Delonix regia galactomannan hydrolysates: Rheological behavior and physicochemical characterization

The galactomannan extracted from Delonix regia (DRGM) seeds was hydrolyzed at different enzyme dosages and reaction times. A linear relation between inverse Molecular weight (Mn) and hydrolysis time was obtained, and the Mn reduction was controlled from 4.86 × 10⁵ to 1.95 × 10⁵ Da. The hydrolysis does not affect galactomannan structure as observed by FT-IR and DRX, maintaining an amorphous structure with only a slight increase in galactose:mannose relationship as observed by ¹H NMR. A rheological behavior shift was observed below Mn = 4.15 × 10⁵ Da when viscoelastic behavior changes from a weak gel to a macromolecular solution in a 3% (w/v) galactomannan hydrolysate. Shear viscosity of 3% (w/v) galactomannan dispersion in water follows closely a power law equation where the consistency index decreased, and the flow behavior index increased with increasing hydrolysis degree. These results indicate the conditions for obtaining specific viscoelastic properties of DRGM dispersions for specific applications by a careful control of the enzymatic hydrolysis process.