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The extraction of carotenoids and chlorophylls using carbon dioxide modified with ethanol as a cosolvent is an alternative to solvent extraction because it provides a high-speed extraction process. In the study described here, carotenoid and chlorophyll extraction with supercritical CO(2 )+ ethanol was explored using freeze-dried powders of three microalgae (Nannochloropsis gaditana, Synechococcus sp. and Dunaliella salina) as the raw materials. The operation conditions were as follows: pressures of 200, 300, 400 and 500 bar, temperatures of 40, 50 and 60 degrees C. Analysis of the extracts was performed by measuring the absorbance and by using empirical correlations. The results demonstrate that it is necessary to work at a temperature of 50-60 degrees C and a pressure range of 300-500 bar, depending on the type of microalgae, in order to obtain the highest yield of pigments. The best carotenoid/chlorophyll ratios were obtained by using supercritical fluid extraction + cosolvent instead of using conventional extraction. The higher selectivity of the former process should facilitate the separation and purification of the two extracted pigments.

<p class="MsoNormal"> <span lang="EN-GB">The work described here is based on a comparative study of carotenoids and fatty acids extracted from <i>Synechococcus </i>sp. with (1) pure supercritical CO₂, (2) CO₂ with 5% (v/v) ethanol as cosolvent and (3) ultrasound-assisted extraction using <i>N</i>,</span><span lang="EN-GB"> </span><i><span lang="EN-GB">N</span></i><span lang="EN-GB">-dimethylformamide (DMF). The effects of extraction conditions on supercritical CO₂ extraction with and within cosolvent were analyzed at different temperatures (40℃, 50<span style="white-space:normal;"><span style="white-space:normal;">℃</span></span> and 60<span style="white-space:normal;"><span style="white-space:normal;">℃</span></span>) and pressures (200, 300 and 400 bars). SFE with CO₂proved to be the most selective method for the extraction of <i>β</i>-carotene, but under these conditions the contents of zeaxanthin and fatty acids were only comparable to or lower than those obtained with techniques that use SFE cosolvent. The SFE technique with CO₂ and ethanol simultaneously extracted <i>β</i>-carotene and zeaxanthin and not only increased the concentrations of fatty acids obtained, but also helped to remove fatty acids (palmitoleic and lino</span><span lang="EN-GB">lenic acid) that were not obtained with pure CO₂. </span><span lang="EN-US">Comparison of the supercritical technology with the ultrasound-as</span><span lang="EN-US">sisted extraction (UAE) shows that the former technique is the most appropriate due to the fact that ethanol is generally regarded as a safe solvent in comparison to DMF.</span> </p>

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