Characterisation of acorn oils extracted by hexane and by supercritical carbon dioxide

Abstract

Acorn fruit oils from two species of oak, Quercus rotundifolia L. (holm-oak) and Quercus suber L. (cork-oak), were extracted by n-hexane. The acorn fruit of Quercus rotundifolia L. was also extracted by supercritical CO2 at 18 MPa and 313 K, a superficial velocity of 2.5 × 10-4 ms-1, and a particle size diameter of 2.7 × 10-4 m. The oils were characterised in terms of fatty acids, triglycerides, sterols, tocopherols, and phospholipids. The main fatty acid in both fruit species was oleic acid (about 65%), followed by linoleic acid (about 16.5-17%) and palmitic acid (about 12.1-13.4%). The main triglyceride found in acorn oils was the OOO (oleic, oleic, oleic) triglyceride (33-38%), followed by the POO (palmitic, oleic, oleic) triglyceride (12.6-18.2%). In terms of sterols, the main component in acorn oils of both species was β-sitosterol (83.5-89%), followed by stigmasterol (about 3%). However, in Quercus suber L., acorn oil was found to consist to 10.2% of campesterol. The amount of cholesterol was low (0.27% for the Quercus rotundifolia L. oil extracted by supercritical fluid extraction, and 0.18% for the oil extracted by n-hexane). The Quercus suber L. acorn oil presented 0.1% of cholesterol. The total amount of tocopherols in Quercus rotundifolia L. acorn oils was almost the same when the oil was extracted by n-hexane (973 mg/kg oil) or by supercritical CO 2 (1006 mg/kg oil). The Quercus suber L. acorn oil presented a high value of total tocopherols (1486 mg/kg oil). The supercritical CO2 did not extract the phospholipids. The amount of phospholipids was very similar for both species of oak acorn oils extracted by n-hexane. Oxidative stability was also studied, by using the peroxide value and the Rancimat method, revealing that all the oils were significantly protected against oxidation. The influence of storage, under several conditions, on the oxidative stability was also studied. The Quercus rotundifolia L. oil extracted by n-hexane was better protected against oxidation after a few days of storage at 60°C. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.