Effect of processing on some properties of cowpea (Vigna unguiculata), seed, protein, starch, flour and akara

Abstract

Large brown eye Kano white cowpea (Vigna unguiculata) seeds were processed into three batches of flour by wetting, drying individually at 30, 80, and 120°C, decorticating and dry milling. Starch was extracted from the cowpea seed and protein from the flour using water as solvent. The water-extractable proteins were purified by dialysis and analysed by electrophoresis. The cowpea flour was used to produce akara balls (fried paste). The microstructure of the cowpea cotyledon, flour, starch and akara crumb were examined with a scanning electron microscope (SEM). Electrophoretic separation revealed that some of the protein fractions from the sample extracted from 30°C dried cowpea were absent in the sample extracted from the 80°C and 120°C dried cowpeas or their quantities had decreased. In the SEM study, no difference was observed in the microstructure of the three flour samples except in the size and shape of the starch granules and particles of protein and cell wall material. The starch granules from the cowpea dried at 120°C had surface defects. Cavities occurred in the cotyledons of the 80 and 120°C dried cowpea seeds, some starch granules, protein matrix and sometimes the entire cell contents were lost from the cell. The protein sheet in the akara crumb became thicker as temperature increased to 80 and 120°C.