Survival of Anisakis simplex in Microwave-Processed Arrowtooth Flounder (Atheresthes stomias)

Abstract

The purpose of this study was to define the relationship between survival and temperature of nematodes of the species Anisakis simplex in microwave-processed arrowtooth flounder (Atheresthes stomias). Ten fillets (each 126 to 467 g, 0.5 to 1.75 cm thick), with an average of five larvae of Anisakis simplex per fillet, were processed to target temperatures on high (100%) power using a commercial 700-W microwave oven. Fillets were neither covered nor rotated and had a temperature probe inserted to two-thirds depth into the thickest portion. After the fillet was digested using a 1% pepsin solution, the viability of nematodes was determined by viewing them under a dissecting microscope. Survival rates were 31% at 140°F (60°C), 11% at 150°F (65°C), 2% at 160°F (71°C), 3% at 165°F (74°C), and 0% at 170°F (77°C). Microwave processing of standardized fillet “sandwiches,” 14 cm long, 4.5 cm wide, and approximately 1.75 cm high, each of which was preinoculated with 10 live nematodes, resulted in no survival at either 160°F or 170°F. Using ultraviolet light to detect both viable and nonviable nematodes in fillet sandwiches as an alternative method to pepsin digestion resulted in survival rates of 1% at 140°F (60°C), 3% at 145°F (63°C), and 0% at 150°F (65°C). Smaller fillet sandwiches, which most likely had fewer cold spots during microwave processing, required 150°F (65°C), whereas larger whole fillets required 170°F (77°C) to kill larvae of Anisakis simplex. The parasites were most likely inactivated by a thermal mechanism of microwave treatment. Damage to the nematodes was often evident from ruptured cuticles that were no longer resistant to digestive enzymes. The high hydrostatic pressure and low chloride content of the pseudocoelomic fluid probably contributed greatly to the damage incurred by the larvae.