OPTIMISATION OF FUNCTIONAL PROPERTIES AND QUALITY CHARACTERISTICS OF SORGHUM-BASED FLOUR WITH PLANTAIN AND TIGERNUT FLOURS

Abstract

Sorghum-based flour was enhanced with plantain and tigernut flours to produce composite flour in order to enhance its protein, fibre, minerals, antioxidants, glycemic index and resistant starch contents. The proximate composition and functional properties were optimised using optimal model design of response surface methodology. The independent variables were sorghum flour (70–90%), plantain flour (5.36–20%) and tigernut flour (2.99–10%). The optimum blends, that is, blends with overall best protein, ash and fibre contents were chosen for further analyses (mineral contents, soluble and insoluble dietary fibre, resistant starch, dietary fibre, pasting characteristics, glycemic index and antioxidant properties) using standard procedures. The control was 100% sorghum flour contained (0.39%) fibre and (6.13%) protein. The optimum blends with overall best fibre and protein contents obtained were runs 2- 90% sorghum, 0% plantain and 10% tigernut flours (1.29 fibre and 10.15 protein), 6 - 75.92% sorghum, 14.08% plantain and 10% tigernut flours (1.19 fibre and 8.05 protein), 7- 70% sorghum, 20% plantain and 10% tigernut (1.29 fibre and 8.53 protein) and 11 - 82.43% sorghum, 7.57% plantain and 10% tigernut flours (0.79 fibre and 9.80 protein). Increase in foaming capacity was recorded in most of the optimised composite flour, the highest value was recorded in run 2 (20.97) and 11 (19.67), while it reduced in run 1, 6 and 10 compared to the control. Substitution of sorghum flour with plantain and tigernut however reduced the water absorption capacity of the optimised composite flour (1.54 to 2.31 compared to the control sample which had 2.69. Decrease in oil absorption was also observed when compared to the value of the control which had 2.06, except in run -15 which had 2.16. In addition, substitution of sorghum flour with plantain and tigernut flour at 20% and 10% significantly (p = 0.05) increased the resistant starch and soluble dietary fibre which helps in reduction of the glycemic index of the composite flour. However, the pasting characteristics of the composite flour was significantly different from 100% sorghum, the value obtained for the setback and breakdown indicates that composite flour had lower tendency to retrograde and its high peak temperature and time indicates that it is able to withstand high heat compared to the control. The study therefore showed that addition of plantain and tigernut flour (20% and 10%) to sorghum flour to produce composite flour greatly enhanced its nutrient quality in term of protein, fibre, mineral, resistant starch, soluble fibre, pasting characteristics, antioxidant properties and low glycemic index which may make it serve as a potential food for the treatment or management of coeliac disease and diabetes.