Submitted to: Journal of the Association of Official Analytical Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 1998
Publication Date: N/A
Interpretive Summary: Current Federal regulations require that foods be analyzed and labeled with the content of total fat and saturated fat. To determine fat content, food processors must measure various components of the fat. During the analysis of a low fat cake, the fat content was greatly overestimated. Further tests, needed to determine why this was happening, showed that a compound called methyl levulinate was interfering with the fat analysis. Methyl levulinate is produced from the sugar in the cake. The effect of methyl levulinate on fat content varies with the amounts of fat and sugar in the food and the influence of this compound is greatest in low fat/high sugar foods. The recognition of the potential interference of methyl levulinate in analysis of low fat/high sugar foods will lead to more accurate fat determinations of these types of foods. This information can be used by food manufacturers and nutritionists.
Technical Abstract: Gas chromatographic fatty acid methyl ester (GC-FAME) analyses of some acid-hydrolyzed foods revealed a large peak that did not correspond to any FAME standards. The unknown peak eluted just after the C-12 FAME. If the fatty acid response factor and conversion factor for the nearest calibrated peak (C-12 FAME) was used to determine the total fat, the resulting total fat determination was much higher than expected. This peak was present only in acid-hydrolyzed samples and was absent in extracts using supercritical CO2 or solvents without acid hydrolysis. The compound was isolated, analyzed by mass spectrometry and nuclear magnetic spectroscopy, and proven by synthesis to be methyl-4-oxo- pentanoic acid (methyl levulinate). The source of the methyl levulinate was determined to be sugar in the product formula. Levulinic acid is produced by acid hydrolysis of sugar and transesterified by BF3/MeOH to methyl levulinate. Although methyl levulinate may appear in the GC analyses of any acid hydrolyzed products containing sugar, if the ratio of fat to sugar is high, the impact of methyl levulinate on fat determination would be small. On the other hand, the presence of methyl levulinate in analyses of low fat/high sugar products is potentially problematic if not recognized, although GC analysis can account for the presence of this compound.