Reduction in Toxicity of PSP Infested Oysters during Canning Process

Abstract

Attempts were made to reduce toxicity of the oysters infested with PSP by retorting process. The homogenates of toxic oysters were directly, or after adjusting pH, packed into retorting pouches, and heated in an autoclave or in a boiling water bath. Mouse bioassay and high performance liquid chromatographic analysis of the homogenates before and after heating demonstrated that autoclaving could reduce toxicity more rapidly than boiling, and that the reduction occurred more effectively when pH was adjusted to 7.5 with NaOH. However, in case of pH 3.0, toxicity score was slightly decreased, or increased. This phenomenon would be mainly due to conversion of C 1,2 with low toxicity into GTX2,3 with high toxicity. When autoclaved adjusting the pH to 7.2 with 3 types of chemicals instead of NaOH, the homogenates of toxic oysters were also detoxified very effectively. Sodium bicarbonate (NaHCO 3) was the most effective among them, requiring the shortest heating time of 5 min to reduce toxicity to less than 4 MU/g. In case of the other chemicals (sodium and ammonium phosphate buffers), however, a small amount of decarbamoyl toxins remained even after 15 min of heating. The authentic specimens of C1,2 and GTX2,3 were added to non-toxic oyster homogenates, and autoclaved similarly. The results showed that all of these components were decomposed more effectively when pH-adjusting chemicals, especially NaHCO3 was used. Without the chemicals, or with ammonium phosphate buffer, C1,2 seemed to be converted not via GTX2,3 but directly into dcGTX2,3.