The effect of lipolytic enzymes of Bacillus spp. on quality of ultra-high-temperature-treated milk

Abstract

Lipolysis was monitored based on determining the concentration of free fatty acids in milk, on the model case of UHT milk contamination with spores of 15 B. licheniformis, B. subtilis and B. cereus strains isolated from farm environment and raw milk. Lipolysis was not recorded at storage temperature of 4°C, whereas significant changes in levels of free fatty acids were shown at storage temperature of 24°C. After 3 weeks of storage the initial content of 41.97 mmol·kg-1 of fat rose to as much as 1,617.22 mmol·kg-1 of fat. The extent of the change depended mainly on the Bacillus spp. species and the storage period and, to a certain degree, also on the initial number of microorganisms. Significant lipolytic activity was detected in association with B. licheniformis and B. cereus species. It was found that spores of resistant B. licheniformis strains may survive 100°C/10 min and 135°C/5 s heating and show lipolytic activity.