This report of the American Dairy Science Association Committee on the Nomenclature, Classification, and Methodology of Milk Proteins reviews changes in the nomenclature of milk proteins necessitated by recent advances of our knowledge of milk proteins. Identification of major caseins and whey proteins continues to be based upon their primary structures. Nomenclature of the immunoglobulins consistent with new international standards has been developed, and all bovine immunoglobulins have been characterized at the molecular level. Other significant findings related to nomenclature and protein methodology are elucidation of several new genetic variants of the major milk proteins, establishment by sequencing techniques and sequence alignment of the bovine caseins and whey proteins as the reference point for the nomenclature of all homologous milk proteins, completion of crystallographic studies for major whey proteins, and advances in the study of lactoferrin, allowing it to be added to the list of fully characterized milk proteins.

The bovine milk fat globule membrane (MFGM) is an important, biologically relevant membrane due to its functional and health properties. Its composition has been thoroughly studied but its structure, especially the lateral organization of its components, still remains unclear. We have used confocal laser scanning microscopy (CLSM) to investigate the surface structure of the MFGM in globules with different degree of processing using two types of fluorescently-labeled phospholipid probes and a protein dye. Using this technique, we have observed heterogeneities in the distribution of MFGM lipids and proteins relating to the processing and size of the globules. The effect of pretreating the milk (centrifugation, pasteurization-homogenization and churning) was studied by double-staining the surface of the milk fat globules, followed by observation using CLSM, and by determining the phospholipid profile of raw milk, raw cream, processed milk and buttermilk powder. Our findings agree with other techniques by showing that the composition of the MFGM changes with processing through the loss of phospholipids and the adsorption of caseins and whey proteins onto the surface.

Buttermilk contains the milk fat globule membrane (MFGM), a material that possesses many complex lipids that function as nutritionally valuable molecules. Milk-derived sphingolipids and phospholipids affect numerous cell functions, including regulating growth and development, molecular transport systems, stress responses, cross membrane trafficking, and absorption processes. We developed a two-step method to produce buttermilk derivative ingredients containing increased concentrations of the polar MFGM lipids by microfiltration and supercritical fluid extraction (SFE). These processes offer environmentally benign alternatives to conventional lipid fractionation methods that rely on toxic solvents. Firstly, using a ceramic tubular membrane with 0.8-micron pore size, we evaluated the cross flow microfiltration system that maximally concentrated the polar MFGM lipids using a 2n factorial design; the experimental factors were buttermilk source (fresh, or reconstituted from powder) and temperature (50 degrees C, and 4 degrees C). Secondly, a SFE process using supercritical carbon dioxide removed exclusively nonpolar lipid material from the microfiltered buttermilk product. Lipid analysis showed that after SFE, the product contained a significantly reduced concentration of nonpolar lipids, and a significantly increased concentration of polar lipids derived from the MFGM. Particle size analysis revealed an impact of SFE on the product structure. The efficiency of the SFE system using the microfiltration-processed powder was compared much more favorably to using buttermilk powder.

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Buttermilk is a dairy ingredient widely used in the food industry because of its emulsifying capacity and its positive impact on flavor. Commercial buttermilk is sweet buttermilk, a by-product from churning sweet cream into butter. However, other sources of buttermilk exist, including cultured and whey buttermilk obtained from churning of cultured cream and whey cream, respectively. The compositional and functional properties (protein solubility, viscosity, emulsifying and foaming properties) of sweet, sour, and whey buttermilk were determined at different pH levels and compared with those of skim milk and whey. Composition of sweet and cultured buttermilk was similar to skim milk, and composition of whey buttermilk was similar to whey, with the exception of fat content, which was higher in buttermilk than in skim milk or whey (6 to 20% vs. 0.3 to 0.4%). Functional properties of whey buttermilk were independent of pH, whereas sweet and cultured buttermilk exhibited lower protein solubility and emulsifying properties as well as a higher viscosity at low pH (pH