Effect of starch properties and zein content of commercial maize hybrids on kinetics of starch digestibility in an in vitro poultry model

The kinetics of starch digestion is a key determinant of poultry performance. Research so far has shown that starch digestibility kinetics depends on the molecular structure of starch but also on the properties of the complex matrix in which starch granules are embedded in most feedstuffs. However, the manner in which genotype differences in the same plant affect starch digestibility kinetics has not yet been addressed. The present study explored the extent to which the starch digestibility rate in commercial high-yielding maize hybrids depended on amylose / amylopectin content, starch granule size and shape, and zein in total starch (TS) content.Hybrids differed in all the traits examined, giving the following ranges: amylose content, 165-207 g kg-1 DM; zein in TS content, 70-89 g kg-1 DM; starch granule equivalent diameter, 11.5-12.3 μm, and in vitro starch digestion rate, 1.22-1.44 h-1 . The starch digestion rate correlated negatively with zein in TS content (r = -0.36) and positively with equivalent diameter (r = 0.45). The negative correlation between starch digestion rate and zein in TS suggests that some zein remained after grinding and pepsin incubation and acted as a barrier to amylolytic enzymes.When starch granules are embedded in a complex protein matrix, zein limits their accessibility to enzymes and affects the starch digestibility rate. Surprisingly, our results suggest that when enzymes reach starch granules, they digest a greater proportion of the starch when the granules are larger. © 2019 Society of Chemical Industry.