The lactoperoxidase (LP) system is a naturally occurring system which was first discovered in raw milk. Different groups of bacteria show a varying degree of resistance to the LP system. Gram-negative catalase-positive organisms, such as pseudomonads, coliforms, salmonellae, and shigellae, are inhibited by the LP system. Depending on the medium pH, temperature, incubation time, cell density, and the particular donor, these microorganisms may be killed. It has been shown that the LP system can increase storage times of raw milk by delaying growth of psychrotrophs; perhaps this method could be used to extend the shelf life of other foods.

The antibacterial activity of the lactoperoxidase system (LP system) on the growth and survival of Salmonella typhimurium in tryptic soy broth (TSB) was determined. The LP system, consisting of lactoperoxidase (1 μg/ml), potassium thiocynante (KSCN) (5.9 mM) and H2O2 (2.5 mM), was found to have both bacteriostatic and bactericidal activities against strains of S. typhimurium. The bactericidal activity was clearly dependent on the initial inoculum level. Levels of 102 - 105 CFU/ml were killed at 37°C as opposed to the bacteriostatic activity with inoculum levels of 106 - 107 CFU/ml, which exhibited a 25-h lag. The LP system also enhanced thermal inactivation of S. typhimurium. D50°C-values were > 60 min (untreated broth) and 12 min (LP system activated); corresponding D52°c-values were 20 min and 7.5 min; corresponding D55°c-values were 14 min and 4 min; corresponding D60°C -values were 5 min and 2.5 min and corresponding Devalues were .31 min and .20 min.

The antibacterial activity of the lactoperoxidase (LP) system on the growth and survival of a naladixic acid resistant strain of Salmonella typhimurium on poultry was determined. The LP system treatment, which consisted of lactoperoxidase (1 μg/ml), potassium thiocyanate (5.9 mM), and hydrogen peroxide (2.5 mM) (final concentrations) in water, reduced the level of Salmonella on inoculated chicken legs. The magnitude of reduction was dependent on temperature and time. For a water temperature of 25C and a time of 30 min, a 13.2% reduction was seen, as compared to a water temperature of 60C and a time of 15 min which showed a 80.6% reduction. In a 48 h shelf‐life study, the LP system controlled growth of psychrotrophic bacteria on chicken legs. Hunterlab color values (L, a, b) for chicken thigh skin and oxidative deterioration as measured by TBA values for chicken thigh meat did not significantly differ (p < 0.01 and p < 0.05, respectively) between control and treated thighs.