FST 3102 Dairy Science PDF

# FST 3102 DAIRY SCIENCE ## 4. COMPOSITION, CHEMISTRY & PROPERTIES OF MILK FAT By: Gayani Dias Senior Lecturer Department of Food Science and Technology Sabaragamuwa University of Sri Lanka **Image:** A slide presentation describing milk fat **Image:** A slide presentation with the title "Milk f...

# FST 3102 DAIRY SCIENCE ## 4. COMPOSITION, CHEMISTRY & PROPERTIES OF MILK FAT By: Gayani Dias Senior Lecturer Department of Food Science and Technology Sabaragamuwa University of Sri Lanka **Image:** A slide presentation describing milk fat **Image:** A slide presentation with the title "Milk fat" and bullet points: * Milk contains approximately ...% (w/v) fat * Milk fat contributes to development in dairy products. That imparts soft, watery, flat hard, and rich-tasting qualities and overcomes characteristics. * The fat content of milk is of economic importance because... * Milk fat is present as microscopic globules with a protein membrane that contributes to the stability of the oil/water emulsion **Image:** A slide presentation with the title "Milk fat contd." with bullet points: * More than ... types of fatty acids have been identified in milk but only a small fraction of these are present in concentrations above 1% (by mass). * Triglycerides (96-98% of milk fat) are the main constituent of milk fat. * Milk fat also contains low levels of mono- (0.4%) and di-glycerides (2%) and minor constituents such as ... (1%), sphingolipids, and cholesterol (<0.5%). * Free fatty acids are also present in milk (0.1%). **Image:** A slide presentation with the title "Milk fat contd." with bullet points: * Fatty acids can differ in ... , presence of double bonds ... and type of... * The properties of milk fat vary with the fatty acid composition. * Triglycerides are very ... and not surface active and they act as a solvent for many other apolar substances such as sterols, carotenoids, and tocopherol. * The most polar lipids found in milk fat are ... * Milk lipids are found in three different phases of milk: fat globules, fat globule membrane, and the ... **Image:** A slide presentation with the title "Distribution of lipid in milk" | Constituents | Location in milk | | --------------------- | -------------------------------------------------- | | Tri glycerides | Fat globule | | Phospholipids | Fat globule membrane & milk serum | | Sterols | Fat globule, fat globule membrane, milk serum | | Free fatty acids | Fat globule & milk serum | | Waxes | Fat globule | | Fat soluble vitamins | Fat globule | **Image:** A slide presentation with the title "Heat induced changes in MF contd." with bullet points: * These interactions are stronger than the agglutinin-mediated mechanism thus a harder and less soluble cream layer is formed. * This layer does not dissolve upon shaking and visual solid fat lumps are present, leading to consumer rejection. * Milk fat is composed of various triglycerides, which melt at different temperatures. As milk is heated, these fats begin to melt, leading to a separation of fat from the aqueous phase of milk. * Heating sometimes induces the lipolysis and autoxidation of milk fat. * The C14:0 and C16:0 B-hydroxy fatty acids spontaneously form lactones upon heating which enhance the flavor of butter. **Image:** A slide presentation with the title "Surface tension" with bullet points: * Surface tension (ST) of milk is important in emulsification, foaming, and spreading properties. * ST of milk fat is influenced by its composition, temperature, and the presence of other components like proteins and emulsifiers. * Typical values for the surface tension of milk fat at room temperature (approximately 20°C) range from 25 to 35 (mN/m). * Read the 'surface tension of the milk' note. **Image:** A slide presentation with the title "Principal fatty acids in milk fat" | Fatty acid | % of total fatty-acid content | Molting point (°C) | Number of atoms (H C O) | Notes | | --------------- | ---------------------------- | ------------------- | ----------------------- | -------------------------------------------------------- | | **Saturated** | | | | | | Butyric acid | 3.0 - 4.5 | -7.9 | 8 4 2 | Liquid at room temperature | | Caproic acid | 1.3 - 2.2 | -1.5 | 12 6 2 | Room temperature | | Caprylic acid | 0.8 - 2.5 | +16.5 | 16 8 2 | | | Capric acid | 1.6 - 3.8 | +31.4 | 20 10 2 | Solid at room temperature | | Lauric acid | 2.0 - 5.0 | +43.6 | 24 12 2 | | | Myristic acid | 7.0 - 11.0 | +53.8 | 28 14 2 | | | Palmitic acid | 25.0 - 29.0 | +62.6 | 32 16 2 | | | Stearic acid | 7.0 - 3.0 | +69.3 | 36 18 2 | | | **Unsaturated** | | | | | | Oleic acid | 30.0 - 40.0 | +14.0 | 34 18 2 | Liquid at room temperature | | Linoleic acid | 2.0 - 3.0 | -5.0 | 32 18 2 | | | Linolenic acid | up to 1.0 | -5.0 | 30 18 2 | | | Arachidonic acid | up to 1.0 | -49.5 | 32 20 2 | | **Image:** A slide presentation with the title "Heat induced changes in milk fat" with bullet points: * The triacylglycerols in the core of the MFG are not affected by heat treatment. * Fat globule membrane (MFGM) around the MFG mainly changes in composition upon heating. * Heat-induced deactivation of the agglutination mechanism causes the milk fat globules to interact with each other through MFGM proteins or heat-denatured whey proteins (especially ß-lactoglobulin) and casein micelles. **Image:** A slide presentation with the title "Milk fat globule membrane (MFGM)" with bullet points: * MFGM accounted for 2-6% of fat globules and its properties are completely different from both milk fat and plasma. * MFGM only ... nm thick, tri-layer membrane surrounding the globules. * The major components of the fat globule membrane (FGM) are protein (70%) and phospholipids (25%). Cerebrosides (3%), cholesterol (2%), nucleic acids, enzymes, trace elements (metals), and bound water are present in MFGM. * Certain enzymes such as ... and ... , as well as certain important minerals like ... and ... , are attached to the fat globule membrane. * The MFGM decreases the lipid-serum interface to very low values (1 to 2.5 mN/m). This prevents the MFG from immediate flocculation and coalescence, as well as protecting them from enzymatic action. **Image:** A slide presentation with the title "Fat destabilization" with bullet points: * Fat destabilization is necessary for structure formation in butter, whipping cream, and ice cream. * Fat destabilization refers to the process of clustering and clumping (partial coalescence) of the fat globules which leads to the development of a continuous internal fat network or matrix structure in the product. * Fat destabilization (sometimes "fat agglomeration") is a general term that describes the summation of several different phenomena. * Four major phenomena are associated with the physical instability of emulsions: (1) flocculation, (2) creaming, (3) coalescence, and (4) breaking. In addition, partial coalescence can occur. **Image:** A slide presentation showing the changes in fat droplets during the following processes: * **Partial Coalescence of Fat Globules:** fat globules are partially clumped together, but not completely fused. * **Gravitational Separation:** The fat globules are shown to be moving upwards (creaming) or downwards (sedimentation) under the influence of gravity. * **Aggregation:** the fat globules shown to be clumped together in two ways: Flocculation (the fat globules are loosely clumped) and Coalescence (the fat globules are completely fused). **Image:** A slide presentation with the title "Physical changes in milk fat during" with bullet points: * Cream separation * Homogenization * Fat destabilization (by churning) * Heating * Fat crystallization **Image:** A slide presentation showing a diagram of the milk fat globule membrane (MFGM) * **Glycosylated Proteins:** are on the outer part of the membrane. * **Liquid Disordered Phase:** is at the center of the membrane * **Liquid Ordered Domain:** is the middle part of the membrane * **Monolayer of phospholipids:** is the layer beneath the liquid ordered domain * **Bilayer of polar lipids:** is the layer beneath the monolayer * **Triacylglycerols:** are the core of the milk fat globule. **Image:** A slide presentation showing a diagram of a milk fat globule, with following components * **Phospholipids** * **Lipoproteins** * **Glycerides** * **Cerebrosides** * **Proteins** * **Nucleic Acids** * **Enzymes** * **Metals** * **Water** * **Triglycerides** * **Diglycerides** * **Fatty Acids** * **Sterols** * **Carotenoids** * **Vitamins: A, D, E, K** **Image:** A slide presentation with the title "Milk fat globules (MFG)" with bullet points: * Milk fat is present in the milk as globules with diameters ranging from 0.1 to 22 µm (average size is 4-6 µm). * There are around 15 billion milk fat globules per ml. of milk. * The globules contain a nonpolar core of triglycerides, diglycerides, fatty acids, cholesterol esters, fat-soluble vitamins, and flavor compounds (diacetyl, lactone, sterols, butyric FA, caprylic FA, lipids). * The core of milk fat is protected and stable in the aqueous environment of milk by the presence of a protective coating on the surface of the spherical globules known as the milk fat globule membrane (MFGM). **Image:** A slide presentation with the title "Cream separation" with bullet points: * The separation of the fat globules from milk serum is called "cream separation. * Fat globules will cream due to the differences in densities between the fat and plasma phases of milk. * Immunoglobulin M (IgM) in milk, forms a cryoglobulin complex with lipoproteins in MFGM. This complex precipitates onto the fat globules and causes flocculation. This is known as cold agglutination. * IgM is denatured at time-temperature combinations such as 65°C/10 min or 75°C/2 min and slows down the cold agglutination. * As fat globules cluster, the speed of rising increases and sweeps up the smaller globules with them. The cream layer forms very rapidly, within 20 to 30 min., in cold milk. **Image:** A slide presentation with the title "Fat as emulsion contd." with bullet points: * Milk fat globule membrane and its components are amphiphilic, and they are considered to be excellent emulsifiers. * Emulsion prepared by MFGM was stable at the temperature range of 35-85°C. * MFGM is getting more focus, as it is considered to be a more natural emulsifier than the plant-based emulsifiers often used today, and the content of the beneficial sphingomyelin is higher in MFGM than other emulsifiers. **Image:** A slide presentation with the title "Crystallization behavior" with bullet points: * Milk fat is liquid above 40°C and completely solid below -40°C. * Between these extremes milk fat is a mixture of crystals and oil, where oil is the continuous phase. * Milk fat contains a large number of triacylglyerols, making the process of crystallization complex. * Crystals in fat globules generally cannot grow larger than the globule diameter. * Most crystals are much smaller than globule size and they flocculate into a network, giving the globules rigidity. **Image:** A slide presentation with the title "Milk fat contd." with bullet points: * More than 400 types of fatty acids have been identified in milk but only a small fraction of these are present in concentrations above 1% (by mass). * Triglycerides (96-98% of milk fat) are the main constituent of milk fat. * Milk fat also contains low levels of mono- (0.4%) and di-glycerides (2%) and minor constituents such as phospholipids (1%), sphingolipids, and cholesterol (<0.5%). * Free fatty acids are also present in milk (0.1%). **Image:** A slide presentation with the title "Terms related to milk fat" with bullet points: * **Skim milk/milk plasma:** milk fat has been removed * **Milk cream:** the fat part that rises to the surface when milk is allowed to stand and is not homogenized. * **Butter milk:** a liquid that remains after churning butter * **Milk Serum:** liquid portion of milk, remaining after removal of the casein and fat. * **Anhydrous milk fat:** Dairy product with a minimum of 99.8% milk fat content. * **Butter:** Butter typically contains about 80% milk fat. The rest is primarily water and milk solids. **Image:** A slide presentation with the title "Meltability" with bullet points: * Milk fat melts over a wide temperature range, from approximately -40°C to 40°C. * Most abundant fatty acids in milk are myristic, palmitic, stearic and oleic acids. * The first three acids are solid and the last is liquid at room temperature. * Variation in the amounts of fatty acids affects the hardness of the fat. * Fat with a high content of high-melting fatty acids, such as palmitic acid, will be hard. * Fat with a high content of low-melting oleic acid makes soft butter. **Image:** A slide presentation with the title "Autoxidation of milk" with bullet points: * Autoxidation may affect milk lipids by generating hydroperoxides. * These may decompose into carbonyl compounds with undesirable taste and odor that are described as painty, fishy, or metallic flavors. * Milk lipid oxidation may be