Elucidating the phase behavior and emulsifying properties of mung bean protein isolate and carboxymethyl cellulose...

Interactions between proteins and polysaccharides are crucial for developing structured plant-based foods, yet the influence of polysaccharide charge density is not fully understood. This study investigates the complexation between mung bean protein isolate (MBPI) and carboxymethyl cellulose (CMC) with varying degrees of substitution (DS 0.7, 0.9, and 1.2), focusing on their phase behavior and emulsifying properties. Results showed that insoluble complex formation, driven by a combination of electrostatic attraction, hydrogen bonding, and hydrophobic interactions, was optimal at pH 3.0 with a 4:1 MBPI:CMC weight ratio. The impact of CMC's DS was conditional; while negligible in dilute, salt-free systems, a higher DS facilitated complexation at more neutral pH levels in concentrated dispersions. Ionic strength was identified as a key modulator, capable of transitioning the complex structure from a solid precipitate to a liquid coacervate. Notably, complexes formed with low-DS CMC transitioned at 0.1-0.2 M NaCl, whereas the more robust high-DS complexes required a higher concentration of 0.5 M NaCl. Functionally, the complexes were effective emulsifiers, particularly at pH 2.0 and 5.0, away from the point of maximum precipitation. Complexes prepared with lower-DS CMC (0.7) consistently outperformed their higher-DS (1.2) counterparts, as the overly rigid structures formed by high-charge-density interactions were less effective at stabilizing the oil-water interface. This work provides a strategic framework for designing novel, functional plant-based ingredients by controlling biopolymer interactions.