CONTINUOUS FRACTIONATION OF FRIED OIL BY SUPERCRITICAL CO 2 L. Sesti Osséo a , G. Caputo a , I. Gracia b and E. Reverchon a a Dipartimento di Ingegneria Chimica e Alimentare. Università degli Studi di Salerno. Via Ponte Don Melillo, 84084 Fisciano (SA), Italy. FAX. +39089964057 E-Mail: ereverchon@unisa.it b Departamento de Ingeniería Química. Universidad de Castilla-La Mancha. Facultad de Ciencias Químicas. Avda. Camilo José Cela nº 10. 13004 Ciudad Real. España. ABSTRACT Fried oils are a waste generated from food industries and restaurants that are usually discarded because oxidized lipids degrade the quality of the fried food. The development of new purification technologies has been of increasing interest over the last years, because the fried oil still contains a large quantity of triglycerides that could be recycled. Fractionation by supercritical Carbon Dioxide (SC-CO 2 ) might be an effective way for the purification of fried oils because SC-CO 2 can selectively separate oil components on the basis of their polarity and molecular weight. In this work we studied the fractionation of fried peanut oil by SC-CO 2 continuous fractionation. The fractionation has been carried out in a continuous packed column with an inner diameter of 17.5 mm and an effective height of 1920 mm, with the feed at about 800 mm from the top. The content of polymeric compounds (POL), triglycerides (TG) and low molecular weight compounds (LMWC) in the fractionated streams was evaluated by high-pressure size exclusion chromatography. We studied the influence of pressure (in the range 15-35 MPa), of temperature (in the range 25-55 °C), on the process yield and on the composition of extracted streams. Operation conditions were optimised to separate POL and TG fractions in the separation column. Experimental results indicate that the optimal operating conditions leading to maximal TG to POL separation and maximum recovery of TG in the extract were at 35 MPa, 55°C and at solvent to feed ratio of 50. INTRODUCTION Food industry uses a large quantity of fats and oils for the preparation various kind of fried foods. During the frying process, fat and oil chemical changes are due to high process temperatures. The main reactions during deep-fat frying include formation of coniugated dienes, formation and decomposition of hydroperoxides, formation of low molecular carbonyl compounds, hydrolysis of triglycerides, and polymerization via complex free radicals. These changes produce a degradation of chemical, physico-chemical and organoleptic characteristics of the oil, and after several heating cycles the oil must be discarded [1, 2, 3]. This residue cannot be reused because of the high content of pollutants; nevertheless the oil still contains a large proportion of valuable compounds. Thus, environmental and economical reasons justify the hypothesis of a regeneration process. The target of the regeneration of used-frying oil should be the removal of the low molecular weight (LMWC) and polymer (POL) compounds. In the last ten years, several attempts have been made to purify the used frying oil, especially using adsorbent treatments [4-8].