Thermal degradation of paralytic shellfish poisoning toxins in scallop digestive glands

Abstract

Digestive glands containing paralytic shellfish poisoning (PSP) toxins were isolated from toxic scallops. Citrate/phosphate buffers with the pH values ranging from 3 to 7 were added to achieve predetermined pH levels. The samples were heated at 90, 100, 110, 120 and 130°C using a computer controlled oil bath, and three tubes at each pH level were transferred into an ice bath immediately after predetermined heating times for up to 120 min. Both heated and unheated homogenates were analyzed for toxins qualitatively and quantitatively by high performance liquid chromatography (HPLC). Gonyautoxin (GTX) 2 and 3, saxitoxin (STX), neosaxitoxin (NEO) and C toxins were identified by HPLC. All toxins were most sensitive to higher temperatures and higher pH values. However, under gentle heating conditions and low pH, GTX 2 and 3 increased slightly. One explanation for this could be the increased extraction efficiency by heating. However, the conversion of sulfocarbamate toxins to highly toxic carbamate toxins upon heating in the presence of acid known as “Proctor” enhancement, could be another possible explanation for the apparent conversion of C1 and C2 toxins to GTX 2/3. The increase in STX may possibly be due to the conversion of GTX 2/3 and NEO into STX. The kinetics of thermal destruction were qualitatively similar to the thermal destruction of microorganisms. That is, the log survival of heated toxins was inversely proportional to time of heating and log decimal reduction time inversely related to temperature of heating. Efficacy of thermal destruction was highly dependent on pH, with more rapid thermal destruction at higher pH levels. The levels of individual toxins in the homogenate and those generated during heating could be reduced significantly by heating at 130°C at pH 6–7.