Measuring the three forms of ellagic acid: suitability of extraction solvents

Accurate quantification of ellagic acid and its derivatives, ellagic acid glycosides and ellagitannins, present in plant-based foods is a vital prerequisite for any study of their health-promoting properties. This goal is impeded by the lack of commercially available standards and the fact that these three forms differ widely in solubility. This disparity necessitates careful attention being paid to the choice of extraction solvents to ensure that precise and reproducible content measurements are achieved. This work sought to devise an extraction protocol that is effective for all ellagic acid forms whilst keeping the water-insoluble free ellagic acid solubilised during all analysis stages. To overcome this unavailability of commercial standards, the designated “targeted” ellagic acid derivatives identified in the selected fruit were monitored during the course of extraction that employed a number of commonly used solvents. Large variations in the extraction yield of the solvents tested for the ellagic acid and its derivatives were identified, extending even to the different fruit samples for the same form. It is regarded as unlikely that any selected extraction solvent could be universally employed to effectively extract all the ellagic acid compounds; however, the use of the solvent 50:50 vol. methanol-dimethylformamide satisfied most requirements.