CHEMICAL COMPOSITION, PHYSICOCHEMICAL AND ANTIOXIDANT PROPERTIES OF ORANGE FLESHED SWEET POTATO (Ipomea batata. Lam) FLOUR AND ITS PRODUCTS

Abstract

Vitamin A deficiency (VAD) is one of the major causes of avoidable blindness affecting the vulnerable groups (Children and women of reproductive age). Food-based intervention might reduce the problem of VAD in Sub-Sahara Africa. Pro-vitamin A enriched foods can be developed to prevent the occurrence of VAD through the use of locally available pro-vitamin A-rich foods sources such as orange fleshed sweet potato (OFSP). The objective of the research was to produce baked food (bread and biscuit) from the blends of sweet potato flour, soy concentrate powder (SC), date palm powder (DP) and potato starch powder (PS) to combat the prevalence of VAD. Three varieties of sweet potatoes used in this study includes mother’s delight orange fleshed sweet potato (OFSP 1), king J orange fleshed sweet potato (OFSP 2) and cream fleshed sweet potato (CFSP). The OFSP varieties were cultivated and harvested at five month maturity. The sweet potatoes tubers were processed into flour. It was observed that OFSP 1 had the highest Beta carotene content of 18.83mg/100g. The flour were combined with SC, PD and DP powder to make composite flour using optimal mixture design of the Response Surface Methodology (Design expert 8.0.3.1 version).Thirteen runs were generated for each varieties of the sweet potato to make a sum of thirty nine runs in all. The blend samples were analyzed for proximate, minerals, functional, pasting (RVU) characteristics, rheological (mixolab) parameters, dietary fibre, proteins, and carotenoid (pre cursor of vitamin A) contents. Samples were selected based on either high protein or carotenoid content from the thirty-nine runs generated from RSM. Two samples were selected from each varieties of sweet potato used while wheat flour was used as the control. Physical parameters of the blends in term of proximate contents, mineral elements, functional properties, antinutritional contents, glycemic index, amylase and amylopectin were analyzed using standard methods. The blends were used for the production of bread and biscuit, both products were then analyzed separately in terms of proximate, minerals,antinutrients, antioxidants, effective concentration (Ec50), glycemic index, colour, in-vitrostarch digestibility, amino acid profile, Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM) and sensory characteristics using nine point Hedonic scale. The most abundant mineral elements in the baked samples were potassium, phosphorous, calcium and magnesium. It was observed that all the antinutritional factor were below the required limit according to FAO standard. The estimated glycemic index of the samples selected based on high protein content were observed to have a low glycemic index while the samples selected based on carotenoids exhibited medium estimated glycemic index. Both the bread and biscuit exhibited good antioxidant properties and low Ec50 value. Glutamic acid was the abundant amino acid observed in both the baked samples. The Predicted Protein Efficiency Ratio (P-PER) of the baked product was higher than the recommended FAO standard (1.5). The beta carotene content loses in bread were above 50%, products from king J OFSP compared favourably with wheat sample.