Biodegradable Polymeric Films Incorporated with Nisin: Characterization and Efficiency against Listeria monocytogenes

Nisin (0.2 IU per cm(2) films) containing biodegradable films were produced from pea protein isolate (PPI), whey protein isolate (WPI), and polylactic acid (PLA). Nisin was released over 4 h at 22 A degrees C and 8 h at 4 A degrees C. PPI released more nisin compared to other films suppressing the growth of Listeria monocytogenes (P < 0.05) based upon diffusion into agar and liquid culture media. The population of bacteria after 48 h in liquid media was 6 CFU/mL (1 log(10) increase) in PPI, 8.47 CFU/mL (3.47 log(10) increase) in WPI and 9 CFU/mL (4 log(10) increase) in PLA, which was significantly lower in protein based films compared to PLA (P < 0.05). The inhibition zone in agar test was significantly higher (P < 0.05) in PPI and WPI, compared to PLA film, which might be due to the higher hydration in protein based films. Fourier transform infrared spectroscopy (FTIR) showed that nisin altered the intensity of amide I peaks in protein based films suggesting that nisin can bind to the protein functional groups in PPI and WPI. Thermogram showed that nisin did not influence the glass transition and melting temperatures of the films. Nisin containing films exhibited significantly lower enthalpy compared to control films (P < 0.05). PeakForce Quantitative Nano Mechanical Property Mapping (PeakForce QNM) was applied to extract material and mechanical properties in PPI, WPI and PLA films with and without nisin. Results showed significant reductions in material and mechanical properties of protein based films containing nisin compared to PLA films.