Dry and Wet Milling of Red Cowpea

Abstract

Red cowpea flours, starch and protein were prepared using dry and wet processing methods. At optimum condition, dry dehulling with an abrasive dehuller gave 75% yield of dehulled seeds with 30% hull remaining and 18% cotyledon loss compared with 70% yield, 2% hull remaining and 20% cotyledon loss from wet dehulling of soaked seeds (8–10h at 30°C) using a stone mill with 3.5mm clearance. There was little difference in chemical composition between flour made from either dry or wet dehulled seeds. Double air classification of dry-dehulled flour produced starch and protein fractions with separation efficiencies of 94.0 and 72.6%, respectively. This resulted in 61.5% yield with 94.0% recovery for starch and 38.5% yield with 72.6% recovery for protein. Fat, minerals, dietary fiber, sugars and damaged starch were air classified along with the protein fraction. Wet processing of whole seeds produced starch with an average yield of 34.1% with 75.4% recovery and protein isolate with an average yield of 19.4% with 63.8% recovery. No damaged starch was found in starch isolated by wet process.