Effects of cooking and heat treatment on concentration and tissue distribution of okadaic acid and dinophysistoxin-2 in mussels (Mytilus edulis)

Abstract

Using high performance liquid chromatography with mass spectrometry the influence of conventional steaming and other heat treatments on the level of azaspiracids, okadaic acid and dinophysistoxin-2 in mussels (Mytilus edulis) was investigated. A prior study looking at the influence of steaming on the concentration and distribution of azaspiracids showed significant increases in concentration as a result. Described is a follow-up study using two separate mussel samples, where the contribution of water loss during steaming to increases of toxin levels was examined. In addition to water loss it was demonstrated that heating of fresh azaspiracid contaminated mussels resulted in significant increases in the quantity of the desmethyl analogue (azaspiracid-3) measured. A systematic heat treatment experiment confirmed these findings and showed that azaspiracid-3 was the most thermally instable of the three regulated azaspiracid analogues. In parallel, the same studies were carried out for okadaic acid and dinophysistoxin-2 also naturally present in the samples used. Concentration increases correlated with water loss during steaming. More so than for azaspiracids, increased distribution of okadaic acid and dinophysistoxin-2 from the digestive glands to the remainder tissues was observed as a result of the processes examined. This suggests that analysis of whole flesh tissues, as opposed to dissected digestive glands, is more appropriate for regulatory purposes, particularly if cooked samples are being analysed. The findings of the studies reported here have importance in terms of the methodology applied in regulatory phycotoxin monitoring programmes. Therefore, options for sample pre-treatment are discussed.