Effects of Quality Enhancement of Frozen Tuna Fillets Using Ultrasound-Assisted Salting: Physicochemical Properties, Histology, and Proteomics

Salting pretreatment is an effective method to improve the quality of frozen fish. This study investigated the quality changes and proteomic profile differences of frozen yellowfin tuna fillets pretreated with ultrasound-assisted salting (UAS) and static salting (SS). This study was centered on three aspects: physicochemical indicators’ determination, histological observation, and proteomic analysis. The results showed that UAS significantly increased yield, salt content, and water-holding capacity (WHC), decreased total volatile base nitrogen (TVBN) compared to SS (p < 0.05), and significantly increased water in the protein matrix within myofibrils. Histological observations showed that the tissue cells in the UAS group were less affected by frozen damage, with a more swollen structure and rougher surface of myofibrils observed. Furthermore, 4D label-free proteomics revealed 56 differentially abundant proteins (DAPs) in UAS vs. NT comparison, mainly structural proteins, metabolic enzymes, proteasomes, and their subunits, which are associated with metabolic pathways such as calcium signaling pathway, gap junction, actin cytoskeletal regulation, and necroptosis, which are intimately associated with quality changes in freeze-stored tuna fillets. In brief, UAS enhances the potential for the application of salting pretreatment to improve frozen meat quality, and 4D label-free proteomics provides knowledge to reveal the potential links between quality and molecular changes in processed frozen meat to optimize future UAS meat processing.