Decontamination of Salmonella enterica spp. on shell eggs by Allium cepa L. dry scales extracts

Salmonellae are a major global diarrheal diseases agent and are commonly found in a variety of foods. However, eggs appear to be one of the most important sources of infection ultimately leading to salmonellosis. Here we investigate a potential utilization of onion (Allium cepa L.) dry scales extracts and decoction for disinfection of eggshells contaminated with Salmonella enterica spp. Antimicrobial activity was screened by a microplate dilution method against 32 environmental and 1 reference Salmonella strains, at 106 and 103 CFU/ml starting cell concentration. Also, the efficacy of egg submersion treatment was tested. At high contamination level of 106 Salmonella cells per ml, extracts exhibited MIC and MBC values in the range of 0.08-2.50 mg/ml and 0.31-10.0 mg/ml, respectively. Ethanol extract had the most potent antibacterial activity followed by methanol, ethyl-acetate and acetone extracts. Pure decoction had MIC and MBC in the range of 250-500 mg/ml. When testing a lower level of contamination (103 CFU/ml) which is more similar to real life levels, MIC and MBCs were 8 to 14 times lower. Submersion of artificially contaminated eggs in ethanol extracts and decoctions resulted in the complete elimination of Salmonella after 8 minutes of exposure. Thus, a reduction of a minimum of 3.71 log units was achieved during the 8 minutes of treatment. Having in mind natural levels of Salmonella eggshell counts are far lower it can be implied that such treatment could be highly effective in practical application. Results show that tested onion dry scale decontamination solutions are an efficient, cost-effective and eco-friendly options for eggshell decontamination, and are especially promising for use in organic egg production.