Bovine Milk Lipids Research Articles

Heat Treatment of Bovine Milk Influences Gastric Emptying of Lactose but not its Apparent Small Intestinal Disappearance in the Growing Pig as a Model for the Adult Human.

Heat treatment influences gastric emptying of proteins and lipids in bovine milk. Whether heat treatment influences lactose gastric emptying and small intestinal lactose disappearance remains unknown. This study aimed to determine the gastric emptying of lactose and its disappearance from the small intestine of the growing pig as a model for the adult human. After 10 d of adaptation, fasted 9-wk-old pigs (n = 48) consumed 500 mL of pasteurized or ultra-high-temperature (UHT) bovine milk before being killed at 20, 60, 120, or 180 min post-feeding. Gastric, small, and large intestinal contents were collected to determine the gastric emptying of lactose, its apparent small intestinal disappearance, and its release into the large intestine. Portal vein blood samples were also collected to measure galactose concentration over time. Data were analyzed using nonlinear and polynomial models. The gastric emptying of lactose was faster for pigs fed pasteurized milk than those fed UHT milk (P ≤ 0.05). For example, 14 ± 2.9% and 24 ± 2.2% (mean ± standard error) of lactose, respectively, were retained in the stomach at 60 min post-feeding. The apparent small intestinal disappearance of lactose increased to 88 ± 2.4% over time, but it did not differ between milk types. Similarly, the plasma galactose concentration in the portal vein increased during the first post-feeding hour but did not differ between milk types. Lactose reached the large intestine during the first 20 min post-feeding, and the amount of lactose released into the large intestine did not change over time (523 μmol on average across post-feeding times after back transformation of 6.26 ± 0.37) or between milk types. Heat treatment influenced the gastric emptying of lactose but did not impact subsequent small intestinal apparent disappearance and portal blood plasma galactose appearance.

An interactive R-based custom quantification program for semi-quantitative analysis of triacylglycerols in bovine milk.

The R programming language, RStudio, and open-source software solutions for analysis of liquid chromatography-mass spectrometry (LC-MS) data have been used with user-written R-based custom quantification programs (CQP) for semi-quantification of triacylglycerols (TAGs) in bovine milk lipid extracts. Using the peak-finding capabilities of the package "xcms" in RStudio, peaks were integrated, and retention times aligned, normalized, and then used for semi-quantitative analysis of a custom set of four extraction internal standards (EISs) and 29 TAG regioisomers using the choice of four analytical internal standards (AISs). Alternating stereospecific numbering (sn) 1,3 TAG regioisomers (standards 1, 3, and 5 of six calibration standards) and sn-1,2 TAG regioisomers (standards 2, 4, and 6 of six standards) were used to make a set of six calibration standards, which were used for quantification using a linear fit model, polynomial fit model, power fit model, level-bracketed linear fit, replicate-bracketed polynomial fit, replicate-bracketed power fit, and replicate- and level-bracketed linear fit and response factors. For example, the linear fit for EIS1 gave an unacceptable coefficient of determination (CoD), r2 = 0.9616, whereas the polynomial fit gave r2 = 0.9908 and the power fit gave r2 = 0.9928, while the double-bracketed linear fit gave CoDs of r2 = 0.9960, 0.9848, and 0.9781 for the three brackets, yet gave the least % difference to known calibration concentrations. For unparalleled transparency, the CQP produced webpages that allowed every step in the data processing and quantification sequence to be verified and reproduced, and contained interactive figures. The data are publicly available using a digital object identifier (DOI). The R code can be downloaded and used with the downloadable data to reproduce the results, to modify the code and further customize the results, or to copy and paste and adapt the code to other quantification applications.

