The committee members will address cooperatively modifying milk fat composition to improve manufacturing qualities and to address consumer concerns. To accomplish this, efforts will be co-ordinated to
1) Identify metabolic functions in dairy animals which regulate
the composition of milk fat;
2) Quantify effects of diet manipulation on milk composition;
and
3) Characterize the quality of modified milk fat for manufacturing
purposes and acceptability as
human food.
JUSTIFICATION
Dairy products are an important source of vital nutrients in the human diet. Nevertheless, many health-conscious consumers perceive dairy products to contain excessive amounts of total fat, saturated fat, and cholesterol. Butter and other high-fat dairy products are excluded from diets designed to decrease blood cholesterol and prevent or treat coronary heart disease (Ney, 1991). Dairy products provide only 15% of the total fat in the diet, but 25% of the total saturated fat (O’Donnell, 1993).
This proposed project addresses four goals/objectives outlined by FAIR ‘95 (1993) which address enhancing the quality of dairy products for human consumption. They are:
Goal 1. Identify and quantify societal concerns about food products
from animals and
production systems to enhance communication between consumers and the food
industry.
Objective 1. Identify societal concerns that affect the marketplace through food choices.
Goal 2. Meet consumer needs in domestic and international markets
for competitive and high
quality food products from animals.
Objective 2. Enhance the quality of food products from animals.
Goal 3. Develop integrated food animal management systems and
animal health systems
that support efficient, competitive, and sustainable production of safe
and wholesome
food consistent with animal and environmental well-being.
Objective 2. Develop research data basis and integrate them into
decision-support systems for
producers.
Goal 5. Improve industry wide, quality control systems for food products from animals.
Objective 3. Identify human nutritional needs for specific consumer
populations in relationship
to the composition of food products from animals.
Further, the proposed project addresses priority research initiatives
on
1) nutrition, food safety, and health;
2) processes and products; and
3) animal systems identified by the Strategic Agenda for the State
Agricultural Experiment Stations, "Opportunities to Meet Changing Needs"
(ESCOP, 1994).
The fatty acid composition of milk fat is shown in Table 1. Approximately 64% of the fatty acids in milk are saturated. Recent research has shown, however, that not all saturated fatty acids increase blood cholesterol in humans.
TABLE 1. Fatty acid composition of a reference milk fat.
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Fatty acids of less than 12 carbon atoms are neutral or actually may decrease cholesterol. Stearic acid (C18:0) acts similarly to oleic acid (cis-C18:1) to decrease cholesterol (Ney, 1991). Only three saturated fatty acids (lauric, C12:0; myristic, C14:0; and palmitic, C16:0) now are considered to be hypercholesterolemic. These three fatty acids constitute about 44% of total milk fatty acids (Table 1). According to a group of nutritionists from industry and academia (O’Donnell, 1989), the "ideal" milk fat for human health would contain <10% polyunsaturated fatty acids, < 8% saturated fatty acids, and > 82% monounsaturated fatty acids. Fatty acids with less than 12 carbons are not included in this total. Concerns about the negative effects of trans-isomers of unsaturated fatty acids (Ney, 1991) indicates that any increases in poly- or monounsaturated fatty acids in milk should be primarily in the cis configuration.
Real or perceived concerns about the effects of milk fat on health and
well-being not only decreases the economic value of dairy products (and
thus producer incomes), but more importantly may compromise consumption
of highly nutritious foods. Dairy products contribute the following
percentages of total intakes for adults: Ca, 42-46; P, 18-23; K, 13-15;
Mg, 10-13; and Zn, 10-12. For adolescents and children, dairy foods
contributed much greater percentages of these nutrients (O’Donnell, 1993).
Thus, it is important for public health and well-being that consumption
of dairy products be maintained or increased so that intake of important
nutrients is not compromised.
Modification of the fatty acid profile of milk should be beneficial
to human health and improve the image of dairy products to health-conscious
consumers. As a consequence, sales of dairy products should increase,
which would be of direct benefit to dairy producers and processors.
Research to this end has been encouraged in several forums on research
priorities, including the FAIR 95 agenda (1993), ESCOP (1994), and a roundtable
discussion by prominent nutrition researchers (Berner, 1993b). Although
it is not likely that the "ideal" milk fat composition could be achieved,
manipulation of the composition of milk fat is possible through feeding
practices for dairy cows (Grummer, 1991; Palmquist et al., 1993).
