Lipolysis of menhaden oil triacylglycerols and the corresponding fatty acid alkyl esters by pancreatic lipase in vitro: a reexamination.

Ly Yang,A Kuksis,Jj Myher

doi:10.1016/s0022-2275(20)42768-3

Abstract

In order to distinguish between possible fatty acid differences during lumenal lipolysis and cellular absorption, we have reinvestigated the in vitro hydrolysis of menhaden oil and its alkyl esters by pancreatic lipase. For this purpose we incubated menhaden oil or its fatty acid methyl and ethyl esters with porcine pancreatic lipase in the presence of bile salts and determined the composition of the released free fatty acids, monoacylglycerols, diacylglycerols, and residual triacylglycerols, or the free fatty acids and residual alkyl esters, respectively, by thin-layer and gas-liquid chromatography. There was significant discrimination against the delta 4- to delta 7-unsaturated fatty acids of both medium and long chain lengths during the hydrolysis of menhaden oil and its fatty acid ethyl esters. In general, the ethyl esters were hydrolyzed 10-50 times more slowly than the corresponding glyceryl esters, depending on the exact ratio of the two substrate types. None of the triacylglycerols or ethyl esters, however, was completely resistant to hydrolysis resulting in an eventual cleavage of all the alkyl esters and presumably all the primary ester bonds in the triacylglycerol molecules. Since the rate of release of the least resistant fatty acid exceeded that of the most resistant acid by only a factor of 6, it is concluded that in the presence of a large excess of lipase the liberated fatty acids would approach the composition of the dietary alkyl or glyceryl esters, as observed during lumenal lipolysis (Yang, L.-Y., A. Kuksis, and J. J. Myher. 1989. Biochem. Cell Biol. 67: 192-204).

Highlights

In order to distinguish between possible fatty acid differences during lumenal lipolysis and cellular absorption, we have reinvestigated the in vitro hydrolysis of menhaden oil and its alkyl esters by pancreatic lipase
The present study demonstrates that the relative rates of in vitro hydrolysis of the least and most resistant fatty acids differ only by a factor of 6, which is unlikely to result in significant differences in the free fatty acid composition under rapid and extensive hydrolysis in the lumen, it clearly leads to a nonrepresentative initial release of fatty acids in vitro
Relative rates of hydrolysis of alkyl and glyceryl esters. These were determined by comparing the relative extent of hydrolysis of ethyl and methyl oleate and trioleoylglycerol under conditions where all three substrates were hydrolyzed to a detectable degree

Summary

Introduction

In order to distinguish between possible fatty acid differences during lumenal lipolysis and cellular absorption, we have reinvestigated the in vitro hydrolysis of menhaden oil and its alkyl esters by pancreatic lipase. A recent review on the digestion and absorption of marine oils has concluded that the polyunsaturated long chain fatty acids are probably completely absorbed despite a possible lower relative rate of release from the esters by pancreatic lipase [10].

Results

Conclusion