Resistance to α-amylase digestion in four native high-amylose maize starches

Native and processed high-amylose maize starch (HAMS) is an important source of resistant starch (RS). The objectives of this work were to use an in vitro procedure to estimate the RS content of native granules from a series of ae-containing HAMS genotypes, and to examine the nature of the (x-amylase resistant starch (ARS). By the method of Englyst et at (1992), RS for ae V, ae VII, ae su2, and ae du were estimated to be 66.0, 69.5, 69.5, and 40.6%, respectively. By transmission electron microscopy, most of the residual granules from ae V, ae VII, and ae su2 showed little evidence of digestion. Partially digested granules had a radial digestion pattern in the interior and an enzyme-resistant layer near the surface. Size and chain-length profile of constituents of ARS were similar to those of the native HAMS (unlike type 3 RS), consistent with complete hydrolysis in susceptible granule regions. Between crossed polarizers, many iodine-stained native and residual HAMS granules had blue centers and pink exteriors, which may be due to a difference in orientation of the amylose-iodine complexes in the exterior. Four granule color types were observed for ae du, differing in enzyme resistance. The high-enzyme resistance of native HAMS granules may result from altered granule organization, which appears to vary among and within granules from ae-containing genotypes.