Inactivation of Escherichia coli and Listeria innocua in Milk by Combined Treatment with High Hydrostatic Pressure and the Lactoperoxidase System

Abstract

We have studied inactivation of four strains each of Escherichia coli and Listeria innocua in milk by the combined use of high hydrostatic pressure and the lactoperoxidase-thiocyanate-hydrogen peroxide system as a potential mild food preservation method. The lactoperoxidase system alone exerted a bacteriostatic effect on both species for at least 24 h at room temperature, but none of the strains was inactivated. Upon high-pressure treatment in the presence of the lactoperoxidase system, different results were obtained for E. coli and L. innocua. For none of the E. coli strains did the lactoperoxidase system increase the inactivation compared to a treatment with high pressure alone. However, a strong synergistic interaction of both treatments was observed for L. innocua. Inactivation exceeding 7 decades was achieved for all strains with a mild treatment (400 MPa, 15 min, 20°C), which in the absence of the lactoperoxidase system caused only 2 to 5 decades of inactivation depending on the strain. Milk as a substrate was found to have a considerable effect protecting E. coli and L. innocua against pressure inactivation and reducing the effectiveness of the lactoperoxidase system under pressure on L. innocua. Time course experiments showed that L. innocua counts continued to decrease in the first hours after pressure treatment in the presence of the lactoperoxidase system. E. coli counts remained constant for at least 24 h, except after treatment at the highest pressure level (600 MPa, 15 min, 20°C), in which case, in the presence of the lactoperoxidase system, a transient decrease was observed, indicating sublethal injury rather than true inactivation.

Factors moderating Listeria monocytogenes growth in raw milk and in soft cheese made from raw milk

“…Results obtained by Garcia-Graells et al [16] also showed that adding LPS inhibited the growth of L. innocua in milk: no growth was observed for 24 h at 20 °C.…”

Role of Porins in Sensitivity of Escherichia coli to Antibacterial Activity of the Lactoperoxidase Enzyme System

“…Furthermore, besides studies of the potential of "natural" preservative systems such as the LP system to increase the safety and extend the shelf-life of perishable foods and other products, studies are also needed to address the potential emergence of LP tolerance. Finally, our research group has previously reported that a sublethal treatment with high hydrostatic pressure strongly sensitizes bacteria to the LP system, opening perspectives for the application of this combined treatment for mild food preservation (9,10). The implications of the LP tolerance reported in the present work on the efficiency of this combined treatment should be further investigated.…”

The antimicrobial effect of wine on Listeria innocua in a model stomach system

“…The eVect of the addition of diVerent amounts of red wine on the survival of L. innocua in the stomach model L. innocua was chosen as a nonpathogenic model organism for L. monocytogenes. The suitability of L. innocua as a substitute for L. monocytogenes is based on the fact that it has been shown that both species behave in a similar manner when submitted to several diVerent types of environmental stresses (García-Graells, Valckx, & Michiels, 2000;Piyasena et al, 1998). In order to determine the inXuence of a red wine (total acidity of 5.9 g/L, volatile acidity of 0.64 g/ L and pH 3.59) on the survival of L. innocua NCTC 11288 during a simulated meal in a stomach model, assays were made with the addition of 30 mL, 60 mL and 130 mL of wine which, proportionally to the amount of food in the stomach model, correspond, approximately, to half a glass, a glass and half a bottle, respectively.…”