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Ethanol was used for the extraction and purification of lipids from the biomass of the microalga Phaeodactylum tricornutum. This microalga is an oil-rich substrate with a high proportion of eicosapentaenoic acid (EPA). The process consisted of two steps. First, ethanol (96% vol/vol) was used to extract the lipids from the lyophilized biomass. Second, a biphasic system was formed by adding water and hexane to the extracted crude oil. In this way, most of the lipids were transferred to the hexanic phase while most impurities remained in the hydroalcoholic phase. The first step was carried out by two consecutive extractions at room temperature, each with 5 mL ethanol per gram of biomass, for 10 and 1.25 h, respectively. Under these conditions, over 90% of the saponifiable lipids in the biomass were extracted. In the second step, the percentage of water in the hydroalcoholic phase, the hexane/hydroalcoholic phase ratio and the number of extraction steps were optimized. A water content of 40% vol/vol in the hydroalcoholic phase provided the highest lipid recovery. A recovery yield of 80% was obtained by four consecutive extractions with a hexane/ hydroalcoholic phase ratio of 0.2 (vol/vol). Equilibrium distribution data of the lipids between the hydroethanolic and the hexanic phases were also obtained in order to predict the lipid recovery yield of the extraction. This process is an alternative to the traditional methods of lipid extraction, which uses less toxic solvents and reduces the total amount of solvents used.

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The influence of water content on the lipase-catalyzed acidolysis of triolein (glycerol-trioleate, TO) and caprylic acid (CA) in hexane, using an immobilized enzyme was studied. An adequate water content (R W ) ranged from near zero to 0.1 g of water/g of dry enzyme. Over these values there was a decrease in the rate of incorporation of CA into triglyceride. This decrease was attributed to the progressive flooding of the carrier's pores, in which the enzyme was immobilized. The flooding reduced the number of the enzyme molecules at the water-hexane interface and therefore, hindered the accessibility of the hydrophobic substrates (TO and CA) to the enzyme. A simple physical model based on a characterization of the immobilized enzyme particle by mercury porosimetry was developed. The model agreed well with both the experimental data and the prior published data. The model may partly explain the observed inhibition when using low molecular weight alcohols and carboxylic acids in immobilized lipase-catalyzed processes.