Physicochemical and microstructural changes in minced fish muscles as affected by cryoprotectants

Alginate, carrageenan, soy protein concentrate (SPC), sodium tripolyphosphate (STPP), and sorbitol were chosen as potential cryoprotectants. Their effects on physicochemical and sensory properties of frozen red hake (Urophycis chuss) and Alaska pollock (Theragra chalcogramma ) mince at −20°C for 17 weeks were investigated. The mince was mixed with 0.3% STPP, 4% sorbitol and either 0.2–0.4% alginate, 0.2–0.4% iota-carrageenan, or 4% SPC. Changes in texture, microstructure, and profiles of proteins, free amino acids and lipids of fresh and frozen mince were evaluated. The addition of alginate, STPP, and sorbitol significantly improved the dispersibility of uncooked red hake mince with reduced penetration and shear forces. They reduced cooking loss and controlled protein denaturation as evidenced by the higher water-, salt-, SDS-soluble proteins, and sulfhydryl group contents compared to the control sample. Sorbitol and STPP with or without SPC and ι-carrageenan did not improve the dispersibility. Polymerization of myosin heavy chain via disulfide bond formation was one of the causes of the textural deterioration in the red hake mince. The difference in freeze-induced textural changes between red hake and Alaska pollock may be attributed to the inherent chemical composition and properties, such as calcium which may cause membrane aggregation and protein cross-linking responsible for texture hardening. Inhibition of calcium activity by alginate and STPP may have prevented the development of texture hardness. The stereomicrograph revealed that the control formed more compact structure compared to that with alginate. Such structural difference was confirmed by the SEM micrographs where muscle fibers were less interweaved together with alginate added. The results of the present study suggest that a combination of 0.4% alginate + 4% sorbitol + 0.3% STPP can effectively control muscle fiber interaction and myofibrillar protein denaturation and aggregation of fish mince during frozen storage