Supercritical CO2 extraction of walnut oil from pre-pressed fruits

MARCELA MARTÍNEZ; DAMIÁN MAESTRI; MIGUEL MATTEA

Iguazú

Conferencia; I Iberoamerican Conference on Supercritical Fluids; 2007

Plapiqui (Argentina)

  SUPERCRITICAL CO2 EXTRACTION OF WALNUT OIL FROM PRE-PRESSED FRUITS   M. Martinez, D. Maestri, M. Mattea*   Universidad Nacional de Río Cuarto Ruta 8 - km 601 – Argentina Keywords: Walnut, Supercritical CO2, Oil Quality, Pressed Cake Abstract: Walnut fruits (Juglans regia L.) contain high levels (52-70%) of oil with good nutritional and organoleptic values. It is usually extracted by pressing, yielding a cake with considerable residual oil content which can be extracted with a suitable method that preserves its quality. The aim of this work was to assess the supercritical CO2 extraction kinetics of pre-pressed walnut fruits and the oil quality obtained from them. Walnut fruits (Franquette variety) were collected from Catamarca (Argentine) and treated in a screw press. The cake resulting from the screw pressing with a 17% of residual oil was ground and size classified between 2.4-4.8mm. Extractions were performed with CO2 in a high pressure pilot plant with single stage separation and solvent recycle. The effects of two different pressures (200 and 400bar) and temperatures (50-70ºC) with regard to oil yield and quality, and time required for extraction were analyzed. In each experiment, 400g of material were used. At each condition, the extraction rate changes with the mass of solvent. At first, the mass of oil extracted is determined by the oil solubility in CO2 and a linear relationship was observed, where the slope results the solubility of oil in CO2 at the experiment conditions. This behavior was detected at very low CO2 mass. After that, the extraction rate is governed by solubility and diffusion, and continuously diminished with time. Chemical analyses of extracted oils were determined according to standard methods of AOAC. The acid values of oils extracted at different conditions were bellow 0.6. Tocopherol and carotenoids contents were significantly higher than those obtained by pressing. The color changed along the extraction from a whitish clear product to a yellow one. Extraction conditions did not affect significantly the fatty acid composition.