Electrostatic Hydrogels Based on Amaranth Proteins and Xanthan Gum: Water-binding, Microstructural, Rheological and Textural Properties

This work investigated the effect of an amaranth protein concentrate (APC) and xanthan gum (XG) in a (1:1–5:1) ratio on the gelation process, microstructure, water-binding, rheological, and textural properties of electrostatic hydrogels. The materials were prepared to keep 1% of biopolymer content and without heating nor cross-linking agents addition. Although turbidity measurements showed an unclear trend depending on the ratio, the maximum turbidity values indicated that high ratios (≥ 3:1) produce a more aggregated microstructure due to the excess of APC. Image analysis of confocal micrographs revealed ratio 1:1 showed the lowest pore density and lacunarity value, and the highest fractal dimension (Df) value indicating a more dense and homogeneous gel network compared to those of higher ratios. The pore size ranged from 3.08 to 5.58 μm, with the ratio 5:1 with the highest value. Concerning water holding capacity (WHC), it varied from 59.7 to 96.6%, with ratios 5:1 and 1:1 being the ones with the lowest and highest values, respectively. In addition, dynamic oscillatory measurements demonstrated the strong gel character of ratio 1:1, and texture profile analysis showed that other gels than ratio 1:1 were less elastic, cohesive, and with less chewiness and resilience. APC:XG hydrogels produced at a 1:1 ratio have the potential for food applications such as delivery systems for heat-sensitive compounds due to their convenient structural characteristics and high water-holding capacity. In this way, and to the best of our knowledge, the evaluation of microstructural, water-binding, and rheological properties of protein-polysaccharide electrostatic hydrogels based on a complex mixture of plant proteins with xanthan gum, is reported for the first time.