Lipid class and fatty acid composition of Pseudo-nitzschia multiseries and Pseudo-nitzschia pungens and effects of lipolytic enzyme deactivation

Lipid class and fatty acid compositions of stationary phase cultures of the toxic diatoms Pseudo-nitzschia multiseries and P. pungens were determined. The lipid class compositions of both diatoms were similar, with phospholipids, triacylglycerols and acetone-mobile polar lipids as the major classes. Both pennate diatoms also displayed similar fatty acid compositions that were typical of diatoms. with high levels of 14:0, 16:1n-7, 16:2n-4 and 20:5n-3. In addition, elevated levels (> 7%) of the fatty acid 16:4n-1 were found in both species and this fatty acid has potential as a signature compound in differentiating Pseudo-nitzschia species from other diatoms. The taxonomic similarities of the diatoms were apparent in the very similar lipid class and fatty acid compositions. Treatment of cells with boiling water was effective in deactivating lipolytic enzymes and resulted in a significant decrease (P < 0.05) in free fatty acids, a breakdown indicator and a general increase in polyunsaturated fatty acids in all samples. Thus, the routine use of boiling water to deactivate lipolytic enzymes in diatom samples is recommended. (C) 1999 Elsevier Science Ltd. All rights reserved.