Culture supernatant fluids (2 ml) were mixed with 1 ml of
0Æ5 mol l)1 citrate-phosphate buffer (pH 5Æ0, 6Æ5 and 8Æ0)
and 1 ml of sterile milk. After incubation overnight at
25 C, the liberation of free fatty acids, expressed as
equivalent oleic acid, was determined by the above acid–
base titration method (Mahieu 1983).