Determination of water distribution in starch-protein composite gels by NMR relaxometry and CLSM imaging

Water distribution in multicomponent gels strongly influences their structural and textural properties. This study aimed to determine the water distribution in composite starch-protein gels and use these results to estimate mechanical properties. Two approaches were used: Time Domain Nuclear Magnetic Resonance (TD-NMR) and Confocal Laser Scanning Microscopy (CLSM). Both single component maize starch (MS) and pea protein isolate (PPI) gels with increasing dry matter and composite gels with 20 wt% total dry matter and varying MS-PPI ratios were prepared. TD-NMR revealed different water populations in both single component gels, with higher water mobility in starch gels. In composite gels, increasing starch-protein ratio led to increased overall water mobility, even though total water availability decreased with higher starch content. TD-NMR measurements were used to determine starch and protein concentrations in each phase, from which volume fractions were calculated. CLSM images provided direct information on the volume fractions of both phases, from which respective concentrations were determined. The two approaches delivered similar results for high MS fractions, whereas discrepancies were found for low MS fractions. Phase composition was then used to estimate gel stiffness using theoretical models for dispersed and bicontinuous structures, which agreed well with measured values. For high dry matter gels, precise determination of MS concentration and volume fractions is not required to estimate mechanical properties. Determining water distribution in composite gels provides opportunities to modulate structure and mechanical properties based on the water holding capacity (WHC) of individual ingredients, with potential for the design of plant-based foods. • Water competition caused uneven water distribution during composite gel formation. • TD-NMR and CLSM quantified water distribution in starch–protein composite gels. • Starch-rich gels showed higher water mobility despite lower water availability. • Phase composition data was sufficient to estimate stiffness of composite gels. • High dry matter gels required no precise phase quantification to estimate stiffness.