Preparation and gas chromatographic-mass spectrometric analysis of N-acetyl-O-trimethylsilyl derivatives of long-chain base residues of natural sphingomyelin

A procedure for the preparation of long-chain base residues of egg yolk, bovine milk and bovine brain sphingomyelin was developed. The bases were converted to N-acetyl-O-trimethylsilyl (TMS) derivatives before being submitted to gas chromatography and mass spectrometry. The chromatographic profile of the milk sample was complex with thirteen peaks, whereas the profiles of brain and egg yolk long-chain bases were simple and remarkably similar.

Molecular species analysis of phospholipids

The elucidation of phospholipid molecular species composition provides detailed structural information concerning various lipids and thus offers descriptions of crucial determinants of membrane physical and biological properties. Various methods differing in labor intensity, mode of separation and detection, type of calibration, as well as other factors, have been published. Thus precision and accuracy are expected to vary considerably between methods. Qualitative and quantitative aspects of different procedures for molecular species analysis of individual phospholipid classes are discussed in this review. Special emphasis has been given to the characterization of biological tissue samples.

High-performance liquid chromatography method with light-scattering detection for measurements of lipid class composition: analysis of brains from alcoholics

A high-performance liquid chromatographic method with evaporative light-scattering detection was developed for the analysis of intact lipid classes in nervous tissue. The method had the ability to resolve plasmalogen-phosphatidyl-ethanolamine and diacyl-phosphatidylethanolamine along with other major phospholipid classes in a single run. This technique was employed for the investigation of the effects of chronic alcohol consumption on the membrane lipid class composition of human brains (alcoholics, n = 13; controls, n = 11). Measurements were performed on cholesterol, cerebrosides, sulfatides, phospholipids and sphingolipids in total lipid extracts of white matter, gray matter and cerebellar regions of human brains. No significant differences in the lipid class composition between the groups were observed.

Hydrolysis of galactolipids by human pancreatic lipolytic enzymes and duodenal contents

Monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG) and sulfoquinovosyldiacylglycerols (SQDG) are major lipids in vegetable food. Their digestion and absorption are unknown. This study examines the hydrolysis of galactolipids in vitro with human duodenal contents, pancreatic juice, and purified human pancreatic lipases. Galactolipids were incubated with human duodenal contents, pancreatic juice, pure pancreatic carboxyl ester lipase (CEL), and colipase-dependent lipase with colipase (Lip-Col). Hydrolysis was estimated as release of free fatty acids and by the use of [3H]galactose or [3H]fatty acid-labeled DGDG. Pancreatic juice and duodenal contents hydrolyzed DGDG to fatty acids, digalactosylmonoacylglycerol (DGMG) and water-soluble galactose-containing compounds. The hydrolysis of DGDG was bile salt-dependent and had a pH optimum at 6.5-7.5. Human pancreatic juice released fatty acids from MGDG, DGDG, and SQDG. Purified CEL hydrolyzed all three substrates; the hydrolysis rate was MGDG > SQDG > DGDG. Pure Lip-Col had activity toward MGDG but had little activity against DGDG. Separation of pancreatic juice by Sephadex G100 gel filtration chromatography revealed two peaks with galactolipase activity that coincided with CEL (molecular mass 100 kD) and lipase (molecular mass 50 kD) peaks. In contrast to pure Lip-Col enzymes of the latter peak were as active against DGDG as against MGDG. Thus, DGDG is hydrolyzed both by CEL and by a pancreatic enzyme(s) with a molecular mass of 40-50 kD to fatty acids and lyso DGDG. MGDG, DGDG, and SQDG are all hydrolyzed by human pancreatic juice. Pure CEL hydrolyzed all three substrates.

Quantification and comparison of some natural sphingomyelins by on-line high-performance liquid chromatography/discharge-assisted thermospray mass spectrometry

Sphingomyelins obtained from bovine brain, chicken egg yolk and bovine milk fat were analysed. Separation was performed by reversed-phase high-performance liquid chromatography utilizing a binary solvent gradient consisting of n-butanol-water-1-propanol-isooctane. Detection was accomplished by light scattering and on-line discharge-assisted thermospray (plasmaspray) ionization mass spectrometry. The positive ion mass spectra exhibit prominent ions related to the amine base structure and fragments which can be utilized for identification of molecular species. The abundance of the fragments containing the fatty acid reflects relatively well the fatty acid composition of natural sphingomyelin mixtures. Bovine brain sphingomyelin has, for example, two distinctive major molecular species composed of C24:1 and C18:0 acids as indicated by the m/z 630.6 and m/z 548.5 ions, respectively. While egg yolk exhibits ions of m/z 520.6 which indicate the presence of C16:0, bovine milk sphingomyelin has several prominent ions of m/z 632.5, 618.6 and 604.7, reflecting the proportions of C24:0, C23:0 and C22:0, respectively.

Advances in planar chromatography for the separation of food lipids

A survey of the advances in planar chromatography for the separation of food lipids is presented. Techniques of planar chromatography [densitometry, preparative thin-layer chromatography (TLC) and TLC with flame ionization detection, etc.] together with applications from the areas of dairy, marine and plant lipids are discussed. Additives such as lecithins (emulsifying agents) are also considered.