The objectives of this study were to understand how intrinsic and extrinsic factors of o2 and QPM starches affected the enzyme digestibility of their starches, to develop novel and economical technologies to produce RS for health benefits. Enzyme digestibilities of starch present in opaque-2 maize (o2) and quality protein maize (QPM) were analyzed to evaluate the uses of the two maize mutants for food, feed, and ethanol production. The starch granules of the dry-ground o2 maize and QPM were hydrolyzed faster than those of the dryground wild-type (WT) maize using porcine-pancreatic alpha-amylase (PPA). The differences in the hydrolysis rates of these starch granules were attributed to the lower protein content of the o2-maize kernels in general and the lower amylose content of the severe o2 mutant B46o2 and QPM starches than the WT counterparts when subjected to PPA hydrolysis. The starch granules in the dry-ground maize samples were also hydrolyzed faster than the starch granule isolated from whole kernels by wet milling. This difference could be attributed to the presence of mechanically damaged starch granules and endogenous amylases in the dryground maize samples. All the results suggested that the starch granules in the o2 maize and

QPM are desirable for feed and ethanol production.

A novel starch with high enzyme resistance was produced by complexing high-amylose maize starch VII (HA7) with fatty acid (FA) to increase the starch-lipid complex content of the HA7 granules and to enhance the enzyme resistance. The production of the HA7-FA

complex involved pre-swelling and debranching HA7 starch to facilitate the starch-lipid complex formation. The resistant starch (RS) contents of the HA7-FA complex made from stearic acid and palmitic acid were up to 75% determined using AOAC Method 991.43 for dietary fiber. The presence of the amylose-lipid complex in the HA7-FA products was confirmed using DSC thermograms and X-ray diffractograms. The increase in the enzyme resistance of the HA7-FA products was attributed to the amylose-lipid complex formation and the restriction of starch granule swelling during cooking. The restricted swelling of the starch granules reduced the accessibility of amylase to hydrolyze the starch. Bread made from 60% of the HA7-palmitic acid (PA) complex containing 34.4% RS was used for a human-feeding study. After ingesting the HA7-PA bread, the postprandial plasma-glucose and insulin responses of 20 healthy male human subjects was reduced by 45% and 57%, respectively, from that obtained after ingesting white bread as the control. The results suggested that the HA7-PA can be used for interventions of insulin resistance and metabolic syndrome including diabetes, obesity, and cardiovascular disease.

Extrusion cooking was used to enhance the RS content of normal-maize starch. Acid-modified normal-maize starch was extrusion cooked followed by hydrothermal treatment at 110yC. The RS contents of the extruded products were not significantly different from those obtained from the batch-cooked products. The RS contents of the batch-cooked and extruded products increased up to 17% and 33% determined using the AOAC Method 991.43 and Englyst's method, respectively, after the hydrothermal treatment. The RS contents of the batch-cooked and extruded products were attributed to the presence of retrograded amylose and crystalline starch-lipid complex. Both had melting temperatures above 100yC.