Optimization of Focused Ultrasound Extraction (FUSE) and Supercritical Fluid Extraction (SFE) of Citrus Peel Volatile Oi
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Optimization of Focused Ultrasound Extraction (FUSE) and Supercritical Fluid Extraction (SFE) of Citrus Peel Volatile Oils and Antioxidants J. Omar & I. Alonso & A. Garaikoetxea & N. Etxebarria
Received: 13 September 2012 / Accepted: 15 November 2012 / Published online: 28 November 2012 # Springer Science+Business Media New York 2012
Abstract In order to evaluate the use of citrus peel as a potential source of volatile oils and antioxidants in food industry, supercritical fluid extraction (SFE) and focused ultrasound extraction (FUSE) techniques have been thoroughly studied. Based on experimental designs and considering the extraction of monoterpenes among the volatile oils, the total phenol content, and the antioxidants, the most adequate extraction conditions have been defined for lemon and then applied to other citrus. The optimum SFE conditions for volatile oils and antioxidants were the following: pressure, 100 and 170 bar; temperature, 35 °C for both; flow, 1 mL/min in both cases; EtOH%, 0 and 40 %, respectively. FUSE extraction of the volatile oils was carried out with cyclohexane and the antioxidants with ethanol. The optimum instrumental conditions were roughly the same (extraction time 5 min, cycles 5 s−1, and amplitude 30 % in both cases, and 10 and 15 mL, respectively, in the case of solvent volumes). Based on successive extractions, FUSE revealed a more efficient technique owing to the solvent features. Finally, a stability test of the content of aromas and antioxidant capacity was carried out and aromas were stable stored at 4 °C for 6 weeks and the antioxidant capacity, in the same conditions, for 13 weeks. Keywords Citrus volatile oils . Citrus antioxidants . SFE . FUSE . Optimisation J. Omar (*) : A. Garaikoetxea : N. Etxebarria Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country, PO Box 644, Bilbao 48080 Basque Country, Spain e-mail: [email protected] I. Alonso Idoki SFC Technologies, Technologic Park of Zamudio, Ibaizabal Bidea, Building 502, 48160 Derio Biscay, Spain
Introduction Citrus peel is typically considered a waste material as it is the residue obtained after the extraction of the juice from citrus fruit. However, owing to the high levels in volatile compounds and polyphenols, it can be a very valuable residue. In fact, citrus volatile compounds are complex mixtures containing from a few dozen to several hundred constituents (Mondello et al. 2005), especially hydrocarbons (monoterpenes and sesquiterpenes) and oxygenated terpenes. The proportion of these constituents as individual compounds in the oil composition differs from trace levels to over 90 %. Precisely, trace components are important, since they give to the oil the featuring natural odor (Pourmortazavi and Hajimirsadeghi 2007). Concerning phenolic compounds, they are secondary plant metabolites which posses an aromatic ring bearing one or more hydroxyl groups. Following the terminology critically revised recently by Quideau et al. (2011) among plant phenols, we will consider
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