Effect of pH and proportion on structural properties of Hylon VII starch - gellan gum blends processed in a microwave hermetic system.

Abstract

High-amylose starch (S) can interact with gellan gum (GG), a pH-sensitive polysaccharide, to form gel structures. This study investigates the effect of pH (3, 5, and 7) on the structural properties of S-GG blends, prepared at different proportions (75S/25G, 50S/50G, and 25S/75G). Blends were hydrothermally processed using microwave heating in a hermetic vessel, ensuring rapid and uniform treatment. Starch gelatinization was confirmed by SEM and DSC analysis. FTIR revealed hydrogen bonding as the stabilizing factor in blends. XRD revealed hexagonal P6₁ phase corresponding to amylose B type while GG exhibited a trigonal P3₁. GG showed a higher crystallinity (15.19, 16.7, and 22.02 %) than S (5.34, 8.94, and 8.81 %) at pH 3, 5, and 7, respectively, dominating the structural arrangement of blends. The network mesh size changed from 6.38 nm (0S/100G, pH 5) to 36.73 nm (75S/25G, pH 7) as S increased. The pH-sensitivity of GG was more evident in 75S/25G, with G' (748.0, 120.5, and 83.1 Pa), G'' (157.0, 28.0, and 20.75 Pa), and η* (121.5, 19.65, and 13.05 Pa·s) at pH 3, 5, and 7, respectively. These results highlight the effect of pH and proportion on targeted S-GG blends structures intended for applications as biodegradable packaging or encapsulation systems.