African yam bean hull chemical composition and its effects on rat's mineral retention, serum biochemical components and enzymatic activities.

The influence of yam bean hull on rat's mineral metabolism, serum composition and enzymatic activities was investigated. The chemical composition of the bean's hull shows a reasonably high crude protein (11.4%) but very low contents of crude fat (2.6%), phytic acid (82 mg/100 g) and phytin-phosphorus (23 mg/100 g). K and Ca are the major minerals present in yam bean hull. The hull, rich in cell wall polysaccharides, is composed of cellulose (35.4%), non-cellulose fractions made of pectin and hemicellulose put together (41.9%) and lignin (3.6%). The growth and feed conversion efficiency of rats fed yam bean hull diet were significantly better than rats fed pure cellulose and cellulose-free diets. Conversely, the metabolizable energy of yam bean hull diet (16.4 MJ/kg) was significantly (p < 0.05) lower than that of either cellulose-free (17.8 MJ/kg) or pure cellulose diet (17 MJ/kg). The retention of the minerals examined, except for Ca, was lower when the hull was included in diet as compared to the control (fibre-free) diet. The fibre containing diets decreased serum cholesterol, glutamic oxaloacetate transaminase (SGOT) and glutamic pyruvate transaminase (SGPT). Yam bean hull had no effect on packed cell volume and serum total protein.