Nutritional and functional properties of flour and protein isolates from germinated Solojo Cowpea Vigna unguiculata (l.) Walp.

Abstract

Nutritional and functional properties of flours derived from two (2) varieties of cowpea, Dark-Ash Solojo (DAS) and Brown Solojo (BS) were studied before and after dehulling of the germinated seeds. Ungerminated seeds were used as the control. Protein isolates from dehulled defatted solojo cowpea seeds were prepared using isoelectric (CPIA) procedure. Dehulled samples had a higher protein solubility compared with germinated and control samples. Both varieties of cowpea (DAS and BS) investigated were soaked in distilled water and germinated at varying periods i.e. 0, 6, 24, 36, 48 and 72hrs. Protein isolates were obtained from the treated and processed samples by isoelectric precipitation method which was subsequently followed by proximate and anti-nutritional analyses. Functional properties were also analysed which include Water Absorption Capacity (WAC) and Oil Absorption Capacity (OAC) of the protein isolates using standard methods. Amino acids and molecular weight of the protein isolates were determined by amino acid analyser and sodium-dodecyl-sulphate-polyacrylamide-gel-electrophoresis. Surface morphology, functional group and thermal properties were determined for protein isolates by scanning electron microscopy, Fourier Transform Infrared (FTIR) spectrometry and differential scanning calorimetry, respectively. Data were analysed by descriptive statistics and ANOVA at α0.05. The moisture content, crude protein, crude fat, crude fibre and total ash of DAS ranged from 9.00-11.40, 24.82-31.00, 1.56-2.66, 1.43-1.67, and 3.20-4.14%, respectively; while those of BS flours ranged from 7.10-9.50, 24.90-30.14, 1.17-2.37, 1.06-1.52 and 3.05-3.93%, respectively. The protein contents for DAS were 81.57±0.53, 86.44±0.84, 89.39±1.51, 90.23±0.53, 91.81±0.77 and 94.85±0.86, while for BS were 84.39±0.39, 85.44±0.56, 90.05±0.10, 90.47±0.89, 92.78±0.28 and 95.81±0.19% for 0, 6, 24, 36, 48 and 72 hrs, respectively. On dehulling, the fat absorption capacities of samples were reduced and the differences were statistically significant. The emulsification capacities of control samples ranged from 50 to 198 ml oil emulsified per gram of sample. On germination and dehulling, the emulsification capacities, activities and stabilities of samples increased significantly. There were increases in foaming capacities and reduction in foam stabilities of the two cowpea varieties investigated on germination and dehulling. Thus, the study showed that germination and dehulling improved the functional properties of the Solojo Cowpea studied.