Manufaturing - Butter/Milkfat - 1998
Modification of Cream Functionality by a Novel Adsorption Process - Rafael Jiménez-Flores, Cal Poly San Luis Obispo
The Effect of Milkfat on Mechanisms of Satiety in Humans - Paul A. Davis,UC Davis
Conjugated Linoleic Acid (CLA) Content of Milkfat From Lactating Dairy Cows and Selected Dairy Products - Edward DePeters, UC Davis
Nutrition and Genetic Effects on the Fatty Acid Composition of Milkfat - Edward DePeters, UC Davis
Modification of Milkfat to Improve Manufacturing Properties and Nutritional Quality - Edward J. DePeters, UC Davis
Regulation of Gene Expression by Butryic Acid - Bruce German, UC Davis
Milkfat as a Nutritional Delivery System for Fat-Soluble Nutrients - Bruce German, UC Davis
Genetic Modification of the Composition of Milkfat: Molecular Identification of Polymorphisms Associated With the Stearoyl-CoA Desaturase Gene in Dairy Cows - Juan F. Medrano, UC Davis
Modification of the Composition of Milkfat in Dairy Cows Utilizing Genetic Selection - Juan F. Medrano, UC Davis
The Evaluation of the Efficacy of Increasing the Monounsaturated to Saturated Milkfat Ratio via Expression of a Steroyl-CoA Desaturase Transgene - James D. Murray, UC Davis
Composite Whey Protein Gels Containing Fractionated Milkfat: An Application For Fractionated Milkfat - Moshe Rosenberg, UC Davis
Modification of Cream Functionality by a Novel Adsorption Process
Rafael Jiménez-Flores, Cal Poly San Luis Obispo
This research has shown that treatment of cream with biosilicates results in significant changes in the functionality of cream and subsequently results in altered physical properties of products made with the modified cream. Certain biosilicates (amorphous silicate compounds commonly used as filtration aids in the food industry) have been shown to have specific affinity for some components of the milkfat globule membrane. Therefore, biosilicates can be used to induce changes in the chemical composition of the milkfat globule membrane, thus affecting the functionality of the milk or cream. Exploiting this phenomenon, biosilicates may be used to manufacture modified cream or milk at the industrial level that would behave differently in a food system, lending new or novel texture to the finished product. Presently, dairy spreads with altered texture have been developed in the laboratory using modified cream. However, to recognize the successful full-scale implementation of this new technology, the following objectives must be accomplished:
- Continue to study the parameters that control this process in a pilot plant setting
- Characterize the physical properties and chemical composition of the treated creams.
- Evaluate modified creams for their processing characteristics in developing spreads and frozen desserts of normal and low-fat composition.
- Evaluate the microbiological and regulatory aspects of this process.
The first two objectives were addressed by an in-depth study of the effects of cream modification on the textural properties of cream and spreads manufactured from these creams. Further developments will complete our findings. In working toward the third objective, creams treated with three types of biosilicates were used to manufacture ice cream at the pilot plant level. Characteristics of the ice cream mix and/or finished product were evaluated for sensory differences, stability, texture and melt properties. Apparent differences were observed in viscosity of the treated cream, and in melting rate and hardness of the finished ice cream product. These observations indicate that these modified creams can impart altered rheological characteristics to frozen dairy desserts. In addition to experimentation with product manufacture, current work is in progress to develop a feasible processing method for treatment of cream or milk with the biosilicates. Concurrently, a method to remove the biosilicates from the cream using a plate and frame filter is being developed.
This project has the potential of enabling a feasible method for the manufacture and sale of value-added milk or cream, while simultaneously contributing to the larger goal of finding new uses for milkfat. This end-user tailored milk or cream could then be used to develop traditional or low-fat dairy products with improved or novel texture. An alternative processing tool has been identified that has the potential to modify cream function in several ways. These modifications, if better understood and applied judiciously, can be used for the improvement or modification of texture in traditional products, or could be applied for the development of new products. Biosilicates indeed have a profound effect in the final texture of products elaborated with treated creams. Further characterization is necessary to achieve effective use of this tool in formulated dairy foods. Finally, the main challenge facing this technology is to optimize the processing parameters necessary to scale up this procedure.
