Effect of Milling and Particle Size on Functionality and Physicochemical Properties of Cowpea Flour

Abstract

ABSTRACTCowpeas (Vigna unguiculata) were milled through 0.5‐, 1.0‐, and 2.0‐ mm screens, and the flour was subsequently separated into different particle‐size ranges. Such procedures caused only minimal changes in moisture, fat, protein, ash, and total carbohydrate. The amount of extractable starch, however, varied from 34.5 to 52%. The effects of both mill screen and sieve mesh size were significant (P < 0.05). Differences in milling and separation procedures resulted in significant variations in water absorption (0.41–2.81 g of water/g of flour), solids lost (0.34–1.17 g/g of flour), and protein solubility (21.2–37.4%) (P < 0.05). Finely milled flours (91% moisture) had lower initial gelatinization temperatures (70–73°C), as measured by differential scanning calorimetry (DSC) (P < 0.01). Gelatinization peaks in high‐moisture flour were similar to that of pure starch. At lower moisture, a second peak was observed indicative of protein. Light‐scattering analysis showed that different conditions produced a bimodal particle‐size distribution when samples were suspended in water. The small size had relatively constant diameters (19–21 μm) and was associated with starch granules. The latter had a large size distribution and varying peak size and was associated with aggregated flour particles. These results indicate that changes in processing produces cowpea flours with differing chemical and physical properties.