Physicochemical characterization of protein isolates of amaranth and common bean and a study of their compatibility with xanthan gum

Vegetables are considered to be a sustainable source of promising biomaterials such as proteins and polysaccharides. In this study, four protein isolates (amaranth protein isolate API, amaranth globulin-rich protein isolate AGR, bean protein isolate BPI, and bean phaseolin-rich protein isolate BPR) were structurally characterized under different pH conditions (2-12) and their compatibility behavior with xanthan gum (XG) in aqueous medium was described. All protein isolates showed beta turn and beta sheet (78.24-81.11%), as the major secondary structures without statistically significant difference under the pH conditions surveyed. Protein isolates show solubility at pH <= 3 (40.4-85.1%) and pH >= 8 (57.6-99.9%) and surface hydrophobicity results suggest protein denaturation at pH <= 3. In the compatibility study, API/XG ratios between 1:1 and 5:1 at pH from 7 to 9 and the BPI/XG ratios from 1:1 to 20:1 at pH 7 form gels that do not require heating nor crosslinking agent addition. Zeta potential results, on the other hand, evidenced that formation of gels is driven by attractive electrostatic interaction of the charged regions of both biopolymers and intermolecular interactions such as hydrogen bonds. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In this study, four protein isolates were structurally characterized under different pH conditions and their compatibility behavior with xanthan gum in aqueous medium was described. The results showed that the protein isolates exhibited similar secondary structures under certain pH conditions and formed gels without the need for heating or crosslinking agents under specific conditions, driven by electrostatic and intermolecular interactions.