Viability of Listeria monocytogenes in Milk Treated with Hydrogen Peroxide

The susceptibility of Listeria monocytogenes to hydrogen peroxide in sterilized and raw milk was studied. In raw milk, L. monocytogenes was less susceptible to H₂O₂ than milk microflora. The ratio of L. monocytogenes to total milk micro-organisms (natural microflora plus added L. monocytogenes ) increased when raw milk was stored at refrigeration temperature (4°C), due to a selective enrichment of Listeria present in milk. In sterilized milk, a concentration of 0.0495% H₂O₂ and 9 h were required to produce complete destruction of L. monocytogenes when this microorganism was in pure culture, although a reduction in listeria counts was observed at 1.5 h. When sterilized milk was simultaneously contaminated with L. monocytogenes , Staphylococcus aureus and Streptococcus faecalis , a decrease in L. monocytogenes count during the first 24 h was observed at 0.0495% H₂O₂. From this time L. monocytogenes recovered and multiplied reaching levels similar to the initial counts at the end of the experiment.