Antibacterial performance of solvent cast polycaprolactone (PCL) films containing essential oils

The increase of consumer demand for higher quality and longer shelf-life in foods, while reducing the use of non-compostable packaging materials, has encouraged research on biopolymers incorporating natural antimicrobial compounds. Cinnamaldehyde (CNMA) and allyl isothiocyanate (AITC) were incorporated into polycaprolactone (PCL) films by solvent casting. The release study was carried out by means of ATR and transmission FTIR spectroscopy and showed high volatility of the essential oils during the film forming process. While only negligible quantities of AITC were retained in the polymer matrix after film curing, the release of CNMA was prolonged for at least 50 h at room temperature. PCL films incorporating 10 wt.-% and 20 wt.-% CNMA were further investigated using both a macrodilution technique and a vapour diffusion technique. MICs against Salmonella enterica, and Listeria monocytogenes in the liquid phase were determined to be 5.87 and 4.49 mM, for films containing 10 and 20 wt.-% of CNMA with regard to the polymer in solution. The influence of relative humidity (RH) and temperature on the antimicrobial performance of the active films was investigated in the vapour phase. RH was not found to play a key role in the release and antimicrobial performance of the films, while decreasing temperatures resulted in a considerable increase in the antimicrobial effect. In a sealed environment, a concentration of less than 5.34 mg CNMA/L air from PCL with 20 wt.-% CNMA was able to cause complete inhibition of bacterial growth at 4 °C and 10 °C during at least 30 days. These results suggest that the combination of cold storage with biodegradable polyesters incorporating CNMA or other EOs could be an interesting approach in active packaging technologies.