Antimicrobial efficacy and release kinetics of thymol from zein films

A comprehensive study on thymol loaded zein films is presented in this work. In particular, the antimicrobial efficacy of developed active zein films was tested against three different spoilage microorganisms (cells and spores of Bacillus cereus, Candida lusitaniae and Pseudomonas spp.) and one GRAS (Generally recognized as safe) microbial strain (Streptococcus thermophilus). Results show that the films are effective against the selected spoilage food borne microorganisms, without compromising the growth of S. thermophilus. Release tests were also run at 25 °C to investigate the thymol release mechanism. Results show that the Fick’s Second Law satisfactorily describes the release kinetic. Moreover, it was also found that the thymol diffusion coefficient does not depend to a great extent on the thymol concentration. On the other hand, thymol sorption isotherm in zein showed an upward concavity as in the case of low molecular weight compound sorption in polymeric matrix. Finally, antimicrobial effectiveness of developed active film as compared to thymol directly added to the inoculated growing medium was assessed on Pseudomonas spp. by comparing results obtained from direct addiction of thymol to that obtained from released thymol. Results show that differences are negligible.