Evaluation of antioxidant activity and safety of onion ( Allium cepa L.) peels

Abstract

Background: Onion peel is a raw material rich in biologically active compounds; however, within the framework of food waste management in Mongolia, detailed studies and safety evaluations of this material remain insufÏcient. Therefore, it is necessary to scientifically determine the properties of onion peel waste generated from the food production sector and explore its potential for reuse. Aim: To evaluate the safety parameters of red and white onion (Allium cepa L.) peels generated during food processing and to determine their bioactive compound content and antioxidant activity. Materials and Methods: Red and white onion peels were used in this study. Safety parameters were determined using atomic absorption spectrometry (for heavy metals) and GC-MS/MS and LC-MS/MS (for pesticide residues). The raw materials were extracted with 70% ethanol, and dry extracts were obtained using a vacuum evaporator and freeze dryer. Total phenolic content (TPC) and total flavonoid content (TFC) were measured by spectrophotometric methods, while antioxidant activity was evaluated using the DPPH radical scavenging assay. Results: The analysis showed that the levels of lead, cadmium, and 205 pesticide residues in onion peels did not exceed the permissible limits, indicating that the material is safe. Phytochemical analysis revealed the presence of quercetin and luteolin derivatives in the dry extracts. The TPC (27.40±1.64%) and TFC (17.95±1.47%) of red onion peel extract were significantly higher than those of white onion peel extract (20.34±0.34% and 12.69±1.44%, respectively). The IC₅₀ values were 17.58 μg·mL⁻¹ for red onion and 19.41 μg·mL⁻¹ for white onion, indicating strong antioxidant activity for natural composite extracts. Conclusion: Onion peel waste meets safety requirements and exhibits strong antioxidant activity. These findings demonstrate its potential as a valuable raw material for the development of antioxidant preparations and functional food additives aimed at preventing oxidative stress.