Direct high‐temperature intervention restructures fermented freshwater surimi gels: time‐dependent remodeling and aggregation in an acidified myofibrillar protein model

BACKGROUND: The mode of heat treatment can either promote protein gel network formation or cause network destabilization in acidified fermented surimi, but the underlying process-structure-function relationship remains unclear. We hypothesized that direct high-temperature intervention (DHTI) at 90 °C would favor gel restructuring by coupling suppression of cathepsin L (CTSL) activity with protein crosslinking, whereas prolonged high-temperature exposure would eventually cause excessive aggregation and functional decline. Fermented freshwater surimi (FFS) was heated at 40 °C for 1 h (HT40), 90 °C for 30 min (HT90), or 40 °C for 1 h followed by 90 °C for 30 min (HT40 + 90), with an unheated control. An acidified myofibrillar protein (AMP) model was heated directly at 90 °C for 0-60 min to resolve time-dependent protein remodeling. RESULTS: Among heat-treated FFS groups, HT90 produced the highest gel strength, water-holding capacity (WHC), and whiteness. It reduced residual CTSL activity by 90.71%, increased disulfide bond content by 71.58%, and formed a compact, continuous network. HT40 + 90 showed lower endpoint CTSL activity than HT90 but lower WHC and a less continuous network, indicating that endpoint protease activity alone did not determine gel quality. In the AMP model, particle size increased sharply during the first 5 min, whereas solubility and total sulfhydryl content progressively decreased. Gel strength peaked at 5 min, then declined, and WHC decreased significantly after 40 min of heating. CONCLUSION: DHTI favored FFS gel restructuring, accompanied by reduced residual CTSL activity and enhanced covalent crosslinking, whereas prolonged heating drove excessive aggregation and loss of network functionality.