The Impact of Varying Stages of Maturity on the Chemical Composition and Antioxidant Activity of Yacon (Smallanthus sonchifolius) Leafy Vegetable

Yacon tubers are of global interest due to their prebiotic potential while yacon leaves contain phenolic compounds with potential health benefits. In Kenya, yacon is a newly introduced root crop that is of interest to consumers; however, their main challenge to consumption is determining the appropriate time to harvest the leaves. The chemical makeup of yacon leaves varies depending on the planting site, growing season, harvest time, and growth stages. The current research determined the impact of varying stages of maturity on the chemical composition and antioxidant potential of yacon leaves grown in a farm at Naromoru, Kenya. The leaves were harvested at 2, 3, 4, and 5 months of growth, then subjected to oven drying and stored at 4 °C awaiting analysis. The DPPH assay was used to measure radical scavenging activity, and the Folin–Ciocalteu method was followed in the determination of total phenolic content. Chemical composition was done by Kjedahl method (Crude protein), Soxhlet method (crude fat), and oven drying (moisture content). From the results, the level of maturity significantly (p < 0.05) influenced the levels of crude protein, fat and carbohydrates, TPC, and antioxidant activity in the harvested yacon leaves. The crude protein level was highest (28.45%) for the 2nd month of harvest and was lowest in the 5th month (16.75%), while crude fat increased from 3.51% in the 2nd month to 4.20% in the 5th month. Carbohydrates increased from 46.01% to 56.65% in 2nd month to the 5th month, respectively. Both the TPC and antioxidant activity decreased significantly (p < 0.05) as the leaves matured. TPC was highest in the 2nd month of harvest and lowest in the 5th month of harvest, 439.33 and 81.00 mgGAE/100 g, respectively. Thus, harvesting yacon leaves at the early stages of growth is crucial to fully benefit from the phytochemical and nutritional composition of the leaves.