Efficient procedure for extracting maize and sorghum kernel proteins reveals higher prolamin contents than the conventional method

A new method to separate maize proteins into zein (prolamin) and nonzein classes was used to quantitatively measure the prolamins (zein and kafirin) and nonprolamins in five maize and sorghum genotypes. Some 90-95% of protein was extracted using a pH 10 buffer containing 1% sodium dodecyl sulfate and 2% 2-mercaptoethanol. Ethanol or t-butanol was added to the maize and sorghum extracts at 70 or 60%, respectively, to precipitate nonprolamin proteins; those remaining in solution were prolamins. The amount of protein in these fractions was compared to that obtained with the conventional Landry-Moureaux method which uses aqueous alcohol plus 0.6% 2-mercaptoethanol as the extraction solvent. Using this new method, zein contents of 50-60% of total protein were found for maize whole grain flours, with 62-74% zein endosperm alone. Kafirin contents were 68-73% in sorghum whole grain flours, and 77-82% in sorghum endosperm. Prolamin nonprolamin fractions were judged to be pure based on SDS-PAGE. Zein contents determined by the new method were between 5-12% higher than those obtained by the conventional procedure; kafirin contents 12-22% higher. This new method provides a highly reproducible, accurate procedure for determining the content of prolamin and prolamin proteins. Yet it is simpler and faster than the convent fractionation method.