Multifunctional properties of the transmembrane LPxTG-motif protein derived from Limosilactobacillus reuteri SH-23

The LPxTG-motif protein is an important transmembrane protein with high hydrophilicity and stability, as evidenced by its stress tolerance and adhesion ability. In this study, a novel LPxTG-motif protein with esterase activity (LEP) was expressed, and the multifunctional properties such as adhesion properties and esterase activity were also investigated. When cocultured with Limosilactobacillus reuteri SH-23, the adhesion ability of L. reuteri SH-23 to HT-29 cells was improved, and this adhesion was further found relating to the potential target protein Pyruvate kinase M1/2 (PKM) of HT-29 cells. In addition, as a multifunctional protein, LEP can promote the hydrolysis of bovine milk lipids with its esterase activity, and the activity was enhanced in the presence of Zn2+ and Mn2+ at pH 7. Furthermore, the polyunsaturated fatty acids (PUFA) such as linoleic acid and eicosapentaenoic acid were found to increase during the hydrolyzing process. These unique properties of LEP provide a comprehensive understanding of the adhesion function and PUFA releasing properties of the multifunctional protein derived from L. reuteri SH-23 and shed light on the beneficial effect of this Lactobacillus strain on the colonization of the gastrointestinal tract.

Varying Levels of Medium‐Chain Fatty Acids Affect Triacylglycerol Composition and Crystallization Behavior of African Elephant Milk Fat

AbstractAfrican elephant milk fats from different stages of lactation are studied to investigate the link between high contents of medium‐chain fatty acids (MCFA), triacylglycerol (TAG) species, and crystallization in a milk fat system. The elephant milk fats contain high amounts of MCFA, specifically C8:0, C10:0, and C12:0, which mainly form medium molecular weight TAG species (C26–C34). The milk fats with the highest MCFA levels (97% and 82%) correspond to mid‐ and late‐lactation stages. These milk fats display simpler TAG compositions and crystallization behaviors. The great majority of mid‐ and late‐lactation milk fats are comprised of medium molecular weight (C28–C30) TAG. Both melting and crystallization are sharp events, and only β’ polymorph is observed. At early lactation, with 66% MCFA, a more diverse fatty acid composition is observed, and TAG species with medium molecular weight (C30–C34) and high molecular weight (C36–C44) are the dominant. Under dynamic conditions, crystallization and melting take place gradually over a wide temperature range, both α and β’ polymorph crystals are observed.Practical Applications: Mammals of different species provide milk lipids with a wide variety of fatty acid composition yet with common stereospecific features. The study of milk lipids, other than the common bovine milk lipids, allows the investigation of crystallographic properties in relation to fatty acid composition while preserving the stereospecific arrangement. Specifically, the study of elephant milk fats from different stages of lactation provides insight in to the effect of varying contents of medium‐chain fatty acids and fatty acid diversity on triacylglycerol composition and crystallization behavior.

Qualitative and Quantitative Study of Glycosphingolipids in Human Milk and Bovine Milk Using High Performance Liquid Chromatography-Data-Dependent Acquisition-Mass Spectrometry.

Cerebrosides (Crb; including glucosylceramide and galactosylceramide) and lactosylceramide (LacCer) are structurally complex lipids found in many eukaryotic cell membranes, where they play important roles in cell growth, apoptosis, cell recognition and signaling. They are also found in mammalian milk as part of the milk fat globule membrane (MFGM), making milk an important dietary component for the rapidly growing infant. This study reports the development of a robust analytical method for the identification and characterization of 44 Crb and 23 LacCer molecular species in milk, using high performance liquid chromatography–tandem mass spectrometry in data-dependent acquisition mode. For the first time, it also compares the distributions of these species in human and bovine milks, a commercial MFGM-enriched dairy ingredient (MFGM Lipid 100) and commercial standards purified from bovine milk. A method for quantifying Crb and LacCer in milk using mass spectrometry in neutral loss scan mode was developed and validated for human milk, bovine milk and MFGM Lipid 100. Human milk was found to contain approximately 9.9–17.4 µg Crb/mL and 1.3–3.0 µg LacCer/mL, whereas bovine milk (pooled milk from a Friesian herd) contained 9.8–12.0 and 14.3–16.2 µg/mL of these lipids, respectively. The process used to produce MFGM Lipid 100 was shown to have enriched these components to 448 and 1036 µg/g, respectively. No significant changes in the concentrations of both Crb and LacCer were observed during lactation.

