Supercritical fluid extraction and characterisation of oil from hazelnut

Abstract

Hazelnut (Corylus avellana L.) oil was extracted with compressed carbon dioxide in the temperature range of 308—321 K and in the pressure range of 18—23.4 MPa. In addition the influence of the superficial velocity, within a tubular extractor was studied. Physical and chemical characteristics of the oil were obtained. The results including contents of free fatty acids, sterols, triacylglycerols and tocopherols were compared with those obtained when n-hexane was used as solvent. No significant differences were found when the oils extracted by both methods were analysed. The main fatty acid was the oleic acid (83—85%), followed by linoleic acid (6—8%) and palmitic acid (5—6%). The main triglyceride found in hazelnut oils was the trioleylglycerol (OOO) (63.4—69.6%), followed by the linoleyl-dioleylglycerol (LOO) (11.6—15.5%) and palmitoyl-dioleylglycerol (POO) (9.9—10.4%). In terms of sterols, the main component was β-sitos-terol (∼83%) followed by campesterol (∼6%). The amount of cholesterol was very low (∼0.2%). The CO2 extracted oil contained about 17% more tocopherols (458.7 μg/g oil) than the oil extracted by n-hexane (382.8 μg/g). Oxidative stability was studied by using the induction time determined by the Rancimat method. The oil obtained by supercritical fluid extraction (SFE) was slightly more protected against oxidation (8.7 h for SFE extracted oil and 6.7 h for the hazelnut oil extracted with n-hexane). Both oils presented high stability index values (7.81 for the oil extracted by n-hexane and 8.7 for the oil extracted with supercritical CO2). Oil extracted by supercritical CO2 was clearer than the one extracted by n-hexane, showing some refining. Besides, the acidity index was 1.6 for the n-hexane extracted oil and 0.9 for the oil extracted with supercritical carbon dioxide. The central composite non-factorial design was used to optimise the extraction conditions, using the Statistica, version 5 software (Statsoft). The best results, in terms of recoveries of hazelnut oil by SFE, were found at 22.5 MPa, 308 K and superficial velocity of 6.0 × 10—4 ms—1.