Incorporation of lactic acid as an antimicrobial agent in polyamide food-packaging films

With a view to develop an effective antimicrobial packaging method for fresh meat, the utility of a commercial bi-axially oriented polyamide film (15 pm thickness) as a carrier for lactic acid was studied. In a first trial, films were immersed in food-grade lactic acid of various concentrations (10, 20, 40, 80 %) for 70 min, and subsequently dried for 24 h at 40 +/- 1 degrees C and 10% RH The higher the acid concentration, the higher was the weight gain of the finished films (2.8- 10.2 %), whereas films which had been immersed in bidistilled water and then dried, lost 2.5 % weight. Acid uptake was confirmed by thermo-gravimetric analysis. To assess the acid release, lactic acid augmented films were immersed in water for 1 h and 24 h. Equilibrium was reached within 1 h. Acid release was 40-50, ca. 60, ca. 80, and 61-67 mu g/cm(2) for 10, 20, 40 and 80 % acid treatment, respectively. Although acid release was highest in 40 % acid treated films, the 80 % acid treated films had the lowest variation in results and were considered for optimizing dipping and drying treatment. Acid release was highest in films which had received acid treatment for 120 min and had been dried for 24 h. Measuring the thickness of cross sections of acid treated films indicated that the distribution of the acid in the film was homogeneous. Relying on the hygroscopic nature of polyamides to allow uptake of organic acids in the packaging matrix is a promising approach to develop novel antimicrobial packaging options for meat.