Isolates of Pseudomonas spp. from cold-stored raw milk show variation in proteolytic and lipolytic properties

Abstract

The diversity of seven strains of Pseudomonas spp., isolated from raw milk, was studied for growth and proteolytic and lipolytic activity in milk at 4, 8 and 22 °C. Proteolysis was demonstrated by capillary electrophoresis (CE) and the liberation of free amino acids and free fatty acids were analysed by HPLC and GC, respectively. Activity varied considerably, according to strain, temperature and incubation time. After 9 days, proteolysis was demonstrated at 4 °C for several strains, but an increase in free amino acids was only notable at 22 °C. Lipolysis was most prominent at 22 °C although some activity was seen at 4 and 8 °C. All strains showing proteolytic activity were also lipolytic whereas two strains were only lipolytic. The results indicate that the strain of Pseudomonas and its properties determine the nature and seriousness of some of the deleterious changes that may occur in milk and milk products.