For example, feeding supplemental fats may increase contents of C18:0 and
C18:1 while decreasing contents of C14:0 and C16:0; at the same time, however,
content of more of more desirable short-chain fatty acids also decrease.
Karijord et al. (1982) reported the composition and its variance of milk
fat from Norwegian dairy herds. The coefficients of variation for
individual fatty acids of milk fat ranged from 9-22%. The stage of
lactation and month of season accounted for 10-25% of the variance, with
the remainder being attributed to individual animal variation. The
stage of lactation was more important than the season with regard to variance.
Nutritional inputs were not considered in the model. Karijord, et
al. (1982) concluded that genetic approaches might be used to alter milk
fat composition. A recent review (Gibson, 1991) concluded, however,
that practical possibilities are limited to make changes through traditional
breeding approaches or transgenic technologies. Increased knowledge
of the control and regulation of milk fat composition by mammary tissue
is needed to develop, through rational scientific approaches, new dietary
strategies for alteration of milk fat. Quantifying changes produced
by defined nutritional manipulations in carefully designed and coordinated
scientific experimentation will allow quantitative prediction of changes
in milk fat composition that could be expected by feeding specialized diets
to dairy cows.
Milk fat composition also can be altered by manufacturing processes, such as fractionation, blending or interesterification. These practices, however, may compromise flavor, mouth feel, or other physical properties of the modified dairy products (Berner, 1993a). Also, the variation in milk fat composition which now exists in commercial milk causes difficulty to produce consistent milk fat fractions. Consistent, high quality milk fat fractions are required to develop some new dairy foods. Technologies also exist or are being developed to remove cholesterol from milk fat; these technologies may increase consumer acceptance but have limited nutritional impact because dairy products are a minor source (5%) of dietary cholesterol (Berner, 1993a).
A coordinated effort to study nutritional regulation and manipulation of milk fat composition offers the best opportunity for successfully producing milk of altered fat composition. Such an ambitious goal likely will not be achieved by a single investigator or institution. Cooperative research through the regional research system is a rational approach to focus attention and progress on this important topic. By collecting data for a coordinated data base, a modeling approach can be used to predict dietary effects on milk fat composition and processing qualities. Success of such approaches will depend on generating additional data with a variety of dietary strategies to parametrize the model. Specialized technologies to evaluate the composition and functionality of milk, such as determination of positional isomers and manufacturing characteristics, would best be shared through cooperative research to avoid unnecessary duplication of expensive equipment or specialized labor. Furthermore, it is essential that any changes in milk fat composition be evaluated for resultant effects on flavor, texture, and processing characteristics of milk and dairy products. Because few experiment stations possess dairy products research centers with such capabilities, a cooperative approach will be necessary to properly evaluate milk with altered fat composition.
RELATED CURRENT AND PREVIOUS WORK
Genetic selection for increased milk fat percentage leads to increased proportions of short-chain fatty acids in milk fat and decreased proportions of long-chain fatty acids (Karijord et al., 1982). Milk fat composition is strongly influenced by stage of lactation; proportion of short chains are low initially and increases until at least 8 to 10 wk. into lactation. Seasonal and regional differences in milk fat composition are measurable, most likely because of local differences in feed supplies (Palmquist et al, 1993).
The fundamental processes of milk fat synthesis are well established
and explain the occurrence of high amounts of saturated fatty acids in
milk. Milk fat is synthesized from fatty acids (FA) which are obtained
from blood or by de nova synthesis in the mammary gland. Fatty acids
synthesized de nova contain 4 to 16 carbons and are saturated. Blood
FA is derived from diet or from lipolysis in adipose tissue. Approximately
50 to 60% of milk FA is of dietary origin; therefore, FA composition of
milk can be influenced by diet. Modifications of dietary FA prior
to incorporation into milk fat include biohydrogenation in the rumen and
desaturation of stearic acid by intestinal, adipose, or mammary tissue.
Consequently, milk FA tend to be lower in polyunsaturated FA and higher
in oleic acid than is dietary fat.
The most thorough modern summaries of the distribution of FA in milk
fat and dairy products are by Jensen et al. (1991) and Jensen (1992).
