Comparison of the Effect of Acids in Solvent Mixtures for Extraction of Phenolic Compounds From Aronia melanocarpa

Thirty-two different solvent mixtures containing methanol and acid (acetic, formic, and hydrochloric); methanol, water, and acid; and pure methanol were tested for their efficiency for extraction of phenolic compounds from aronia (Aronia melanocarpa) belonging to the groups of anthocyanins, flavonols, and hydroxycinnamic acid derivatives. Thirteen compounds were detected and quantified in the extracts using HPIVDAD/ESI-MS. The yield of each compound and group was evaluated with regard to the extraction solvent composition. Extraction mixtures containing HCl were superior to the ones containing acetic or formic acid for the extraction yield of total phenolic compounds, which was especially pronounced for anthocyanins. The solvent mixture containing methanol/water/HCl (90:8:2, v/v/v) gave best results for the qualitative and quantitative assay of anthocyanins. However, this solvent mixture caused O-methylation of 3- and 5-caffeoylquinic acids transforming them to 3- and 5-feruloylquinic acids, respectively, during extraction. This peculiar finding must be taken into account during sample preparation for the analysis of polyphenols in any sample. It was observed that this O-methylation is specific for dihydroxycinnamic acid compounds containing neighboring hydroxyl groups. These results suggest the need for a detailed study of the behavior of various polyphenolic compounds during extraction with solvent mixtures containing methanol/HCl since it is very often used for the analysis of anthocyanins.