Effects on Salmonella shell contamination and trans-shell penetration of coating hens' eggs with chitosan

Chitosan is a biopolymer with antimicrobial activity and film-forming properties. In this study, the effects on Salmonella shell contamination and trans-shell penetration of coating hens' eggs with chitosan was evaluated. A chitosan was selected from eight types (four non-commercial and four commercial) based on its antimicrobial activity against Salmonella enterica serovar Enteritidis (S. Enteritidis). For this purpose, a contact plate method was developed and chitosans were applied at a concentration of 0.25% (w/v). A commercial type with a molecular weight of 310-375 kDa and a deacetylation degree of 75% that reduced S. Enteritidis by 0.71 log(10) colony forming units compared to the control (without chitosan) was selected for further studies. The chitosan was shown to have antimicrobial activity against other egg borne bacteria, i.e., Acinetobacter baumannii, Alcaligenes sp., Carnobacterium sp., Pseudomonas sp., Serratia marcescens and Staphylococcus warneri, and against S. enterica serovar Typhimurium, Escherichia coli and Listeria monocytogenes. The effects of various concentrations of the selected chitosan (0.25%, 1% and 2%) on Salmonella shell contamination and trans-shell penetration were assessed using the agar molding technique. Effective reduction of eggshell contamination could not be demonstrated, but trans-shell penetration was significantly reduced in the presence of a 2% chitosan eggshell coating, with only 6.1% of the eggs being penetrated compared to 24.5% of the uncoated eggs. It was concluded that the 2% chitosan coating has the potential to reduce contamination of egg contents resulting from trans-shell penetration by S. Enteritidis.