Proteolytic and Lipolytic Activities of Psychrotrophic Bacteria Originated from Raw Milk

Abstract

The proteolytic (in skim milk agar) and lipolytic (in Tributyrin agar and Clossry's agar) activities of the bacteria isolated at 5°C for 10 days and 20°C for 4 days incubations from raw milk were tested at 5°C for 10 days, 20°C for 4 days, and 35°C for 2 days incubations respectively.Of the 792 strains isolated at 5°C incubation, 23.1% showed the proteolytic activity, and 40.9% showed the lipolytic activity in the Tributyrin agar, and 48.0% in Clossry's agar. Of the 588 strains isolated at 20°C incubation, 37.9, 17.9, and 23.6% showed the proteolytic or lipolytic activity respectively.In the 792 strains isolated at 5°C incubation, the number of strains showed both proteolysis and lipolysis at 20°C incubation was the most, and the one at 5°C incubation was next. On the other hand, in the 588 strains isolated at 20°C incubation, the greatest number of strains showed both proteolysis and lipolysis was at 20°C incubation, and the next was at 35°C incubation.The percentage of strains showed proteolytic activity was high in Bacillus, coliform bacteria, Pseudomonas isolated at 5°C incubation, and was high in Pseudomonas, Alcaligenes-Achromobacter, Flavobacterium, Streptococcus, coliform bacteria isolated at 20°C incubation. Most of gram-negative bacilli showed proteolytic activity at 5 and 20°C incubation, and, most of gram-positive bacilli and cocci showed at 20°C and 35°C.The percentage of strains showed lipolytic activities to both tributyrin and butter-fat was more than 70% in Bacillus, Acinetobacter, Alcaligenes-Achromobacter, unclassified gram-negative bacilli and coliform bacteria isolated at 5°C incubation, also Pseudomonas showed lipolysis to butter-fat in more than 70% of strains. In the strains isolated at 20°C incubation, Acinetobacter, Pseudomonas, Staphylococcus, Aeromonas, and coliform bacteria had respectively high percentage of strains showed lipolysis in both tributyrin and butter-fat.Coliform bacteria and Pseudomonas were main proteolytic and lipolytic activators, and most strains of them showed strongly their activities at 20°C incubation.