Exploring Biochemical Reactions of Proteins, Carbohydrates, and Lipids through a Milk-Based Demonstration and an Inquiry-Based Worksheet: A COVID-19 Laboratory Experience

The COVID-19 pandemic has placed pressure on institutions, and especially instructors, to deliver course content in innovative ways, often with limited resources. In face-to-face learning, many chemistry instructors value inquiry-based learning with real-world applications. These types of learning activities cultivate student interest and, thus, motivate students to achieve their best. However, inquiry-based learning can be more challenging in an online environment, especially given limited resources and preparation time. This paper describes an inquiry-based laboratory demonstration that is inexpensive and easy to conduct outside of the traditional laboratory setting and yet provides a valuable learning experience for second-semester organic chemistry students. In this activity, students apply their knowledge of chemistry to the proteins, carbohydrates, and lipids in bovine milk, studying the casein protein, lactose, fatty acids, and more. Students complete a pre-lab assignment individually, watch prerecorded demonstrations via the Zoom video-conferencing platform, and complete a guided inquiry worksheet in groups, via breakout rooms. These activities help students review concepts such as solubility, hydrogen bonding, and acidity and invite them to apply new material on carbonyl chemistry, hydrolysis, and the relationship between protein structure and function. Because this learning activity challenges students to explore real-world implications, it deepens their understanding of the intricate interplay between organic chemistry, biochemistry, and microbiology and thus prepares them for further scientific inquiry in these areas.

Characterization and comparison of lipids in bovine colostrum and mature milk based on UHPLC-QTOF-MS lipidomics

Lipids in bovine milk have several biological activities, with implications for human health and the physical functionality of foods. However, alterations in the lipid profile of bovine milk during lactation are not well-studied. This study aimed to identify differences in lipids between bovine colostrum and mature milk, using a lipidomics approach. Using an advanced mass spectrometry-based quantitative lipidomics approach, 335 lipids assigned to 13 subclasses were characterized in bovine colostrum (BC) and mature milk (BM). In total, 63 significantly differential lipids (SDLs) were identified. Among the 63 SDLs, the levels of 21 lipids were significantly lower in BM than in BC, including 5 glycerophosphatidylethanolamines (PEs), 1 glycerophosphatidylglycerol (PG), and 15 triacylglycerols (TGs). The levels of the remaining 42 lipids increased in BM, including 1 cardiolipin (CL), 9 diacylglycerols (DGs), 9 dihexosylceramides (Hex2Cers), 3 hexosylceramides (HexCers), 3 glycerophosphatidic acids (PAs), 2 glycerophosphatidylcholines (PCs), 12 PEs, and 3 TGs. Furthermore, the correlations and related metabolic pathways of these 63 SDLs were analyzed to explore the mechanisms that alter bovine milk lipids during lactation. The seven most relevant pathways identified herein, ranked in accordance with their degree of influence on lactation, were glycerophospholipid metabolism, sphingolipid metabolism, glycerolipid metabolism, glycosylphosphatidylinositol-anchor biosynthesis, linoleic acid metabolism, alpha-linolenic acid metabolism, and arachidonic acid metabolism. Our results provide essential insights into mechanisms underlying alterations in bovine milk lipids during different lactation periods, along with practical information of specific nutrition and quality assessments for the dairy industry.

Comprehensive Characterization of Bovine Milk Lipids: Phospholipids, Sphingolipids, Glycolipids, and Ceramides.

