Responses of the nutritional value of the orange fleshed ‘Bophelo’ sweet potato (Ipomoea batatas L.) cultivar under various processing techniques

Abstract

Sweet potato (Ipomoea batatas L.) is a nutrient-dense root crop that is high in antioxidants. However, consumption was observed to decline, mainly as a result of the limited post-harvest processing methods. The boiling method is commonly used, however, leaching of the essential nutrients into the boiling water affects its nutritional value. Therefore, the objective of the study was to investigate the effect of various processing techniques on the nutritional value of the orange fleshed ‘Bophelo’ sweet potato cultivar. A 2 × 3 factorial experiment, arranged in a completely randomized design (CRD), was conducted. Factors A comprised 2 preparations (unpeeled and peeled) methods and factor B comprised three processing (boiling, deep-frying and roasting) methods, which served as treatments, in triplicates. The unprocessed, raw-peeled and unpeeled samples represented the control. Data on vitamin C, beta carotene, total phenolic, starch and protein were determined and recorded. In the peeled form, roasted samples had the highest nutritional accumulation (vitamin C 21.03 mg/100 mL, beta-carotene 64.6 μg/100 g, starch 5.86 g/mL and protein 0.3 mg/L), whereas in the unpeeled form, higher total phenolic (80.7 mg/GAE/g) was retained. The deep-frying method favoured vitamin C (10.00 mg/100 mL) and starch (13.6 g/mL) in the peeled form, but in the unpeeled form, beta-carotene (32.0 μg/100 g), total phenolic (66.2 mg/GAE/g) and protein (1.5 mg/L) were retained. The boiling method retained low levels of vitamin C (3.35 mg/100 mL), beta carotene (54.8 μg/100 g), total phenolic (43.5 mg/GAE/g) and protein (1.3 mg/L) in peeled forms, whereas starch (8.59 g/ml) was retained in the unpeeled samples. In conclusion, the roasting method demonstrated high retention of the tested nutritional value in ‘Bophelo’ sweet potato samples.