A CRIS search revealed 60 projects related to milk production and/or dietary
effects on milk composition, and/or milk fat quality. Twenty-five
of these projects addressed feeding effects on milk composition; however,
the main focus was on milk protein. Only six included detailed evaluation
of feeding effects on milk fat composition. Nine projects were related
to evaluation of modified fat in dairy products with respect to physical
and chemical characteristics of product quality and flavor. Of the
lipid studies, fourteen were research projects of W-181 (revised) members
of their colleagues, whereas five were from investigators outside the proposed
project. One outside investigator had a closely related project (MD-C-114)
but chose not to participate in W-181 because of prior commitments.
Thus, the proposed revised project will bring together those investigators
already working in the field without serious duplication by those outside
the project. The skills are extant; the project should increase productivity
and decrease unnecessary duplication.
Metabolic Regulation
The physical properties (primarily fluidity or melting point) of milk fat are critical as the fat must be liquid at body temperature. Three metabolic processes within the mammary gland influence the fluidity of the milk fat: 1) chain length of FA synthesized de novo; 2) desaturation of stearate to oleate; 3) positional distribution of FA on glycerol. Considerable information on the metabolic processes and regulation of milk fat synthesis is available, with comprehensive studies from the laboratories of Kinsella, and Knudsen and colleagues. Pathways and regulation of de novo synthesis are by the classical pathways (Dils, 1983), with acetate, lactate, and -OH-butyrate as primary carbon sources, and glucose as the primary source of reducing equivalents (Forsberg et al., 1985).
Regulation of the pattern (chain length) of FA synthesized de novo is not well-defined. Many non-ruminant mammalian species regulate synthesis of short- and medium-chain fatty acids (SCFA and MCFA, respectively) by a specific enzyme (thioesterase II) which cleaves the MCFA from the fatty acid synthetase (FAS) enzyme complex (Smith, 1980). However, ruminants do not possess this enzyme; rather, the mammary gland FAS exhibits both medium-chain thioesterase and transacylase activity (Knudsen and Grunnet, 1982). The transacylase which transfers the activated primer chain to the FAS complex has broad chain-length specificity, so that there is competition both for transfer to and removal from the FAS of acyl chains containing from 2 to 12 carbons. Relative distribution is influenced by the affinity of the transacylase for substrates [highest affinity is for butyrate (Knudsen and Grunnet, 1980)] and seems to be modified by the concentration of malonyl CoA (Hansen and Knudsen, 1980). Malonyl CoA concentration, in turn, is regulated to some extent by the concentration of long-chain acyl CoA in the cell (Bauman and Davis, 1974). Relative supply of palmitic (C16:0) vs. oleic (C18:1) acids may influence the pattern of SCFA and MCFA synthesized (Hansen and Knudsen, 1987).
Saturated LCFA absorbed from the intestine would cause milk fat to be solid if excessive amounts were incorporated. Melting point is lowered by activity of stearoyl CoA desaturase (Kinsella, 1972) to convert stearic acid (m.p. 70 C) to oleic acid (m.p. 5-7 C); to a lesser extent, palmitic acid is desaturated by the same enzyme. As very little polyunsaturated FA (typically high in fluidity-sensitive membranes) are available for synthesis of milk fat triglyceride, synthesis of SCFA and MCFA and stearoyl-CoA desaturase activity to modify milk fat fluidity is critical. Contributions of SCFA, MCFA, and LCFA to milk fat synthesis seem to be regulated in ruminants, but not tightly so, as variations in fluidity of milk fat are documented (Banks et al., 1989).
The third factor which influences physical properties of milk fat is
the distribution of the various FA on the glycerol molecule (Palmquist
et al., 1993). Although specificity of acyltransferases has been
demonstrated (Marshall and Knudsen, 1977), there is little documentation
as to whether transferase activity can be modified. Feeding C18:2
protected from ruminal biohydrogenation decreased the proportion of C16:0
and increased the proportion of C18:2 at the sn-2 position of glycerol
(Jensen et al., 1991).