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The Effect of Milkfat on Mechanisms of Satiety in Humans
Paul A. Davis, UC Davis
Our research objective was to examine the effect of the source of fat (dairy, non-dairy) and level of fat—i.e., 20 percent of the energy as fat (en fat), 38 percent en fat—on measures of meal-related satiety. This was approached in part by examining the satiety response to dairy fat as it relates to plasma cholecystokinin (CKK) concentrations, a possible mediator of fat-induced satiety. In a randomized crossover design, male and female adult subjects consumed four isoenergetic test meals at least one week apart. The four meals were prepared using commercially available foods that contained one-third of the average daily energy intake of males and females. The meals were prepared as: low-fat dairy and low-fat, non-dairy (20 percent en fat; D20, ND20, respectively) and high-fat dairy (38 percent en fat; D38, ND38, respectively). The polyunsaturated: saturated fatty acid ratio for the meals was 0.125:1, respectively. Palatability was similar among meals and were consumed easily by all subjects.
Subjective measures of satiety and corresponding blood samples were successfully collected from subjects before and after consuming the test meals for determination of feelings of hunger, fullness, desire to eat and prospective consumption as well as plasma glucose, insulin and CCK. All the planned plasma-based biochemical analyses were performed, and the results were analyzed by repeated measures of analysis of variance.
In the present study, meals containing dairy fat were shown to produce a larger response in CCK, a mediator of satiety, than did non-dairy fats with a similar fatty acid composition. However, this difference in CCK response was not reflected in heightened feelings of satiety and, in general, subsequent energy intake was not affected significantly. However, males tended to eat more than usual on study days (test meal + subsequent energy intake vs. average daily energy intake measured from background dietary food intake records), whereas females did not.
The exact nature and the potential significance of these gender-related differences in the responses to dairy products remain to be determined. These findings provide an initial and tentative basis for raising the question of potentially great significance to the dairy industry: Can or should dairy foods be formulated and/or marketed in different ways to men and women? Can one develop and then subsequently successfully market dairy-derived foods that make use of or exploit the differences that appear to characterize male and female satiety responses to the ingestion of dairy food? While the data from this project provides initial support for a gender-related satiety effect, the complexity of the responses requires more research to take advantage of any gender differences. One area for further exploration could be whether foods containing dairy fat will have a different affect on subsequent food intake than foods composed of fats with a different fatty acid profile.
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Conjugated Linoleic Acid (CLA) Content of Milkfat From Lactating Dairy Cows and Selected Dairy Products
Edward DePeters, UC Davis
The objective of this research was to evaluate the ability to modify the conjugated linoleic acid (CLA) concentration in milkfat of lactating cows by dietary strategies. Conjugated linoleic acid, an isomer of linoleic acid, is a mixture of isomers with conjugated double bonds. Previous research with rodents demonstrated anticarcino-genic properties of CLA. Dietary sources of CLA include milkfat, dairy products and meat. In general, CLA is presented in greater amounts in lipids from animal sources than in lipids from plant sources, and ruminant food products contain more CLA than non-ruminant food products.
