Quality of farmed Atlantic halibut (Hippoglossus hippoglossus); a comparative study of sub-chilling in refrigerated saltwater vs traditional ice chilling

Atlantic halibut ( Hippoglossus hippoglossus ) were slaughtered and sub-chilled in refrigerated seawater (˗1.5 °C) for 24 h prior to packaging in expanded polystyrene (EPS) boxes with or without ice. These were compared to halibut traditionally packaged directly in EPS boxes with ice, without prior sub-chilling. All boxes were stored at 4 °C for 24 h and thereafter at 0 °C. The microbial growth in halibut flesh was analysed by traditional plate count methods and skin samples were analysed for total bacteria and selected spoilage bacteria by quantitative Polymerase Chain Reaction. Quality Index Method (QIM) was performed on whole halibut as a proxy for sensorial quality. After 21 days of storage, total bacteria count in traditionally iced halibut was log 7.07 colony forming units (cfu) per gram, significantly higher than both sub-chilled groups; 5.60 (without ice) and 5.56 cfu/g (with ice). Hence, microbial shelf-life for both sub-chilled groups were estimated to 23 days, compared to 17 days for traditionally stored halibut, based on linear regression for reaching log 6 bacteria per gram. QIM-analysis after 22 days of storage revealed that sub-chilled halibut had significantly lower QIM-score than traditionally iced halibut. . This included smell, physical appearance (eyes and skin), and mucus. • Sub-chilled fish had lower total QIM-scores • Sub-chilled fish were perceived (QIM-score) better on skin, mucus and gill smell • Sub-chilling resulted in mucus-free fish throughout the storage period • Growth of bacteria was delayed by 5-6 days in sub-chilled fish • Shelf-life was increased from 17 (iced) to 23 days (sub-chilled)