Changes in Carotenoids and Polyphenols during the Growth Stages of Orange-Fleshed Sweet Potato (Ipomoea batatas (L.) Lam.)

The storage roots of orange-fleshed sweet potato contain high levels of polyphenols and carotenoids. Little information is available on changes in the content and composition of these secondary metabolites during the growth stages of the root system. We investigated changes in carotenoids, polyphenols, and anthocyanins in the root system of the orange-fleshed sweet potato ‘Tamaakane’ from the post-planting stage. Carotenoids and polyphenols accumulated immediately after root-system formation at 15 days after transplanting (DAT). The levels of carotenoids increased by 45 DAT and decreased once the storage root enlargement began, but increased rapidly thereafter. After 90 DAT, β-carotene accounted for >90% of the total carotenoids, and the frequency remained stable until maturity. Total polyphenol content increased significantly towards 45 DAT and then gradually decreased as the storage roots began to thicken. No anthocyanin was detected in the root systems of ‘Tamaakane’ at any stage. The content and composition of these secondary metabolites are discussed in terms of agronomic aspects, as they might contribute to a strategy to protect storage roots while engaging with each other against biotic or abiotic stresses at the growth stage of the root system.