Study on the pilot-scale extraction of onion oleoresin using supercritical CO2

Supercritical carbon dioxide (SC-CO2) was used to produce oleoresin from dried onion by pilot-scale extraction. The results showed that the extraction pressure and temperature affected the yield and sulphur concentration of onion oleoresin. Increase of the temperature from 45 to 65 degrees C at 300 bar resulted in an increase of the yield and the sulphur concentration of oleoresin. At the same temperature (45 degrees C) the yield was also higher at 300 bar than 100 bar while sulphur concentration of oleoresin got smaller at 300 bar than at 100 bar. The volatile composition of oleoresin displayed practically no differences as a function of extraction parameters, Comparison of different extraction methods showed that the yield after SC-CO2 extraction was 22 times higher than that after steam distillation, but it was 14 or 39 times less than that after alcohol extraction, shaking at 25 degrees C or in Soxhlet apparatus, respectively. The concentration of sulphur was the highest in steam distilled onion oil while it was the lowest in the extract of hexane and alcohol (at 25 degrees C). The results of sensory evaluation showed that oleoresin extracted by SC-CO2 was the first in ranking (at level of significance 0.05), before steam distilled oil and alcoholic extract. There was no significant difference between steam distilled oil and alcoholic extract in ranking, but the alcoholic extract was the least desirable, since the intensity of its off odour attribute was the highest. (C) 1998 SCI.