Bovine milk gangliosides: Changes in ceramide moiety with stage of lactation

The stage of lactation is one of the most important factors that influence milk composition. Changes in fatty acids from triacylglycerols and phosphol ipids have already been reported. In this study, we looked for a lactationa l change in the ganglioside lipid moiety since ganglioside contents and pat terns vary strongly with stage of lactation. Individual gangliosides from f our stages were isolated, methanolyzed to cleave the bonds between individu al constituents, and derivatized for gas-liquid chromatography and gas chro matography/mass spectrometry analyses. Ceramide components, both fatty acid s (as methyl esters derivatives) and long-chain bases, were identified and quantified. The results pointed to a marked change in ceramide from colostr um to milk that was characterized by a dramatic decrease in saturated and t he longest-chain fatty acids as well as an increase in 18:1 and 18:2. The m ajor long-chain base along lactation was a recently described structure, 3- ethoxy-15:0 sphinganine. Other new long-chain base structures appeared in t hese gangliosides. All these changes suggest differences in the fluidity of the fat globule membrane, reflecting physiological variations in cows with respect to milk production.