Optimizing alkaline and enzymatic extraction of black bean proteins: a comparative study of kinetics, functionality, and nutritional properties

Abstract

This study aimed to elucidate the impact of fundamental extraction parameters on protein extraction yields, kinetics, functionality, and nutritional properties of black bean proteins generated by the aqueous (AEP) and enzyme-assisted extraction processes (EAEP). Extractions evaluating the interplay of different solids-to-liquid ratios (SLR) and protease concentrations revealed a 14% increase in total protein extractability (TPE) for more concentrated slurries (1 : 7.5 SLR), demonstrating lower water requirements for enzymatic extractions. Kinetic modeling revealed that aqueous extractions followed first order (R² = 0.94) and Peleg's (R² = 0.91) models while enzymatic extractions exhibited multi-step kinetics with a burst-drop initial phase (0–20 min) followed by an increase corresponding to first order (R² = 0.94) and Peleg's models (R² = 0.92). The optimized AEP (pH 9.0, 50 °C, 1 : 15 SLR, 30 min) and EAEP (pH 9.0, 50 °C, 1 : 7.5 SLR, 1.0% enzyme, 60 min) achieved 82 and 78% TPE, respectively. EAEP increased the degree of hydrolysis from 4.6 to 21.1% and shifted the protein isoelectric point from pH 3.4 to <2. EAEP proteins exhibited significantly higher solubility in acidic conditions and foaming capacity at pH 3.4 but were unable to form emulsions at pH 3.4 and 7.0. Proteolysis also increased in vitro protein digestibility from 34 to 61%, decreased trypsin inhibitor activity from 136 to 100 TUI per mg protein, and reduced hemagglutination activity from 640 to 320 HU per mg protein, demonstrating that enzyme addition is a useful strategy to not only reduce water usage in aqueous extractions, but also enhance the nutritional properties of black bean proteins.