The supernatant was
subjected to acid precipitation by adding 6 N HCl to achieve
a final pH of 2.0 and allowing the precipitate to form at 4 曟.
The precipitate was pelleted at 10 000 rpm for 20 min, redissolved
in distilled water, adjusted to pH 7.0, freezedried,
and weighed. The dried surfactant was extracted with
acetone and dried with the aid of a rotary evaporator under
vacuum[18].