Effects of High-Pressure Processing and Lipid Fortification on Hoki (Macruronus novaezelandiae) Surimi Structure, Oxidative Stability, and In Vitro Digestion

High-pressure processing (HPP) and lipid fortification affect surimi functionality, but their combined effects on oxidation and digestion-related responses remain insufficiently characterised. Hoki (Macruronus novaezelandiae) surimi containing 10% (v/w) canola oil, flaxseed oil, or no-added-oil control was treated at 0–600 MPa. Technological properties, colour, thiobarbituric acid reactive substances (TBARS), microstructure, protein banding, and free amino acid (FAA) release during in vitro digestion were assessed. Oil fortification affected moisture and fat content, while pressure had limited effects on bulk proximate composition. Pressure reduced cooking loss and increased water-binding capacity (WBC) and slice shear force (gel resistance to shearing), with WBC showing an oil fortification × pressure interaction (p < 0.001). Oil-containing gels showed higher WBC, lightness, yellowness, and whiteness than the control. TBARS values were affected by oil fortification, pressure, and their interaction (p < 0.001), were highest in flaxseed samples, and decreased with pressure in the measured subset. Microstructure indicated improved network integration at moderate pressure, whereas higher pressure produced denser, less uniform structures. FAA release was governed mainly by digestion phase (p < 0.001), with limited, non-linear pressure effects. Overall, HPP and lipid fortification influenced hoki surimi through matrix-level changes in functionality, oxidation, structure, and FAA release.