Efficient Fractionation and Analysis of Fatty Acids and their Salts in Fat, Oil and Grease (FOG) Deposits

A fractionation methodology of fat, oil and grease (FOG) deposits was developed based on the insolubility of fatty acid salts in dichloromethane (DCM) and the relatively high solubility of fatty acids and triglycerides in DCM. Using this method, coupled with spectral analysis, it was shown that fatty acids rather than fatty acid salts were the predominant species in FOG deposits obtained from three metropolitan locations in the United States and that fatty acid triglycerides were either not detected or were present in very small concentrations. This solubility-based fractionation approach also revealed the presence of nitrogen-containing compounds that had not been previously detected in FOG deposits including peptides and (or) proteins. The comparison of the ratios of stearic acid salts to stearic acid versus the ratio of palmitic acid salts to palmitic acid in FOG deposits may indicate that the initial step in FOG deposit formation is the preferential precipitation of stearic acid salts.