Influence of hypochlorite concentration, pH and temperature on inactivation of Listeria monocytogenes

The effect of hypochlorite on Listeria monocytogenes at varying concentrations, pH, temperature, and type of solution (with or without peptone in phosphate buffer) was studied. L. monocytogenes was reduced by about 3.55, 4.17, 4.56 and 5.59 log units, respectively, after 30 sec of exposure to 5, 10, 50 and 100 mg L-1 hypochlorite in phosphate buffer (pH 6.5) at 30degreesC. There was an increase in the rate of disinfection (p<0.05) with an increase in temperature from 20degrees to 40degreesC. Hypochlorite had a greater antimicrobial effect on L. monocytogenes at pH 4.5 than at 5.5, 6.5 and 8.5. Addition of 0.1% peptone provided a marked neutralization of the chlorine in the phosphate buffer. Survival curves showed two distinct phases in the destruction of L. monocytogenes. At all hypochlorite concentrations, the first phase (about 30 see) was characterized by a higher rate of inactivation, shown by a steeper inactivation slope, which was followed a more gradual slope.