Isolation, structure, and characterization of the putative soluble amyloses from potato, wheat, and rice starches

Amylose, a putative linear alpha-(1-->4)-glucan and a component of most starches, was isolated from potato, rice, and wheat starches by forming the 1-butanol complex in a solution of the starches. It previously had been found that these amyloses were incompletely hydrolyzed by beta-amylase, indicating that it was partially branched. Solubilization of the butanol complex in water and steam distillation of the 1-butanol, followed by cooling to 4 degrees C gave precipitation of the double helical, linear, retrograded amylose over a 15 h period, leaving the soluble amylose in solution. The soluble amyloses were precipitated with two volumes of ethanol, and the precipitate was solubilized and reprecipitated to remove traces of linear amylose. The precipitated, soluble amyloses, were partially branched and had properties intermediate between linear amylose and amylopectin. The water solubility of the potato amylose was 10.52 mg/mL, with a number-average degree of polymerization (DP(n)) of 8440 and 2.1% branch linkages that had a DP(n) of 48; the water solubility of the rice amylose was 8.83 mg/mL, with a DP(n) of 2911 and 1.4% branch linkages that had a DP(n) of 72; and the water solubility of wheat amylose was 6.33 mg/mL, with a DP(n) of 1160 and 1.6% branch linkages that had a DP(n) of 64. The three soluble amyloses have structures and properties intermediate between the nearly water insoluble (