Antimicrobial efficiency of carvacrol vapour related to mass partition coefficient when incorporated in chitosan based films aimed for active packaging

Chitosan-based packaging films were investigated for antimicrobial efficiency against food spoilage microorganisms through headspace technique. Five chitosan based films containing carvacrol with known mass partition coefficient (Kmass) in the range from 10−4 to 10−8 were produced and their antimicrobial activity was evaluated. Bacillus subtilis, Escherichia coli, Listeria innocua and Salmonella enteritidis were exposed to active films either just after inoculation or just after an incubation phase. When tests were made at inoculation time for carvacrol concentration of 3.13 × 10−8 g mL−1 and low Kmass, films revealed antimicrobial efficiency against all tested microorganisms. When already grown colonies were exposed to films, those with lower Kmass displayed moderate inhibitory action against tested Gram-negative and strong efficiency against tested Gram-positive bacteria. From all results, the minimal vapour inhibitory concentration was considered as 4.62 × 10−8 g mL−1 (Kmass = 1.13 × 10−6) for B. subtilis, E. coli and L. innocua, 1.08 × 10−7 g mL−1 (Kmass = 1.01 × 10−4) for S. enteritidis. Films with the carvacrol vapour concentrations of 4.62 × 10−8 g mL−1 and 6.41 × 10−8 g mL−1 had strong antimicrobial effect at t0 and t1 except for S. enteritidis that was the most resistant bacterium. Concentration of 3.13 × 10−8 g mL−1 was efficient at t0 but not at t1. Concentration of 6.28 × 10−9 g mL−1 did not have any antimicrobial effect against all tested microorganisms, both at t0 and t1. Lag phase, doubling time of bacteria and concentration of released volatile compounds are key factors of antimicrobial efficacy. Antimicrobial tests and observations permitted a comparison of bioactivity potential of the activated chitosan films and the examination of the relationship between the antimicrobial properties and the mass partition coefficient.