Freshwater fish represents a crucial source of high-quality protein, providing vital dietary animal protein for millions worldwide (McIntyre, Reidy Liermann, & Revenga, 2016). Over recent decades, there has been a notable increase in both global freshwater fish production and the demand for freshwater fish-derived products (McIntyre et al., 2016; Stentiford & Holt, 2022). Among them, surimi and surimi gel products have gained significant attention due to their robust nutritional profile and desirable textural attributes (Zhang et al., 2023). Grass carp (Ctenopharyngodon idellus) is the most productive freshwater fish in China and even in the world (Sun et al., 2019). It holds a significant economic position in the Chinese freshwater aquaculture market, with production already exceeding 5.5 million tons in 2020 (Yuduan, Gao, Jiang, Xia, & Yang, 2022). Grass carp is an excellent and preferred raw material for making surimi or surimi gel products due to its low market price, high nutritional quality, high production, and continuous yield. However, the shelf life of grass carp surimi is limited by various biochemical reactions and microbial metabolism processes, leading to deterioration in texture and flavor. These quality deteriorations pose significant health risks for consumers and result in economic losses (Yu et al., 2018).

Freezing is one of the most common methods employed to maintain the quality of surimi and extend its shelf life. However, freezing is associated with significant texture degradation and poor gel performance of surimi (Cao et al., 2022). Myofibrillar protein (MP) is one of the main components of surimi, responsible for its gel formation. Structural and functional alterations in MP during freezing are identified as key factors contributing to the compromised texture and gel properties of surimi. Previous studies have also reported that freezing induces partial denaturation and/or aggregation of MP, resulting in less effective gel formation compared to fresh surimi (Zhang et al., 2022). In addition, the freeze concentration effect causes lateral contraction of MP due to dehydration (Zhang & Ertbjerg, 2019), which in turn affects the functional characteristics of MP. Therefore, it is imperative to delve into the underlying mechanisms associated with the alteration in MP quality during freezing to facilitate the development of high-quality surimi and related products.

Presently, the main method to inhibit the quality decline of surimi during freezing is to add cryoprotectants. For example, saccharide is a common cryoprotectant. However, the addition of sugar will not only affect the taste of the surimi itself but also increase the calories, which is not acceptable to many consumers (Cao et al., 2022). With the increasing health awareness of consumers, natural and non-additive surimi is becoming more and more popular among consumers (Zhang et al., 2023).

It is interesting to note that the collaborative technology of high-pressure and low-temperature, encompassing pressure shift freezing (PSF) and pressure-assisted freezing (PAF), modifies the ice crystal formation process within a sample during freezing, consequently altering the size and type of ice crystals formed (Li et al., 2022). Moreover, PSF treatment has been demonstrated to yield small and uniformly distributed ice crystals in samples, thereby minimizing mechanical damage to food materials during freezing (Su et al., 2014). Currently, high-pressure and low-temperature collaborative technology primarily remains at the laboratory stage, with limited instances of application in large-scale industrial production. The primary deterrents include the high equipment requirements associated with the technology and the incompleteness of research on the underlying mechanisms governing the influence of high-pressure and low-temperature collaborative technology on food material characteristics (Zhang et al., 2022).

Although some studies have reported the advantage of PSF in inhibiting the quality degradation of frozen foods (Zhang et al., 2023), the majority of the studies on high-pressure and low-temperature freezing mainly explored the effect of ice crystal size on physical properties of fish or surimi gels. However, the underlying mechanism governing the modification of myofibrillar protein (MP) properties following exposure to high pressure and low temperature remains largely unexplored. The characteristics of MP are paramount for the quality and gelation ability of surimi. MP gelation is a pivotal process with significant implications for its functional properties, involving intricate physical and chemical changes in the structure and functional attributes of MP (Li, Wang, Kong, Shi, & Xia, 2019).

Thus, this study aimed to explore the effect of low temperature and high-pressure collaborative treatment on MP turbidity, solubility, particle size, and intermolecular chemical forces of grass carp. In addition, the thermal properties of MP, the microstructure, and the three-dimensional network structure of MP gel along with the mechanism involved in the change of MP. The output of this study will provide theoretical guidance for high-pressure and low-temperature collaborative processing and industrial production of related aquatic products.