Importance and efficiency of in-depth antimicrobial activity for the control of listeria development with nisin-incorporated sodium caseinate films

The effect of antimicrobial sodium caseinate-based films was investigated on inhibition of Listeria innocua in cheese. Nisin was incorporated into sorbitol-plasticized sodium caseinate films at 1000 IU/cm² and the films were prepared by casting methods. Mini red Babybel® cheese was chosen as a semi-soft cheese model. The antimicrobial activity was studied based on the contact between antimicrobial films and surface-contaminated as well as in-depth contaminated cheese samples during a 7-day storage at 4 °C. The active films produced resulted in a reduction of 1.1 log CFU/g reduction in L. innocua counts in surface-inoculated cheese samples after 1 week of storage as compared to control samples. Regarding in-depth inoculated cheese samples, antimicrobial effectiveness was found to be dependent on the distance from the contact surface with the films containing nisin to the cheese matrix. The inactivation rates obtained were 1.1, 0.9 and 0.25 log CFU/g with slice 1 (distance from contact surface d = 1 mm), slice 2 (d = 2 mm) and slice 3 (d = 3 mm), respectively. Our study demonstrates the potential application of antimicrobial films as a promising method to overcome problems associated with post-process contamination, thus enhancing the safety and extending the shelf life of food products.