Accurate and reliable quantification of total microalgal fuel potential as fatty acid methyl esters by in situ transesterification

TLDR

In algal biofuels, lipids—particularly aliphatic fatty acids—are the most important biomass constituents, and accurate quantification is essential for comparing strains, growth conditions, and monitoring processes. The study develops a robust, small‑scale, single‑step in situ transesterification procedure to quantify algal lipids as fatty acid methyl esters across diverse species and conditions. The method tests varying reaction time, temperature, and biomass water content, evaluates different catalysts—including HCl—and measures FAME yield and profile in four algal species. Whole‑biomass transesterification accurately reflects true fuel yield, with HCl providing high conversion and 1.9 % RSD, and the authors achieve full mass‑balance closure relative to traditional extraction.

Abstract

In the context of algal biofuels, lipids, or better aliphatic chains of the fatty acids, are perhaps the most important constituents of algal biomass. Accurate quantification of lipids and their respective fuel yield is crucial for comparison of algal strains and growth conditions and for process monitoring. As an alternative to traditional solvent-based lipid extraction procedures, we have developed a robust whole-biomass in situ transesterification procedure for quantification of algal lipids (as fatty acid methyl esters, FAMEs) that (a) can be carried out on a small scale (using 4–7 mg of biomass), (b) is applicable to a range of different species, (c) consists of a single-step reaction, (d) is robust over a range of different temperature and time combinations, and (e) tolerant to at least 50% water in the biomass. Unlike gravimetric lipid quantification, which can over- or underestimate the lipid content, whole biomass transesterification reflects the true potential fuel yield of algal biomass. We report here on the comparison of the yield of FAMEs by using different catalysts and catalyst combinations, with the acid catalyst HCl providing a consistently high level of conversion of fatty acids with a precision of 1.9% relative standard deviation. We investigate the influence of reaction time, temperature, and biomass water content on the measured FAME content and profile for 4 different samples of algae (replete and deplete Chlorella vulgaris, replete Phaeodactylum tricornutum, and replete Nannochloropsis sp.). We conclude by demonstrating a full mass balance closure of all fatty acids around a traditional lipid extraction process.