Inactivation of Salmonella on whole cantaloupe by application of an antimicrobial coating containing chitosan and allyl isothiocyanate.

This study investigated the antimicrobial effect of a chitosan coating+allyl isothiocyanate (AIT) and nisin against Salmonella on whole fresh cantaloupes. Cantaloupes were inoculated with a cocktail of three Salmonella strains and treated with chitosan, chitosan+AIT, chitosan+nisin, and chitosan+AIT+nisin coatings. With AIT concentrations increasing from 10 to 60 μl/ml, the antibacterial effects of coating treatments against Salmonella increased. Chitosan coatings with 60 μl/ml AIT (chitosan+60AIT) reduced more than 5 log₁₀ CFU/cm² of Salmonella. The addition of nisin to the chitosan-AIT coating synergistically increased the antibacterial effect; coatings with nisin (25 mg/ml or 25,000 IU/ml)+30 μl/ml AIT resulted in a 4.8 log₁₀ reduction of Salmonella. The chitosan+60AIT coating significantly (p<0.05) reduced populations of native bacteria on cantaloupes to ca. 2 log₁₀ CFU/cm² during the first 6 days and populations remained unchanged through day 14 at 10 °C. The same coating treatment completely inactivated mold and yeast on cantaloupe at day 1 and no regrowth occurred even up to 14 days of storage. Scanning electron microscopy revealed that cell membrane damage and leakage of intercellular components occurred as a result of the chitosan-AIT coating treatments. No visual changes in overall appearance and color of cantaloupe rind and flesh due to coating treatments were observed. These results indicate that the application of an antimicrobial coating may be an effective method for decontamination of cantaloupes.