Rapid, colorimetric quantification of lipid from algal cultures

Algae have significant potential as a source of biomass for the production of biofuels, due to their high growth rates and high cellular lipid content. Studies that address the use of algae as biofuels often require the frequent measurement of algal lipid content. Traditional methods for the quantification of lipid are, however, costly if sub-contracted, or involve the use of expensive analytical equipment that is not available in many labs. This study describes a simple, colorimetric method for the quantification of algal lipid from small amounts of culture. The technique is derived from a method for the quantification of fatty acids dissolved in chloroform. Algal lipids are saponified to fatty acids and then mixed with a copper reagent. Chloroform-extractable copper soaps of long-chain fatty acids are then colorimetrically measured by the addition of diethyldithiocarbamate to develop a yellow colored product. Linear responses for fatty acids in the range of C10:0 to C16:0 were observed for a concentration range between 0.025 and 1 μmol of fatty acid per 200 μL of sample. Fatty acids with chain lengths of less than twelve carbons produced significantly reduced signal. Decenoic acid yielded a slightly, but significantly lower signal than decanoic acid indicating that the assay underestimates the presence of unsaturated fatty acids. Lipid contents of Phaeodactylum tricornutum and Chlorella vulgaris CM2 were monitored for eight days during exponential growth to demonstrate the feasibility of the technique as a monitoring methodology. Overall, the method allowed reliable detection and quantification of fatty acid content from 1 to 2 mL of algal culture. Adaptation of the technique to micro-centrifuge format allows assaying 30 samples in less than 2 h. Considering reagents and time, the total cost per assay was estimated at less than $5, representing a significant cost savings over traditional lipid quantification procedures.