CHARACTERISATION AND FUNCTIONAL PROPERTIES OF FLOUR AND PROTEIN ISOLATED FROM GERMINATED SOLOJO COWPEA Vignaunguiculata (L.) WALP

Abstract

The increasing world population has led to shortage in protein supply which necessitated the quest for new protein sources, particularly from legume. Legumes, naturally do not possess suitable functionality for application in food industry.To improve functionality, different methods of modification (physical, chemical, enzymatic) have been utilised by researchers though withsome limitations. However, the use of germination has not been fully explored especially for underutilised Solojocowpea. Therefore, the aim of this study was to evaluate the potential of germination in improving the nutritional and functional properties of flours and proteins isolated from Solojo cowpea.

Two varieties of cowpea, Dark-Ash Solojo (DAS) and Brown Solojo (BS) were bought from Bodija Market in Ibadan, cleaned and divided into six portions. The DAS and BS were soaked in distilled water and germinated for 0,6, 24, 36, 48 and 72hrs. The treated samples were dehusked, dried, milled into flour and defatted. Protein was isolated by isoelectric precipitation method. Proximate, antinutritional analysis and functional properties [Water Absorption Capacity (WAC), Oil Absorption Capacity (OAC)] of the flours and protein isolates were determined by standard methods. Amino acids and molecular weight of the protein isolates were determined by amino acid analyser and sodium-dodecyl-sulphate-polyacrylamide-gel-electrophoresis. Surfacemorphology, 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 DASranged 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. Germination reduced the values of all the parameters except protein content which increased significantly with time, thus indicative of more available proteins.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. Germination reduced trypsin inhibitor from 5.84 to 3.80mg/100g; 7.37 to 0.60mg/100g and phytate from 34.61 to17.22mg/100g and 36.80 to 14.09 for DAS and BS, respectively.The WAC increased from 0.90 – 4.14 g/g for both varieties while OAC decreased from 0.81 to 0.70g/gfor DAS, but increased from 0.70 to 0.77g/g for BS. Methionine content increased with germination from 0.75 to 1.15g/100g (DAS) and 0.78 to 1.22g/100g (BS). The molecular weight profile showed that the higher molecular weight proteins disintegrated during germination into short chain peptides from 102-17 kDa. This was corroborated by the surface morphology for the two protein isolates. The C=Ostretch (1657cm-1), N-Hstretch(3350 cm-1) and C-Nbend(1241cm-1), typical of proteins were identified from thespectrum. The protein isolates from both varieties had thermal stability from 305 to 320oC

Germination improved the nutritive and functional properties of the flour and protein isolates of Dark-Ash and Brown Solojo. Therefore, germinated Solojo cowpea can serve as alternative sources of protein for the food industry.