MICROSTRUCTURAL AND PHYSICOCHEMICAL PROPERTIES OF OXIDIZED POTATO STARCH FOR PAPER COATING

Heat-induced structural changes were examined for a series of potato starches differing in degree of oxidation and prepared as 25 and 35% dispersions. The molecular weight of amylopectin decreased markedly with the degree of oxidation. Microstructural studies revealed that all oxidized potato starch dispersions heated to 90-degrees-C contained whole granules. The least oxidized potato starch (Raisamyl 316) paste contained large numbers of swollen granules filled with dissolved amylose. In the more oxidized potato starch dispersions, both amylopectin and amylose were solubilized within the granule. Mixing of the amylose and amylopectin occurred and amylose- and amylopectin-rich domains could be seen inside the granule. At 35% concentration, all starches studied formed a gel during cooling (from 90 to 30-degrees-C). The lower the degree of oxidation, the higher the gelling temperature. Raisamyl 310 formed the firmest gel. The gel formation of most oxidized potato starches was weak. Raising the heating temperature from 90 to 120-degrees-C, in combination with shearing, delayed the gelation.