Extraction of Antioxidants and Tannins from Walnut Husks Using Supercritical Carbon Dioxide with an Ethanol Modifier

During the processing of nuts, a considerable amount of material such as husks and shells are produced and often discarded as compost or landfill.  In producing walnuts for retail sale, the husks are often discarded.  Walnut husks contain tannins and polyphenolic compounds and the husk may be used for treatment of intestinal parasites and fungal infections.  Supercritical fluids, due to their high diffusivity are excellent solvents for extracting chemical species from plant matter.  Supercritical carbon dioxide, by itself has a relatively low dielectric constant, and ethanol can be added as a modifier to help improve the extraction of polyphenolic and tannin compounds.  The effects of temperature and ethanol content with constant density supercritical carbon dioxide with ethanol upon the extraction of ground walnut husks was evaluated using a factorial design of experiments.  Extractions were performed in a 22 mL stainless reactor.  Temperature was varied between 50 and 70 °C and ethanol mole fraction between 10 and 20%.  Both dried and damp walnut husks were evaluated.  The antioxidant potential was evaluated using the total phenolic content (TPC) assay, ferric reducing ability of plasma (FRAP) assay and DPPH assay.  DNA protection abilities of the extracts, as well as chemical composition, will also be presented.