Ph.D. McGill University Ste.Anne de Bellevue, Quebec, Canada
Objective: With increasing emphasis on the use of biopolymers in food packaging, an active-packaging system based on incorporation of EOs in soy protein isolate (SPI) films was investigated for the purpose of inhibiting the growth of Listeria monocytogenes on ready-to-eat foods.
Methodology: Oregano and cinnamon EOs and carvacrol shown high antimicrobial activity against L. monocytogenes were added to 5% SPI film-forming solutions at concentrations of 1-3% (w/v). Their effects on the characteristics of SPI films, including mechanical properties, water vapor permeability, opacity, and water solubility, were evaluated. In addition, Fourier transform infrared (FTIR) spectroscopic characterization of the films was employed to examine the effects of the EOs on protein secondary structure and to study the diffusion kinetics of the EOs. Results: The type of EO, the concentrations of glycerol and EO in the film-forming solution, and the emulsification treatment employed in preparing the films influenced their mechanical properties, water vapor permeabilities, and opacities. Films incorporating 2% of EO exhibited high antilisterial activities in vapor phase. FTIR spectroscopic characterization of the films indicated interactions between soy proteins and EOs resulted in some transformation of β-sheet to α-helical structure, consistent with a plasticizing effect of the EOs. The EO diffusion kinetics were well fit by a Weibull model, with a high correlation coefficient (>0.995) and low RMSE (<0.001).
Conclusion: SPI films incorporating EOs exhibiting antilisterial activity have potential utility as active-packaging for ready-to-eat foods. Information on protein-EO interactions influencing film properties and release of active compounds are provided by FTIR spectroscopy and can aid further development of active-packaging.
