Gel properties of acid-induced gels obtained at room temperature and based on common bean proteins and xanthan gum

This work investigates the effect of pH (4.0, 4.5) and the protein-polysaccharide ratio (1:1-5:1) on the intermolecular interactions and gel properties of food hydrogels based on bean protein isolate (BPI) and xanthan gum (XG). Mixed hydrogels induced by acidification with glucone-delta-lactone (GDL) were obtained at room temperature, without the use of crosslinking agents, and using 1% (w/v) of total biopolymer content. The studies on intermolecular forces by a protein solubility assay and FTIR analyses showed that BPI promotes electrostatic associations with XG that depend on pH and ratio. Interestingly, hydrophobic interactions were predominant at ratios 1:1 and 2:1 even when no denaturing heat treatment was employed. In addition, the absence of heating throughout the gelation process caused no changes in the secondary structure of bean proteins as demonstrated by Raman spectroscopy. Concerning gel properties, hydrogels at pH 4.5 showed higher water holding capacity (up to 98.09%) than gels at pH 4.0 (up to 95.65%). Despite this observation, more compact and stronger gel structures were assembled at pH 4.0 as shown by SEM, dynamic oscillatory measurements, and texture profile analysis. Regarding the effect of ratio, the lowest ratios showed the best performance on the evaluated gel properties highlighting that almost all the gels with the 1:1-3:1 ratio exhibited the typical rheological behavior of strong gels. These results indicate that acidification with GDL of BPI:XG systems at ratios 1:1-3:1 at pH 4.0/4.5 and room temperature produce promising mixed hydrogels for functional foods.