Dietary Regulation
Extensive information on the effects of diet on milk fat composition was reviewed by participants in this proposed regional project (Grummer, 1991); Palmquist et al., 1993). Milk fat composition (distribution of the individual fatty acids) varies by breed of cow, stage of lactation, and diet (Palmquist et al., 1993). Only the last is readily manipulated by management. The most dramatic changes in milk fat composition are brought about by feeding supplemental fat. Feeding fat that is rich in 18 carbon FA increases C18:0 and C18:1 content of milk fat and reduces the SCFA content of milk via reduction of de novo fatty acid synthesis. Oleic acid (C18:1) content of milk can be increased substantially if the cow is fed high levels of substrate (C18:0) for stearoyl-CoA desaturase (Bickerstaffe et al., 1972). Palmitic acid (C16:0) content of milk fat is typically reduced when feeding supplemental fat unless the fat is rich in C16:0. Increases in C18:0, C18:1, and decreases in C16:0 contents of milk fat are considered to be positive changes in the milk fatty acid profile and can be achieved by changing in the diet of the cow. However, the extent to which milk fat can be manipulated toward a more desirable fatty acid profile has not been determined. For example, very few dose response curves to supplemental fat have been generated. The few that have been reported have indicated that maximum changes in fatty acid profile have not been obtained within the levels of supplemental fat tested. There are limitations to the amount of fat that can be supplemented to dairy diets due to inefficiencies in postruminal lipid digestion (Palmquist, 1994). Methodologies for increasing absorption of fat from the small intestine need to be identified. Although several methods for dietary manipulation of milk fat are available, the magnitude of change that can be achieved by each method is largely undefined. Combining methods that take advantage of different biological processes have not been attempted but should be. Finally, there needs to be a concerted effort to quantitate animal responses to dietary modifications. Ultimately, it would be desirable to predict accurately changes in milk FA composition caused by diet modification.
In addition to feeding supplemental fat, milk unsaturated FA content (particularly C18:1) can be increased by reducing biohydrogenation in the rumen. Reducing ruminal pH by feeding high levels of nonstructural carbohydrate will limit conversion of unsaturated fatty acids to C18:0 in the rumen (Latham et al., 1972). Encapsulation of fat to prevent biohydrogenation is a strategy that was examined in the early 1970s (McDonald and Scott, 1977) and needs further examination now that there is increased emphasis on modifying milk fat composition. Chemical modification of polyunsaturated fatty acids to reduce microbial hydrogenation is a strategy that is just beginning to be examined by a member of the proposed committee.
Product Quality
The most significant changes in milk fat quality relate to rheological (melting) properties, which influence numerous aspects of character and quality of manufactured dairy products (Mortensen, 1983). The type of fatty acids present in milk fat can influence the flavor and physical properties of dairy products, as well as results of analytical tests for determination of milk fat (Barbano and Lynch, 1987; Stegeman et al., 1992). The mid-infrared spectroscopic method underestimated the fat content of milk that was higher in unsaturated fatty acids (Stegeman et al., 1991). The unique SCFA of milk fat, particularly butyric acid, are important for flavor development in some cheese and fermented dairy products (Barbano and Lynch, 1987). The ratio of saturated to unsaturated fatty acids and the ratio of short- to long-chain fatty acids can affect the meltability and spreadability of butter, and also may affect the body/texture and meltability of cheese. Changing fatty acid composition affects milk fat melting directly, because each fatty acid has a characteristic melting point, and indirectly, by influencing the array of fatty acids in the various positions of the glycerol backbone. This structure is the most important determiner of crystallization behavior and hardness of milk fat, as well as melting point (Connolly and Murphy, 1994). Currently, variability of triglyceride structure in commercial milk fat compromises quality of products produced by crystallization/fractionization of milk fat (Laakso et al., 1992).
Sensory evaluation indicated that butter produced from cows fed high oleic sunflower seeds and regular sunflower seeds were equal or superior in flavor to the control butter (Middaugh et al., 1988). The high oleic sunflower seed and regular sunflower seed treatment butters were softer, more unsaturated, and exhibited acceptable flavor, manufacturing, and storage characteristics. Sensory evaluation of Cheddar cheese indicated that extruded soybean and sunflower diets yielded a product of quality similar to that of the control diet (Lightfield et al., 1993). Cheese made from milk obtained with extruded soybean and sunflower diets contained higher concentrations of unsaturated fatty acids while maintaining acceptable flavor, manufacturing, and storage characteristics. It is anticipated that the total unsaturated fatty acid content could be increased beyond the amounts achieved to date when feeding unsaturated fat sources and without adversely affecting flavor or product processing properties (Baer, 1991).
Research is limited concerning the processing and sensory properties of milk and dairy products containing higher concentrations of unsaturated fatty acids produced by cows fed supplemental fat. Wong et al. (1973) processed milk from cows fed a protected safflower and oil-casein fat source to produce a Cheddar cheese containing 30% linoleic acid. Experimental cheese possessed body and flavor defects; however, an acceptable Cheddar cheese was produced from polyunsaturated milk.
