEHS^--complex, which is soluble in organic solvents, was successfully used as a coating material for a cellulose acetate membrane to create a water-resistant antimicrobial membrane. In addition, the thermoplastic PLⁿ⁺/BEHS^--complex was able to be uniformly mixed with polypropylene by heating, resulting in materials exhibiting antimicrobial activities.