Methods for analysis of esterified and free long-chain fatty acids in high-lipid food processing wastes

Methods to screen the lipid composition of anaerobic food waste digester contents were developed. A colorimetric assay for long-chain fatty acid (LCFA) domains in mixed liquor measuring the partitioning of a lipophilic dye (Sudan III) between the lipid and an aqueous ethanol phase was validated using sheep tallow, deep water fish oil wax esters (orange roughy), olive oil, tripalmitin, tallow mixtures with phosphatidylcholine and cholesterol in a range of 0-10 g/L lipid, and mixed liquor from two different anaerobic digesters. Bacterial and yeast cells at up to 5 gn did not interfere. The assay correlated well with the gravimetric lipid determination by the standard Bligh and Dyer method. Base-catalyzed esterification was employed as an alternative rapid method to trans-methylate esterified fatty acids in the presence of nonesterified lipid for gas chromatographic analysis. Derivatization and solvent extraction of methyl esters was followed by acidification of LCFA soaps and solvent recovery of the liberated fatty acids. Profiles were similar to those obtained using conventional silicic acid chromatography followed by methyl ester analysis.