OBJECTIVES
1. To identify and characterize important regulatory steps in fatty
acid synthesis and desaturation
and their positional distribution on glycerol
in milk fat.
2. To quantify modification of milk fat composition by manipulating the diet of the cow.
3. To characterize the effects of modified milk fats on physical, chemical,
manufacturing, and
sensory properties of dairy products.
PROCEDURES
Objective 1
A. There is a particular need to develop sound biochemical bases to
understand metabolic
regulation of the synthesis of individual
milk fatty acids, in particular 12:0 and 14:0, which
are of specific public concern today.
Objective 1 addresses these needs.
Regulatory aspects of fatty acid synthesis and incorporation into triacylglycerol will be studied in mammary tissue explants, in isolated cells, in cell culture, or by preparing subcellular components of mammary tissue using standard enzymatic procedures (IL, OH, VA, WA). In certain unique studies, metabolic limits for incorporation of specific fatty acids (varying in unsaturation or chain length) in vivo will be characterized by infusing these intestinally or intravenously (IL, OH). Kinetic characteristics of stearoyl-CoA desaturase will be determined in microsomal fractions of mammary tissue (IL), and factors regulating SCFA synthesis will be determined in homogenates or explants (IL).
Influence of dietary trans-18:1 on fatty acid synthesis by an established mouse mammary epithelial cell line, which produces neutral lipids when stimulated by lactogenic hormones during growth on an extracellular matrix, will be studied (VA). This group is studying rates of fatty acid elongation and fatty acid incorporation into triacylglyceride, activities of acetyl-CoA carboxylase and stearoyl-CoA desaturase, and plasma membrane fluidity in response to varying amounts of 18:0, cis-18:1, and trans-18:1 in the incubation medium. These studies will be developed further in a bovine mammary cell (MAC-T) line to determine the extent to which concentrations of lipid precursors regulate rates of de nova fatty acid synthesis and desaturation of exogenous stearic acid. Collaboration (IL and VA) to develop isolated cells (Hansen et al., 1986) as a metabolic model to study regulation of milk synthesis will be developed.
Objective 2
Several investigators will use dietary fat supplements to manipulate milk fat composition (CA, IL, OH, SC, SD, VA, WA, WI). Experimental designs will utilize multiple levels of fat supplementation to develop dose response curves so that diet fat effects on milk fat composition may be quantitated. Stage of lactation of cows will be defined in order to remove confounding effects of adipose mobilization on milk fat composition. Correlary studies will examine effects of adipose tissue mobilization on milk fat composition.
In addition to level of supplemental fat, effects of sources of dietary fat are an experimental objective, e.g., whole oil seeds (SD), intestinally-infused vegetable oils (IL), fish oils (OH,VA), varying fatty acid chain-length (OH), and ruminally-protected unsaturated fat (OH, SC). Factors modifying biohydrogenating activity of ruminal microorganisms will be characterized (CA, OH, SC, VA). Because digestibility of fat declines at high intakes and thereby influences amount of fat available to tissues, studies to define factors limiting fatty acid absorption and to improve fatty acid digestibility will be appropriate contributions to this objective (CA, IL, OH, VA, WI).
Objective 3
B. Milk and fat from the core group of feeding studies (Objective 2)
will be sent to several of
the cooperating milk processing research groups
to evaluate changes in milk fat composition
on manufacturing quality and consumer acceptance.
These interactions will be developed
and strengthened through the regional process.
Milk obtained from studies addressing Objective 2 will be utilized to examine effects on quality of ice cream (IL) and yield and flavor of low fat cheese (SD). Influence of increasing milk fat unsaturation on quantification of milk fat by infrared spectroscopy will be quantified (SD). The quality and sensory attributes of low cholesterol dairy products produced from butter oil by steam-stripping will be evaluated (MN). Quantification of flavor characteristics in modified fat products by gas-liquid chromatography will be developed (MN). In model systems, the emulsification of modified milk fat and its subsequent effects on milk gel formation will be studied. Emulsification will be evaluated microscopically, and gel formation properties will be assessed by formagraph and rheological measures. The behavior of fats in powders as a component of food products will be evaluated in terms of reconstitution properties and sensory acceptability (MN). To gain information on functionality of modified milk fats, solid fat content will be determined by nuclear magnetic resonance, and temperature of phase transitions will be determined by differential scanning calorimetry (WI). Positional arrangements of fatty acids on the glycerol molecule will be determined when appropriate (CA, WI). Milk from all studies will be used to update a national data base on seasonal, regional, and feeding effects on composition of the milk supply (NY).
