Factors Affecting Protein Extraction from Cowpea

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Mohamed, Mona Ibrahim Abd Alla
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Cowpea proteins were extracted using distilled and tap water; NaCl (0.5 and 1.0M); NaOH (0.01, 0.1 and 1.0N), 70% ethanol, and phosphate buffer (0.4 ionic strength) at pH 7.0 for different extraction times (30, 60, 90,120 and 150 min.) with different flour to solvent ratios (1:25, 1:20, 1:15, 1:10). Maximum protein extractability was 81% for tap and distilled water and 76, 78% for 0.5 and 1.0 M NaCl, respectively and were 91, 78 and 5% for 0.01M NaOH, phosphate buffer (0.4 ionic strength) and 70% ethanol, respectively. There were no significant differences between % of protein extracted by different molarities of NaOH (0.01, 0.1 and 1.0M). Minimum protein extracted was obtained using 70% ethanol. Optimum extraction time varied with solvent nature; it was 30 min. for water and phosphate buffer, 90 min. for 70% ethanol and 150 min. for NaCl and NaOH. The original non- protein nitrogen (NPN) of cowpea was found to be 3.2% and it increased to 15.5, 6.5, 16.5 and 10.2% by extraction with water , 0.5M NaCl , 0.01 NaOH and phosphate buffer (0.40 ionic strength) , respectively. This value decreased to 2.9% when 70% alcohol was used for extraction. There were no differences between magnetic and mechanical stirrers efficiency. Defatting the cowpea did not improve the efficiency of protein extractability. The nitrogen solubility of cowpea flour was (94.8% at pH 11, 56% at pH 1).The minimum nitrogen solubility (11%) was observed at isoelectric pH (4).
University of khartoum