Effects of liquid nitrogen freezing, immersion freezing, and air freezing on properties of Perca fluviatilis fillets and analysis of potential protein markers based on label-free proteomics

The effects of liquid nitrogen freezing (LNF), immersion freezing (IF), and air freezing (AF) combined with thawing in running water at 20 degrees C on the quality of Perca fluviatilis fillets were investigated using label-free proteomics technology. The ice crystal equivalent diameter (12.30 +/- 0.33 mu m) and ice crystal area ratio (7.61 +/- 2.81%) of LNF were significantly lower than IF and AF (P < 0.05). The ice crystals of LNF were small and evenly distributed, and the mechanical damage to the cell structure is small. LNF samples were closer to fresh samples regarding texture. Proteomic analysis identified a total of 11 differentially abundant proteins (DAPs) associated with LNF, IF, and AF. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that these DAPs were primarily catalytic proteins, metabolic enzymes, and structural proteins involved in metabolic pathways such as pyruvate metabolism, glycolysis, and arginine and proline metabolism. Among them, tubulin beta chain (A0A8C3G6F1), carbonic anhydrase (A0A2P1JP97), immunoglobulin-like and fibronectin type III domain-containing protein 1 (A0A484DE91), and tubulin are predicted to serve as potential protein markers for freezing, thawing loss, hardness, and springiness of Perca fluviatilis fillets post-thawing. These findings provide a basis for further research into the quality change induced by protein degradation of frozen Perca fluviatilis.