Submitted to: Cereal Chemistry
Grain sorghum is a highly water and nutrient efficient cereal grain that has potential to an important feedstock for bio-fuels production. Starch content in grains is a key component of ethanol fermentation, but at least in sorghum, proteins also play a role in governing fermentation efficiency. To test the hypothesis that kafirin (prolamin) seed storage proteins specifically influence the efficiency of biofuel production in sorghum, ten diverse genetic lines with allelic variation in the β-, γ- and δ kafirins, including three β-kafirin null mutants, were tested for ethanol conversion and fermentation efficiency. Our selected lines showed wide variation in grain biochemical features such as total protein, starch and free amino acid (FAN) content. Starch content and protein digestibility were positively correlated to overall ethanol yield and an increased FAN content enhanced fermentation efficiency.
Investigation of the impact of kafirin on ethanol production indicated that variation in the β-kafirin allele is correlated to grain digestibility and FAN, with subsequent negative effects on ethanol yield. A large seeded variety, carrying a novel γ-kafirin allele, was rich in FAN and exhibited excellent short term fermentation efficiency, but produced a low overall ethanol yield predominantly due to low starch content. RP-HPLC profiling of the alcohol-soluble kafirin protein fraction in the seed endosperm revealed a significant relationship between a specific protein peak and grain digestibility, providing further evidence for direct links between seed protein composition and end-uses such as digestibility and bioethanol production.
Originally published by CGAHR Research Kernels October 2013
Contact Scott Bean, telephone 785-776-2725, email Scott.Bean@ars.usda.gov