Microwave-assisted Extraction of Hibiscus sabdariffa Antioxidants: Method Developmet and Validation

An increased understanding of antioxidant properties in edible flowers, especially Hibiscus sabdariffa (Roselle), shows the importance of a rapid and reliable determination of phenolic compounds from Roselle. The present study reports in the development and validation of the analytical extraction method for phenolic compounds using microwave-assisted extraction (MAE). Prior to the optimization, a study for the identification of phenolic compounds revealed that chlorogenic acid, protocatechuic acid, caffeic acid, and rutin were presented in Roselle. Three factors affecting MAE, viz. temperature, solvent composition, and sample to solvent ratio were studied applying a Box-Behnken Design (BBD) in conjunction with response surface methodology (RSM) to optimized the MAE condition. The maximum extraction recovery can be achieved using the extraction temperature of 68 °C, solvent composition of 59% MeOH in water, and 1:20 of ratio sample to solvent. The kinetic experiment was studied, achieving full recoveries at 25 min. Subsequently, method validation showed a satisfactory result, including lower LOD and LOQ values ranging from 0.22 µg L^-1 (rutin) to 0.62 µg L^-1 (chlorogenic acid). Both precisions and accuracy met the acceptances by AOAC. Finally, the method was successfully applied to quantify phenolics in the two most common varieties of Roselle.