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Updated: Aug 16, 2025
Author Spotlight: Eco-Friendly Extraction of Bioactive Compounds Using Polyol-Based Microwave-Assisted Techniques
Published on: August 23, 2024
Optimization of a Microwave Assisted Extraction Method for Maximum Flavonols and Antioxidant Activity of Onion
Ana V González-de-Peredo1, Mercedes Vázquez-Espinosa1, Estrella Espada-Bellido1
1Department of Analytical Chemistry, Faculty of Sciences, Agrifood Campus of International Excellence (ceiA3), University of Cadiz, IVAGRO, 11510 Puerto Real, Spain.
Abstract:
Nowadays, consumers demand bioactive foods that have the potential to limit the risk of suffering from several medical conditions. Onions present these desirable capabilities owing to its high content in antioxidant bioactive compounds. This work has used a Box-Behnken design with a response surface methodology to determine the best conditions in which to extract the polyphenols that are found in onions. Two extraction methods-one for the extraction of total flavonols and another one intended to obtain extracts with the highest possible antioxidant activity-have been developed and optimized. The following factors have been studied: temperature, %methanol in water, solvent pH, and sample-solvent volumetric ratio. The optimal conditions for the extraction of flavonols were 93.8% methanol in water, pH 2, 50 °C extraction temperature and 0.2:17.9 g:mL sample-solvent ratio. The best antioxidant activity levels were registered when using 74.2% methanol in water, pH 2, 99.9 °C extraction temperature and 0.2:18.2 g:mL sample-solvent ratio. Both optimized methods used short extraction times, and presented good precision levels and successful results when used with an assortment of onion varieties. According to total flavonols and antioxidant activity data, with 7.557 ± 0.3261 and 12.08 ± 0.0379 mg g-1, respectively, the developed methods achieved comparable or even superior results to those obtained by other authors.
Insights
Optimized extraction methods for onions yield high levels of beneficial polyphenols, specifically flavonols and antioxidant compounds. These efficient techniques offer comparable or superior results to existing methods for various onion types.
Area of Science:
- Food Science
- Analytical Chemistry
- Phytochemistry
Background:
- Consumer demand for bioactive foods is increasing due to their health benefits.
- Onions are rich in antioxidant bioactive compounds, making them a valuable food source.
- Polyphenols in onions contribute to their health-promoting properties.
Purpose of the Study:
- To optimize extraction conditions for polyphenols from onions.
- To develop two distinct extraction methods: one for total flavonols and another for maximum antioxidant activity.
- To identify optimal parameters including temperature, methanol concentration, pH, and sample-solvent ratio.
Main Methods:
- Utilized a Box-Behnken design and response surface methodology for optimization.
- Investigated factors: extraction temperature, % methanol in water, solvent pH, and sample-solvent ratio.
- Developed and validated two optimized extraction protocols.
Main Results:
- Optimal flavonol extraction: 93.8% methanol, pH 2, 50°C, 0.2:17.9 g:mL ratio.
- Optimal antioxidant activity extraction: 74.2% methanol, pH 2, 99.9°C, 0.2:18.2 g:mL ratio.
- Both methods demonstrated short extraction times, high precision, and effectiveness across different onion varieties.
Conclusions:
- Successfully optimized two methods for extracting key bioactive compounds from onions.
- Achieved high yields of total flavonols (7.557 ± 0.3261 mg g⁻¹) and antioxidant activity (12.08 ± 0.0379 mg g⁻¹).
- The developed methods are efficient, precise, and applicable to diverse onion types, offering significant potential for the food industry.