The potential beneficial effects of CLA offer an opportunity to reposition milkfat as a healthy component in the diet of humans. However, little information is available on the mechanism controlling the concentration of CLA in milkfat. The effects of diet fed to the lactating cow and genetics of the cow on CLA content of milkfat were studied. Feeding dietary fat to lactating cows increased the CLA content of milkfat. A fat source higher in unsaturated fatty acid composition increased CLA concentration greater than a more saturated fat source. Increasing the amount of fat in the diet increased the CLA content of milk. Canola oil was used as a source of lipid in two studies that involved cows surgically fitted with ruminal and duodenal cannulas. Continuously infusing canola oil into the rumen increased the CLA content of milkfat. In contrast, infusion of canola oil into the abomasum, a method to bypass ruminal biohydro-genation, did not increase milkfat CLA content compared to the control diet. These data suggest that a possible source of CLA is ruminal biohydrogenation of fatty acids. Breed of cow influenced the CLA content of milkfat. Thus, knowledge concerning the genetic control of CLA is important. Jersey cows had lower CLA in their milkfat compared to Holstein and Brown Swiss cows. We propose that this difference is related to the stearoyl Co-A desaturase enzyme system.
Increasing the monounsa-turated fatty acid and CLA content of milkfat improves the nutritional value of milk for humans. A synthetic source of CLA was fed to transgenic mice. The mice developed spontaneous, visible tumors at 80 to 110 days of age. Diets of mice were supplemented to provide 0, 0.5, and 1.0 percent CLA. Supplementing the diet with CLA did not influence the development of tumors using the transgenic mouse model. Research information is accumulating on the beneficial effects of CLA for human health. Dairy products will be a source of the natural, biologically active isomer of CLA, which may reposition milkfat as beneficial to human health.
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Nutrition and Genetic Effects on the Fatty Acid Composition of Milkfat
Edward DePeters, UC Davis
The objective of this research was to determine the influence of nutrition and genetics of the lactating cow on the monounsaturated fatty acid content of the milkfat. Increasing the C18:1 content of milk relative to saturated fatty acids improves both the nutritional value and the consumer image of milkfat in dairy products. Textural properties of butter were shown in previous research conducted collaboratively by Cal Poly San Luis Obispo and UC Davis to be enhanced by elevated C18:1 and reduced medium chain fatty acids, in particular C16:0. In the present study preharvest factors were studied including diet fed to the cow and breed of cow. Canola oil was used to alter the composition of the diet because of its unsaturated fatty acid composition.
A diet containing no fat was compared to a diet containing approximately 300g canola oil daily. A similar amount of canola oil was also provided by continuous infusion into either the rumen or the abomasum. Infusion into the rumen was similar to adding fat to the diet since the fat was exposed to ruminal biohydrogenation. Infusion of fat into the abomasum was similar to rumen bypass fat since the fat was not exposed to ruminal biohydrogenation. All canola oil treatments increased the C18:1 and decreased the C16:0 content of milkfat. Canola oil also increased the C18:0 (stearic acid) content of milkfat. All canola oil treatments altered the stereospecific distribution of fatty acids and the triglyceride structure of milkfat. Breed of cow did not affect the fatty acid composition of milkfat. Holstein, Brown Swiss and Ayrshire cows had similar fatty acid composition. The D9 desaturase enzyme, measured as the ratio of C18:1 to C18:0 did not differ for breed.
These findings are in contradiction to our earlier research in which Jersey cows had the lowest C18:1 and Brown Swiss cows had the highest C18:1 content with Holstein cows intermediate. Desaturase activity was highest in Brown Swiss cows and lowest in Jersey cows. It is not known why breed did not affect milkfat composition in the present study. Identifying a genetic difference in desaturase activity will allow the development of strategies to increase enzyme activity to increase the monounsaturated fatty acid composition of milkfat. Nutrition is a preharvest technology that can be used to modify the composition of milkfat.
Feeding fat in the diet of lactating cows reduces the medium chain, saturated fatty acids and increases the 18 carbon fatty acids, in particular C18:1. These changes will have beneficial effects on the nutritional value and manufacturing properties of milkfat.