A comprehensive survey on phospholipids (PLs), sphingolipids, glycolipids, and ceramides (Cer) of bovine milk was conducted by liquid chromatography tandem-mass spectrometry. A total of 514 species belonging to 15 classes were identified by an automated search tool (LipidSearch) and a manual analysis of MS2 spectra. Over 60 species were detected for the classes of phosphatidylcholine (PC), phosphatidylinositol, phosphatidylserine, and sphingomyelin (SM), between 20 and 45 species for phosphatidylethanolamine (PE), phosphatidic acid (PA), and lactosylceramide (LacCer), and between 7 and 20 species for phosphatidylglycerol (PG), lyso-phosphatidylcholine, lyso-phosphatidylethanolamine, glucosylceramide (GluCer), PC-plasmalogen (PC-P), PE-plasmalogen, ganglioside, and Cer. The structural assignment for PL classes is straightforward based on class-specific product ion/neutral losses and fatty acid-related product ions. By contrast, structural determination of lipid classes containing a backbone of sphingoid bases (SM, GluCer, LacCer, ganglioside, and Cer) is much more challenging, and combining MS2/MS3 information acquired in both positive and negative modes is sometimes needed. The quantification of all 15 classes of lipids was performed at the species level. A large variation in abundance was observed across the lipid classes; PC, PE, and SM are the most abundant polar lipid classes, with concentrations reaching 120, 150, and 90 μmol/L, respectively, whereas PA, PG, and PC-P are present at very low levels (<1.5 μmol/L) and the remaining classes at an intermediate level (2-45 μmol/L). This is the first comprehensive characterization of minor lipid classes from bovine milk and the information provided can be used as a reference for studying milk lipids.

Chemometric studies of the effects of milk fat replacement with different proportions of vegetable oils in the formulation of fat-filled milk powders: Implications for quality assurance

Bovine milk lipids can be replaced with cheaper indigenous vegetable oils to produce milk alternatives with healthier saturated/unsaturated fat balance for those in areas where milk supply is poor or even absent. A wide range of vegetable oils can be used, but their impacts when blended with skimmed milk powder to formulate filled milk powder (FMP) are still unknown. We investigate the baseline variances in 12 types of FMP produced onsite with 3 proportions (10%, 20% and 30%) of 4 different vegetable oils (i.e., coconut, palm, soya-bean and sunflower) using fatty acid- and near infrared spectra profiles. Chemometric analyses revealed 8 significant overlapping clusters of FMP types but 100% classification efficiency was achieved. Sunflower oil, and particularly soya-bean FMP types had statistically the lowest indices of atherogenicity and thrombogenicity. This appears to be the first chemometrics study of FMP; the spectral analytical models used may be effective for product monitoring.

Expanded uncertainties of preconcentration neutron activation measurements of extractable organo-chlorine, bromine and iodine compounds in bovine milk lipids

Milk is known to contain organohalogen compounds. A mixture of hexane and isopropanol was used to extract lipids from bovine milk and neutron activation analysis (NAA) was employed to measure extractable organohalogens in the lipids. The samples were irradiated in a neutron flux of 2.5 × 1011 cm2 s−1 for 10 min, allowed to decay for 2 min, and counted for 10 min. Uncertainties associated with the preconcentration NAA measurements were investigated in detail. The mass fractions of halogens in mg kg−1 and their relative expanded uncertainties in percent in bovine milk lipids were: 32 (8.4 %), 2.65 (9.8 %) and 0.211 (6.6 %) for Cl, Br and I, respectively.

Bovine complex milk lipid containing gangliosides for prevention of rotavirus infection and diarrhoea in northern Indian infants.

