Postharvest ultraviolet B (UVB) light treatment offers a sustainable strategy to enhance the nutraceutical quality of leafy vegetables by promoting bioactive compound accumulation. This study evaluated the short-term effects of UVB exposure on the phenolic content, antioxidant capacity, and anti-inflammatory properties of amaranth (Amaranthus spp.) leaves. UVB treatment significantly increased total phenolic content, with rutin as the predominant compound, rising from 2727.88 mg/kg to 4173.66 mg/kg after 7 minutes of exposure (5.04 kJ/m2), a 53% increase. The highest cellular antioxidant activity (CAA), 67.81%, was observed at the same dose, coinciding with peak rutin levels. Nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated macrophages decreased by up to 47% under the same conditions. However, prolonged UVB exposure reduced bioactivity, likely due to phenolic degradation. These findings demonstrate that brief UVB exposure rapidly enhances the nutraceutical properties of amaranth leaves, offering a practical biofortification approach for developing functional ingredients or nutraceuticals.
