Comparison of Catalysts for Direct Transesterification of Fatty Acids in Freeze‐Dried Forage Samples

Abstract

Preparation of fatty acid methyl esters from forages comparing methanolic boron‐trifluoride (BF3) to methanolic hydrochloric acid (HCl) as a catalyst in single‐step direct transesterification has not been reported. Our objective was to compare 1.09 M methanolic HCl to 1.03 M (7%) methanolic BF3 as catalysts for direct transesterification of fatty acids in freeze‐dried forage samples. Thin‐layer chromatographic analysis revealed complete conversion of total lipid extracts to fatty acid methyl esters using both catalysts. Additionally, gas–liquid chromatography analysis confirmed similar (P = 0.95) total fatty acid concentrations for both catalysts. Regression analysis indicated that similar values for total concentration would be obtained (P < 0.0001; r2 = 0.96; slope = 0.98 ± 0.03) between the two catalysts. Concentrations of most individual fatty acids were similar (P = 0.17–0.99) for both catalysts. Summed weight percentages of identified fatty acids, as well as sum of unidentified peaks, were not affected (P = 0.27) by catalyst (91.8 and 8.7% vs. 90.8 and 9.2% for HCl and BF3, respectively). We conclude that 1.09 M methanolic HCl is an appropriate substitute for 1.03 M methanolic BF3 for preparation of fatty acid methyl esters from freeze‐dried forage samples. This result is of interest because HCL is both less costly and less caustic than BF3