Analysis of the Leaves of Five Sweet Potato Varieties for Their Nutrient, Mineral and Phytochemical Properties

Aim: To determine the nutrients, minerals and phytochemicals contained in leaves of five sweet potato varieties.

Study Design: The study was carried out in the dry season from November 2018 to March 2019, using a randomized complete block design (RCBD).During planting, 10 cm length of each 30 cm long soft wood vine cutting was inserted into the soil and immediately watered. A space of 60cm was left between the plants and there were five vine cuttings planted per ridge. The order of planting the vine cuttings was the same on each replicate ridge. Each treatment had three replications with each replicate having five plants to give a total of75 vine cuttings in all. Leaves of the sweet potato varieties; Agric white (AW), Agric orange flesh (AO), Red skin (RS), Orange flesh (OF) and Red local (RL) were parceled; each variety in a separate parcel, appropriately labelled and sent to the Food Science Laboratory of Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, for analysis.

Study Site: The sweet potatoes were cultivated in the experimental field of Ecological Agriculture Department, Bolgatanga Technical Universityin Bolgatanga Municipality of Upper East Region, Ghana.

Methodology: Proximate analysis was done and nutrient content expressed in percentages (%). Concentrations of the minerals iron (Fe), potassium (K), calcium (Ca), zinc (Zn), manganese (Mn) and magnesium in milligrams per kilogram (Mg/Kg) were determined. Total phenolic content (TPC) as well as the concentrations of carotenoids and Flavonoids were also estimated and expressed in Mg/Kg. Antioxidant properties of the leaves was determined and reported in mg/Kg.

Results: Proximate analysis of the leaves show that all five sweet potato varieties are very nutritious. Leaves of AW variety recorded the highest protein (6.17± 0.43%) and carbohydrates (8.61 ± 0.32%). The content of crude fibre is generally high in leaves of all varieties, ranging from1.42 ± 0.50% in AO to 2.42 ± 0.18% in OF. The proportion of fat in all the varieties is similar, averaging 2,096 ± 0.046%, with the highest of 2.25 ± 0.06% in AO. The two orange flesh varieties, OF and AO, had the highest and higher concentrations of iron (Fe) of 2,020.41 and 467.11 mg/Kg respectively. Magnesium (Mg) is the element that occurred in highest concentration of all the minerals, with an average concentration of 7,991.02 mg/Kg. The OF variety contained the highest concentration of total phenol of 875.00 ± 95.86 mg/Kg. With an average of 4,915.00 ± 166.00 mg/Kg, the concentration of flavonoids in all five varieties in the current study is similar. The concentration of total carotene decreased in the order RL>RS>AW>AO>OF, with the RL variety containing 124.22 ± 10.00 mg/Kg while the OF one possessed 49.39 ± 2.00 mg/Kg. The content pattern of beta carotene was RL> RS> AW> OF> AO, with RL variety containing 4.56 ± .03mg/Kg as AO had 1.57 ± 0.53 mg/Kg. The capacity of phytochemicals in the sweet potato varieties to scavenge and inhibit free radicals as well as reactive oxygen species [using the DPPH (1,1-diphenyl-2-picrylhydrazyl) assay] was highest in the OF variety (51.073%).

Conclusion: Leaves of the five sweet potato varieties studied are rich in diverse nutrients and phytochemicals. Therefore, encouraging the growth and consumption of both leaves and root tubers is a cheaper means of reducing malnutrition and enhancing good public health. It is therefore, essential for more investigations to establish the nutrient content and nutrachemical capabilities of both roots and leaves of the different varieties of sweet potato in the different environments so as to equip the general public with appropriate information to guide dieting choices.