Extraction of canola oil with supercritical carbon dioxide

Abstract

The objective of the study was to extract canola oil from seed (Brassica napus) by means of supercritical carbon dioxide (sc-CO2). Extractions were performed with a laboratory scale supercritical fluid extractor (LECO TFE 2000) of the latest design and performance. Extracts were analysed by GC-FID and GC-GC/TOF-MS and a total of 49 components in the extracted oil could be identified. The composition of the sc-CO2 derived canola oil was in excellent agreement with that of canola oil in the marketplace, while the chemical specification of the sc- CO2 oil was benchmarked against an industrial standard. The density of sc-CO2 was found to be the variable which controls the extraction as the fluid becomes capable of chemically dissolving the canola oil from the seed matrix once its density (and thus its solvent strength) approaches liquid-like values (0.8 < p < 1.0 g/mL). The solubility of the oil in sc-CO2 could be measured at a given set of conditions (0.036 g per gram of sc-CO2 at 300 atm and 50°C) by utilising the static extraction mode of the supercritical extractor, whereas the oil content of the seed could by determined (0.14 - 0.22 g oil per gram of seed) by exhaustive extraction utilising the dynamic mode of the supercritical extractor. The conditions at which a maximum yield of oil could be obtained (80°C, 600 atm, 70 min) were determined by performing runs according to a statistical design and processing the data by computer assisted surface response analysis. The temperature and pressure dependencies of the extraction were also studied in order to calculate activation parameters (Ea ~ 0 kJ/mol, AV' = -130 mL/mol) and hence assisted in confirming the mechanistic steps (chemical dissolution, diffusion controlled transport) of the extraction process. Finally the effect of pre-drying of seed and using different cultivars of seed on the extraction was studied.