The lipid in milk (milk fat) is found in the form of droplets known as milk lipid globules (MLG). These milk lipid globules are encompassed by a unit membrane known as the milk lipid globule membrane (MLGM) which is derived from the apical plasma membrane of the mammary epithelial cell during secretion. In lactating mammary epithelial cells, immediate precursors of milk lipid globules appear to be cytoplasmic lipid droplets (CLD). These cytoplasmic lipid droplets have diameters >1 μm and are characterized by an electron dense, granular surface coat. A previously unrecognized group of structures with diameters <.5 μm, which resemble cytoplasmic lipid droplets in matrix and surface coat appearance, has been observed. The surface coat of these triacylglycerol containing structures, termed micro lipid droplets (μLD), was similar to that of cytoplasmic lipid droplets in enzyme and polypeptide composition. Morphological evidence suggested that these small structures may originate from rough endoplasmic reticulum (RER) and fuse with cytoplasmic lipid droplets. Immunochemical studies showed homology of certain proteins among the rough endoplasmic reticulum, micro lipid droplets and cytoplasmic lipid droplets, which supported the possibility of an endoplasmic reticulum origin of these droplets. The rate of incorporation of [1-¹⁴C]-palmitate and [1,2,3-³H]-glycerol into lipid of RER, μLD, CLD and MIG fractions suggested a possible translocation pathway of triacylglycerols from the rough endoplasmic reticulum to cytoplasmic lipid droplets. The micro lipid droplets seem to provide triacylglycerols to support growth of cytoplasmic lipid droplets. In addition, morphological evidence suggested that these micro lipid droplets can be secreted directly in a manner similar to cytoplasmic lipid droplets, providing for the small lipid globules in milk. Little is known concerning the biochemical processes of milk lipid secretion but it is thought that butyrophilin, a glycoprotein found in milk lipid globule membrane, may play a role. After treatment of mammary epithelial cells with tunicamycin, butyrophilin content of this membrane is reduced. Thus a method for the study of the physiological role of this glycoprotein is proposed. / Master of Science

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Milk samples from three Jersey and three Holstein herds were used to determine if the degree of churning correlated with the initial milkfat assay, and also to determine if the churned milkfat could be measured as accurately as the initial milkfat using the Milko-Tester. Regression lines for the initial milkfat test versus churned milk- fat test fit polynomial curves. The degree of churning was greater for Jerseys than Holsteins and correlated with the initial milkfat test. The repeatability of initial milkfat tests vas 0.98 for Jerseys and 0.99 for Holsteins. However, the repeatability of churned milkfat tests was lower for both breeds, especially for Jerseys. This indicated that the churned sample could not be measured for its milkfat content as accurately as the nonchurned sample. Churned milkfat samples all tested lower than initial milkfat samples, thus the Milko-Tester Mark III was unable to provide an initial fat test estimate following sample churning. Cows were different from each other in the difference between initia1 and churned milk fat tests. This suggested that cows which produce milk with a higher tendency for churning are apt to receive less reliable milkfat tests from central laboratories than other cows, when all milk samples are subjected to churning conditions.

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. With this is bound: Production performance of artificially and nonartificially sired herd-mates in Wisconsin / E.L. Corley, J.W. Duckwall, and E.E. Heizer. Reprinted from Journal of dairy science, vol. XLVI, no. 1 (Jan. 1963), p. 50-56. Includes bibliographical references (leaves 53-54).

Thesis (M.Sc.)--University of Alberta, 1997. / Submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements for the degree of Master of Science, Department of Agricultural, Food and Nutritional Science. Also available online.

