Accumulation and depuration of paralytic shellfish poisoning toxins in the oyster Ostrea rivularis Gould – Chitosan facilitates the toxin depuration

The accumulation and depuration of paralytic shellfish poisoning (PSP) toxins in the oyster of Ostrea rivularis Gould (ORG) were investigated in this study. Firstly, PSP toxin-accumulating in ORG were produced by feeding with the toxic algae Alexandrium minutum cultured in the laboratory. The feeding amounts were designed for three concentrations of 4.0 × 103, 8.0 × 103, and 1.2 × 104 cells/mL. After 20 dayʹs feeding, the toxicity in the ORG became high levels of 28.86, 31.17, and 38.98 MU/g, respectively. And the toxin-accumulating ORG fed only for 2 d with 8.0 × 103 cells/mL which toxicity was 11.93 MU/g were selected for depuration experiment. In the depuration process, the ORG were fed with nontoxic microalgae (MA) of Chlorella spp., chitosan (CTS), and MA + CTS. Feeding with 8.0 × 103 cells/mL MA and 0.05 g/L CTS resulted in the largest PSP toxin reduction in the ORG. After 7 d of depuration feeding, the toxicity of the PSP toxin decreased from 11.93 to 3.47, 1.40, and 0.50 MU/g, as determined by the mouse bioassay (MBA). High performance liquid chromatography – fluorescence detection systems (HPLC–FLD) was applied in the qualitative and quantitative detection of PSP toxins in the ORG during accumulation and depuration. Chromatograms of samples not containing oxidation and acidulating reagents in the mobile phase were used to identify unknown peaks. The HPLC results showed that PSP toxicity before depuration was 9.07 MU/g. After 7 d of depuration, feeding by CTS and MA + CTS was reduced to 1.41 and 0.12 MU/g, respectively. The laboratory experiments showed that CTS had a remarkable effect on PSP removal in ORG. The toxicity and toxin profiles of ORG were investigated by MBA combined with post-column HPLC–FLD. The results of both methods supplemented each other, thereby elucidating the accumulation, depuration, and transformation of PSP toxins from the toxic algae in ORG.