Sweet Potato Varietal Evaluation Trial for Food Nutritional Values

Aim: The aim of this work was 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 and present the findings in a language that the average reader can understand. This
will help consumers to appreciate what they are feeding their bodies with when they eat the different
varieties of sweet potato.
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.
The essence was to provide the same soil and environment so that at harvest, the content of their
nutrients, mineral salts and other food factors can be compared.
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, parceled, appropriately labelled and hand-delivered
to the Food Chemistry Laboratory of Kwame Nkrumah University of Science and Technology for
proximate analysis (%), total carotenoids and beta-carotene concentrations in milligrammes per gram
(mg/g) and concentrations of the minerals, namely magnesium (Mg), sodium (Na), potassium (K),
calcium (Ca), iron (Fe) and zinc (Zn) in milligrammes per kilogramme (mg/kg).
Results: All the five varieties of sweet potato were found to be nutritious. Protein content ranged from
3.82% in the 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 betacarotene.
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.