Abstract
Increases in the proportion of amylose in the starch of wheat grains result in higher levels of resistant starch, a fermentable dietary fiber associated with human health benefits. The objective of this study was to assess the effect of combined mutations in five STARCH BRANCHING ENZYME II (SBEII) genes on starch composition, grain yield and bread-making quality in two hexaploid wheat varieties. Significantly higher amylose (∼60%) and resistant starch content (10-fold) was detected in the SBEII mutants than in the wild-type controls. Mutant lines showed a significant decrease in total starch (6%), kernel weight (3%) and total grain yield (6%). Effects of the mutations in bread-making quality included increases in grain hardness, starch damage, water absorption and flour protein content; and reductions in flour extraction, farinograph development and stability times, starch viscosity, and loaf volume. Several traits showed significant interactions between genotypes, varieties, and environments, suggesting that some of the negative impacts of the combined SBEII mutations can be ameliorated by adequate selection of genetic background and growing location. The deployment of wheat varieties with increased resistant starch will likely require economic incentives to compensate growers and millers for the significant reductions detected in grain and flour yields.
Highlights
Wheat (Triticum spp.) is a major source of carbohydrates for human nutrition, representing nearly 20% of the ingestion of calories worldwide (FAOSTAT, 2015)
High levels of amylose in the starch are associated with increased levels of resistant starch (RS), which is defined as the starch that resists digestion in the small intestine of healthy human individuals
We previously demonstrated that down regulation of five STARCH BRANCHING ENZYME II (SBEII) genes in common wheat led to an increase in the amount of grain amylose (63%) and resistant starch (1057%) (Scho€nhofen et al, 2016)
Summary
Wheat (Triticum spp.) is a major source of carbohydrates for human nutrition, representing nearly 20% of the ingestion of calories worldwide (FAOSTAT, 2015). D-glucose molecules with limited branching (20e30% of the grain starch), whereas amylopectin consists of chains of D-glucose that are highly branched through a-D-(1e6) linkages (70e80% of the grain starch) (Sharma et al, 2008). The linear helical chains of amylose form complexes that limit access and digestion by amylases. High levels of amylose in the starch are associated with increased levels of resistant starch (RS), which is defined as the starch that resists digestion in the small intestine of healthy human individuals. Resistant starch acts as a prebiotic dietary fiber, and plays a beneficial role in human digestive physiology (Sharma et al, 2008). With increased awareness of the impact of diet on human health, many consumers are showing a growing interest in functional foods (Homayouni et al, 2014)
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