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

• Published in: International journal of biological macromolecules 2021-01, Vol.166, p.861-868
• Main Authors: Cortez-Trejo, M.C., Mendoza, S., Loarca-Piña, G., Figueroa-Cárdenas, J.D.
• Format: Article
• Language: English
• Subjects: Amaranth; Amaranthus - chemistry; Common bean; Compatibility; Cross-Linking Reagents - chemistry; Electrostatic interaction; Globulins - chemistry; Hot Temperature; Hydrogels - chemistry; Hydrogen-Ion Concentration; Phaseolus - chemistry; Plant Proteins - chemistry; Polysaccharides, Bacterial - chemistry; Protein Conformation, beta-Strand; Protein isolates; Protein Stability; Xanthan gum
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2020.10.242

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 β turn and β 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. [Display omitted] •Amaranth and bean protein secondary structure is not affected by pH.•PI-XG hydrogels were obtained at low total solids content (1 wt%).•Associative electrostatic interactions between PI and XG occurred even at pH > pI.•Hydrogels were obtained without heat treatment nor crosslinking agent.