Influence of growth conditions on heat-stable phospholipase activity in Pseudomonas.

Many psychrotrophic bacteria contaminating raw milk produce phospholipase that withstands pasteurization and UHT treatments. This enzyme acts on the milk fat globule membrane and exposes triacylglycerides to the action of lipase. Phospholipase production by various isolates of Pseudomonas was investigated. The isolates were cultured aerobically at 8 degrees C in nutrient broth, McKellar's minimal salts medium, Chrisope's medium, and skim milk. Each strain produced phospholipase during the 50 h incubation. Enzyme production varied significantly (P < 0.001) with strain and growth medium. Strains varied significantly (P < 0.001) in their enzyme production in each medium and during the incubation time as well. Strain, incubation time, and the growth medium significantly influenced (P < 0.001) heat stability of the enzyme activity. Pasteurization reduced the activity, but did not eliminate it in skim milk.