Jonathan E. Wenzel

Antioxidant potential of Juglans nigra, black walnut, husks extracted using supercritical carbon dioxide with an ethanol modifier

Abstract The black walnut, Junglas nigra, is indigenous to eastern North America, and abscission of its fruit occurs around October. The fruit consists of a husk, a hard shell, and kernel. The husk is commonly discarded in processing, though it contains phenolic compounds that exhibit antioxidant and antimicrobial properties. For this study, black walnut husks were extracted using supercritical carbon dioxide with an ethanol modifier. The effects of temperature, ethanol concentration, and drying of walnut husks prior to extraction upon antioxidant potential were evaluated using a factorial design of experiments. The solvent density was held constant at 0.75 g/mL. 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. Antioxidant potential was also evaluated using the total phenolic content (TPC) and 1,1‐diphenyl‐2‐picryl‐hydrazyl (DPPH) assays and the FRAP assay was found to linearly correlate to the TPC assay.

Superheated liquid and supercritical denatured ethanol extraction of antioxidants from Crimson red grape stems

Abstract Grapes are widely known for health benefits due to their antioxidant content. In wine production, grape stems are often discarded, though they has a higher content of antioxidants than the juice. The effectiveness of using an environmentally friendly solvent, ethanol, as a superheated liquid and supercritical fluid to extract antioxidant compounds from grape stems of organically grown Crimson Seedless grapes was evaluated. The Ferric Reducing Ability of Plasma (FRAP) assay and the Total Phenolic Content (TPC), or Folin‐Ciocalteu assay, were used to quantify the antioxidant power of grape stem extracts. The extractions were performed at temperatures between 160°C and 300°C at constant density. It was found that the optimal extraction temperature was 204°C, at superheated liquid conditions, with a FRAP value of 0.670 mmol Trolox Equivalent/g of dry grape stem. The FRAP values were higher than other studies that extracted antioxidants from grape stems using single‐pass batch extraction.

Kinetics of the Non-catalytic Water Gas Shift Reaction in Supercritical Water

A kinetic analysis of the noncatalytic water gas shift reaction in a supercritical water medium was investigated using a specially designed 383 mL Haynes Alloy 230 tubular reactor at a constant pressure of 24.12 ± 0.04 MPa, water to carbon monoxide molar feed ratios of 5 to 37 moles of water per mole of carbon monoxide, and at temperatures varying from 768 to 1,048 K. The carbon monoxide concentration in the effluent gas reached a minimum of one mole-percent at 1,048 K, which corresponds to a 98% carbon monoxide to carbon dioxide conversion. Using global first-order kinetics a frequency factor of 105.76 ± 1.42 s−1 and an activation energy of 139.8 ± 24.5 kJ/mol was determined. It was also found that the developed kinetic rate model closely fits the experimental reaction data, with a coefficient of determination of R2 = 0.95, over a wide range of temperatures and reactant concentrations.