Comparison of structural and physicochemical properties of lysozyme/carboxymethylcellulose complexes and microgels

Proteins and polysaccharides can be used to assemble colloidal delivery systems suitable for industrial applications, such as functional foods, supplements, pharmaceuticals, and personal care products. The purpose of this work was to compare the physicochemical and structural properties of colloidal delivery systems prepared from lysozyme and carboxymethyl cellulose (CMC) at different biopolymer ratios, pH values, and salt levels. Specifically, the performance of unheated ("complexes") and heated ("microgels") lysozyme-CMC systems were compared. Isothermal turbidity-pH titrations indicated that the critical pH value for complex formation was lower for microgels than for complexes. Complexes were prone to dissociation when the pH or ionic strength was altered due to weakening of electrostatic interactions between the CMC and lysozyme. Conversely, microgels remained intact when the pH or ionic strength was altered, exhibiting swelling or shrinkage rather than dissociation. These results have important implications for the selection of the most appropriate protein/polysaccharide systems to achieve specific functional requirements. Complexes may be more suitable for pH- or salt-based triggered release whereas microgels may be more suitable for sustained release.