Impact of Post-Harvest Drying and Extraction Method Upon Total Phenol, Antioxidant Potential, and Inhibitory Activity of Black Walnut Husks

Document Type

Conference Proceeding

Publication Date


Conference Name

2016 AIChE Annual Meeting


The fruit of the black walnut consists of the kernel, shell and husk. The kernel is often used for consumption and the shells as an abrasive and filler, however the husks are often discarded as compost or landfill. Walnut husks contain tannins and polyphenolic compounds which exhibit antimicrobial properties and can treat inflammation. The naphthoquinones in walnut husks can be used as broad spectrum biocides, bio-herbicides, and have been demonstrated to have cytotoxic effects against melanoma cells. Supercritical fluids, which have 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 compounds. For this study, black walnuts were extracted either using ultrasonic assisted extraction using ethanol or supercritical carbon dioxide extraction with an ethanol modifier. 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. Temperature was varied between 50 and 70C and ethanol mole fraction between 10 and 20%. Both dried and damp walnut husks were evaluated with damp walnut husks exhibiting higher antioxidant potential. The optimal extraction conditions were found to be 68 °C and 20 wt-% ethanol in supercritical carbon dioxide. At these conditions, the antioxidant potential as measured by the ferric reducing ability of plasma (FRAP) assay was 0.027 mmol trolox equivalent/g (mmol TE/g) for dried walnut husk and 0.054 mmol TE/g for walnut husks that were not dried. The antioxidant potential was also evaluated using the total phenolic content (TPC) assay and DPPH assay. The antimicrobial inhibition, quorum sensing inhibition, as well as chemical composition were also evaluated and will also be presented.

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