Slurry ice freezing enhances quality retention in frozen flounder (Paralichthys olivaceus) during storage

• Slurry ice freezing (SIF) produced small, uniform ice crystals in flounder fillets • SIF minimized tissue damage and drip loss compared to air blast freezing (AF) • SIF better preserved texture and protein integrity during frozen storage • AF-treated fillets exhibited a more rapid decline in quality parameters • SIF extended shelf life and maintained freshness of sliced raw flounder This study evaluated the effectiveness of slurry ice freezing (SIF) in preserving the quality of raw sliced olive flounder ( Paralichthys olivaceus ) during frozen storage, in comparison with conventional air blast freezing (AF). Fillets were vacuum-packaged, frozen at -20 °C using SIF or AF, and stored for 90 days. Quality parameters-including color, texture, pH, drip loss, ice crystal morphology, and protein structure-were assessed. SIF significantly reduced the duration of exposure to the maximal ice crystal formation zone (26 min vs. 11 h for AF), resulting in finer ice crystals and less muscle tissue damage. After 60 days of storage, SIF-treated fillets retained a breaking strength of 564.44-594.80 g with an ice crystal ratio of 24.07-24.65%, whereas AF-treated fillets showed reduced strength (244.81-267.85 g) and significantly increased ice crystal ratio (43.42-45.40%). These quality differences were closely associated with microstructural damage and the denaturation of protein secondary and tertiary structures, as evidenced by SDS-PAGE, intrinsic fluorescence, surface hydrophobicity, and Raman spectroscopy. The results support the industrial applicability of SIF as a rapid freezing strategy for producing high-quality frozen sliced raw fish products with extended shelf life and enhanced freshness retention.