Influence of Harvesting Stages on Phytonutrients and Antioxidant Properties of Leaves of Five Purple-Fleshed Sweet Potato (Ipomoea batatas) Genotypes

Abstract

Sweet potatoes (Ipomoea batatas) are highly profitable, contribute to food security, and their leaves contain phytonutrients. This study examined the optimal leaf harvesting stage by harvesting newly formed leaves (leaves 1 to 5) to achieve the highest concentration of carotenoids, phenolic compounds, antioxidant properties and mineral content. Leaves of five purple-fleshed sweet potato genotypes ‘2019-11-2’ and ‘2019-1-1’, ‘Purple-purple’, and from the USA ‘08-21P’ and ‘16-283P’ were harvested based on tuber life cycle [vegetative 8 weeks after planting (VS-8WAP), tuber initiation (TIS-12WAP), and tuber maturation phases (TMS-16WAP)]. At the 8WAP stage, leaves of genotype ‘2019-11-2’ had the highest concentrations of cyanidin-caffeoyl-sophoroside-glucoside (17.64 mg/kg), cyanidin-caffeoyl-feruloyl-sophoroside-glucoside (41.51 mg/kg), peonidin-caffeoyl-hydroxybenzoyl-sophoriside-glucoside (45.25 mg/kg), and peonidin caffeoyl-feruloyl-sophoriside-glucoside (24.47 mg/kg), as well as antioxidant scavenging activity. In contrast, ‘Purple-purple’ harvested at TIS-12WAP showed the highest concentration of caffeoylquinic acid derivatives. Zeaxanthin, lutein, all trans-β-carotene, and cis-β-carotene are the most abundant carotenoids in genotype ‘08-21P’ at VS-8WAP. As a result, local genotypes ‘2019-11-2’ harvested at 8WAP and ‘Purple-purple’ harvested at 12WAP are potential sources of anthocyanins and caffeoylquinic acid derivatives. Conversely, USA’s genotype ‘08-21P’ at the VS-8WAP stage is an excellent source of carotenoids. The leaves of USA’s ‘08-21P’ genotype and the local ‘2019-11-2’ genotype at TMS-16WAP exhibited the highest content of Fe and Mn, respectively. The study identified the optimal leaf stage for consumption of leaves and for use as a functional ingredient.