Effect of sonication at different ultrasonic frequencies on the quality and quantity of fatty acids of the oil of Chlorella vulgaris

In order to investigate the effect of sonication on the fatty acids of alga oil, oil of Chlorella vulgaris was extracted by sonication at 20, 40, 60 and 80 kHz. Oil extracted by refluxing alga cells in n-hexane was used as control. Probable changes in the structures of the fatty acids were investigated using gas chromatography and Fourier transform infrared spectroscopy (FT-IR). The retention profiles of the chromatograms were similar with differences observed only in peak heights. The FT-IR spectrum of the hexane extract was similar to the spectra of oil extracted at 20 and 40 kHz. The FT-IR spectra of oil extracted at 60 and 80 kHz were identical but different from the other spectra. Peaks at about 1560 cm-1 which were prominent in the 60 and 80 kHz spectra but absent from the other spectra were assigned to non-oil lipids such as steroids. It was concluded that extraction of oil from C. vulgaris by sonication at 20, 40, 60 and 80 kHz had no degradative effect on the structure of the fatty acids of C. vulgaris.   Key words: Alga, triglycerides, extraction, sonication, chromatography, spectroscopy.