Liberation and separation of phenolic compounds from citrus mandarin peels by microwave heating and its effect on antioxidant activity

The effect of microwave treatment on the phenolic compounds and antioxidant capacity of citrus mandarin peels was evaluated. After microwave treatment, methanol extracts of citrus peels were prepared and the contents of phenolic acids (free and bound) and flavanol, flavanone and flavonol compounds (FCs) were determined by HPLC. Antioxidant capacity of peel extracts was measured using DPPH radical scavenging assay, hydroxyl radical scavenging assay and reducing power. After microwave treatment, the free fraction of phenolic acids increased, whereas the bound fractions decreased and antioxidant activity was increased. The content of total FCs increased with power but at longer irradiation time it was declined which meant that some FCs might be degraded. The results indicated that appropriate microwave treatment could be an efficient process to liberate and activate the bound phenolic compounds and to increase the antioxidant capacity of citrus mandarin peels.