Sweet Potato Varietal Evaluation Trial for Food Nutritional Values

Aim: To explore the nutrients, minerals, beta-carotene and total carotenoid contents of five sweet potato varieties viz., Agric orange flesh, Agric white, Red skin, Orange flesh and T.U. purple.

Study Design: The sweet potato vines at six week stage were cut into 1.2 m each and transplanted in parallel lines on the same 1.2 m x 2.6 m bed, spaced about 0.52 m from each other in Dukumah Garden. There were five such beds and vine cuttings transplanted in the same order on each bed.

Study Site: The study, which took four months, was conducted in the Dukumah Garden in Bolgatanga Municipality (10.7875°N, 0.8580°W) of the Upper East Region of Ghana.

Methodology: The sweet potatoes were harvested four months after transplanting on the same day. Samples of the various varieties were collected, parcelled, appropriately labelled and hand-delivered to the Food Chemistry Laboratory of Kwame Nkrumah University of Science and Technology for the analysis of proximate analysis (%), total carotenoids and beta-carotene concentrations in mg/g and concentrations of the minerals, namely magnesium (Mg), sodium (Na), potassium (K), calcium (Ca), iron (Fe) and zinc (Zn) in mg/kg.

Results: All the five varieties of sweet potato were found to be nutritious. Protein content ranged from 3.82% in Agric white variety to 0.11% in Agric orange flesh. Fat content ranged from 4.84% in orange flesh variety to 1.74% in red skin. Crude fibre content was between 1.77% in Agric orange flesh and 0.10% in T.U. purple. Total carbohydrate varied from 23.2% in Agric orange flesh variety to 15.8% in Agric white one. Moisture was high in all the varieties, ranging from 75.78% in Agric white variety to 71.04% in Orange flesh one. The Orange flesh variety had the highest ash content of 1.56%. All the varieties contained high concentrations of Mg but low concentrations of Na and K. The highest concentration of Ca (8250.70±0.06 mg/kg) was recorded in T.U. purple. The concentrations of Fe in the sweet potato varieties decreased in the following order: T.U. purple>Red skin>Orange flesh>Agric orange flesh>Agric white. The highest (123.12±0.00 mg/kg) and the lowest (33.10±0.00 mg/kg) Zn concentration were recorded in the orange flesh and Agric white varieties, respectively. The concentration of beta-carotene (mg/kg) in five sweet potato varieties was in the following order: Agric orange flesh<<Agric white<Red skin<Orange flesh<T.U. purple.

Conclusion: The five varieties of sweet potato were found to be rich in proteins, total carbohydrates and fats. They were observed to vary in macro- and micronutrients, beta-carotene and total carotenoids contents. T.U. purple variety was identified to be the richest source of Ca and beta-carotene. Thus, the sweet potato varieties may be of considerable importance in ameliorating nutrient, mineral as well as beta-carotene malnutrition in poorly resourced areas of the developing countries.