Effect of ozonation and γ-irradiation on post-harvest decontamination of mussels (Mytillus galloprovincialis) containing diarrhetic shellfish toxins

Abstract

Contamination of shellfish with diarrhetic shellfish poisoning (DSP) toxins readily occurs during algal blooms. Such phenomena raise important public health concerns and thus comprise a constant challenge to shellfish farmers, the seafood industry and health services, considering the increasing occurrence of toxic episodes around the world. To avoid the detrimental effects of such episodes, research has focused on the use of various detoxification methodologies that should be rapid, efficient, easy to apply, and will not alter the quality and sensory properties of shellfish. In the present study, both ozonation (15 mg kg⁻¹ for 6 h) and γ-irradiation (6 kGy) were utilised in order to reduce the toxin content of contaminated shucked mussels, collected during the DSP episodes of 2007 and 2009 in Greece. DSP toxicity was monitored using the mouse bioassay (MBA) whilst the determination of toxin content of the okadaic acid (OA) group (both free and esterified forms) was carried out by LC/MS/MS analysis. Toxin reduction using γ-irradiation was in the range of 12–36%, 8–53% and 10–41% for free OA, OA esters and total OA, respectively. The appearance and texture of irradiated mussels deteriorated, pointing to a low potential for commercial use of this method. Ozonation of mussels resulted in toxin reduction in the range of 6–100%, 25–83% and 21–66% for free OA, OA esters and total OA, respectively. Reduction of OA content was substantially higher in homogenised mussel tissue compared with that of whole shucked mussels. In addition, differences detected with regard to quality parameters (TBA, sensory attributes) between ozonated and control mussels were not considerable. Even though varying percentage reductions in OA and its derivatives were achieved using ozonation under specific experimental conditions tested, it is postulated that upon optimisation ozonation may have the potential for post-harvest commercial DSP detoxification of shucked mussels.

Keywords:

• DSP toxins
• decontamination
• mussels
• ozonation
• irradiation
• okadaic acid
• LC/MS-MS

Acknowledgements

The authors would like to thank the Mass Spectrometry Unit of the University of Ioannina for providing access to LC-MS/MS facilities. Thanks are also expressed to all relevant prefectural veterinary services for their contribution to the samplings. The collaboration of all staff members of the National Reference Laboratory of Marine Biotoxins is also greatly appreciated.