Polylysine is an effective antimicrobial in its own right but in combination with modified atmospheric packaging (CO₂ as the gas) or with other antimicrobials, and even with food products stored at ambient delivered better than expected results. It  has good antimicrobial activity over a wide pH range.

ε-Polylysine is a naturally produced homopolymer of 25 to 30 lysine residues, with antimicrobial properties against various Gram-negative and Gram-positive bacteria, as well as yeasts and molds (Shima et al., 1984; Yoshida and Nagasawa 2003; Geornaras et al., 2007; Chang et al., 2010).

The compound is produced by natural fermentation and was approved by the Japanese Ministry of Health, Labour and Welfare in the late 80s. Polylysine then received GRAS status according to the US Food and Drug Administration in 2004

A number of studies have shown how effective polylysine happens to be especially for surface treatments of various meat products. Levels of 0.125% w/w and 0.25% w/w reduced high starting populations of inoculated Salmonella in NRTE (not ready-to-eat) frozen breaded chicken nuggets. This was regardless of the surface browning method, either by oven baking or deep-fat frying. It is also exceptional when used in combination with carvacrol or caprylic acid as was the case in the treatment of Salmonella on NRTE surface-browned, frozen breaded chicken products (Moschonas et al., 2012).

Polylysine appears to cause serious cell membrane changes in micro-organisms such as yeast which alters the protein componentry making it semi-porous (Bo et al., 2016).

In a recent study, beef specimens were treated with 2000 ppm and 8000 ppm polylysine to destroy two test food safety micro-organisms, E. coli and Salmonella (Miya et al., 2014). The beef samples were incubated at a typical chill room temperature of 4°C and the researchers noted a 4.3 log and 2.4 log reduction in bacterial numbers after a 7-day incubation for E. coli O157:H7 and Salmonella respectively.

Polylysine has little taste. In the same study by Miya et al., (2014), they reported as above, that when 5,000 ppm and 8,000 ppm polylysine solutions were added to Japanese amberjack sashimi by immersion at 4 °C for 40 minutes, followed by sensory evaluation. It would appear there was a slight bitterness at 5,000 ppm level.

References

Bo, T., Han, P-P., Su, Q-Z., Fu, P., Guo, F-Z., Zheng, Z.-X., Tan, Z-L.,  Zhong, C., Jia, S-R. (2016) Antimicrobial ε-poly-l-lysine induced changes in cell membrane compositions and properties of Saccharomyces cerevisiae, Food Control 61, pp. 123

Chang, S.-S., Lu, W.-Y.W., Park, S.-H., Kang, D.-H. (2010) Control of foodborne pathogens on ready-to-eat roast beef slurry by ε-polylysine. Int. J. Food Microbiol. 141 pp. 236–41.

Geornaras, I., Yoon, Y., Belk, K.E., Smith, G.C., Sofos, J.N. (2007) Antimicrobial activity of ε-polylysine against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in various food extracts. J. Food Sci. 72 M330–4

Miya, S., Takahashi, H., Hashimoto, M., Nakazawa, M., Kuda, T., Koiso, H., Kimura, B. (2014) Development of a controlling method for Escherichia coli O157:H7 and Salmonella spp. in fresh market beef by using polylysine and modified atmosphere packaging, Food Control, 37, pp. 62

Moschonas, G., Geornaras, I., Stopforth, J. D., Wach, D., Woerner, D. R., Belk, K. E., Smith, G. C. and Sofos, J. N. (2012), Activity of Caprylic Acid, Carvacrol, ɛ-Polylysine and their Combinations against Salmonella in Not-Ready-to-Eat Surface-Browned, Frozen, Breaded Chicken Products. J. Food Sci., 77  M405–M411. doi: 10.1111/j.1750-3841.2012.02757.x

Shima, S., Matsuoka, H., Iwamoto, T., Sakai, H. (1984) Antimicrobial action of ε-poly-l-lysine. Antibiot. 37 pp. 1449–55

Yoshida, T., Nagasawa, T. (2003) ε-Poly-l-lysine: microbial production, biodegradation and application potential. Appl. Microbiol. Biotechnol. 62 pp. 21–26