High-moisture extrusion technology emerges as a prime choice for preparing alternative protein products with a meat-like texture. However, the nutritional aspects of these products, prepared from a blend of plant and animal proteins, remain unclear. This study investigated the nutritional qualities of extrudates derived from soy protein isolate (SPI) and surimi, exploring ratios ranging from 90 : 10 to 50 : 50, with varied extrusion temperature (125 °C, 135 °C and 145 °C) and moisture content (65%, 70% and 75%). Results revealed the significant role played by surimi in enhancing both amino acid and fatty acid contents in high-moisture extrudates originating from SPI and surimi. Notably, the first limiting amino acid score (AAS/MET + CYS) increased significantly from 88.82 to 109.50 as the surimi content increased from 10% to 50%. Moreover, the levels of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in the extrudates significantly increased, concurrently reducing the n-6/n-3 fatty acid ratio. At a higher moisture content (70–75%), increasing extrusion temperature bolstered the fatty acid content in the extrudates. When the SPI–surimi ratio was 90 : 10, the gastric digestibility of the extrudates was the highest (60.20%). Meanwhile, the highest small intestinal digestibility was 93.07% at a SPI–surimi ratio of 70 : 30. At lower extrusion temperatures (125–135 °C), increasing moisture content led to a notable increase in the small intestinal digestibility of the extrudates. SPI–surimi ratios and hydro-thermal combined parameters have significant effects on the in vitro digestibility of high-moisture extrudates. This study could contribute to the improvement of nutritional qualities of alternative protein products based on mixed proteins from soy and surimi.
