Rautenbach et al. (2010) studied the antioxidant content and antioxidant
capacity of four sweet potato varieties that were cultivated under
different water regimes and subjected to thermal processing. The results
showed that the antioxidant content and antioxidant capacity
were affected by cultivar, drought stress, and thermal processing.
Drought stress increased the carotenoid, vitamin C, and polyphenol
contents aswell as the antioxidant capacity of some of the sweet potato
cultivars, especially W-119. Vitamin C content ranging from 15.5 to
32.2 mg/100 g was reported for the raw roots; thermal processing reduced
the vitamin C content by between 8% and 54.2%. The vitamin C
content in cooked roots ranged from 8.1 to 26.7 mg/100. Rautenbach
et al. (2010) argued that although there is no RDA for polyphenols,
the orange-fleshed cultivars contained a similar amount of polyphenols
than fruits and an oxygen radical absorbance capacity (ORAC) value
comparable to many fruits.