Isolates of Lactobacillus delbrueckii subsp. lactis obtained from raw milk samples were compared for the ability to produce hydrogen peroxide (H2O2)at 5°C. Nineteen out of 101 lactobacilli isolated were identified as L. delbrueckii subsp. lactis. The isolates of L. delbrueckii subsp. lactis from most raw milk samples produced more H2O2 than did isolates of other species of lactobacilli from the same samples. Seven isolates of L. delbrueckii subsp. lactis, which produced the highest levels of H2O2 at 5°C were selected for comparison with a laboratory strain, L. delbrueckii subsp. lactis I. In 24 h, isolate RM2-5 produced 7.0 μg/109 cfu in buffer containing 5 mM sodium lactate and 4.4 μg/109 cfu in buffer containing 5 mM glucose. Three other isolates also produced more H2O2 on sodium lactate than on glucose. However, three remaining new isolates produced more H2O2 on glucose than on sodium lactate. All seven of the most active new isolates of L. delbrueckii subsp. lactis produced significantly higher concentrations of H2O2 than did L. delbrueckii subsp. lactis I in both solutions. Strain RM2-5 produced more H2O2 than did the other six most active newly isolated strains of L. delbrueckii subsp. lactis in this comparison.
