Effects of gamma irradiation and stearic acid, alone and in combination, on functional, structural, and molecular characteristics of high amylose maize starch

The effects of gamma irradiation and stearic acid, alone and in combination, on functional, structural, and molecular characteristics of high amylose maize starch (Hylon VII, approximate to 60% amylose) were studied. Stearic acid (0, 1.5, and 5%) was added to Hylon VII starch, and then irradiated at 0, 30, and 60 kGy. Gamma irradiation significantly (p <= 0.05) increased solubility, water absorption capacity, and oil absorption capacity as well as decreased swelling power (at 90 and 95 degrees C) of Hylon VII starch. These changes related well with increased amylose and decreased amylopectin content, decreased MW, and decreased transition endotherms of the starches due to gamma irradiation. Stearic acid addition significantly increased (p <= 0.05) water and oil absorption capacities, relative crystallinity as well as decreased solubility and swelling power of Hylon VII. Gamma irradiation had more effect on the molecular structure of Hylon VII compared with stearic acid. Gamma irradiation alone and with stearic acid did not seem to change the XRD pattern and microstructure of Hylon VII. The similar XRD pattern and morphology observed for irradiated and non-irradiated Hylon VII suggests that gamma irradiation depolymerizes amylose, and amylopectin mostly in the amorphous region of the starch to produce less branched or unbranched amylopectin. Gamma irradiation with stearic acid has potential in Hylon VII modification.