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Several components of milk fat globule membranes (MFGMs) have been reported to display beneficial health properties and some of them have been implicated in the defense of newborns against pathogens. These observations prompted us to determine the glycosphingolipid content of MFGMs and their interaction with pathogens. A comparative study with whole milk components was also carried out. Milk fat globules and MFGMs were isolated from milk. Gangliosides and neutral glycosphingolipids were obtained from MFGMs and whole milk and their fatty acid contents were determined by gas chromatography-mass spectrometry (GC-MS). MFGMs and whole milk showed similar ganglioside and neutral glycosphingolipid contents, with whole milk having more GM3 and glucosylceramide and less GD3, O-acetyl GD3, O-acetyl GT3, and lactosylceramide. The fatty acid content of gangliosides from both sources showed a similar composition. However, the neutral glycosphingolipid fatty acid content seemed to be quite different. Whole milk had fewer very-long-chain fatty acids (18.1% vs. 46.4% in MFGMs) and more medium-chain and unsaturated C18:1 and C18:2 fatty acids. Milk fat globules, MFGMs, lactosylceramide, and gangliosides GM3 and GD3 were observed to bind enterotoxigenic Escherichia coli strains. Furthermore, bacterial hemagglutination was inhibited by MFGMs and glycosphingolipids.

Milk glycosphingolipids (GSL) have been reported to participate in the newborn's defense against pathogens. Taking this into account, in this study we determined the neutral GSL content of ovine milk, including its fatty acid profile. Its role in bacterial adhesion was also addressed by immunodetection of separate GSL in a high-performance thin-layer chromatography overlay assay. Ovine milk has a neutral GSL pattern similar to human milk and includes lactosylceramide (LacCer; 45.7%), monohexosylceramide (glucosylceramide and galactosylceramide, 31.2%), globotriaosylceramide (Gb3; 19.1%), and globotetraosylceramide (Gb4; 3.5%). Globotriaosylceramide and Gb4 are present in human but not bovine milk. Neutral GSL contained C23:0 and C24:0 as the most abundant fatty acids, a finding consistent with its high content of very long chain fatty acids (longer than C20). Most fatty acids were saturated and had a low content of polyunsaturated fatty acids. Bovine enterotoxigenic Escherichia coli strains bound strongly to LacCer and showed a weak binding to monohexosylceramide. The K99 strain also bound strongly to Gb3, and F41 to Gb4. Lactosylceramide, monohexosylceramide, and Gb3 were also observed to bind to human uropathogenic E. coli strains. The results reported here show the ability of neutral GSL in ovine milk to bind to E. coli strains. These compounds could be used as an alternative and available source to supplement infant or bovine formulas with a view to preventing bacterial infections.

RESUMEN Contenido de ácidos grasos de las diferentes clases de fosfolípidos de la leche de oveja y de cabraSe ha analizado el contenido, distribución de las especies individuales y la composición en ácidos grasos de los fosfolípidos (FL) de la leche de oveja y de cabra. Se ha estudiado también la unión de cepas enterotoxigénicas y uropatogénicas de Escherichia coli a estos compuestos y el efecto de los FL sobre la hemaglutinación provocada por estas bacterias mediante inmunodetección en placa y ensayos en placas multipocillo, respectivamente. La leche de oveja y de cabra contiene más FL que la de vaca, pero menos que la leche humana. El perfil de FL individuales es similar en la leche de oveja y de cabra e incluye esfingomielina, fosfatidilcolina, fosfatidiletanolamina, fosfatidilserina y fosfatidilinositol. En cuanto a la composición en ácidos grasos, los FL de ambos tipos de leche presentan un contenido elevado de ácidos grasos de cadena larga (más de 16 carbonos) y no saturados, siendo el más abundante C18:1. La leche de oveja contiene ácidos grasos más largos y menos saturados, mientras que los de la leche de cabra son más cortos y más saturados. No se ha encontrado adhesión de ninguna de las cepas bacterianas estudiadas a los FL individuales de la leche de oveja o de cabra .Tampoco se ha observado inhibición de la hemaglutinación producida por las bacterias por los FL. Estos compuestos son constituyentes fundamentales de la membrana de los glóbulos de grasa de la leche, pero a la vista de los resultados obtenidos, no parece que participen en la defensa del recién nacido frente a infecciones bacterianas. PALABRAS CLAVE: Ácidos grasos -Adhesión bacteriana -Fosfolípidos -Leche de cabra -Leche de oveja. SUMMARY Phospholipid classes and fatty acid composition of ewe's and goat's milksThe content, distribution of individual species, and the fatty acid composition of phospholipids (PL) from ewe's and goat's milk were analyzed. The binding of enterotoxigenic and uropathogenic Escherichia coli strains to PL and the inhibition of bacterial hemagglutination by PL were addressed using high performance thin-layer chromatography-overlay assays and microtiter plates, respectively. Ovine and caprine milk contained more PL than bovine milk but less than human milk. The profile of individual PL was similar, including sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol in both ovine and caprine milk. Regarding the fatty acid composition, a high content of long-chain fatty acids (more than C16) and unsaturated fatty acids, with C18:1 as the most abundant was found in ovine and caprine milk PL. Ovine milk has longer and less saturated fatty acids while caprine milk has shorter and more saturated ones. Neither the adhesion of any bacterial strains assayed to the individual PL from ovine or caprine milk nor the inhibition of bacterial hemagglutination by PL were observed. These are important constituents of the milk fat globule membrane, but it seems that they do not play a ro...

Sialoglycoconjugate contents of several milk replacers (MR) currently used in Spain have been determined. The ingestion of these compounds by calves fed bovine milk or MR is also discussed. Total sialic acids and glycoprotein-, oligosaccharide-, casein-, and lipid-bound sialic acids and free sialic acid were determined. High sialic acid contents in all the fractions studied, including total sialic acids, were found. N-acetylneuraminic acid was found to be the major sialic acid in MR. However, MR-D and H had a high N-glycolylneuraminic acid (NeuGc) content in all fractions (15-40%), while E and F only had a high NeuGc content in the glycoprotein fraction. Five different sialyloligosaccharides -3'-sialyllactose, 6'-sialyllactose, 3'-sialyllactosamine, 6'-sialyllactosamine, and disialyllactose, which are the most abundant oligosaccharides in bovine milk-were detected in the MR. Samples B to I contained high amounts of these oligosaccharides. The content of individual gangliosides was very similar to that of bovine milk, with GD3 as the major ganglioside. Although MR are not formulated as regards their sialic acid content, high amounts of sialic acid-containing glycoconjugates with high levels of NeuGc, a sialic acid critical in the adhesion of some Escherichia coli strains to calf intestinal epithelium were detected. The ingestion of MR analyzed in this work could protect newborn calves from several enteric pathogens.Additional key words: gangliosides, milk oligosaccharides, sialic acids. ResumenContenido de sialoglicoconjugados de algunos lactorreemplazantes usados en la alimentación de terneros recién nacidos