The effects of environmental conditions on the lipolytic activity of strains of Penicillium roqueforti

The lipolytic activity of 30 strains of Penicillium roqueforti was investigated by agar diffusion tests on tributyrin (esterase activity) and olive oil agar (lipase activity), by titration of the free fatty acids (FFA) produced and by gas chromatographic analysis of the individual FFA released after growth at 25 or 10°C in butterfat emulsions containing 0, 2 or 7% NaCl. All strains investigated by the agar diffusion tests possessed esterase activity and 23 strains were also able to hydrolyse olive oil, but differences in esterase activity were seen. The agar diffusion tests and the titration of FFA showed that the amount of FFA released by a strain of P. roqueforti is determined by both esterase and lipase activity. A large release of FFA was only seen for strains with the ability to hydrolyse both short- and long-chained fatty acids, while strains with esterase activity produced smaller amounts of FFA. Between 7 and 14 days of incubation a steep increase in the release of FFA was observed both by the titration and by GC analysis, and then a decline from 14 to 21 days, probably caused by conversion of FFA to methyl ketones. Identical FFA profiles were found for two strains with different lipolytic activity. Long-chained fatty acids dominated the profile, while the short-chained fatty acids only were detected in small amounts and mainly in the end of incubation. Both strains were stimulated by NaCl in the emulsions.