Pasting Properties of Cowpea Flour: Effects of Soaking and Decortication Method

Abstract

Pasting properties of flour prepared from 12 diverse cowpea varieties as affected by dry and wet decortication processes were determined using a Brabender viscoamylograph. Dry decorticated flour (DDF) was prepared from seeds wetted, dried, and mechanically dehulled; wet decorticated flour (WDF) was prepared from seeds soaked, manually decorticated, dried, and milled to flour. No pasting peak was obtained during heating of flour slurry to 95 °C for both DDF and WDF for all cowpea varieties. WDF samples had higher paste viscosities than DDF samples. Presoaking of seeds (2, 4, 8, or 16 h) affected paste viscosities, especially hot paste viscosity (HTPV), and particle size distribution. Maximum HTPV and highest quantities of medium-size particles (mesh 40−80, 0.42−0.177 mm) were attained with flour prepared from seeds presoaked for 4 h. Presoaking for more than 4 h did not yield further increase in HTPV. Cowpea flour with at least 65% of medium-size particles exhibited the best hydrothermal properties, leading to increased rate of moisture absorption and higher HTPV during aqueous heating of slurry. Keywords: Cowpea (Vigna unguiculata) flour; pasting properties; presoaking; decortication