Rapid and Conventional Freezing Conditions of Fish for the Prevention of Human Anisakiasis

In recent years, rapid freezers have been used to freeze and preserve seafood, with advances in freezing technology. However, limited studies have examined the effect of rapid freezing on the viability of <i>Anisakis</i> larvae in fish muscle. In this study, freezing experiments were conducted on <i>Anisakis</i> larvae alone (bare group) and on larvae embedded in mackerel fish (embedded group) using an air-blast freezer (rapid freezing) as the most popular rapid-freezing method, passing through the zone of maximum ice crystal formation within 30 min, and a natural convection freezer (conventional freezing) set at -20 °C. In the bare group experiments, all larvae died after 8 min of rapid freezing and after more than 2 h of conventional freezing. In the rapid-freezing experiments on the embedded group, only a few larvae were alive when the core temperature of the fish reached -20 °C, whereas all larvae died when the core temperature reached -35 °C. With conventional freezing, only a few larvae were alive for 24 h after freezing at -20 °C. In contrast, all larvae died after freezing at -20 °C for 24 h after the fish core temperature reached -20 °C under both rapid and conventional freezing conditions. In the embedded group, the standard deviation of the time taken for the fish core temperature to reach -20 °C was <15 min for rapid freezing and 171 min for conventional freezing. The results showed that the time taken for the core temperature to reach -20 °C varies by several hours in conventional freezing, depending on the fish size. Thus, the most crucial freezing conditions to avoid anisakiasis are either rapidly freezing the fish to a core temperature of -35 °C or keeping the fish core temperature at -20 °C for at least 24 h.