Bioactive Compounds, Antioxidant Activity, and Potentially Toxic Elements in Onion (Allium cepa L.) Cultivars

Abstract

Onion (Allium cepa L.) is one of the most widely consumed vegetables globally, valued not only for its culinary applications but also for its nutritional and functional properties. It is a rich source of bioactive compounds, particularly phenolic substances, which are strongly associated with antioxidant activity and potential health benefits. However, onions may also accumulate potentially toxic elements from the environment, posing risks to food safety.  This study aimed to evaluate the total polyphenol content (TPC), antioxidant activity (AA), vitamin C content, and the concentrations of selected potentially toxic elements (cadmium, lead) in three onion cultivars (Medusa, Conservor F1, Karmen). Significant differences (p <0.05) were observed among cultivars for all evaluated parameters. The highest TPC and AA were recorded in the cultivar Karmen (781.3 mg GAE.kg^-1, 1.54 mmol TE.kg^-1), followed by Konzervor (597.8 mg GAE.kg^-1, 0.49 mmol TE.kg^-1) and Medusa (512.2 mg GAE.kg^-1, 0.32 mmol TE.kg^-1), confirming the strong association between phenolic compounds and antioxidant capacity. Vitamin C content showed less pronounced variability, with a range from 68.3 to 75.3 mg.kg^-1. Regarding food safety, Cd concentrations ranged from 0.02 to 0.09 mg.kg⁻¹, and Pb concentrations from 0.29 to 0.36 mg.kg⁻¹. When compared with the maximum levels established by Commission Regulation (EU) 2023/915, all samples exceeded the Pb limits, and all samples except one exceeded the Cd limits. Overall, the results demonstrate that onions serve as both a valuable source of bioactive compounds and a potential pathway for dietary exposure to toxic elements, highlighting the need for continuous monitoring and optimized agricultural practices to ensure food safety and nutritional quality.