Rotavirus (RV) is a leading cause of morbidity and mortality in children younger than 5 years of age, presenting commonly with diarrhoeal symptoms. In a prospective 12-week double-blind randomised controlled trial we assessed acceptability and efficacy of a high-ganglioside complex milk lipid (CML) for prevention of RV infection in 450 infants, ages 8 to 24 months, at 3 sites in northern India. Prevalence of diarrhoea and RV was unseasonably low at baseline (all-cause diarrhoea [ACD], n = 16; RV diarrhoea [RVD], n = 2; RV infection, RV positive [RV+], n = 20) and throughout the trial, with only 110 total episodes of ACD for 12 weeks (CML, n = 62; control, n = 48) of which 10 were RVD (CML, n = 4; control, n = 6). Mean duration that RVD persisted was lower in the CML group (2.3 ± 0.5 days) than that in the control group (3.8 ± 1.3 days, P = 0.03), but only 3 of 450 end of trial stool samples were identified as RV+ (<1%; CML, n = 2; control, n = 1). This hampered the assessment of efficacy of CML, despite the large a priori determined sample size. During the trial similar numbers of infants reported adverse events (AEs: CML 41%, control 46%), with the majority of events classified as mild and not related to the intervention. In conclusion, further clinical trials against a higher background of seasonal prevalence are necessary to assess efficacy of this nutritional intervention to prevent RVD. More important, however, high-ganglioside CML was acceptable for long-term consumption in infants ages 8 to 24 months.

The effects of bovine milk fat on human health

Recent years have witnessed a growing interest in the nutritional value and health benefits of food products of animal origin. Numerous research studies have been undertaken to evaluate the effects of bovine milk, a key dietary component, on human health. Fat is one of the most important components in bovine milk, and its content ranges from 2.8% to 8.1%, subject to the breed of cattle, nutritional aspects, individual characteristics, lactation period, milk production hygiene and season. The aim of this study was to review the latest literature concerning the health effects of components found in bovine milk fat. This paper is a literature review, and it analyzes the composition of bovine milk fat and its effects on human health. The available sources were grouped thematically, and an attempt was made to characterize various milk fat components and their effects on human health. The unique nutritional value of bovine milk can be attributed to the presence of short-chain fatty acids and medium-chain fatty acids which are important sources of energy for the muscles, heart, liver, kidneys, blood platelets and nervous system. They do not pose an obesity risk; they prevent ulcerative colitis, cancer, atherosclerosis and hypertension; they have anti-inflammatory and antibacterial effects, and they boost natural immunity. Milk contains cholesterol, a lipid derivative which stabilizes and stiffens cell membranes, builds the cell cytoskeleton, protects nerve fibers and acts as a precursor of steroid hormones, bile acids and vitamin D 3 . Bovine milk lipids do not exert hypercholesterolemic or atherogenic effects in the human body. A growing tendency to replace animal fats, mainly milk fat, with vegetable fats is a matter of concern.

Potential of polar lipids from bovine milk to regulate the rodent dorsal hair cycle

Among the lipids in bovine milk, minor components such as conjugated linoleic acids and phospholipids are more attractive than triacylglycerols from the standpoint of biological activity. To explore novel functions of bovine milk polar lipids (MPL), topical application to murine dorsal skin was introduced as an assay system. The acetone-insoluble lipid fraction derived from bovine milk was dispersed in ethanol and applied to 9-wk-old C57BL/6N female mice for 3wk. In combination with visual assessment of the dorsal pigmentation, the progression of the hair cycle was estimated by calculating the ratio of subcutis to dermis thickness. The administration of MPL led to earlier progression of the hair cycle compared with administration of the vehicle. In some cases, the extent of MPL-induced hair cycle progression was comparable to that in animals treated with minoxidil, the most well-known reagent that initiates anagen. These results indicate that the MPL preparation contains a dermal penetrative component that can regulate the hair cycle and, thus, this preparation possesses potential for cosmetic use.