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Modification of Milkfat to Improve Manufacturing Properties and Nutritional Quality
Edward J. DePeters, UC Davis
The objective of this research project is to improve the manufacturing properties and nutritional quality of milkfat. Diet and genetics are being used to alter the fatty acid composition of the milkfat. Our goal is to increase the monounsaturated fatty acid composition (oleic acid; C18:1) and decrease the saturated fatty acid content of milkfat. In addition, an increase in the conjugated linoleic acid (CLA) concentration in the milkfat of lactating cows is desired. Conjugated linoleic acid refers to a mixture of positional and geometric isomers of linoleic acid (C18:2 CIS 9 CIS 12). Conjugated linoleic acid is reported to possess anticarcinogenic properties. The effects of CLA include inhibition of mammary tumors in mice, inhibition of proliferation of malignant cancer cells, and reduced generation of cancer in mice. The biologically active isomer of CLA was identified as C18:2 CIS 9 trans 11.
The CLA content of milkfat may be important in determining the health value of milkfat. Diet effects were studied by infusing canola oil either into the rumen or into the abomasum. Ruminal infusion of canola oil represents what would happen if fat is added to the diet of lactating cows. The fat is exposed to ruminal biohydrogenation of unsaturated fatty acids. Abomasal infusion of canola oil represents what would happen if the unsaturated fatty acids in dietary fat were protected from ruminal biohydrogenation. Infusing canola oil into the rumen increased both the C18:0 and C18:1 content of milkfat. The increase in C18:1 in milkfat was proposed to be a consequence of the ∆9 desaturase enzyme system.
Abomasal infusion of canola oil did not increase the C18:0 content of milkfat because unsaturated fatty acids in canola oil were not subjected to ruminal biohydrogenation. Abomasal infusion of canola oil increased the C18:1 content of milkfat. The origin of the C18:1 in milkfat was proposed to be from the C18:1 in the canola oil. Protection of dietary fat from ruminal biohydrogenation increases C18:1 without increasing C18:0. The CLA content of milkfat; however, is increased by ruminal infusion compared to abomasal infusion. The increase in CLA with ruminal infusion of canola oil may be a consequence of the ∆9 desaturase converting C18:1 trans 11, which is produced by ruminal hydrogenation of unsaturated fatty acids, to CLA.
Diet can be used to modify the monounsaturated fatty acid and CLA compositions of milkfat. Breed of dairy cattle altered the monounsaturated fatty acid composition and CLA content of milkfat. Milkfat from Holstein and Brown Swiss cows was higher in monounsaturated (C18:1) fatty acid composition compared to Jersey cows. Previous research at UC Davis demonstrated that the ∆9 desaturase was lower in Jersey cows compared to Holstein and Brown Swiss cows. The current data support our earlier observation. The CLA content of milkfat was also higher for Holstein and Brown Swiss cows compared to Jersey cows. The ∆9 desaturase may be responsible for this change in CLA. In the future it may he possible to identify animals with high desaturase activity and transfer desirable genes to improve the fatty acid composition of milkfat. The research conducted thus far demonstrated that diet and breed of cow could modify the CLA content of milkfat. The potential benefit of increasing the CLA content of milkfat is still being studied.
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Regulation of Gene Expression by Butryic Acid
J. Bruce German, UC Davis
Butyric acid is a short chain fatty acid that occurs naturally in the diet from two sources: fermentation of dietary fiber in the lower bowel and on the sn-3 position of bovine milkfat. Studies on the mechanisms of action of short chain fatty acids toward cancerous cells has shown that butyric acid modifies the structure of nuclear proteins, which causes cancerous cells to die by the process of apoptosis.
In the initial phases of this project, experiments demonstrated that butyric acid as a glyceride (the form present in bovine milkfat) produced similar benefits toward cancerous cells in culture, suggesting that milkfat may alter the growth of cells in the upper gastrointestinal tract and liver. In subsequent experiments, we demonstrated that butyric acid promoted apoptosis in cancerous liver cells. In experiments to determine the mechanisms underlying these effects, cancerous liver cells were shown to undergo changes in nuclear structure, DNA fragmentation and membrane composition consistent with death by apoptosis when exposed to butyric acid. In contrast, healthy liver cells, including phagocytic Kupffer cells, were apparently unaffected or beneficially affected in that they produced more molecules appropriate to their normal signaling functions.
