By Mohamed El Hattab, Hala Sultan Saif Al Easa, Annie Tabaries, Louis Piovetti and Jean-Michel Kornprobst

Abstract: Abstract: We report the results of a study of volatile compounds from the brown alga Hormophysa cuneiformis collected off the northwest coast of Qatar in May 2002. For this work two extraction methods were used: conventional hydrodistillation of the crude diethyl ether extract of the alga and supercritical CO₂ extraction of the same crude extract with two different stationary phases for the trapping. The volatiles obtained from both methods were compared after analysis by GC and GC/MS. The major constituents were squalene, described for the first time in a large amount from a macroalga, fatty acids and corresponding esters. Key Word Index: Hormophysa cuneiformis, Cystoseiraceae, brown alga, extract composition, tetradecanoic acid, hexadecanoic acid, linoleic acid, ethyl arachidonate, squalene, volatile isolation methods.

Introduction
Supercritical fluid extraction (SFE) is an advanced separation technique based on the enhanced solvating power of substances such as carbon dioxide above their critical point. Its usefulness for sample extraction is due to the combination of gaslike mass transfer properties and liquidlike solvating characteristics with diffusion coefficients greater than that of a liquid (1). The use of supercritical CO₂ (SC-CO₂) for extraction of the volatiles has become an important application (2) because it improves the organoleptic properties of the end product. For example, Reverchon and coworkers developed a process to fractionate jasmine (3) and rose (4) concretes by SC-CO₂. The process was based on increasing of supercritical solvent density and by using multistage separation technique.

From our knowledge, the SC-CO₂ extraction was rarely used to obtain volatiles from algae. In contrast, conventional hydrodistillation (5,6) was often used, also the “closed-loopstripping” method (7–9) and, one time, the focused microwave-assisted hydrodistillation (10). These techniques were used particularly to obtain the volatiles from the brown algae of the genus Dictyopteris (5,6,8–10).

In this study, we report for the first time the identification and determination of volatile compounds from the brown alga Hormophysa cuneiformis. We applied the supercritical carbon dioxide fractionation to prepare a volatile fraction from the concrete of this species obtained by solvent extraction with diethylether. A volatile fraction was also prepared by classical hydrodistillation. Both volatile fractions were analyzed by gas chromatography and gas chromatography/mass spectrometry to compare their chemical composition.