Maize Kernel Hardness, Endosperm Zein Profiles, and Ethanol Production

Abstract

Maize (Zea mays L.) grain is an important feedstock for the ethanol-producing industry. However, little is known about the optimum grain quality for optimizing ethanol yielding efficiencies. We specifically investigated the response of ethanol yields (L Mg⁻¹) to kernel hardness, and its physiological determinant endosperm zein protein profiles, as affected by genotype selection, field nitrogen (N) fertilization, and crop growth environment. We measured ethanol yield and related this to different kernel hardness indicators, kernel composition, and zein profiles. We also described changes in field ethanol yield (L ha⁻¹), by taking into account the crop yield (Mg ha⁻¹). Hard endosperm genotypes always yielded less ethanol than softer endosperm ones per grain mass (L Mg⁻¹). Higher N fertilization rates increased kernel hardness and decreased ethanol yield (L Mg⁻¹) on soft endosperm dented genotypes but had no effect on hard endosperm ones. Ethanol yield was negatively correlated with kernel density, kernel protein concentration, and Z1 and Z2 zein fractions. Within Z2, 15 kDa β-zein explained the largest ethanol yield variation generated by genotypes, N fertilizations, and growth environments. However, and although these differences were as large as 10%, ethanol field yield (L ha⁻¹) was mainly driven by crop yields (r ² 0.98) due to the large crop yield (Mg ha⁻¹) differences observed across treatments. Together, our results helped describe the magnitude that changes in maize kernel hardness can have over ethanol yield, both through genotype selection or crop management. A particular Z2 zein protein rises as relevant for future genetic manipulations of maize ethanol yield determination.