1696
Relationship of in vitro starch digestion to corn kernel measurements from farms in Michigan
With mature grain, increased kernel vitreousness and prolamin content reduce in vitro starch digestion. Does this apply for grain harvested at corn silage maturity? To answer this question, samples of whole plant corn silage and shelled grain from 5 Pioneer hybrids at silage harvest were gathered from 15 environmentally diverse locations in Michigan in 2013. Starch availability (7 h in vitro starch disappearance) and nutrient composition were evaluated at a commercial laboratory; vitreousness was appraised as kernel specific gravity by gas displacement. Impacts of hybrid and location on nutrient composition, starch availability, and vitreousness were evaluated by GLM procedures of SAS. Differences (P < 0.01) among hybrids were noted for DM, CP, fat, starch, and pycnometer density, and for starch availability (P < 0.02). Farm of origin also had an impact (P < 0.02) on every component except NDF content of grain. Across all samples, prolamin content was not closely related to in vitro starch availability (r = -0.06; P = 0.63) but increased as CP content of grain increased (r = 0.74; P < 0.01). Among all measurements, in vitro starch availability was predicted best but still poorly (R2 = 0.17) by the equation: Starch availability = 38.33 – 0.124 x grain DM + 0.585 x grain starch percentage. As harvest DM increased, specific gravity and prolamin content tended (P < 0.10) to increase. Starch availability decreased as kernel specific gravity increased (P < 0.05). Perhaps because of its high dependence on kernel protein content, prolamin content was not closely related to starch availability of grain samples harvested when corn silage was harvested. Had all grain samples had been obtained from fields equal in N fertility, the relationship of prolamin to starch availability likely would have been closer. The range in starch digestibility among these silage hybrids was less than half the range among farms (2.9 versus 6.3 percentage points); this questions the accuracy of predicting starch availability from hybrid genetics alone. Low in vitro starch digestion of dry vitreous hybrids may reflect high prevalence of larger particles from dry coarsely ground grain although other factors (e.g., fine grinding, fermentation) also will impact on in vivo starch availability.
Keywords:
Prolamin, starch digestion, vitreousness