Influence of low-dose functional agents and long cooling die temperature on physicochemical, functional and digestibility characteristics of microalgae-fortified high-moisture meat analogs

• Long cooling die temperature and low-level food additives jointly modulated the physicochemical, structural, functional properties and in vitro digestibility of HMMAs. • Haematococcus pluvialis (HP) (0.5%) enhanced protein digestibility and improved functional attributes. • Only 0.01% functional additives, when paired with an appropriate long cooling die temperature, markedly modified HMMA fibrous structuring and physicochemical quality. • Additives and long cooling die conditions significantly influenced the parabolic microstructural appearance profile, reflecting changes in phase separation and protein alignment. • Distinct improvements in digestion profiles were observed: 0.5% HP enhanced fragmentation near 35 kDa, while 0.5% HP with NaCl improved digestion at ∼20 kDa. High-moisture extrusion cooking (HMEC) is a key technology for producing plant-based high-moisture meat analogs (HMMAs) with meat-like fibrous textures. HMMA quality depends on raw materials, extrusion conditions, and cooling die temperature, while functional additives further enhance structural and textural stability. This study examined the effects of three functional agents as salt (NaCl), sodium bicarbonate (NaHCO₃), and acetic acid (CH 3 COOH), and long cooling die temperature on HMMA properties. Soy flour and wheat gluten were extruded with 0.5% Haematococcus pluvialis (HP) and 0.01% additives using a twin-screw extruder (67% feed moisture, 370 rpm, 130°C barrel temperature). Physical attributes (color, rehydration, textural integrity, cooking yield), texture, microstructure (including X-ray tomography), functional properties, and digestibility were assessed. Results showed that rehydration capacity increased by up to 25% with the addition of NaCl and CH 3 COOH, while incorporating all three agents improved textural integrity by 18%. NaHCO 3 further enhanced cooking yield by 2.5%. Low-dose additives combined with long cooling die conditions altered the parabolic microstructural patterns and modified the visual microstructure. HP fortification elevated total carotenoid content and boosted antioxidant activities (ABTS and FRAP). Distinct digestive behaviors were observed; 0.5% HP promoted greater protein fragmentation near 35 kDa, while the combination of 0.5% HP and NaCl enhanced peptide release at around 20 kDa. Our findings highlighted how targeted formulation and processing strategies simultaneously improved texture, nutritional quality, and digestibility in plant-based meat analogs.