Thermoplastic starch/polybutylene adipate terephthalate film coated with gelatin containing nisin Z and lauric arginate for control of foodborne pathogens associated with chilled and frozen seafood.

In order to control foodborne pathogens on seafood products, an antimicrobial, thermoplastic starch/polybutylene adipate terephthalate (TPS/PBAT; 40/60) film was produced by coating gelatin (15% v/v) containing lauric arginate (LAE; 0.8 mg/cm2), alone or combination with nisin Z (69.4 AU/cm2) to produce LAE-Gelatin-TPS/PBAT and Nisin-LAE-Gelatin-TPS/PBAT films, respectively. Both films were investigated for control of Vibrio parahaemolyticus ATCC 17802 and Salmonella Typhimurium ATCC 14028 on bigeye snapper (Lutjanus lineolatus) and tiger prawn (Penaeus monodon) slices during long-term (28 days), refrigerated (4 °C; chilled) and frozen (-20 °C) storage up to 90 days. S. Typhimurium ATCC 14028, experimentally inoculated onto bigeye snapper and tiger prawn slices, treated with the LAE-Gelatin-TPS/PBAT film, and stored at 4 °C was reduced 3.2 log10 CFU/g after 28 days and 7 log10 CFU/g after 21 days, respectively. Nisin-LAE-Gelatin-TPS/PBAT film reduced S. Typhimurium ATCC 14028 on bigeye snapper and tiger prawn slices 3.5 log10 CFU/g after 28 days and 7 log10 CFU/g after 14 days at 4 °C, respectively. The LAE-Gelatin-TPS/PBAT and Nisin-LAE-Gelatin-TPS/PBAT films and storage for 28 days at 4 °C reduced V. parahaemolyticus inoculated on chilled bigeye snapper slices approximately 2.6 and 4.2 log10 CFU/g, respectively. Both films reduced V. parahaemolyticus inoculated on chilled tiger prawn slices approximately 7.1 log10 CFU/g after 28 days at 4 °C. The LAE-Gelatin-TPS/PBAT and Nisin-LAE-Gelatin-TPS/PBAT films also reduced S. Typhimurium, inoculated on bigeye snapper and tiger prawn slices, 5.8 and 5.6 log10 CFU/g, respectively, after 60 days at -20 °C. V. parahaemolyticus was reduced by 5.8 log10 CFU/g on frozen bigeye snapper and tiger prawn slices after treatment with Nisin-LAE-Gelatin-TPS/PBAT film after 14 and 21 days, respectively. However, the LAE-Gelatin-TPS/PBAT film reduced V. parahaemolyticus 5.8 log10 CFU/g on both frozen seafood slices after 28 days. The results obtained from this study indicate the LAE-Gelatin-TPS/PBAT and Nisin-LAE-Gelatin-TPS/PBAT films displayed excellent inhibition against S. Typhimurium and V. parahaemolyticus on chilled and frozen seafood.

Incorporation of nisin Z and lauric arginate into pullulan films to inhibit foodborne pathogens associated with fresh and ready-to-eat muscle foods.

A combination of food grade compounds with edible films, used to inhibit foodborne pathogens associated with fresh or further processed muscle foods, is receiving considerable attention. In this study, pullulan films containing lauric arginate (LAE) and nisin Z (produced by Lactococcus lactis subsp. lactis I8-7-3 and isolated from catfish gut), alone or in combination, were investigated for controlling foodborne pathogens on fresh and further processed muscle foods after long-term refrigerated storage. Salmonella Typhimurium and Salmonella Enteritidis on raw turkey breast slices wrapped with a film containing LAE or the combination of LAE with nisin Z were reduced throughout the experiment, 2.5 to 4.5 log10 CFU/cm(2) and 3.5 to 5.1 log10 CFU/cm(2), respectively. Film containing a combination of LAE with nisin Z reduced Staphylococcus aureus and Listeria monocytogenes Scott A inoculated onto ham surfaces by approximately 5.53 and 5.62 log10 CFU/cm(2), respectively during refrigerated storage. Escherichia coli O157:H7, O111, and O26 also were reduced by >4 log 10CFU/cm(2) on raw beef slices after treatment with the combination film and refrigerated storage. The results obtained from this study indicate the LAE- and LAE-nisin Z-containing pullulan films displayed excellent inhibition against foodborne pathogens on fresh and further processed muscle foods.

Effect of lauric arginate, nisin Z, and a combination against several food-related bacteria.

The effects of lauric arginate (LAE) and nisin Z, alone or in combination, on cell damage were investigated against Escherichia coli O157:H7, Listeria monocytogenes and Brochothrix thermosphacta, by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, efflux of potassium and phosphate ions, and growth inhibition. A combination of LAE with nisin Z caused severe and dramatic changes in the cytoplasmic membrane and cell lysis of both Gram-positive and Gram-negative bacteria. The combination treatment also caused significant potassium and phosphate ion leakage of E. coli O157:H7, L. monocytogenes and B. thermosphacta, when compared with other treatments: 16.62±1.05, 50.35±0.81 and 45.47±1.15mg/L of potassium ion and 122.66±8.81, 97.96±3.31 and 26.47±13.97mg/L of phosphate ion after treatment for 6h, respectively. Bacteria were reduced by approximately 7log10CFU/mL within the first hour of treatment and then cells were unable to grow for the remainder of the experiment. Treatment with LAE alone resulted in changes in cellular morphology, coagulation of the cytoplasm, and low level leakage of potassium and phosphate ions in all bacteria tested. Treatment of L. monocytogenes and B. thermosphacta with nisin Z (320AU/mL of final concentration) resulted in the formation of membrane channels and leakage of potassium and phosphate ions at rather high levels; but the bacteriocin was not effective against E. coli O157:H7. LAE or nisin Z reduced growth of both L. monocytogenes and B. thermosphacta by approximately 7log10CFU/mL. Conversely, E. coli O157:H7 was not inhibited by treatments with nisin Z, but decreased by approximately 4.45log10CFU/mL after treatment with LAE. These findings provide additional information on the mode of action of these compounds on bacterial populations.