Characterization of Anthocyanins in Sweet Potato Leaves Grown in Various Stages and Conditions

Abstract

Phytochemical-enriched edible greens, sweet potato leaves (Ipomoea batatas L.), have become popular due to potential health benefits. However, the phytochemical contents in sweet potato leaves and their subsequent change over harvest stages and growth condition are mostly unknown. In this study, the anthocyanin profile and content in leaves of four sweet potato cultivars, i.e., white-skinned and white-fleshed Bonita, red-skinned and orange-fleshed Beauregard, red-skinned and white-fleshed Murasaki and purple-skinned and purple-fleshed P40, were evaluated. Fourteen anthocyanins were isolated and identified by HPLC-MSI/MS. The most abundant was cyanidin 3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside, which comprised up to 20% of the total anthocyanins. Of the young leaves (1st and 2nd slip cuttings), Bonita contained the highest anthocyanin content followed by P40. Of the mature leaves (vine stage), Beauregard had the greatest anthocyanin (592.5 ± 86.4 mg/kg DW) and total phenolic (52.2 ± 3 mg GAE/g DW). It should be noted that the lowest anthocyanin and total phenolic content of shoots were found in P40, while tubers of P40 contain the highest content of each. Furthermore, the increase in leaf anthocyanin content over the growth stages that was observed in three of the cultivars but not in P40. No significant difference of anthocyanin content was found in Beauregard leaves grown in the high tunnels when compared with that in the open field. This study demonstrated for the first time that anthocyanin levels were significantly changed in response to various growth stages but not high tunnel condition, indicating that the effect of anthocyanin biosynthesis in sweet potato leaves is highly variable and genotype specific.