# Cryoprotective Effects of Tuna Skin Antifreeze Peptides on the Quality of Salmon Flesh During Low-Temperature Fluctuations

## TL;DR

This study shows that antifreeze peptides from tuna skin can protect salmon quality during freezing and thawing cycles, offering a natural preservation solution.

## Contribution

The novel contribution is demonstrating the cryoprotective effects of tuna skin-derived antifreeze peptides on salmon flesh quality during temperature fluctuations.

## Key findings

- Tuna skin-derived antifreeze peptides improved salmon texture, color, and water retention during freeze-thaw cycles.
- Neutral protease-treated peptides preserved protein structure and inhibited oxidation better than other treatments.
- Microstructural analysis showed better muscle fiber integrity in samples treated with neutral protease-derived peptides.

## Abstract

Repetitive temperature fluctuations during transportation and storage promote ice crystal formation in salmon flesh, leading to protein denaturation, lipid oxidation, and quality loss. Tuna skin, a major by-product of tuna processing, is a potential source of antifreeze peptides (AFPs) but remains underutilized. This study examined the cryoprotective effects of tuna skin-derived AFPs on salmon cubes subjected to repeated freeze–thaw cycles. Cubes treated with AFPs from three groups of protein hydrolysates prepared using trypsin, pepsin, or neutral protease were evaluated for texture, color, water holding capacity (WHC), volatile odor profiles, protein conformation, biochemical indices, and microstructure. AFP treatment improved textural properties, maintained color stability, and reduced thawing, cooking, and centrifugal losses. The neutral protease-treated group exhibited the optimal cryoprotective ability and it also limited aldehyde and sulfide accumulation, preserved the retention rate of α-helix structure at 49% which was higher than 39% in controls, and enhanced Ca2+-ATPase activity to 1.75 μmol Pi·mg−1·h−1 with a 45.8% increase compared to controls, and significantly inhibited protein and lipid oxidation. Microstructural analysis showed compact fibers and intact sarcolemma in the neutral protease-treated group samples, contrasting with severe disruption in controls. This study showed that tuna skin AFPs mitigate freeze–thaw damage in salmon cubes by stabilizing proteins and reducing oxidative deterioration, highlighting their potential as natural, healthy cryoprotectants for seafood preservation, meeting the growing demand of the food industry for clean-label, low-calorie preservation solutions, while advancing the circular economy of aquatic processing via the valorization of tuna skin by-products for high-value seafood applications.