FORMULATION AND CHARACTERISATION OF FUNCTIONAL BISCUIT FROM ORANGE-FLESHED SWEET POTATO AND OKARA COMPOSITE FLOUR

Abstract

ABSTRACT Unhealthy eating habits and lifestyles are predisposing factors to risks of non-communicable diseases (NCDs). Functional foods contains health promoting properties or prevent diseases beyond providing nutrients. The consumption of varieties of functional foods could reduce the prevalence of NCDs. The objective of this study was to formulate and characterise functional biscuits from indigenous food crops;namely, orange-fleshed sweet potato (OFSP) and okara (OKR). Simplex lattice mixture design was used to generate eight experimental runs to investigate the effect of flour blends formulation (80-90% OFSP and 10-20% OKR) on some quality attributes of the flour blends and biscuits. The flour blends were analysed for moisture (MC), protein (PC), fat (FC), ash (AC), fibre (FIB), carbohydrate (CH), DPPH free radical scavenging ability (DPPH), total phenol (TP), total flavonoid, total dietary fibre (TDF), total carotenoid (TC), phytate (PHY), saponin (SAP), trypsin inhibitor activity (TIA), potassium (k), iron (fe), phosphorus (p), calcium (ca), bulk density (BD), water absorption capacity (WAC), oil absorption capacity (OAC), emulsification capacity (EC), and protein solubility (PS) using standard laboratory procedures. The biscuits were analysed for proximate composition, physical properties and overall acceptance. Data from experimental runs were analysed using one way ANOVA, regression model and numerical optimisation. The nutritional and anti-nutritional analyses as well as texture profile analysis, colour analysis and quantitative descriptive sensory tests were conducted on the optimised biscuit sample. The range of mean values of MC, PC, FC, AC, FIB and CH were 6.61-6.93%, 8.79-12.32%, 2.44-3.60%, 2.47-2.60%, 5.33-8.16% and 66.74-74.00% respectively. Mean values of k, fe, p, ca were 240.30-246.60 mg/g, 11.83-12.60 mg/g, 76.12-107.14 mg/g and 52.65-70.88 mg/grespectively while those of DPPH, TF, TP, TC, TDF, SAP, PHY, TIA were 87.93-90.77%, 28.36-30.72 mg/g, 33.61-34.59 mg/g, 49.95-56.25 mg/g, 8.22-13.86%, 5.69-6.40 mg/g, 30.69-34.46 mg/g and 1.90-2.78% respectively. Range of mean values of OAC, WAC, BD, EC and PS ranged from 92.00-110.33%, 177.00-188.00%, 0.620-0.690 g/ml, 5.93-6.50% and 1.17-1.40% respectively. Interaction between OFSP and OKR significantly (p<0.05) influenced the FIB, PC, CHO, P, CA, SAP, PHY, DPPH and TDF levels in the flour blends. Interaction between OFSP and OKR significantly (p<0.05) influenced biscuits overall acceptance. Numerical optimisation techniques were used to obtain the optimum flour blend (82.595% OFSP and 17.405% OKR) with a desirability of 0.520. The optimized OFSP ­ OKR biscuit had PC and energy value of 16.40±0.23% and 357.03±2.83kcal respectively. The DPPH, TF, TP, TC, TDF were 90.09±0.04%, 30.15±9.81 mg/g, 33.90±6.06 mg/g, 49.57±0.78 mg/g, 12.40±1.44% while SAP, PHY, TIA were 5.87±0.01 mg/g, 26.69±2.62 mg/g and 2.44±0.02% respectively. The textural attributes of the optimised OFSP - OKR biscuit were hardness (16717.00±1043.58 N), stringiness (0.61±0.02 mm), adhesiveness (3.11±1.37 J), springiness (0.61±0.02), resilience (3.11±1.37 J), chewiness (6353.33±719.45 N) and cohesiveness (0.63±0.01). The descriptive sensory profile of the optimised OFSP - OKR biscuit revealed intensity scores (7.20 - 8.43) for golden brown, sweet taste and aroma. In conclusion, biscuit from the optimum ratio of OFSP – OKR had a high sensory acceptance and its chemical and antioxidant properties validate its potential as a functional biscuit.