Effect of molecular mass and degree of substitution of carboxymethyl cellulose on the formation electrostatic complexes with lentil protein isolate.

The electrostatic interaction between lentil protein isolate (LPI) and carboxymethyl cellulose (CMC) of different molar mass (MM; 90 and 250 kDa) and degree of substitution (DS; 0.7, 0.9 and 1.2%) was examined during a turbidimetric pH acid-titration over a pH (8.0-1.5) and mixing ratio (LPI: CMC; 1:1-10:1) rang. For LPI-CMC (0.7% DS, 250 kDa) at a 1:1 ratio, pHs linked soluble (pHc) and insoluble complexes (pHϕ1) being formed, maximum coacervation (pHopt) and the dissolution of complexes (pHϕ2) occurred at pHs of 6.8, 2.6, 2.1 and 1.7, respectively. As the mixing ratio increased, pHc and pHϕ2 remained unchanged; however, pHϕ1 and pHopt shifted to higher pHs until plateauing at a 4:1 mixing ratio. Molecular mass and DS had no significant effect on critical pHs but did have an impact on the size and number of complexes formed. The maximum optical density at pHopt was found to decrease from 0.495 to 0.406 as the DS increased from 0.7% to 1.2% on the CMC (constant at 250 kDa), suggesting that complexes were likely smaller as they scattered less light. As the MM of CMC decreased from 250 to 90 kDa (at 0.7% DS), maximum optical density increased from 0.495 to 0.527, respectively. Confocal laser scanning microscopy preformed at pHopt showed an increasing number of aggregates as the DS or MM of CMC decreased. From isothermal titration calorimetry (ITC), larger enthalpy values in LPI-CMC with increased DS and MM were observed.