Listeria monocytogenes Inhibition by Whey Protein Films and Coatings Incorporating the Lactoperoxidase System

Antimicrobial effects of whey protein isolate (WPI) films and coatings incorporating the lactoperoxidase system (LPOS) against Listeria monocytogenes were studied by turbidity, plate counting, disc-covering, and disc-surface-spreading tests using various growth media. Survival of L. monocytogenes applied to smoked salmon before or after the coating was monitored immediately after application and during storage at 4 °C and 10 °C for up to 35 d. Tensile properties (elastic modulus [EM], tensile strength [TS], elongation [E]), oxygen permeability (OP), and color (Hunter L, a, b) of WPI films, with and without LPOS, were also compared. LPOS inhibited L. monocytogenes in broth and on agar media. WPI films incorporating 29 mg of LPOS per gram of film (dry basis) inhibited 4.2 log colony-forming units (CFU)/cm2 of L. monocytogenes inoculated on agar media. WPI coatings prepared with LPOS at 0.7% (w/w) in a coating solution (40 mg LPOS/g coating [dry basis]) initially reduced >3 and 1 log CFU/g of L. monocytogenes and total aerobic microorganisms in smoked salmon, respectively. The WPI coatings incorporating LPOS prevented the growth of L. monocytogenes in smoked salmon at 4 °C and 10 °C for 35 d and 14 d, respectively. The tensile properties, oxygen permeability, and color of WPI films were not significantly changed by incorporation of LPOS (P>0.05).