A method of reencapsulating native and reduced-cholesterol butteroil within natural membrane material and proteins of milk such that milkfat globule size and function resembled native cream as closely as possible was developed and evaluated. By replacing the native butteroil with reduced-cholesterol butteroil, an approximate cholesterol reduction of 80% was possible. Milkfat globule membrane material and proteins associated with the lipid phase were evaluated indirectly by measuring light scattering and phosphodiesterase activity in centrifuged reformulated raw cream. Functional stability of cream was measured by evaluating emulsion stability. Optimum conditions for reformulation using ultrasound included ratios of 1:1:1 (butteroil:buttermilk/aqueous phase:skim milk), emulsification time of 2.0 minutes for a 15 ml sample, and emulsification temperature of 42°C. Optimized conditions were used in scale-up reformulation of 750 ml samples replacing ultrasound with homogenization. Treatments included both native butteroil and reduced-cholesterol reformulated creams and unwashed natural cream as the control. Reformulation conditions included phase ratios of 1:1:1 (butteroil:buttermilk/aqueous phase:skim milk), homogenization temperature of 42°C, two-stage homogenization pressures of 500 psig/2000 psig, and product passed through the homogenizer twice. Much more membrane material and proteins became reenveloped into the cream phase with the homogenization process than with ultrasound. Stability of raw homogenized creams over 4 days at 2°C was evaluated by light scattering, phosphodiesterase, and emulsion stability. Overall, there were significant differences among treatments for light scattering and phosphodiesterase assays but not for emulsion stability. Significant differences among days within treatments indicated that the raw creams did change significantly over the time of storage. No differences were found among replications within treatments. Churn time, as a measure of functional stability, was measured on the first day after reformulation. No differences among treatments were observed. Practical applications of this reenvelopment method may include the use of butteroil in a wider range of reformulated dairy products including fluid milk, ice creams, and cheese products. Development of any full-fat reduced-cholesterol product will require a reformulation step unless cholesterol is directly removed from the food. / Master of Science

An investigation was made to determine: a) the effects of milk fat mix products (MFM) on quality, relative consumer preference and cost for manufacture of ice cream and ice milk products, and b) to make recommendations for continued use of MFM products in ice cream and ice milk. The study consisted of 15 experimental ice cream and 15 experimental ice milk products. The ice cream contained 10%, 12% and 14% fat and the ice milk 2%, 4% and 6% fat. Ice cream and ice milk made with cream as the source of fat were designated as controls. These products were compared with ice cream and ice milk made with a butteroil MFM and three imported MFM products. The ice cream and ice milk products were scored for flavor, body and texture and melting quality. Relative consumer preference was determined by ten consumer panelists using the Triangular procedure. Results showed that the control and the butteroil ice cream and ice milk products were superior in quality and were preferred by the consumer panel. When off-flavors were observed in MFM products, they carried over into the ice cream and ice milk and significantly lowered relative consumer preference. The peroxide test indicated oxidation of the fat. There was a significant cost advantage in using imported MFM products in-ice cream and ice milk with the percent saving being more substantial as the fat levels increased. / Master of Science

Twenty-five multiparous cows in their second trimester of lactation were randomly assigned in a 5 x 5 latin square rotation to five silages: control (N), chopped added (CA), ground added (GA), chopped ensiled (CE), and ground ensiled (GE). Chopped (2-6 cm) or ground (< .5 cm) hay was added to corn green chop at 12.5% of the total forage dry matter before ensiling (CE and GE). Chopped or ground hay was also added to the control silage at the same rate prior to feeding (CA and GA). Silages were supplemented to contain 14% crude protein and 1.67 Mcal/kg on a dry matter basis and fed as a total mixed ration. Hay-containing rations averaged 22% ADF, compared to 20% ADF in the control ration. Each cow received the assigned ration for three weeks and milk samples were collected on days 19 and 20 of each feeding period. Means ± S.E. for N, CA, GA, CE and GE were: percent milk fat 3.07 ± .08, 3.31 ± .09, 3.37 ± .08, 3.28 ± .08; percent total solids 11.7 ± .11, 11.8 ± .12, 11.9 ± .12, 12.02 ± .13, 11.94 ± .12; and dry matter intake per kg metabolic body weight .170 ± .003, .161 ± .003, .163 ± .004, .158 ± .004, .166 ± .004, respectively. Percent milk fat was significantly higher in rations CE, CA, and GE when compared to N. Milk production and percent milk protein did not differ. The results indicate increased milk fat production when chopped hay (added or ensiled) or ground hay (ensiled) is included in corn silage based rations for dairy cattle. Whether chopped or ground, hay added at time of ensiling tended to stimulate milk fat production more than hay added just prior to feeding. The beneficial effect of increased hay fiber length on milk fat production was evident whether hay was ensiled with or added to corn silage. / M.S.