ABSTRACT

This study was conducted to investigate the effects of substitution of wheat flour with three underutilised legumes and soybean flours on the pasting and physicochemical properties of the composite flour blends and biscuit crackers. Nine blends were prepared by homogenously mixing wheat, soybean and one of the three underutilized legumes in the proportion of 50:20:30, 40:20:40, 60:20:20 (for African yam bean); 40:10:50, 40:20:40, 60:10:30 (for Bambara) and 60:10:30, 40:20:40, 50:10:40 (for pigeon pea). 100% wheat flour served as control. Functional and pasting properties of the composite flour produced from wheat, soybean and three underutilized legumes (African yam bean, Bambara groundnut and pigeon pea) as well as physical, chemical and sensory properties of the cracker biscuits were determined using standard methods. There were significant differences (p<0.05) in the functional and pasting properties of the composite flours. Wheat-soy-legume composite flours showed decreased bulk density, oil and water absorption capacities, while swelling index, gelation time, foam and emulsion capacities increased  with increase in addition of legume/soy flour. The peak viscosity, trough and final viscosity values of the composite flour samples were lowest in AYA (50 % wheat: 20 % soybean: 30 % African yam bean) and highest in BMC (60 % wheat:10 % soybean:30 % Bambara)  ranging from 145.12RVU to 174.75RVU in BMC, 89.32-120.64RVU and 110.67-263.88RVU respectively. The result indicated that the flour blends had lower peak viscosity, trough, final and set back viscosity than the control (p<0.05). The composite flour crackers were significantly higher (p<0.05) in protein, ash, fat and fibre components than control (wheat) crackers. Addition of legume/soybean flour to wheat flour increased the protein (13.00 - 20.91 %), fat (5.0 -7.3 %), ash (1.98- 2.35%), crude fibre (2.52 -3.32 %) and energy value (377.73 - 409.08 kcal), while moisture and carbohydrate contents decreased in the composite flour biscuit cracker samples compared to control. Significant differences (p<0.05) were found in the physical dimensions of the composite flour crackers. Higher values were observed for thickness (0.61-0.78 cm), diameter (2.26-3.90 cm), weight (4.52 – 7.72 g) and spread ratio (33.73-61.97) of the crackers from flour blends compared to control with increased addition of legume/soy flour. Cracker samples showed varied degree of acceptability in terms of texture, colour, taste, odour and overall acceptability (p<0.05) compared to control. Mean sensory scores of all sensory attributes for AYC crackers (60 % wheat: 20 % soybean: 20 % African yam bean) were similar (p>0.05) to 100 % wheat crackers. The study concluded that substitution of wheat flour with legume flours up to 40% produced cracker biscuits with improved nutritional and acceptable sensory qualities. This result if widely explored, will enhance the utilization of these underutilized legumes.