Inactivation of Anisakis larvae in salt-fermented squid and pollock tripe by freezing, salting, and combined treatment with chlorine and ultrasound

The effects of freezing (−20 °C and −40 °C for 6 h, 12 h, and 1-21 days), salting (5, 10, 15, and 20% NaCl for 3 h, 6 h, 12 h, and 1-7 days), and a combined treatment with chlorine (500, 1000, 1500, and 2000 ppm) and ultrasound (37 kHz frequency and 1200 W for 5, 10, 15, 20, and 30 min) were investigated to observe the inactivation of Anisakis larvae in salt-fermented squid and pollock tripe or in the test tube. All larvae inoculated in squid and pollock tripe were inactivated after 48 h at −20 °C and 24 h at −40 °C. The average recovery rates of the larvae inoculated in squid and pollock tripe were 94.4% and 95.2%, respectively. The viabilities of larvae were 81.7% in 5% NaCl and 26.7% in 10% NaCl after 7 days of storage. However, all larvae were inactivated when submerged in 15% NaCl after 7 days of storage and 20% NaCl after 6 days of storage. Viability was reduced from 43.3% to 13.3% when ultrasound alone was used to treat live larvae in test tubes for 15-20 min. Furthermore, although no reduction effect on viability of larvae was observed when chlorine alone was used for treatment, 0% viability was observed using the combined treatment of 1500 ppm chlorine and ultrasound for 30 min. Interestingly, when the viscera of heavily parasitized conger eels were treated with chlorine and ultrasound, there was no reduction effect on viability of the larvae on the viscera. These results could be used to provide more specific guidelines for manufacturers and consumers about the freezing and salting conditions necessary to kill Anisakis larvae in salt-fermented squid and pollock tripe.