Polylysine

Polylysine refers to several types of lysine homopolymers, which may differ from each other in terms of stereochemistry and link position. Polylysine refers to several types of lysine homopolymers, which may differ from each other in terms of stereochemistry and link position. The precursor amino acid lysine contains two amino groups, one at the α-carbon and one at the ε-carbon. Either can be the location of polymerization, resulting in α-polylysine or ε-polylysine. Polylysine is a homopolypeptide belonging to the group of cationic polymers: at pH 7, polylysine contains a positively charged hydrophilic amino group. α-Polylysine is a synthetic polymer, which can be composed of either L-lysine or D-lysine. 'L' and 'D' refer to the chirality at lysine's central carbon. This results in poly-L-lysine (PLL) and poly-D-lysine (PDL) respectively. ε-Polylysine (ε-poly-L-lysine, EPL) is typically produced as a homopolypeptide of approximately 25–30 L-lysine residues. According to research, ε-polylysine is adsorbed electrostatically to the cell surface of the bacteria, followed by a stripping of the outer membrane. This eventually leads to the abnormal distribution of the cytoplasm causing damage to the bacterial cell that is produced by bacterial fermentation. ε-Poly-L-lysine is used as a natural preservative in food products. Production of polylysine by natural fermentation is only observed in strains of bacteria in the genus Streptomyces. Streptomyces albulus is most often used in scientific studies and is also used for the commercial production of ε-polylysine. α-Polylysine is synthetically produced by a basic polycondensation reaction. The production of ε-polylysine by natural fermentation was first described by researchers Shoji Shima and Heiichi Sakai in 1977. Since the late 1980s, polylysine has been approved by the Japanese Ministry of Health, Labour and Welfare as a preservative in food. In January 2004, polylysine became generally recognized as safe (GRAS) certified in the United States. ε-Polylysine is used commercially as a food preservative in Japan, Korea and in imported items sold in the United States. Food products containing polylysine are mainly found in Japan. The use of polylysine is common in food applications such as boiled rice, cooked vegetables, soups, noodles and sliced fish (sushi). Literature studies have reported an antimicrobial effect of ε-polylysine against yeast, fungi, Gram-positive bacteria and Gram-negative bacteria.