Hurdle technologies using natural plant extracts and nisin to control Listeria monocytogenes in model, soy protein edible film and ready-to-eat turkey frankfurter systems

Foodborne pathogens are of great concern to consumers and are responsible for significant annual losses to the food industry. Listeria monocytogenes, E.coli O157:H7, and Salmonella Typhimurium are major foodborne pathogens that are responsible for a significant number of outbreaks from raw and ready-to-eat (RTE) poultry and beef products. Combinations of natural extracts may possess synergistic or additive antimicrobial properties therefore co-treatment with such compounds serves as a potential intervention strategy for controlling foodborne pathogens. Therefore, the objectives of this study were to evaluate the inhibitory effect of selected plant extracts against major foodborne pathogens in laboratory medium and to determine the antimicrobial activity of nisin when combined with the most effective extract(s), applied against the most sensitive pathogen(s), and tested in model systems including soy protein edible films and turkey frankfurters. Among these extracts, grape seed (GSE) and green tea extract (GTE) demonstrated the greatest inhibitory activities against L. monocytogenes moreover, in each of the three model systems, the inhibitory activity of GSE 1% and GTE 1% was enhanced by the addition of nisin (10,000 IU). The antimicrobial activity of these combined natural extracts was confirmed by the extensive cell damage and morphological changes in L. monocytogenes as visualized by Transmission electron microscopy (TEM) at 80 kV, (x 50,000). The physical and antimicrobial properties were determined for soy protein edible films containing GSE 1%, GTE 1%, or nisin (10,000 IU) combined with either GSE 1% or GTE 1%. The soy protein edible films containing nisin (10,000 IU) with either GSE 1% or GTE 1% significantly inhibited L. monocytogenes growth with a, respective, 2.9 and 3.6 log CFU/ml reduction in population compared to control film without these antimicrobials. Furthermore, combinations of nisin (10,000 IU) with GSE 1% or GTE 1% alone reduced the growth of L. monocytogenes by more than 2 log cycles CFU/g on high fat turkey frankfurters stored at 4 and 10°C after 28 d. These natural antimicrobial combinations have applications in controlling L. monocytogenes contaminations in a number of food products including RTE poultry and beef products.