Optimisation of total phenolic acids extraction from mandarin peels using microwave energy: The importance of the Maillard reaction Original Research Article

Microwave processing has been used for the extraction of antioxidants from mandarin peels using deionised water as the solvent. Optimum extraction conditions under constant heat load per unit mass were as follows: microwave power, 400 W; extraction time, 3 min; solid to solvent ratio, 1:2; and extraction temperature below 135 °C. These conditions did not change the colour of the extract significantly under neutral (pH 4.5–4.9) and acidic conditions (pH 1.5–2.5). The amounts of antioxidants, which were extracted when the heat load per unit mass was held constant, were not significantly affected by the solid to solvent ratio used, so the maximum solid to solvent ratio of 1:2 used here is recommended to minimise the amount of solvent used. The colour of the extract was more greatly affected by the extraction temperature than by the solid to solvent ratio. The total phenolic contents of mandarin peels were evaluated using the Folin–Ciocalteu assay (FCR) and the trends were compared with the results of the Oxygen Absorbance Radical Capacity (ORAC) assays. The presence of Maillard rections and Maillard by-products were also investigated at higher extraction temperatures and analysed by the High Performance Liquid Chromatography (HPLC) method. The results demonstrated that microwave extraction (MWE) is a fast and reliable method for phenolic compound extraction from citrus marc with the minimum use of solvent.