Optimization of formulation for the production of nutrient enhanced flour from orange-fleshed sweet potatoes, grain amaranth, biofortified bean and maize flour

Instant composite flours are preferred by consumers due to their convenience in preparation and longer shelf life. Extrusion cooking is one of the recent technologies reported to improve nutrient content of instant flours. However, there is sparseness of information regarding use of extrusion cooking in production of OFSP-based composite flour. The aim of this study was to develop and optimize a formulation for the production of nutrient enhanced OFSP-based composite flour containing grain amaranth, biofortified beans, and maize flour. Extrusion cooking was carried out using a twin-screw extruder at a barrel temperature of 60, 120 and 150℃, screw speed of 350 rpm and feed moisture of 5%. Response surface methodology (RSM) was used to optimize product formulation. The variables were OFSP (20-68%), maize (0-30%), biofortified bean (20-40%), and grain amaranth (10-30%), The response variables considered were protein, beta-carotene, iron and zinc contents and viscosity. Special cubic models were found to adequately represent the relationship between dependent and independent variables. Models for the prediction of these values in raw and extruded flours for protein, beta carotene, iron, zinc and viscosity had R2 values between 0.93-1.00, with non significant lack of fits (p < 0.05). Four optimal formulations were selected from optimization results, two from each treatment. The first optimal formulation (RF1), in raw composite flour constituted OFSP 37.8%, bean flour 32.2% and grain amaranth flour 30.0% with response values of protein content 17.67%, beta carotene content 1.27 mg/100 g, iron content 2.12 mg/100 g, zinc content 1.16 mg/100 g and viscosity 555.56 cPs with a desirability value of 0.8. The second optimal formulation (RF2) in raw composite flour constituted OFSP 20.0%, maize flour 30.0%, bean flour 40.0% and grain amaranth flour 10.0% with responses predicted for optimization of protein content 17.17%, beta carotene 1.36 mg/100 g, iron 2.55 mg/100 g, zinc 2.81 mg/100 g and viscosity 908.71 cPs with a desirability value of 0.7. The first optimal formulation (EF1) in extruded composite flours constituted OFSP 46.6%, bean flour 36.9% and grain amaranth flour 16.5% with response values of protein 16.79%, beta carotene 0.88 mg/100 g, iron 2.57 mg/100 g, zinc 1.23 mg/100 g and viscosity 34.7 cPs and desirability of 0.8 whereas the second optimal formulation constituted OFSP 49.0%, maize flour 5.9%, bean flour 35.1% and grain amaranth flour 10.0% with response values of protein 15.28%, beta carotene 1.01 mg/100g, iron 2.17 mg/100 g, zinc 1.35 mg/100 g and viscosity 37.56 cPs with a desirability value of 0.7. There were significant (p<0.05) differences in moisture, protein, dietary fibre, ash, fat, carbohydrates and gross energy. The moisture content and crude fat decreased from 7.72 to 5.84% and 5.65 to 2.30%, respectively. The crude protein, dietary fibre, ash and carbohydrates increased from 15.45 to 18.16%, 0.46 to 4.04%, 1.39 to 3.81% and 79.02 to 86.87%, respectively, whereas the gross energy varied between 427.74 and 437.75 kcal. The peak, trough, breakdown, final and setback viscosities varied significantly (p<0.05) from 125.33-2449, 17.0-1362.33, 6.67-1083.33, 33-4056 and 15.33-2686 RVU, respectively. The phytochemical content ranged between 167.8 to 537.37 mg GAE/100 g phenolics, 137.45 to 376.63 mg VCE/100 g total antioxidants, 0.31 to 5.76 mg QE/g flavonoids, 14.81 to 97.51 mg CatE/100 g tannins and 1.61 to 1.74 mg/100 g phytates. The developed OFSP-based composite flours were found to be nutritionally superior to commercial flour.