Determination of free sterols in red an d brown algae by FTIR spectroscopy

A new analytical method was developed for the...

A new analytical method was developed for the determination of free sterols in the extracts of the red alga Asparagopsis armata and the brown one Cystoseira sedoides by using FTIR spectrometry. Sterols samples were globally refered to cholesterol content because it is the major sterol contained in red algae [1] and to fucosterol because it is the principal one contained in brown ones [2]. The method involves the use of cholesterol as reference standard in the case of red alga and a correction factor of 1.259 ±0.003, which represents the ratio between the slopes of calibration lines obtained from fucosterol and cholesterol in the case of brown alga. To isolate the sterols, the lipidic extract of the algae were heated in methanol and diluted with water and then preconcentrated on DSC-18 solid phase cartridges and eluted with 1 mL dichloromethane stabilized with β-amylene. The determination of free sterols by Fourier transform infrared spectrometry was carried out by considering the specific band of cholesterol at 1047 cm-1 corrected with a baseline established between 1060 and 1014 cm-1. The sterols content were obtained by the external calibration. The concentrations obtained were 1.9 ± 0.5 % and 1.5 ± 0.4 % in Asparagopsis armata and Cystoseira sedoides, respectively.

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