Evaluation of antioxidant capacity in sweet potato [Ipomoea batatas (L.) Lam] cultivars for functional food applications

Underutilisation of nutrient-rich traditional crops like the sweet potato (SP) poses challenges in food security as well as health problems. To date, other fruits and vegetable crops have been used successfully in the manufacturing of various food products due to their excellent nutrient properties. However, the suitability of the different SP cultivars on the development of antioxidant-rich food products has not been investigated. The objective of this study was to determine the antioxidant levels of different SP cultivars suitable for use in the development of antioxidant-rich SP food products. Four SP cultivars, ‘Bophelo’, ‘Blesbok’, ‘Mvuvhelo’ and ‘Mafutha’ were used. The study was a 4 × 2 factorial, with the treatments arranged in a CRD, with 5 replications, where factor A was SP cultivars and factor B was the processing methods (‘peeled’ and ‘unpeeled’). The ‘unpeeled Bophelo’ cultivar served as a standard. Data on total phenolic (TP), beta carotene (BC) and vitamin C (Vit C) were determined. The interaction of SP cultivars and processing methods indicated highly significant (P≤ 0.01) effects in TP, BC and Vit C for all tested SP cultivars. Relative to the standard SP, ‘peeled Mvuvhelo’, followed by ‘peeled Blesbok’ and ‘peeled Mafutha’, contained higher TP of 39.75, 37.02 and 36.06 mg GAE/100gdw, respectively. The highest BC content (75.62 µg/100g) was recorded in the standard (‘unpeeled Blesbok’) SP, followed by the ‘unpeeled Mafutha’ (70.79 µg/100g), ‘peeled Bophelo’ (49.80 µg/100g) and ‘peeled Mafutha’ (38.90 µg/100g), respectively. ‘Blesbok’ SP cultivar exhibited the highest Vit C content in both ‘unpeeled’ and ‘peeled’ forms, comprising 52.56 and 41.57 µg/100g, respectively, when compared to the standard. In conclusion, the high accumulation of the tested antioxidants was observed in ‘Bophelo and Mvuvhelo’, SP cultivars except for Vit C, which was the highest in the ‘Blesbok’ cultivar.