The study by Haiqiang Chen et al, published in the Journal of Food Science, found that use of chitosan, particularly when used in coatings, was able to inhibit the growth of LM and could potentially be an effective tool for the fish processing sector in efforts to tackle the bacteria.
The group said they launched the project as LM-contamination of ready-to-eat foods, such as cold-smoked salmon, is a common cause of foodbourne illness outbreaks and usually occurs in the post-processing phase. In 2009 the US Department of Agriculture (USDA) estimated that 15 per cent of all smoked fish is tainted with LM.
Chitosan is a natural polymer obtained by deacetylation of chitin, which is the major constituent of the exoskeleton of crustaceans. It is insoluble in water, but soluble in various acidic solvents such as dilute hydrochloric, formic, and acetic acids.
Chitosan efficacy
The aim of the study was to evaluate the performance of chitosan-based edible coatings and films incorporating three generally recognized as safe (GRAS) antimicrobials; sodium lactate (SL), sodium diacetate (SD), and potassium sorbate (PS), against L. monocytogenes on cold-smoked salmon.
Salmon samples were surface-inoculated with a 5-strain cocktail of LM to a final concentration of 4.4 log CFU/cm2 and then either coated with chitosan solutions or wrapped with chitosan films with or without the antimicrobials. The samples were then vacuum packaged and stored at 4°C for 30 days.
The scientists found that chitosan coatings, with or without the antimicrobials, consistently showed higher efficacy against LM than chitosan films with the same compositions.
Chitosan films containing 1.2 per cent SL/0.25 per SD or 2.4 per cent per SL, achieved ≥ 1.3 log reductions of LM during refrigerated storage period, said the group.
However, chitosan coatings containing 1.2 per cent SL/0.25 per cent SD or 0.15 per cent PS/0.125 per cent SD, were more effective and achieved ≥ 2.8 log reductions.
“Our research thus holds great promise to enhance the microbiological safety of RTE fishery products,” said the study.
Control of Listeria monocytogenes on cold-smoked salmon using chitosan-based antimicrobial coatings and films by Zheng Jiang, Hudaa Neetoo, Haiqiang Chen, published by Journal of Food Science, Vol. 76, Nr. 1, 2011/ DOI: 10.1111/j.1750-3841.2010.01925.x