Extraction of phenolic compounds from elder berry and different grape marc varieties using organic solvents and/or supercritical carbon dioxide

Optimal operating conditions for the extraction of phenolic compounds from grape marc and elder berry have been investigated. The aim was to obtain extracts with high anthocyanin content, which show stability during storage and would be potentially interesting for commercial applications as natural colorants. For this purpose three varieties of grape marc, native to Slovenia (Refošk, Merlot and Cabernet), were studied. The results were compared with the extraction of elder berry, which is known for its high anthocyanin content. Single-step batch extractions were performed with ethanol, ethyl-acetate and acetone in different ratios with water. Temperatures of 20 °C, 40 °C and 60 °C were applied. Influence of the change in pH values of the extraction media was investigated regarding the yield and degradation of anthocyanins. Two-step extractions, combining supercritical fluid extractions (SFE) and conventional batch extractions, were applied. The most efficient conventional solvents in single-step extractions were mixtures of organic solvent and water at 60 °C. Pre-treatment of the natural material with supercritical CO2 (with or without ethanol as co-solvent) improved the extraction of polyphenols from the grape marc. This method provides an alternative to the pre-treatment of the plant materials, replacing toxic organic solvents (e.g. hexane). Acidified extraction media resulted in higher anthocyanin content in the extracts. However, the degradation of the anthocyanins during storage was higher, which led to the loss of the intensive colour. The addition of a commercially available rosemary extract to the extraction solvent improved the stability of the grape marc extract during storage.