INDIVIDUAL AND COMBINED PERFORMANCE OF NISIN AND POTASSIUM SORBATE SUPPORTED IN TAPIOCA STARCH EDIBLE FILMS

C. BASCH, J. CARPENCO, R.J. JAGUS AND S. FLORES

Congreso; International Congress on Engineering and Food (ICEF 11).; 2011

Edible films with antimicrobial activity based on preservative releasing provide a promising form of active packaging systems applicable in food processing. They allow a better efficiency in food protection as they offer more stability on the antimicrobial agents, and ensure the control of its release toward food. The objective of this research was to study the individual and combined effect of nisin and potassium sorbate, supported in tapioca starch edible films, on L. innocua and Zygosaccharomyces bailii, as well as the effect of antimicrobials on some physical and mechanical properties. Films were prepared by casting technique. The effect of the edible film as antimicrobial barrier to external hazard as well as the diffusional characteristics of the antimicrobials were studied. The physical properties were evaluated through solubility test, water vapour permeability (WVP), colour attributes, and mechanical characterization by tensile strength and elongation at break. Results obtained showed that the starch based film itself could not inhibit the bacterial or yeast growth at the film medium interface. On the contrary, the starch films containing nisin or nisin/KS yielded a low density of Wisteria growth at the film medium interface and a clear inhibition zone around the film disk (total diameter of inhibition: 2.00 and 1.70 mm for an initial disk diameter of 0.70 mm), showing antimicrobial diffusion to the solid medium. The barrier assay evaluated if the antimicrobials contained in the film are available to act as a barrier for external microbial contamination. Films without antimicrobials or individuals one allowed the Wisteria growth. On the contrary, films containing nisin/KS showed a bacteriostatic effect, reaching at the end of the storage a population of 3.4 log cycle lower than the films without antimicrobials. In the presence of Z. bailii, tested films allowed the yeasts growth. However, nisin/KS films showed a final yeast count of 1.3 log cycle lower than the film without antimicrobials. Regarding mechanical properties, individual or combined antimicrobials exerted a plasticizing effect in comparison with films without preservatives. It was observed a decrease of tensile strength to around 0.62 MPa and an increase of the elongation at break until 3.2, being nisin/KS films the most extensible. The solubility in water was higher, 25-36%, when antimicrobials were incorporated to film formulation. Contrarily, WVP was not affected by the KS and/or nisin presence and it was determined a WVP average value of 1.44 x 10-11 g / Pa m s.  Colour attributes of films showed a slight darkness for antimicrobial films as was established by an increase of YI and b* values. Combined nisin/KS films displayed the highest YI (13.6) and b* (7.1) parameters. These results revealed that the developed antimicrobial film could act as an active packaging being a hurdle against microorganisms present in food systems and as a barrier to further product contamination. In addition, the antimicrobial agents might modify the physical and mechanical properties.