Influence of traditional processing methods on the nutritional composition of lack turtle bean (Phaseolus vulgaris L.) grown in Nigeria

Investigating the effect of different processing methods on nutritional composition of a lesser known crop (black turtle bean) was carried out with a view to providing adequate information towards effective utilization of this crop in various food applications in Africa and other parts of the world. The seeds of black turtle bean (Phaseolus vulgaris L.) were collected from Bokkos town of Plateau State, Nigeria and processed into raw dried, boiled, cooked, roasted, sprouted and fermented flours. Proximate, mineral and amino acid compositions were investigated using standard analytical techniques. The processing methods showed deviations in nutrients from the raw seeds. Crude protein was found to be enhanced by cooking (13.5%), roasting (4.64%) and sprouting (14.35%) methods while all the processing methods were found to reduce the contents of crude fat, fatty acids and metabolizable energy. Processing significantly (p 0.05) affected the content of some minerals in Phaseolus vulgaris seeds. All the processing methods (boiling, cooking, roasting, sprouting and fermenting) increased magnesium, zinc and manganese contents by 44.16, 121.43 and 130.00%; 25.85, 100.00 and 150.00%; 35.54, 74.83 and 70.00%; 31.76, 107.14 and 110.00%; 31.28, 128.57 and 120.00%, respectively whereas sprouting decreased calcium and iron contents by 14.26 and 4.76%, respectively. Generally, raw and processed Phaseolus vulgaris seeds were found to be good sources of essential minerals and harmful lead was not at the detectable range of AAS. The amino acid profile revealed that all the processing methods increased the concentrations of total amino acid (TAA) while only cooking and roasting methods increased the concentrations of total essential amino acid (TEAA) with histidine by 1.46 and 1.95% compared with the raw value. The limiting amino acids (LAA) for both the raw and processed samples were either Met + Cys, Ile or Val. Sufficient proportions of the essential amino acids were retained after processing of the black turtle bean (Phaseolus vulgaris) to meet FAO/WHO dietary requirement.