Submitted to: American Society of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2006
Publication Date: 8/1/2006
Citation: Weston, T.R., Derner, J.D., Murrieta, C.M., Rule, D.C., Hess, B.W. 2006. Comparison of catalysts for direct transesterification of fatty acids in freeze-dried forage samples. In: Proceedings of the American Society of Animal Science. 57:245-248. Interpretive Summary: Determinations of fatty acids in forage samples using the current single step process (boron-trifluoride) are costly, and chemicals used can pose environmental hazards of toxicity and carcinogenic properties. We compared a new method (methanolic hydrochloric acid, HCl) with the current process using freeze dried forage samples from dominant plant species in the northern mixed-grass prairie. Fatty acid concentrations did not differ between the current process and new method for the species studied. The new method is cost effective, more environmentally friendly, appropriate substitute for determining fatty acids (concentrations and weight percentages) from freeze dried forage samples.
Technical Abstract: Our objective was to compare 1.09 M methanolic HCl to 14% BF3 in methanol as catalysts for direct transesterification of fatty acids in freeze-dried forage samples. Samples included blue grama (Bouteloua gracilis), fringed sage (Artemisia frigida), western wheatgrass (Pascopyrum smithii), needle-and-thread (Stipa comata), dalmation toadflax (Linaria dalmatica), needleleaf sedge (Carex eleocharis), and scarlet globemallow (Sphaelercea coccinea). Thin layer chromatographic evaluation revealed complete conversion of total lipid extracts to fatty acid methyl esters using both catalysts. Additionally, GLC analysis confirmed similar (P = 0.96) total fatty acid concentrations for both catalysts. Concentrations of most identified fatty acids (13:0, 14:0, 16:0, 16:1, 17:0, 17:1, 18:0, 18:1, 18:2, 18:3, 19:0, 20:0, 20:1, 22:0, 22:1, 22:3, 24:0, 24:1, and 28:0) were similar (P = 0.17 to 0.99) for both catalysts. Concentrations of 14:0 tended to be greater (P = 0.07) for HCl but weight percentages of 14:0 did not differ (P = 0.23) between catalysts. Concentrations and weight percentages of 17:1 were less (P < 0.0001) for HCl compared with BF3. Boron-trifluoride may cause partial isomerization of predominant fatty acids because the concentrations of unidentified fatty acids with GLC retention times of 8.0, 13.9, and 31.9 min were greater (P = 0.005 to 0.05) for BF3; whereas, only the concentration of unidentified fatty acid eluding at 14.8 min was greater (P = 0.02) for HCl. Nevertheless, total concentration of unidentified fatty acids did not differ (P = 0.71) between catalysts. Additionally, total weight percentages of identified fatty acids and unidentified fatty acids were not affected (P = 0.37) by catalyst (91.2 and 8.8% vs. 90.6 and 9.4% for HCl and BF3, respectively). It is also possible that BF3 is more efficient at catalyzing methylation of less common or unusual fatty acids, but BF3 costs $0.19 per sample more than HCl. We conclude that 1.09 M methanolic HCl is both a cost effective and appropriate substitute for 14% BF3 in methanol for preparation of fatty acid methyl esters from freeze-dried forage samples.