A final series of experiments were performed in the final year of the project to determine if butyric acid delivered to the liver in vivo would produce similar effects to those demonstrated in culture. Butyric acid delivered as a liposomal suspension via the portal vein was taken up by phagocytic cells in the liver. The uptake of butyric acid relative to liposomes without butyric acid stimulated prostaglandin E2 activity in the cells cultured subsequently, demonstrating that the delivery of butyric acid in vivo does indeed alter the cellular physiology consistent with the effects seen in vitro.
These studies to date support the hypothesis that butyric acid is beneficial to growth and signaling of immune cells and in contrast stimulates death of cancer cells. During the next phase of the research we will develop methods to quantify the presence and actions of butyric acid in vivo, in order to document the effects of dietary butyric acid to the health of humans.
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Milkfat as a Nutritional Delivery System for Fat-Soluble Nutrients
J. Bruce German, UC Davis
Milk and milkfat products are potentially excellent sources of absorbable vitamin E. The form of vitamin E in foods is now recognized to be quite important to its nutritional value. The nutritional value of vitamin E is not just the amount of vitamin E anymore. Groundbreaking studies have shown that the isomers of alpha tocopherol vary in their vitamin E activity. Vitamin E is so insoluble that its absorption, transport in blood and delivery to tissues all require other dietary lipids. For example, the transport of the vitamin from the intestine and to tissues occurs solely via lipid-rich lipoproteins. As a result of these observations, it is abundantly clear that the nutritional value of vitamin E is intimately associated with its dietary source. Milk and milkfat have been observed to be potentially excellent vehicles for vitamin E nutriture, but it is not clear, in view of the now accepted health value of vitamin E in the diets of adults, if milk contains sufficient vitamin E for optimal nutrition. It is not clear whether milk that has some of the milkfat removed retains its vitamin E content.
Our results to date support three important conclusions. Milk is a source of alpha tocopherol and levels of gamma tocopherol and the other isomers of vitamin E are quite low. Alpha tocopherol is the most active form of vitamin E, hence milk is indeed a source of highly active isomer. However, the levels of tocopherols in milk mirror the levels of cholesterol, a similarly non-polar molecule. Thus, removal of fat to obtain low-fat milk and dairy products invariably results in the parallel reduction in vitamin E levels. Finally, milk is not a quantitatively significant source of vitamin E. The levels of alpha tocopherol are just adequate to meet essentiality. The predominance of the alpha tocopherol isomer is encouraging in terms of meeting the adequacy of vitamin E requirements, yet the absolute quantities of tocopherol that occur naturally in California milk at the present time would not provide a rich source of tocopherol to adult diets. This project will continue to analyze the contents of vitamin E in milk and explore the most logical means to increase both its content and biological value.
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Genetic Modification of the Composition of Milkfat: Molecular Identification of Polymorphisms Associated With the Stearoyl-CoA Desaturase Gene in Dairy Cows
Juan F. Medrano, UC Davis
Significant milkfat composition differences exist within and between breeds of dairy cattle suggesting that selection would be an effective means to modify the composition of milkfat. To identify genetic markers that could assist in a genetic selection program we have examined the natural DNA sequence variability of candidate genes determining the fatty acid (FA) composition of milk. A prime candidate gene to change the proportion of saturated vs. unsaturated FA in milk is the gene coding for the mammary enzyme stearoyl-CoA-desaturase (SCD). SCD oxidizes palmitic (C16:0) and stearic (C18:0) acids to palmitoleic (C16:1) and oleic (C18:1), respectively and is involved in the production of conjugated linoleic acid (CLA). We have cloned and sequenced the bovine SCD gene and have identified three closely linked polymorphisms in exon V of the gene that make up two conserved haplotypes (A and B) in Holstein, Jersey and Brown Swiss cattle. The first two polymorphisms are silent base pair substitutions corresponding to amino acids proline and tyrosine, respectively. The third base substitution produces a codon change of valine to alanine. This site is located within one of the conserved histidine domains of the protein that is involved in the exchange of electrons from the other enzymes in the desaturase pathway. Therefore, it is possible that the activity of the enzyme could be altered due to the underlying genetic variation of an amino acid substitution in haplotype B.
