Determination of volatile compounds in antioxidant rosemary extracts by multiple headspace solid-phase microextraction and gas chromatography

Abstract

Rosemary extracts are commercialized as natural antioxidants that delay the lipid oxidation process. Residual amounts of rosemary odour-responsible volatile compounds, such as borneol, camphor and verbenone, can remain in the final extract. The presence of these compounds may be undesirable when the extracts are used as food or cosmetic additives. In this paper a MHS–SPME method is proposed to quantify 10 rosemary odour-responsible compounds in a commercial solid rosemary extract. Multiple headspace solid-phase microextraction (MHS–SPME) is a recent technique proposed to eliminate the matrix effect on the quantitative analysis of solid samples. This technique performs few consecutive extractions from the same sample, and the total area corresponding to an exhaustive extraction is calculated as the sum of individual area values obtained from each extraction or by using an equation. The most influential variables of the extraction process, such as type of fibre, temperature and extraction time, were studied. Extraction was carried out using 2.5 mg solid extract and a divinylbenzene-carboxen-polydimethylsiloxane (DVB–CAR–PDMS) fibre at 55 °C for 60 min; calibration was carried out using aqueous standard solutions containing 1% (v/v) ethanol at 40 °C for 45 min. The features of the method were established using aqueous standard solutions. Precision was 4–15%, expressed as RSD, and the method allowed detection limits of 0.4–47 ng for p-cymene and verbenone, respectively. Finally, the method was applied to analyse a rosemary solid extract, and verbenone (356 µg/g), borneol (190 µg/g) and camphor (136 µg/g) were found to be the most abundant compounds. Copyright © 2006 John Wiley & Sons, Ltd.