HEAT-INDUCED STRUCTURAL-CHANGES OF ACID-HYDROLYZED AND HYPOCHLORITE-OXIDIZED BARLEY STARCHES

The effects of hydrolysis and oxidation on the heat-induced structural changes of barley starch dispersions were studied by dynamic viscoela stic methods and light microscopy. The effects of the modifications on the molecular weight of amylose and amylopectin were investigated by high-performance liquid chromatography (HPLC) with post-column iodine staining. Comparison of the molecular weights of oxidized and acid-hyd rolysed barley starch dispersions with the same limiting viscosity val ues showed that the molecular weight of amylose was decreased more by oxidation than by hydrolysis, whereas the molecular weight of amylopec tin was reduced to the same degree. Relative to acid hydrolysis, oxida tion also reduced the temperature at which gel-formation occurred and weakened the gels. Irrespective of the type of modification, large amo unts of granule residues were left after heating at 120 degrees C for 20 min. Microstructural studies of the gels showed that both hydrolyse d and oxidized starches underwent phase separation into amylose- and a mylopectin-rich phases. Copyright (C) 1996 Elsevier Science Ltd