Abstract
Background Microalgae have the potential to rapidly accumulate lipids of high interest for the food, cosmetics, pharmaceutical and energy (e.g. biodiesel) industries. However, current lipid extraction methods show efficiency limitation and until now, extraction protocols have not been fully optimized for specific lipid compounds. The present study thus presents a novel lipid extraction method, consisting in the addition of a water treatment of biomass between the two-stage solvent extraction steps of current extraction methods. The resulting modified method not only enhances lipid extraction efficiency, but also yields a higher triacylglycerols (TAG) ratio, which is highly desirable for biodiesel production.ResultsModification of four existing methods using acetone, chloroform/methanol (Chl/Met), chloroform/methanol/H2O (Chl/Met/H2O) and dichloromethane/methanol (Dic/Met) showed respective lipid extraction yield enhancement of 72.3, 35.8, 60.3 and 60.9%. The modified acetone method resulted in the highest extraction yield, with 68.9 ± 0.2% DW total lipids. Extraction of TAG was particularly improved with the water treatment, especially for the Chl/Met/H2O and Dic/Met methods. The acetone method with the water treatment led to the highest extraction level of TAG with 73.7 ± 7.3 µg/mg DW, which is 130.8 ± 10.6% higher than the maximum value obtained for the four classical methods (31.9 ± 4.6 µg/mg DW). Interestingly, the water treatment preferentially improved the extraction of intracellular fractions, i.e. TAG, sterols, and free fatty acids, compared to the lipid fractions of the cell membranes, which are constituted of phospholipids (PL), acetone mobile polar lipids and hydrocarbons. Finally, from the 32 fatty acids analyzed for both neutral lipids (NL) and polar lipids (PL) fractions, it is clear that the water treatment greatly improves NL-to-PL ratio for the four standard methods assessed.ConclusionWater treatment of biomass after the first solvent extraction step helps the subsequent release of intracellular lipids in the second extraction step, thus improving the global lipids extraction yield. In addition, the water treatment positively modifies the intracellular lipid class ratios of the final extract, in which TAG ratio is significantly increased without changes in the fatty acids composition. The novel method thus provides an efficient way to improve lipid extraction yield of existing methods, as well as selectively favoring TAG, a lipid of the upmost interest for biodiesel production.
Highlights
Microalgae have the potential to rapidly accumulate lipids of high interest for the food, cosmetics, pharmaceutical and energy industries
H2O treatment significantly improves total lipid extraction yield In the present study, we evaluated a modification to current extraction methods for lipids in microalgae, adding a water treatment between two successive solvent extraction stages
Our results show that in the control group, most of the extraction occurred in the first extraction step, with the second extraction yield only accounting for 31.2 ± 2.9% (13.3 ± 1.2% DW), 42.1 ± 1.1% (12.6 ± 0.1% DW), 32.0 ± 1.8% (13.6 ± 1.1% DW) and 32.5 ± 2.5% (12.6 ± 0.5% DW) of total extraction yield for acetone, Chl/Met, Chl/Met/H2O and Dic/ Met methods respectively
Summary
Microalgae have the potential to rapidly accumulate lipids of high interest for the food, cosmetics, pharmaceutical and energy (e.g. biodiesel) industries. The resulting modified method enhances lipid extraction efficiency, and yields a higher triacylglycerols (TAG) ratio, which is highly desirable for biodiesel production. Microalgae cells can accumulate lipids at up to 20–50% of their cell dry weight [3], and which can be used as precursors for biodiesel production after a transesterification step [4, 5]. The downstream process normally accounts for the major part of a bioprocess costs, only limited attention has been placed on the amelioration of lipid extraction protocols [3, 24, 25]; a step still considered as one of the major bottlenecks for commercial-scale biodiesel production [26]. The solvents perform lipid extraction, which explains the amount of work dedicated to identify the most efficient solvents combination
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