To develop a practical DNA diagnostic system introns IV and V of the gene were cloned and sequenced, and a PCR-RFLP created to classify the haplotypes. An analysis of 23 Holstein cows indicates the index of desaturation appears to favor haplotype B. The ratio of C18:1/C18:0 was higher in AB and BB cows, due to lower concentrations of saturated C18:0 FA in milk. The higher index of desaturation of these genotypes was also paralleled by higher concentrations of CLA. These results look encouraging, in terms of identifying a marker associated with the index of FA desaturation in milk; however, further evaluation in a larger sample of cows is required.
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Modification of the Composition of Milkfat in Dairy Cows Utilizing Genetic Selection
Juan F. Medrano, UC Davis
Significant milkfat composition differences exist within and between breeds of dairy cattle, suggesting that selection would be an effective means to modify the composition milkfat. The primary objectives of this research are to clone and sequence candidate genes controlling fatty acid (FA) desaturation and glass transition temperatures (Tg) structure in the bovine mammary gland, and to identify functional polymorphisms in these genes that could be used for marker-assisted selection. We have cloned and sequenced the entire cDNA of the bovine stearoyl-CoA-desaturase (BSCD), the glycerol-3-phosphate acyltransferase (GPAT), and the lysophosphatidic acid acyltransferase (LPAAT) genes. This is the first time that these important bovine genes involved in FA desaturation and structure of the Tg have been cloned and sequenced. The identification of polymorphisms has been initiated by examining the BSCD gene. This gene has been targeted as the means of increasing the proportion of unsaturated fatty acids in milk to make a healthier, softer, more marketable butter. BSCD oxidizes saturated FA to unsaturated FA, primarily palmitic (C16:0) and stearic (C18:0) to palmitoleic (C16:1) and oleic (C18:1), respectively. Currently we have identified three closely linked polymorphisms in exon V of the gene that make up two conserved haplotypes in Holstein, Jersey and Brown Swiss cattle. A DNA diagnostic system has been developed to classify these haplotypes, and we have preliminary evidence suggesting that these polymorphisms could be useful in identifying cows with a higher index of desaturation.
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The Evaluation of the Efficacy of Increasing the Monounsaturated to Saturated Milkfat Ratio via Expression of a Steroyl-CoA Desaturase Transgene
James D. Murray, UC Davis
This research is designed to use transgenic mice as a model to study the effect of expressing a fat synthesis gene in the mammary gland on the fatty acid composition of the resulting milk. It has been suggested that an "ideal" nutritional milkfat based on dietary recommendations would consist of approximately 25 percent saturated fatty acids, 75 percent monounsa-turated fatty acids and 5 percent polyunsaturated fatty acids.
We believe we can direct increased expression of a gene in the mammary gland to alter the fatty acid composition of milk to yield milk containing lower amounts of saturated (considered bad fat for cardiovascular health) and higher amounts of monounsaturated fatty acids. A transgenic mouse model will give us an opportunity to study the mechanisms of function of the transgene in the mammary gland and to model the positive health benefits of altered fatty acids composition of cows’ milk, if extrapolated to transgenic dairy animals.
This project has three sequential goals: 1) To make a gene construct to express the gene in milk and produce transgenic mice carrying this construct. 2) Once we have mice carrying the gene, characterize desaturase expression in the mammary gland at the RNA and protein levels. 3) Once we have lines of transgenic mice in which we can predict the level of expression of the human gene we need to characterize the fatty acid composition of mouse milk and compare it to transgenic mouse milk. If we can show that the composition of fatty acids is significantly altered, then we can expect positive health benefits for humans if the same change was introduced into the mammary gland of a dairy cow. Further research will be required to show if the flavor and functional properties of milk are also affected, but such work will require the production of a small ruminant model (dairy goat) or transgenic dairy cows. Given the expense of producing transgenic cows, it is logical to carry out the initial work in mice to demonstrate that we can significantly alter fat composition before undertaking the production of transgenic ruminants.
