Effect of boiling, pressure cooking and germination on the nutritional and antinutrients content of cowpea (Vigna unguiculata)

Abstract

The study was conducted to investigate the effect of boiling, pressure cooking and germination on the proximate, nutrients, amino acids and anti-nutrients content of cowpea (Vigna unguiculata). The results showed that the germinated cowpeas (GMC) had the highest value of crude protein (22.89%), crude fat (3.81%) and crude fibre (2.10%) followed by raw cowpeas (RWC) and pressure cooked cowpeas (PCC) while boiled cowpeas (BDC) had the least. There was comparable value of ash content in all the samples except for BDC with the least. Boiling had significantly higher moisture content than others. Carbohydrate value ranged from 57.21 to 58.13% for GMC and BDC, respectively and 59.69 to 59.74% for RWC and PCC, respectively. Comparable calorific value of GMC and BDC was significantly higher than that of PCC and RWC. The decreasing order of anti-nutrient factors in treated cowpeas is: GMC > RWC > PCC > BDC. This result inferred that boiling is an adequate processing for drastic reduction of the anti-nutrient factors (phytate, tannin, trypsin inhibitor and total phenol) in cowpeas. On the other hand, germination had increased the amount of methionine, lysine and tryptophan by 10.94, 18.89 and 20.90%, respectively, while the pressure cooking and boiling had mild losses of methionine, lysine and tryptophan. Similarly, germination had increased the amount of macro elements (0.0036 mg/kg for Na, 0.024 mg/kg for K, 0.021 mg/kg for Ca, 0.037 mg/kg for P, and 0.022 mg/kg for Mg) while boiling and pressure cooking had decreased the amount of these macro elements compared with the raw sample. Heat treatments (boiling and pressure cooking) recorded decreased level of micro elements (Fe, Zn, Cu, Mn) while germination had increased the micro elements by 4.66, 3.78, 13.85, and 6.38% for Fe, Zn, Cu, and Mn respectively. Therefore, it could be concluded that the heat treatments (boiling and pressure cooking) had significantly reduced that anti-nutrient factors in cowpeas but germination (sprouting) had excellent nutritional qualities. Future research work should be carried out on combination of heat treatment with germination to reduce the anti-nutrient factors in grain legumes. Key words: Cowpea, antinutritional factors, nutritional composition.