Greater than 90% of heat-stressed cells of Salmonella senftenberg failed to grow on trypticase soy agar. Adding to this medium compounds which are capable of degrading hydrogen peroxide allowed growth of the heat-injured cells. These compounds did not stimulate growth of heated cells of Streptococcus faecium, an organism which does not possess catalase.

No abstract

Nisin at 75 ppm (75 ,ug/g) was superior to 150 ppm of nitrite in inhibiting outgrowth of Clostridium sporogenes PA3679 spores in meat slurries, which had been heated to simulate the process used for cooked ham. The inhibitory activity of nisin decreased as the spore load or pH of the slurries increased. Unlike nitrite, inhibition by nisin was unaffected by high levels of iron either as a constituent of meats or when added as an iron salt. In slurries treated with 75 ppm of nisin, refrigerated storage for 56 days resulted in depletion of nisin to a level low enough to allow outgrowth within 3 to 10 days if the slurries were subsequently abused at 35°C. In contrast, a combination of 40 ppm of nitrite and either 75 or 100 ppm of nisin almost completely inhibited outgrowth in these slurries. The nisin-nitrite combination appeared to have a synergistic effect, and the low concentration of nitrite was sufficient to preserve the color in meats similar to that of products cured with 150 ppm of nitrite.

The formation in culture of dimethyl- and diethyl-nitrosamine from sodium nitrite and secondary amines was brought about by Streptococcus species, but not by members of several other genera tested. This formation appears to be non-enzymic, pH dependent, and may be catalyzed by one or more bacterial metabolic products.

No abstract