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

Cell-free extracts of Streptococcus lac tis (C2) and Streptococcus cremoris (KH) and their mutants S. lactis (25Sp), and S. cremoris (KHA2) were evaluated for acylglycerol acylhydrolase (lipase) activ ity using different triacylglycerols and milk fat emulsions. All cell extracts ex hibited 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 37C and pH 7.0 to 8.5 for tributyrylgly cerol and pH 7.0 for milk fat emulsions. Glutathione (.01 % ppm) (wtlvol) in the growth medium increased lipase activity by 20 to 30%. Activity was greater in extracts from log-phase rather than sta tionary-phase cells. Lipolysis of tributyr ylglycerol 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 (C4:0 to C8:0) were liberated by the mutant rather than parent strains. Both mutant strains liber ated greater amounts of caprylic acid (C8: 0), 1.72 (KHA2) and 1.50 (25Sp) mg/loo g of milk fat. as compared with 1.06