Potassium rate alters the antioxidant capacity and phenolic concentration of basil (Ocimum basilicum L.) leaves

In the current study, we have determined how potassium rate affects the phenolic levels and antioxidant properties of three cultivars of basil (Ocimum basilicum L.) leaves: Dark Opal, Sweet Thai, and Genovese. Potassium rate increased the total phenolic concentration in basil, with basil treated at the highest potassium rate, 5.0 mM K, containing greater phenolic levels than basil treated at the lowest potassium rate, 1.0 mM K (p = 0.008). Basil grown at 5.0 mM K also had higher concentrations of rosmarinic (p = 0.005) and chicoric (p < 0.001) acids compared to lower potassium treatment levels. Correspondingly, 1.0 mM K basil had lower DPPH (2,2′-diphenyl-1-picrylhydrazyl) (p ⩽ 0.005) and FRAP (ferric reducing antioxidant power, p = 0.043) antioxidant capacities compared to basil treated at higher potassium rates. Cultivar was also found to impact the phenolic composition and antioxidant properties of basil, with Sweet Thai having lower total phenolic concentrations and FRAP antioxidant capacities than Dark Opal and Genovese. Although not affected by potassium rate, anthocyanin concentrations varied significantly among the cultivars, with purple Dark Opal basil exhibiting higher anthocyanin levels than Sweet Thai (p = 0.003) and Genovese (p = 0.002).