Initial heating temperature and native lipid affects ordering of amylose during cooling of high-amylose starches

Formation of ordered structures from disordered amylose is practically impo rtant. The thermal behavior of high-amylose maize starches was studied duri ng cooling, following heating, and during subsequent reheating. Four commer cial high-amylose genotype maize starches with varying amylose contents (ae du, ae su2, and ae [nominally both 50 and 70% amylose]) were heated to eit her 120, 140, 160, or 180 degrees C, cooled to 5 degrees C, and reheated to 180 degrees C in a differential scanning calorimeter. Each starch was stud ied with its native lipid, as well as in reduced-lipid and lipid-free form. On cooling of lipid-containing starches, two distinct exotherms were obser ved and attributed to amylose-lipid complex formation and to amylose chain association. A distinct exotherm at approximate to 75 degrees C was attribu ted to amylose-lipid complex formation. The exotherm attributed to amylose chain association on cooling varied according to the initial heat treatment , lipid level, and starch type. Starches with higher amylose contents showe d larger exotherms on cooling. For initial heat treatments to 120 or 140 de grees C, a broad exotherm beginning at approximate to 95 degrees C was obse rved on cooling. In contrast, for initial heat treatments to 160 and 180 de grees C, a sharper exotherm with a peak temperature below approximate to 55 degrees C was observed. Upon reheating, samples that had been initially he ated to 120 or 140 degrees C showed a peak at >140 degrees C that was attri buted to the melting of ordered amylose. Starches initially heated to 160 o r 180 degrees C did not show this peak. This work illustrates that initial heating temperature, as well as lipid content and amylose content, all affe ct amylose chain association during cooling. Thus, this work suggests strat egies for controlling ordering of amylose during processing.