Effects of Rearing Conditions on Oxidation-Reduction Potential Change and ATP Degradation of Live and Dead Scallops (Pecten yessonensis)

The possibility of using oxidation-reduction potential (ORP) as freshness index for scallops (Pecten yessoensis) was investigated. Scallops were divided into three groups and subjected to different rearing conditions : rearing at higher-than-optimum temperatures (at 15-18°C) with aeration, rearing in seawater but without aeration, or removal from seawater and live storage in air at 10°C. The ORP and pH of the adductor muscle of live scallops during rearing were measured at regular time intervals for 24h. Then the adductor muscle in each sample was removed from the valves and stored at 0°C. Changes in ORP, K value, ATP degradation, and D-lactic acid content during storage were monitored. The results showed that live scallops had a reductive characteristic in terms of ORP, which varied between 0.16-0.19V and a pH range from 6.2-7.0. However, ORP generally increased towards a more oxidative state under all the rearing conditions tested. ORP also increased with K value and approached its maximum when K value exceeded 25%. Regardless of rearing conditions, the ORP range that indicates the reasonable freshness of scallops for sashimi was 0.166-0.215V. The postmortem ATP content was highest in the scallops reared in seawater while the fastest ATP degradation observed in the live scallops stored in air. D-lactic acid accumulation during storage was lowest in the samples reared in seawater with aeration. The absence of oxygen supply during rearing promotes enhanced ATP degradation and D-lactic accumulation.