Growth
of psychrotrophic Bacillus spp., such as Bacillus cereus, has been implicated in the
spoilage of pasteurized refrigerated milk, especially when the levels of postpasteurization
contaminants are low. Spores of psychrotrophic Bacillus spp., surviving
pasteurization, germinate and multiply to cause a defect known as bitty. They
produce the enzyme lecithinase, which hydrolyzes phospholipids of the fat globule
membrane, causing aggregation of fat globules that adhere to the container surfaces.
Production of rennin-like enzymes by psychrotrophic Bacillus spp. and others can
cause sweet curdling of milk at a pH higher than that required for acid curdling.8