Enhancement of Antioxidants Content in Amaranths tricolor L. by Adjustment of Cationic Ions in Fertilizer

—This study investigated the effect of cationic nutrient (K, Mg and Ca) concentrations on the biosynthesis of antioxidants while also maintaining the dietary fiber content and mass productivity in Amaranthus tricolor L. Amaranthus tricolor L. was chosen as a model vegetable as it was reported to contain high antioxidants in the leaves. Soilless culture was carried out using a modified Huett solution containing different cationic ion concentrations (K; 28.5, 200.5 and 372.5 ppm, Mg; 2.8, 20 and 37.2 ppm Ca; 9.8, 70 and 130.2 ppm). Mature leaves from each treatment was determined for total phenolic content, antioxidant activity and dietary fiber. It was found that an increase in potassium enhanced the antioxidant activity and total phenolic productivity whereas the mass yield and dietary fiber were not negatively affected. The lowest Mg proportion (2.8 ppm) resulted in no mass productivity. High concentration of Ca (130.2 ppm) could increase the mass yield by up to 34%, compared with the control (70 ppm Ca). However, neither significant effect on antioxidant activity nor total phenolic productivity was observed with varying calcium concentration. The results suggest that producing an antioxidant-rich vegetable, not lowering its original quality, could be achieved by optimization of these nutrient elements.