Acylglycerol Acylhydrolase (Lipase) Activities of Streptococcus lactis, Streptococcus cremoris, and Their Mutants

¹ University of Wisconsin and William S. Middleton Memorial Veterans Hospital, Madison, WI 53706

Cell-free extracts of Streptococcus lactis (C2) and Streptococcus cremoris (KH) and their mutants S. lactis (25Sp), and S. cremoris (KHA2) were evaluated for acylglycerol acylhydrolase (lipase) activity using different triacylglycerols and milk fat emulsions. All cell extracts exhibited lipase activity and hydrolyzed tri-acylglycerol substrates better than milk fat. Highest specific lipase activities were exhibited by S. cremoris (KHA2) with tributyrylglycerol and milk fat emulsions as substrates. Generally, highest specific lipase activity of all extracts occurred at 37°C and pH 7.0 to 8.5 for tributyrylglycerol and pH 7.0 for milk fat emulsions. Glutathione (.01% ppm) (wt/vol) in the growth medium increased lipase activity by 20 to 30%. Activity was greater in extracts from log-phase rather than stationary-phase cells. Lipolysis of tributyrylglycerol emulsion was increased by 3 to 7% over control values in the presence of .38 M (2%) NaCl and was retarded by 24 to 30% of control values in the presence of 3.42 M (20%) NaCl. Larger amounts of short-chain fatty acids (C_4:0 to C_8:0) were liberated by the mutant rather than parent strains. Both mutant strains liberated greater amounts of caprylic acid (C_8:0), 1.72 (KHA2) and 1.50 (25Sp) mg/100 g of milk fat, as compared with 1.06 (KH) and 1.04 (C2) mg/100 g of milk fat liberated by the parent strains. Somewhat greater amounts of palmitic acid (C16:0) and oleic acid (C_18:1) were liberated from milk fat by cell-free extracts of mutant rather than parent strains.

Key Words: Acylglycerol acylhydrolase • lactic acid bacteria • lipase

Submitted on May 5, 1989
Accepted on August 7, 1989