ANTIMICROBIAL EVALUATION OF HYDROXYPROPYLMETHYLCELLULOSE-BASED ACTIVE FILMS INCORPORATED WITH NISIN Z

Presentation: Oral (x) Poster (x)
e-mail: [email protected]

Industries and consumers in general have been looking for new options that certify quality food and safety. Among the alternatives, the active packaging has been highlighted because it interacts intentionally with food in order to improve some of its characteristics. Antimicrobial packaging is a promising type of active packaging as it inhibits or inactivates deteriorating and / or pathogenic microorganisms in packaged foods. A group of compounds that have great potential to be incorporated into active packaging and increase the shelf life of foods is antimicrobial peptides, as is the case of nisin Z. In this context, this work set out to develop and characterize HPMC-based active films incorporated with antimicrobial peptide nisin Z. The minimum inhibitory concentration (MIC) of nisin Z for the microorganisms Staphylococcus aureus, Listeria innocua and Salmonella Choleraesuis was performed in accordance with the broth macro dilution method. The active films were prepared by casting method, where the HPMC polymer dispersions (2% wt.) were heated to 80 °C, added with glycerol as plasticizer (10% wt.) and when the temperature reached 40 °C were incorporated by 0%, 5%, 10%, 15% and 20% (wt.) of nisin Z in relation to the polymer mass. For evaluate the in vitro antimicrobial activity of the films, was applied the agar diffusion method, where discs (Ø = 0.8 cm) of the antimicrobial film with different concentrations were placed in direct contact with the surface of the inoculated agar and after 24 h at 35 °C, the films antimicrobial effectiveness was verified. MIC results showed that nisin Z was more effective in inhibiting Gram-positive bacteria such as S. aureus and L. innocua (both with MIC of 0.19 mg.mL-1) than Salmonella Choleraesuis (MIC of 2.0 mg.mL-1). A similar result was found in the antimicrobial agar diffusion test. By regression analysis, a 2nd degree equation for inhibitory behavior of nisin Z in relation to Staphylococcus aureus (Y1 = 0.086 + 1.099x – 0.1402x2) and Listeria innocua (Y2 = - 0.15 + 1.176x – 0.1570x2) was adjusted. For both equations, it was noted that from the concentrations between 5% and 10% of nisin an optimum range of inhibition was achieved. As for Salmonella Choleraesius, there was no inhibition halo formation at any of the concentrations tested. This can be explained by the fact that the inhibitory effect of nisin is more pronounced for Gram-positive bacteria, such as Staphylococcus aureus and Listeria innocua. Although high concentrations of nisin render the cell wall in the Gram-negative bacteria permeable to this bacteriocin, the nisin concentrations used in the film were not sufficient for the proper diffusion of this active compound to the medium containing Salmonella Choleraesuis. It is possible to conclude that the active films of HPMC did not present inhibitory action for Salmonella Choleraesuis, but it was effective in the in vitro inhibition for the microorganisms Staphylococcus aureus and Listeria innocua, presenting potential of application in foods.

The authors would like to acknowledge CAPES, CNPq, FAPEMIG and Finep for financial support.