Ultrasound-Assisted Extraction and Functional Application of Pithecellobium dulce Seed Protein Isolate in Compound Coating Formulations

This study explores the extraction and application of Pithecellobium dulce seed protein isolate (PSPI) in chocolate compound coating formulations. PSPI was extracted via ultrasonication-assisted isoelectric precipitation under optimized conditions (solute-to-solvent ratio 1:30, pH 12, 10 min), yielding 23.64% with 38.28% recovery. PSPI exhibited high protein content (75.3%), low water activity (0.22), near-neutral pH (6.94), and favourable techno-functional properties, including high water (3.27 g/g) and oil holding capacities (4.81 g/g), improved solubility (↑21.3%), and superior thermal stability compared to skim milk powder (SMP). While in vitro digestibility was slightly lower than SMP (88.52% vs. 92.42%), PSPI outperformed other reported plant protein isolates such as Prosopis africana , conophor nut, and Moringa oleifera . PSPI was partially substituted for SMP in chocolate compound coatings. Among the formulations, PSPIC-2 (20% PSPI substitution) demonstrated the best balance of physicochemical, nutritional, rheological, and sensory properties, showing increased protein and ash content, reduced carbohydrates, higher TSS (↑0.9%) and Casson yield stress (↑4%), with only minor reductions in colour (↓7.9%) and pH (↓3.9%). Sensory analysis confirmed that taste and texture were comparable to the control. These findings support the use of PSPI as a sustainable, plant-based ingredient in functional chocolate compound coatings. • Developed protein-rich chocolate by replacing 10–50% skim milk powder (SMP) with P. dulce protein. • Optimised extraction gave 23.64% protein isolate with 75.3% protein and improved functionality. • Optimised chocolate had high sensory acceptability and matched the control in key quality parameters. • Enhanced emulsifying, solubility, and water-holding capacities improved the nutritional profile. • Chocolate met microbial safety standards and provided a sustainable alternative to SMP.