Biohydrogenation then and now

European Journal of Lipid Science and TechnologyVolume 109, Issue 8 p. 737-739 EditorialFree Access Biohydrogenation then and now Donald L. Palmquist, Donald L. Palmquist Professor Emeritus, Department of Animal Sciences, Ohio Agricultural Research and Development Center/The Ohio Sate University, Wooster, Ohio, USASearch for more papers by this author Donald L. Palmquist, Donald L. Palmquist Professor Emeritus, Department of Animal Sciences, Ohio Agricultural Research and Development Center/The Ohio Sate University, Wooster, Ohio, USASearch for more papers by this author First published: 09 August 2007 https://doi.org/10.1002/ejlt.200700146Citations: 12AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References 1 A. Banks, T. P. Hilditch: CXXX. The glyceride structure of beef tallows. Biochem J. 1931, 25, 1168– 1182. 2 A. Banks, T.P. Hilditch: XXXIV. The body fats of the pig. II. Some aspects of the formation of animal depot fats suggested by the composition of their glycerides and fatty acids. Biochem J. 1932, 26, 298– 308. 3 R. Reiser: Hydrogenation of polyunsatuated fatty acids by the ruminant. Fed Proc. 1951, 10, 236. 4 S. H. Bertram: Biochem Z. 1928, 197, 433 (German); quoted from T.P. Hilditch: The Chemical Co of Natural Fats, 3rd revised edn. John Wiley & Sons, New York (USA) 1956. 5 D. G. Cornwell, R. Backderf, C. L. Wilson, J. B. Brown: The trans-octadecenoic acid content of butterfat. Arch Biochem Biophys. 1953, 46, 364– 375. 6 P. W. Parodi: Conjugated octadecadienoic acids of milk fat. J Dairy Sci. 1977, 60, 1550– 1553. 7 L. Hartman, F. B. Shorland and I.R.C. McDonald: Occurrence of trans-acids in animal fats. Nature. 1954, 174, 185– 186. 8 F. B. Shorland, R. O. Weenink and A. T. Johns: Effect of the rumen on dietary fat. Nature. 1955, 185, 1129– 1130. 9 C. R. Kepler, K. P. Hirons, J. J. McNiell, S. B. Tove: Intermediates and products of the biohydrogenation of linoleic acid by Butyrivibrio fibrisolvens. J Biol Chem. 1966, 241, 1350– 1354. 10 R. M. C. Dawson, P. Kemp: Biohydrogenation of dietary fats in ruminants. In: Physiology of Digestion and Metabolism in the Ruminant. A.T. Phillipson, ed., Oriel Press, Newcastle upon Tyne (UK) 1970, pp. 504– 518. 11 C. G. Harfoot: Lipid metabolism in the rumen. In: Lipid Metabolism in Ruminant Animals. W. W. Christie, ed., Pergamon Press. Oxford (UK) 1981, pp. 21– 54. 12 C. G. Harfoot, G. P. Hazlewood: Lipid metabolism in the rumen. In: The Rumen Microbial Ecosystem, 2nd edn. P. N. Hobson, C. S. Stewart, eds., Blackie Academic and Professional, London (UK) 1997, pp. 382– 426. 13 Y. L. Ha, N. K. Grimm, M. W. Pariza: Anticarcinogens from fried ground beef: heat-altered derivatives of linoleic acid. Carcinogenesis. 1987, 6, 591– 593. 14 M. R. Pollard, F. D. Gunstone, A. T. James, L. J. Morris: Desaturation of positional and geometric isomers of monoenoic fatty acids by microsomal preparations from rat liver. Lipids. 1980, 15, 306– 314. 15 M. M. Mahfouz, A. J. Valicenti and R. T. Holman: Desaturation of isomeric trans-octadecenoic acids by rat liver microsomes. Biochim Biophys Acta. 1980, 618, 1– 12. 16 P. W. Parodi: Conjugated linoleic acid—an anticarcinogenic fatty acid present in milk fat. Austral J Dairy Technol. 1994, 49, 93– 97. 17 D. L. Palmquist, A. L. Lock, K. J. Shingfield, D. E. Bauman: Biosynthesis of conjugated linoleic acid in ruminants and humans. Adv Food Nutr Res. 2005, 50, 179– 217. 18 R. G. Jensen: The composition of bovine milk lipids: January 1995 to December 2000. J Dairy Sci. 2002, 85, 295– 350. Citing Literature Volume109, Issue8Special Issue: Biorumenhydrogenation – a Workshop supported by OECDNo. 8 August 2007Pages 737-739 ReferencesRelatedInformation

Occurrence and biochemical characteristics of natural bioactive substances in bovine milk lipids.

