Lipase activity of resting cells of Aspergillus flavus after solvent washing;: memory effects from endogenous substrate arising from the original growth medium

Aspergillus flavus resting cells were washed with solvents of different polarity for 2, 6, and 24 h and then suspended in isooctane containing either oleic acid and 1-propanol or 1-propanol alone. Propyl oleate and propyl linoleate were produced in all experiments after 24 h due to the presence of residual fatty acids originating from the sunflower oil used for growing the mycelium. After 24 h washing, most solvents produced a 70 to 90% decrease in lipase activity and a 0 to 99% decrease in the amount of residual acids. 0.7 M 1-propanol in hexane was the best washing solvent among all those assayed (93% remaining activity, 0.3% residual oleic acid).