IMPROVEMENT OF PEARL MILLET (Pennisetum glaucum (L.) R. BR) PROLAMIN EXTRACTABILITY: CHROMATOGRAPHIC SEPARATION, CHARACTERIZATION AND FUNCTIONAL PROPERTIES

Abstract

Pearl millet is a gluten free cereal resistant to drought, diseases and pests. The major protein fraction in pearl millet is prolamin the alcohol soluble fraction called pennisetin. Researches on the factors affecting pennisetin extraction and on its functional properties are still very scant. In this paper, the effect of temperature, reducing agents (β-mercaptoethanol, dithiothreitol or sodium metabisulfite) and sodium hydroxide on pennisetin extraction was assessed. Samples were characterized by protein and amino acid (AA) analysis, SDS-Page and reversed phase high-performance liquid chromatography (RP-HPLC). Pennisetin was extracted with high protein purity (90.1%) from pearl millet grain flour (PMF) using 70% aqueous ethanol containing 1% sodium metabisulfite and 0.2% sodium hydroxide at 60°C. SDS-Page confirmed pennisetin extraction and showed three subunits corresponding to the 27-, 22- and 12 kDa-pennisetins. The percentage of essential amino acids in pennisetin (68.55%) was higher than that in PMF (41.64%). The hydrophobic character of pennisetin was confirmed by the presence of 45.49% of hydrophobic amino acids. Functional properties of pennisetin and PMF were investigated. Compared to PMF, pennisetin exhibited comparable oil and water binding capacities and higher foaming capacity and emulsifying activity index but with lower emulsion stability. Pennisetin functional properties were similar or lower relatively to common used proteins of wheat, sorghum, rice or peanut. Excluding water, oil binding and foam capacities, all the functional properties of pennisetin and PMF were significantly different (p≤0.05).The findings suggest increasing the use of pennisetin and PMF as nutritional and health promoting agent for vegans and celiac patients.