Retention of Micro-minerals and Degradation of Anti-nutritional Compounds during the Traditional Rwandan bean Cooking Process

Abstract

Objectives: Beans, Phaseolus vulgaris L., is an important dietary source for micro-minerals. The study objective was to determine retention of micro-minerals and degradation of anti-nutrients during traditional Rwandan bean cooking process. Methods: Four batches of carioca bean variety were studied. Batches coded pink and white were cooked without soaking. Batches coded blue and green were cooked after soaking for 8 hours. A portion of cooked beans were fried. Minerals (Ca, Mg, Cu, Fe, K, Mn, P, Se and Zn) were quantified using inductively coupled plasma atomic emission spectroscopy. Total polyphenols were determined spectrophotometrically based on Folin-Ciocalteu reagent. Phytic acid was determined by HPLC method.  Results: Retention of iron was 78.1, 83.8 and 92.7% in white, blue and green batches of beans, respectively after cooking. Iron loss during soaking ranged from 1.8 to 4.8 mg/Kg. Retention of most minerals after cooking were greater than 90%. Boiling of beans reduced total phenolic content by over 50%. Phenolic content of fried beans was significantly (P ≤ 0.05) higher than in boiled beans due to addition of spices during frying. Soaking did not significantly (P ≥ 0.05) reduce the phytic acid contents of the beans. Reductions in phytic acid contents after boiling were; 5.8, 29.2, 29.5 and 51.2% mg/kg for bean batches coded pink, green, blue and white respectively. Conclusions: Cooking process used in this study resulted into greater retention of iron and zinc and a markable decrease in concentration of anti-nutritional compounds (phytic acid and total polyphenols).