Evaluation of the Effect of Planting Distance and Harvesting Time on the Carotenoids and Phytochemicals of Selected Orange-Fleshed Sweet Potato Varieties

Abstract

We evaluated the carotenoid profile and concentration (by HPLC) and the phytochemical content of two OFSP varieties (Umuspo 3 and Ex-Igbariam) planted at three distances (20 cm, 30 cm and 40 cm) and harvested in two different periods (12th and 16th weeks after planting) respectively. Carotene contents of the outer peel and inner flesh of the sweet potato varieties were also determined. The results showed wide variation in the carotenoid and phytochemical content among the varieties at different planting spaces and harvest periods. Umuspo 3 planted at 20 cm, 30 cm and 40 cm had significantly greater carotenoid concentration than Ex-Igbariam variety. The predominant carotenoid was β-carotene with highest concentration obtained from 40 cm planting distance (92.82µg/g) and 30 cm (80.97µg/g) for Umuspo 3. Ex-Igbariam at 30 cm planting distance contained 2.51µg/g β-carotene when harvested after 16th weeks. Also the highest β-carotene concentration was from Umuspo 3 flesh sample planted 30 and 40 cm (409.45 and 441.15 mg/100g) and the peel for samples planted 30 and 40 cm (490.47 and 640.69 mg/100g, respectively) at the 12th week of harvest. Flavonoids were present in significant amounts (310.62mg/100g) in Umuspo 3 planted at 30 cm and harvested after 12th week while in total polyphenol, significant quantities of ≈42.12mg/100g was present in Ex-Igbariam spaced at 30 cm and 40 cm and harvested after 16th week. Provitamin A carotenoid was calculated and Umuspo 3 pro-vitamin A carotenoid was significantly higher (p< 0.05) with highest concentration (742.26 RE/100g) present in samples from 40 cm planting distance. The results showed that planting space and harvesting period had significant impact on the carotenoid and phytochemical concentrations of OFSP varieties. Planting distances of 30 and 40 cm are recommended for high carotenoid content in the two sweet potato varieties.