Regionality
D. Regionality will bring together scientists competent in all aspects
of our concern for
modifying milk fat: 1) metabolic regulation
of synthesis; 2) predicting milk composition on
product quality, and applying new knowledge
to product development.
Cooperation among investigators will be encouraged in at least three ways: 1) Feeding studies will be regionalized to provide a sufficiently large data base to develop appropriate response curves to fat supplementation and to further develop existing whole animal metabolic models to include effects of dietary fat on milk composition (CA, WA); 2) unique methodologies will be shared to obtain the maximum information from each study; e.g., some laboratories lack the capability to separate the cis/trans isomers of unsaturated fatty acids; this can be provided by other labs through sharing of samples; 3) milk from feeding studies will be provided to cooperating laboratories to determine effects of changed milk fat composition on product quality (CA, IL, MN, NY, SD). Regional cooperation will enhance exchange of milk products for study. Thus, utilization of sophisticated equipment (NMR) and methodologies (triacylglycerol structure, sensory studies) will be enhanced and applied to a wider range of modified milk fats than would be possible in any individual laboratory.
E. Interdependency of states is illustrated by sharing of information
from methodologies unique
to certain laboratories
a. liver biopsy (WI)
b. intestinal cannulae (IL)
c. separation of cis/trans isomers of milk fatty acids (CA, OH)
d. rheology (MN) and nuclear magnetic resonance (WI) of milk fat
e. computer simulation modeling of milk fat composition responses to
dietary fat changes (CA,
WA)
f. collaborative development of mammary cell culture systems
(IL, VA)
Uniform Methodologies
Feeding trials will be designed to develop dose response curves to diet manipulation. All fat quantification will include total fatty acid analysis. Milk fatty acid analysis will utilize techniques that preserve and quantify short chain fatty acids (from butyric), and will include separation of the cis/trans isomers of C18:1.
ORGANIZATION
The technical committee will consist of a chair, secretary, and regional administrative adviser. The executive committee will consist of these three persons and the previous chair, and will be the official nominating body. The Chair and secretary will be elected by the voting members from within their ranks. The Chair is responsible for planning and conducting the annual meeting, for submission of the project annual report, and for facilitating and ensuring effective communication and cooperation among participants. The secretary is responsible for recording minutes and distributing them prior to the Chair preparing the annual reports. Individual station members are responsible for preparing brief annual reports and distributing them to other participants prior to the annual meeting. Additional committees composed of voting or non-voting members may be appointed as needed to solve particular technical problems, to assist in communication with the project, or to report project findings to other interesting parties.
REFERENCES
Baer, R.J. 1991. Alteration of the fatty acid content of milk. J. Food Prot. 54:383.
Banks, W., J.L. Clapperton, D.D. Muir, and A.K. Girdler. 1989.
Whipping properties of cream in relation to milk
composition. J. Dairy Res. 56:97-105.
Barbano, D.M., and J. Lynch. 1987. Milk from BST-treated
cows - its composition and manufacturing properties.
pp.
66-73 in National Invitational Workshop on Bovine Somatotropin, St.
Louis, MO.
Bauman, D.E., and C.L. Davis. 1974. Biosynthesis of milk
fat. pp. 31-75 in B.L. Larson and V.R. Smith, ed.
Lactation, Vol. II. Academic Press, New York, NY.
Berner, L.A. 1993a. Defining role of milk fat in balanced diets.
Advances Food Nutr. Res. 37:
131-257.
Berner, L.A. 1993b. Roundtable discussion on milk fat, dairy foods,
and coronary heart disease risk. J. Nutr.
23:1175-1184.
Bickerstaffe, R., D.E. Noakes, and E.F. Annison. 1972. Quantitative
aspects of fatty acid biohydrogenation, absorption
and transfer into milk fat in the lactating goat, with special reference
to the cis and trans-isomers of octadecenoate and
linoleate. Biochem. J. 130:607-617.
Connolly, B., and J. Murphy. 1994. Potential for enhancing
the nutritional properties of milk fat. Symposium, Fats in
Human Nutrition - Recent research findings and their implications for
the Irish livestock and food industry. Irish Grasslands
and Animal Production Assoc., Dublin.