Bovine milk lipids (BML) contain a number of bioactive substances with positive as well as negative properties, mainly in the class of fatty acids. Besides trans fatty acids (TFA), conjugated linoleic acids (CLA) are of particular interest. Apart from ruminant meat products the main source of CLA in food are BML. Although TFA as well as saturated fatty acids (12:0-16:0) are thought to be positively correlated with atherosclerosis and coronary heart disease, CLA are considered antiatherogenic. Further, CLA are reported to reduce adipose fat and to have anticarcinogenic properties. The varying CLA and TFA contents of lipids from milk and dairy products are positively correlated with one another. However, TFA are also negatively correlated with 12:0-16:0 in BML. Anticarcinogenic effects are also ascribed to butyric acid as well as to some phospholipids and ether lipids present in BML. Moreover, the essential fatty acids 18:2n-6 and 18:3n-3 are found in BML which are involved in a variety of biochemical processes and thus have numerous functions in human metabolism. Contents of the individual bioactive components of BML are summarised taking into account also seasonal variations. The total content of bioactive substances in BML is approximately 75 % but their overall impact on human health considering benefits and drawbacks is difficult to assess.

Incorporation of proteins in sphingomyelin-water gel phases

Sphingomyelin from bovine milk and water form lipid gel phases at room temperature. A sample was used which incorporated of about 55% water, and X-ray diffraction data indicate an aqueous layer thickness of about 28 Å. In order to accommodate proteins in the gel phase, the aqueous layer thickness was increased by solubilizing sodium palmitate into the sphingomyelin bilayer. In this way the gel phase could take up about 80% water. The incorporation of lysozyme, β-lactolylobulin, and α-lactalbumin, was followed and the protein concentration for phase separation to occur was determined. It was found that the degree of incorporation was dependent on the salt concentration, thus the protein used was extensively dialysed. The amount of protein which can be dissolved in the 'thin aqueous layer of the gel phase was suggested to be limited by the dimensions of the layer. These are likely to be reduced as a consequence of the osmotic stress exerted by the 'outside' solution phase at high enough protein concentration.

Dietary and ruminally derived trans-18:1 fatty acids alter bovine milk lipids.

The objectives of this study were to determine whether dietary fish oil enhances production of trans-18:1 isomers in the bovine rumen and whether flow of ruminally derived and/or dietary trans-18:1 to the small intestine is correlated with milk fat production. Four lactating Holstein cows with cannulas in the rumen and proximal duodenum were fed diets with 0% supplemental fat (control diet), 3% hydrogenated tallow fatty acids (HTFA diet), 1.5% menhaden oil plus 1.5% stearic acid (MO+SA diet), or 1.5% soybean oil plus 1.5% partially hydrogenated soybean oil (SBO+HSBO diet) in a 4 x 4 Latin square design. Intakes of trans-18:1 were 0, 12, 0 and 69 g/d when cows were fed the control, HTFA, MO+SA and SBO+HSBO diets, respectively. However, the extent of 18:1 + 18:2(n-6) + 18: 3(n-3) biohydrogenation in the rumen was reduced by consumption of the MO+SA and SBO+HSBO diets. As a result, flow of trans-18:1 to the duodenum was 163 g/d for MO+SA-fed cows and 152 g/d for SBO+HSBO-fed cows compared with 38 g/d for cows fed the HTFA and control diets. Incomplete biohydrogenation accounted for all of the trans-18:1 flow when the MO+SA diet was fed. Compared with results when the HTFA and control diets were fed, milk fat percentage was lower and concentration of trans-18:1 in milk fat was higher when the MO+SA and SBO+HSBO diets were fed. Across all treatments, milk fat percentage decreased linearly with the amount of trans-18:1 flowing to the duodenum and the concentration of trans-18:1 in milk fat. Results indicate that bovine milk fat percentage is depressed by trans-18:1, whether derived from the diet or from incomplete biohydrogenation of unsaturated fatty acids.

