Resistant Starch and Starch Thermal Characteristics in Exotic Corn Lines Grown in Temperate and Tropical Environments

Abstract

Corn as a food that is heated and cooled to allow starch retrogradation has higher levels of resistant starch (RS). Increasing the amount of RS can make corn an even healthier food and may be accomplished by breeding and selection, especially by using exotic germplasm. Sixty breeding lines of introgressed exotic germplasm backgrounds, selected for high yield, were grown in three tropical and temperate locations and analyzed for starch thermal characteristics and RS levels. Although actual values for all starch characteristics were within normal levels, most characteristics had significant genotypic effects, and all had significant location effects. Thermal properties of retrograded starch were more influenced by the environment than the thermal properties of raw starch, making retrograded starch traits more heritable than raw starch traits. This suggests that a breeding strategy based on retrograded starch traits will have a better chance of success than a breeding strategy based on raw starch traits. A significant genotype effect for RS levels indicates that genotypic selection to raise the level of RS and increase the healthful aspects of corn food should be successful. Significant location effects indicate that breeders using winter nurseries to accelerate their breeding progress need to be careful when making selections using RS data collected on seed grown in the tropics. A small but highly significant correlation between RS and some thermal characteristics, especially percentage of retrogradation, indicates that we may be able to select promising genotypes for RS selection based on our extensive database of thermal characteristics collected on a wide number of diverse corn lines.

Resistant Starch: Promise for Improving Human Health

“…Environment. The field production environment has an impact on starch thermal properties (32) and starch digestibility (33). This effect may be a consequence of environmental conditions such as temperature altering the activity of starch biosynthetic enzymes (34).…”

“…Additional genetic variation occurs within botanical sources because of allelic variation in starch biosynthesis genes. In commercial maize varieties, for example, there is little variation in resistant starch levels, but exotic germplasm contains substantial variation in resistant starch content (33,35).…”

Health effects of resistant starch

“…Other factors that affect the resistance of starch include the size and type of starch granules; the physical form of grains and seeds; plant genotype and mutations [genetic engineering can be used to increase RS content (Wei et al 2010;Carciofi et al 2012)]; crop-growing location; associations between starch and other food components [i.e. lipids, proteins, sugars, gums, other fibre types and plant bioactives that inhibit a-amylase (Lochocka et al 2015)]; and food processing methods such as milling, cooking, annealing (physical modification of starch in water at temperatures below gelatinisation), high-pressure processing, autoclaving, cirradiation, extrusion and storage time (Seneviratne & Biliaderis 1991;Englyst et al 1992;Muir & O'dea 1992;Chung et al 2009;Chung & Liu 2010;Rohlfing et al 2010;Singh et al 2010;Pollak et al 2011;Linsberger-Martin et al 2012;Dundar & Gocmen 2013). Grinding of grains during processing can reduce RS1, due to the breakdown of cell walls, and cooking starchy foods in water can lead to gelatinisation, which reduces resistance to digestion.…”

Influence of genotype and environmental adaptation into the maize grain quality traits for nixtamalization

“…Pixley and Bjarnason (2002) reported the higher stability of tryptophan concentration in protein and protein concentration in grain compare to field yield. Crop management practices and locations have been previously reported to affect protein and starch content in maize kernels and therefore affect kernel hardness (Cirilo et al, 2011;Pollak, Scott, & Duvick, 2011). In fact, higher nitrogen input increases the concentration of zeins and affects the protein: starch ratio in the endosperm leading to hard kernels (Narvaez-Gonza´lez et al, 2006;Singletary, Doehlert, Wilson, Muhutch, & Below, 1990).…”