Leaching of amylose from wheat and corn starch.

Wheat starch gave a 21% yield (based on starch) of amylose (AM) when leached at 3% solids under mild agitation, and at a heating rate of 10 degrees C/min to 95 degrees C followed by holding at least 10 min. Annealing wheat starch prior to leaching at 95 degrees C or using a heating rate of 1 degrees C/min during leaching, increased AM yield from 21% to 23% at 3.0% starch solids, and 8% to 16% at 4.5% starch solids. At 0.5% solids, almost all wheat AM (29% of starch) was solubilized into the continuous phase at 95 degrees C, but only one-half of the lipid in the starch co-leached with AM. Corn starch behaved similarly to wheat starch during leaching below 1.5% starch solids, while at 3.0% almost 40% more AM was obtained from wheat than corn starch. Wheat AM molecules isolated by leaching were larger than those obtained by crystallizing its n-butanol complex, and they gave a different size-distribution as evidenced by high-performance size-exclusion chromatography. A triangular phase diagram was useful in depicting the overall process of leaching AM from starch. The critical concentrations of wheat (5.4%) and corn (5.2%) starches were determined using phase diagrams.