To date, we have made two gene constructs. The first transgene is controlled by the goat (b-casein promoter). A second construct was subsequently constructed based on the cattle (b-lactoglobulin promoter) since we were experiencing low viability of microinjected mouse embryos with the first construct and there appeared to be significant obstacles in gaining permission to use the goat (b-casein-based construct in goats or cattle). Both constructs are currently being microinjected into mice in order to produce transgenic lines expressing the transgene.
The importance of this research is demonstrated by previous work that has shown that saturated fatty acids in the diet raise serum cholesterol concentrations and that one-third of the saturated fatty acid in American diets comes from the consumption of dairy products. Milk is very high in short-chain and saturated fatty acid.
Many public health recommendations have been made to reduce intake of saturated fatty acid. Thus milk with an altered fatty acid composition would be of great benefit and value. It is clear that alterations in saturated content can be obtained nutritionally and that human consumption of such altered products can significantly alter cholesterol levels. It is too early in this project to draw any conclusions as to whether or not this approach will alter fatty acid concentration in milk.
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Composite Whey Protein Gels Containing Fractionated Milkfat: An Application For Fractionated Milkfat
Moshe Rosenberg, UC Davis
A broad array of different rheological properties of whey protein gels can be achieved by incorporating selected fractions of fractionated milkfat in the gel to yield a composite gel. The specific objectives of the research are to: 1) Study and quantify the effects of filler (fractionated milkfat fractions) composition and physico-chemical properties; matrix (whey proteins) composition, and matrix-filler interactions on the rheological properties, and structural features of composite gels consisting of whey proteins and fractionated milkfat fractions. 2) Based on the results of the first objective, to develop a series of model whey protein-based, fractionated milkfat-containing composite gels that significantly differ from each other, as well as from protein-only gels, in their viscoelastic and compressive properties.
Rheological properties of composite gels consisting of whey protein isolates (WPI) and four fractions of fractionated milkfat have been investigated and compared to those of AMF-containing and WPI-only gels. Results of our study indicated that incorporation of a selected fraction of milkfat into WPI-based gels significantly affected rheological properties of the gel.
Compressive properties of composite gels containing selected fractions of milkfat differed significantly from each other and from those of WPI-only or AMF-containing gels. Compressive properties were affected by the type and proportion of the included lipid and by temperature. The effect of temperature was related to the lipid-specific, temperature-dependent ratio of solid-to-liquid lipid.
Our results indicated that by appropriate selection of milkfat fraction composition, volume fraction and matrix protein content, a range of engineered emulsion gel properties could be achieved. A comparative parameter, relative increase in hardness (RIH) was established and used to highlight the effects of the lipid phase on compressive properties of the gels. Results indicated that by properly selecting the type of lipid and included proportion, compressive hardness of gels could be increased by up to 91 percent.
The results of our study clearly indicated that the addition of different fractionated milkfat fractions to WPI gels could significantly alter the mechanical properties of the gels. Our study shows that the melting properties of the milkfat fractions added to the composite gel dramatically affect the mechanical properties of the gels.
The results of our study will provide a means to develop new applications for fractionated milkfat as a filler in composite gels consisting of whey proteins. The results of our study will allow development of a series of new composite gels with rheological properties that significantly differ from those gels consisting of only whey proteins. The information can significantly enhance our capabilities in meeting desired texture profiles (needed in different applications) of whey protein-based gels and in developing new rheological profiles of such gels. The resulting understanding, applicable information and model systems will allow the introduction of new applications for fractionated milkfat as functional ingredients as well as expending existing applications for whey proteins beyond those already in existence.
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