Browsing by Author "Rivera, O"

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    Supercritical CO2 extraction of Chilean hop (Humulus lupulus) ecotypes
    (JOHN WILEY & SONS LTD, 2003) del Valle, JM; Rivera, O; Teuber, O; Palma, MT
    Hops (Humulus lupulus L) have very stringent requirements of diurnal light hours during flowering. Thus, the beer industry is permanently assessing new agricultural land to grow hops, southern Chile being an excellent candidate for their introduction. Supercritical carbon dioxide extraction procedures were implemented to assess Chilean hop ecotypes. Based on results of a preliminary study with commercial samples (cv Nugget), 200 bar and 40degreesC were selected as extraction conditions. Very limited increases in extraction rate were observed when applying pressures >200 bar; such pressures did not speed up the extraction of alpha-acids (bitter flavor principles), but rather increased the co-extraction of undesirable compounds (hard resins and chlorophyll pigments). On the other hand, the effects of retrograde condensation phenomena were just starting to subside at 200 bar, and thermal damage of samples could increase at >40 degreesC. Ground cone samples of five local hop ecotypes, originating from Osorno, La junta, Coyhaique and Elizalde Lake, were subsequently tested. Osorno exhibited a higher yield (65 g kg(-1) oleoresin/substrate) than other Chilean ecotypes. Moreover, Osorno extract had a light yellowish color, as well as a higher content of bitter flavors (157 g kg(-1) alpha-acid/extract) and 1.5-7.1 times more representative aroma compounds than extracts of the other ecotypes. However, all these indicators were very low compared with the commercial Nugget sample (134 g kg(-1) oleoresin/substrate, 383 g kg(-1) alpha-acid/extract, 14 times more aroma compounds than Osorno ecotype). (C) 2003 Society of Chemical Industry.
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    Supercritical CO2 processing of pretreated rosehip seeds: effect of process scale on oil extraction kinetics
    (ELSEVIER SCIENCE BV, 2004) del Valle, JM; Rivera, O; Mattea, M; Ruetsch, L; Daghero, J; Flores, A
    Rosehip oil was extracted from milled seeds with supercritical carbon dioxide (SC-CO2). The effects of sample pretreatment and interstitial solvent velocity (0.40-2.45 mm/s) on kinetics of extraction (oil yield versus time) were evaluated at 40degreesC and 300 bar, and at 50degreesC and 400 bar in a one-pass screening system (laboratory scale). Seeds were grinded in a hammer mill or a roller mill with a gap of adjustable thickness, and samples from the hammer mill were further size-classified. Data was fitted to a two-stage model, with extraction rate controlled by oil solubility initially, and by mass transfer in the solid phase at the end. The mass transfer coefficient and axial dispersion of the solute in the supercritical phase, and the solubility of the oil in SC-CO2 were estimated as a function of the extraction conditions using literature correlations, and the "free" oil content (X-f) and mass transfer coefficient in the solid substrate (k(s)) were used as fitting parameters. Both X-f (0.026-0.030 g oil/g substrate) and k(s) (0.6-0.9 x 10(-9) m/s) depended on sample pretreatment but not on the assayed extraction conditions, as expected. Free oil represented 33-41% of the total content, and effective diffusivities of oil in the solid were 330-710 times smaller than binary diffusivities of oil in SC-CO2. Based on best-fitting parameters for kinetic data at the laboratory-scale, extraction kinetics was simulated for a process development unit with solvent recycle (scale-up factor of 30 for the volume of the extraction vessel). It was observed that extraction was slower at the pilot plant than laboratory scale due probably to flow heterogeneity in the extraction vessel, increased dispersion of solute between the extraction and separation vessels, entrainment of oil droplets in recycled gaseous stream, or a combination of these three effects. (C) 2003 Elsevier B.V. All rights reserved.