DePeters, E.J. 1993. Influence of feeding fat to dairy cows on
milk composition. Proc., Cornell Nutr. Conf., pp.
199-215. Rochester, NY.
Dils, R.R. 1983. Milk fat synthesis. pp. 141-157 in T.B. Mephan, ed. Biochemistry of Lactation. Elsevier, Amsterdam.
Experiment Station Committee on Organization and Policy. 1994.
Opportunities to Meet Changing Needs. Research on
Food, Agriculture, and Natural Resources. A Strategic Agenda
for the State Agricultural Experiment Stations. ESCOP
and USDA. Dept. of Agric. Communications. Texas A&M
Univ.
Federation of American Societies of Food Animal Science. 1993.
FAIR ‘95 Executive Summary. Linking Science and
Technology to Societal Benefits: Research priorities for competitive
and sustainable food production from animals.
FASFAS. Champaign, IL.
Forsberg, N.E., R.L. Baldwin, and N.E. Smith. 1985. Roles
of lactate and its interactions with acetate in maintenance
and biosynthesis in bovine mammary tissue. J. Dairy Sci.
68:2550-2556.
Gibson, J.P. 1991. The potential for genetic change in milk fat composition. J. Dairy Sci. 74:3258- 3266.
Grummer, R.R. 1991. Effect of feed on the composition of milk fat. J. Dairy Sci. 74:3244-3257.
Hansen, H.O., and J. Knudsen. 1987. Effect of exogenous long-chain
fatty acids on individual fatty acid synthesis by
dispersed ruminant mammary gland cells. J. Dairy Sci. 70:1350-1354.
Hansen, H.O., D. Tornhave, and J. Knudsen. Synthesis of milk specific
fatty acids and proteins by dispersed goat
mammary gland epithelial cells. Biochem. J. 238:167-172.
Hansen, J.K., and J. Knudsen. 1980. Transacylation as a chain-termination
mechanism in fatty acid synthesis by
mammalian fatty acid synthetase. Biochem. J. 186:287-294.
Jensen, R.G. 1992. Fatty acids in milk and dairy products.
pp. 95-135 in C.K. Chow, ed. Fatty Acids in Foods and
Their Health Implications. Marcel Dekker, Inc., New York, NY.
Jensen, R.G., A.M. Ferris, and C.J. Lammi-Keefe. 1991. Symposium:
Milk fat - composition, function, and potential for
change. J. Dairy Sci. 74:3228-3243.
Karijord, ., N. Standal, and O. Syrstad. 1982. Sources of
variation in composition of milk fat. Z. Tierz. Zeüchtungsbiol.
99:81-93.
Kinsella, J.E. 1972. Stearyl CoA as a precursor of oleic acid
and glycerolipids in mammary microsomes from lactating
bovine: possible regulatory step in milk triglyceride synthesis.
Lipids 7:349-355.
Knudsen, J., and I. Grunnet. 1980. Primer specificity of mammalian
mammary gland fatty acid synthetases. Biochem.
Biophys. Res. Comm. 95:1808-1814.
Knudsen, J., and I. Grunnet. 1982. Transacylation as a chain-termination
mechanism in fatty acid synthesis by mammalian
fatty acid synthetase. Biochem. J. 202:139-143.
Laakso, P.H., K.V.V. Nurmela, and D.R. Homer. 1992. Composition
of the tracylglycerols of butterfat and its fractions
obtained by an industrial melt crystallization process. J. Agric.
Food Chem. 40:2472-2482.
Latham, M.J., J.E. Storry, and M. Elizabeth Sharpe. 1972. Effect
of low-roughage diets on the microflora and lipid
metabolism in the rumen. Appl. Microbiol. 24:871-877.
Lightfield, K.K., R.J. Baer, and D.J. Schingoethe. 1993. Characteristics
of milk and Cheddar cheese from cows fed
unsaturated dietary fat. J. Dairy Sci. 76:1221-1232.
Marshall, M.O., and Jens Knudsen. 1977. Biosynthesis of triacylglycerols
containing short-chain fatty acids in lactating
cow mammary gland. Eur. J. Biochem. 81:259-266.
McDonald, I.W., and T.W. Scott. 1977. Foods of ruminant origin with
elevated content of polyunsaturated fatty acids.
World Review Nutrition Dietetics 26:144-207.
Middaugh, R.P., R.J. Baer, D.P. Casper, D.J. Schingoethe, and S.W. Seas.