Lipid class analysis by normal phase high performance liquid chromatography, development and optimization using multivariate methods

A general method for the analysis of lipid classes by liquid chromatography has been developed using a multivariate optimization strategy to target optimal system conditions. The method was validated using a ruggedness test in the form of a Plackett-Burman design thereby exploring the immediate region around the optimum to ensure stable analytical conditions. Detection and quantitation were optimized by a factorial design in the light scattering detector parameters thus ensuring maximum detector response. This method was found to be suitable for a broad range of lipid sources from vegetable and animal origin, examples of the separation achieved are given for oat kernel, soybean and bovine milk lipids.

Immunological Identification and Determination of Xanthine Oxidase in Cells and Tissues

Antibodies against purified xanthine oxidase (xanthine: O 2 oxidoreductase, EC 1.2.3.2) from bovine milk lipid globule membranes were raised in rabbits and guinea pigs, and immunoglobulins (G) were purified by immuno-adsorption. In addition, a monoclonal antibody against xanthine oxidase was isolated from a murine ‘hybridoma’ cell-line. All antibody preparations recognized the antigen both in its soluble and membrane-bound form in milk lipid globules and mammary tissue as well as the antigen present in the capillary endothelium of lung and liver. Xanthine oxidases from these different sources were purified by immunoaffinity chromatography and compared by one- and two-dimensional gel electrophoresis and by mapping the peptides obtained after complete digestion of the radioiodinated proteins with trypsin. No differences were found between the enzymes isolated from the various bovine tissue preparations. The distribution of xanthine oxidase protein was determined in a selection of bovine cell cultures and tissues using an ultrasensitive enzymic radioimmunoassay. All fractions tested, including material in which we have not detected xanthine oxidase protein by immunolocalization techniques such as brain, macrophages, and MDBK cells, were found to contain some enzyme protein. However, the levels of protein in these cells were much lower (by factors from 10 to 2,000) than the levels in lactating mammary tissue. By comparison, the concentration of the enzyme in eye lens tissue was at the limit of detection, i.e. by two orders of magnitude lower than the lowest values in other cells and tissues. These results are in accordance with the assumption that xanthine oxidase is a constitutive enzyme and that the enzyme protein present in various cell types is indistinguishable, by immunological and enzymic criteria, from milk xanthine oxidase. The very high concentrations of the protein in mammary gland epithelium and in particular in milk lipid globule membranes might reflect a specific function in the secretion of milk lipids. The possible functional significance of the high levels of xanthine oxidase in capillary endothelial cells is discussed.

Incorporation of [Hydrogen—3] Alkylglycerolether and [Carbon—14] Hexadecanol into Bovine Colostrum and Milk Lipids

[Hydrogen—3] glycerol ether and [carbon—14] hexadecanol were infused into the mamary gland or jugular vein of cows in colostral or full phases of lactation to determine their relative rates of synthesis and degradation. Neutral alkylglycerols were both synthesized and cleaved in the bovine gland. Oxidation of fatty alcohols and cleaving of neutral alkylglycerol ethers was faster during the milk than the colostral phase of lactation. In the colostral phase, both increased rate of synthesis and decreased cleavage contributed to increased neutral alkylglycerol concentration; however, synthesis changes were greater.Disappearance of [carbon—14] fatty alcohol and [hydrogen—3] alkylglycerol ether from the blood was the magnitude of fatty acid disappearance in previous studies, but uptake by the mammary gland was slower. Alkylglycerols were taken up from the blood and secreted intact into both colostrum and milk.