1988. Characteristics of milk and butter from
cows fed sunflower seeds. J. Dairy Sci. 71:3179-3187.
Mortensen, B.K. 1983. Physical properties and modification of
milk fat. pp. 159-194 in P.F. Fox, ed. Developments in
Dairy Chemistry - 2. Lipids. Applied Science, London.
Ney, D.M. 1991. Symposium: The role of the nutritional and health benefits
in the marketing of dairy products: Potential
for enhancing the nutrition properties of milk fat. J. Dairy
Sci. 74:4002-4012.
O’Donnell, J.A. 1989. Milk fat technologies and markets: A summary
of the Wisconsin Milk Marketing Board 1988
Milk Fat Roundtable. J. Dairy Sci. 72:3109-3115.
O’Donnell, J.A. 1993. Future and milk fat modification by
production or processing: Integration of nutrition, food
science, and animal science. J. Dairy Sci. 76:1797-1801.
Palmquist, D.L. 1994. The role of dietary fats in efficiency of ruminants. J. Nutr. 124:xxx. (Accepted)
Palmquist, D.L., A.D. Beaulieu, and D.M. Barbano. 1993.
ADSA Foundation Symposium: Milk Fat Synthesis and
Modification: Feed and animal factors influencing milk fat composition.
J. Dairy Sci. 76:1753-1771.
Smith, Stuart. 1980. Mechanism of chain length determination
in biosynthesis of milk fatty acids. J. Dairy Sci.
63:337-352.
Stegeman, G.A., R.J. Baer, D.J. Schingoethe, and D.P. Casper.
1991. Influence of milk fat higher in unsaturated fatty
acids on the accuracy of milk fat analysis by the mid-infrared spectroscopic
method. J. Food Prot. 54:890.
Stegeman, G.A., R.J. Baer, D.J. Schingoethe, and D.P. Casper. 1992.
Composition and flavor of milk and butter from
cows fed unsaturated dietary fat and receiving bovine somatotropin.
J. Dairy Sci. 75:962-970.
Wong, N.P., H.E. Walter, J.H. Vestal, D.E. Lacroix, and J.A. Alford.
1973. Cheddar cheese with increased polyunsaturated fatty
acids. J. Dairy Sci. 56:1271-1275.
PROJECT LEADERS:
| Investigator | Institution and Specialization Specific to
Objectives |
| E.J.De Peters | Univ. of California, Davis
Animal Nutrition and Metabolism |
| R.L.Baldwin | Univ. of California,Davis
Animal Nutrition and Metabolism |
| Bruce German | Milk Fat Composition |
| J.K.Drackley | University of Illinois, Urbana
Animal Nutrition and Metabolism |
| R. Jimenez-Flores | University of Illinois, Urbana
Dairy Products |
| B.A.Crooker | University of Minnesota
Animal Nutrition and Metabolism |
| J.Linn | University of Minnesota
Animal Nutrition |
| D.Otterby | University of Minnesota
Animal Nutrition |
| M.Stern | University of Minnesota
Animal Nutrition |
| D.Smith | University of Minnesota
Dairy Products |
| D.Barbano | Cornell University
Dairy Products |
| D.L.Plamquist | Ohio Agric. Res. and Dev. Center
Animal Nutrition and Metabolism |
| T.C.Jenkins | Clemson University
Animal Nutrition and Meatabolism |
| D.J.Schingoethe | South Dakota State University
Animal Nutrition and Metabolism |
| R.J.Baer | South Dakota State University
Dairy Products |
| J.H.Herbein | Virginia Tech
Animnal Nutrition and Metabolism |
| Susan Duncan | Virginia Tech
Dairy Products |
| J.P.McNamara | Washington State University
Animal Nutrition and Metabolism |
| J.H.Harrison | Washington State University
Animal Nutrition and Metabolism |
| J.K.Hiller | Washington State University
Animal Nutrition and Metabolism |
| R.R.Grummer | University of Wisconsin, Madison
Animal Nutrition and Metabolism |
RESOURCES
| Institution |
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| Univ. of California |
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| Univ. of Illionis |
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| Univ. of Minnesota |
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| Cornell Univ. |
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| Ohio Agri. Res. &
Dev. Center |
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| Clemson Univ. |
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| South Dakota State
Univ. |
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| Virginia tech |
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| Washington State
Univ. |
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| Univ. of Wisconsin |
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