induced by the presence of metal, especially copper, or exposure to light. * Milk fat is relatively resistant to oxidation due to the predominance of saturated fatty acids and the presence of natural antioxidants, such as a-tocopherol and ß-carotene. * MFGM protects MFG by lipolysis and oxidation. **Image:** A slide presentation showing a close-up microscopic image of homogenized MilkFat Globules with the following components: * Adsorbed Casein Micelles * Internal Fat Crystallization **Image:** A slide presentation with the title "Fat as an emulsion" * Fat is distributed in a continuous aqueous phase as an oil-in-water type emulsion. * The membrane prevents the merging of fat globules and the formation of a continuous fat phase. **Image:** A slide presentation with the title "Color & antioxidant potential of milk fat" with bullet points: * The colour of fat depends upon its carotene content and varies with the species, breed and feed of the animal. * The yellow colour of cow milk is because of carotene. * Buffalo milk does not contain carotene. * Milk fat also contains cholesterol and phospholipids (lecithin, phosphatidyl serine, sphingomyelin, inositol and cerebrosides) some of which serve as antioxidants in prolonging the shelf life of ghee. **Image:** A slide presentation with the title "Milk fat globule membrane (MFGM)" with bullet points: * The inner membrane of MFGM is a monolayer of phospholipids consisting of protein and polar lipids in contact with the fat layer. * The other two layers are derived from the plasma membrane consisting of the phospholipids (phospholipid bilayer). * The phospholipids are interspaced with cholesterol, vitamin A, etc. * Proteins, enzymes, etc. are embedded in these layers. * Carbohydrate chains of glycoproteins and glycolipids directed toward the outer surface of the milk fat globule. **Image:** A Slide presentation with the title "Physiochemical properties of milk fat" 1. Surface tension 2. Emulsification 3. Refractive index 4. Melting point 5. Saponification **Image:** A slide presentation with the title "Refractive index " * The degree to which the light waves pass through the liquid fat. * A characteristic feature of the milk fat. * The reading for the milk fat ranges between 1.4537 to 1.4578. * Due to the high proportion of saturated glycerides and short-chain acids in the bovine milk fat, RI is low in comparison to other lipids. * Read the 'refractive of the milk' note. **Image:** A slide presentation with the title "Homogenization" with bullet points: * Homogenization of milk prevents this creaming by decreasing the diameter and size distribution of the fat globules. * Due to the size reduction, there is no longer adequate membrane material to dispose of around the newly formed globules. * A new membrane (recombined membrane), which is very similar in density to the continuous phase begins to coat the new globules. * In the case of buttercream, fat globule disruption leads to the loss of membrane material which migrates to buttermilk. * Stirring may lead to fat globule coalescence and loss of membrane material. **Image:** A slide presentation with the title "Milk fat contd." with bullet points: * Fatty acids can differ in carbon chain length, presence of double bonds (i.e., saturated or unsaturated), degree of saturation, and type or configuration. * The properties of milk fat vary with the fatty acid composition. * Triglycerides are very apolar and not surface active and they act as a solvent for many other apolar substances such as sterols, carotenoids, and tocopherol. * The most polar lipids found in milk fat are phospholipids. * Milk lipids are found in three different phases of milk: fat globules, fat globule membrane, and the milk serum. **Image:** A slide presentation showing a graph with the composition of total lipids in milk | Constituent class | Total lipids (%) | | --------------------- | ------------------ | | Triglycerides | 62 | | Diglycerides | 2.1 | | Monoglycerides | 0.4 | | Sterols | 0.2 - 2.0 | | Free fatty acids | 0.6 - 6.0 | | Phospholipids | 26 - 31 | | Sphingomyelin | 25 | | Phosphatidyl choline | 36 | | Phosphatidyl enthanolamine | 30 | | Phosphatidyl irositol | 11 | | Phosphatidyl serine | 4 | | Glucosyl-ceramide and lactosyl-ceramide | 6 | | Lysophosphatidyl choline | 2 | * Phospholipid classes given as % of total Phospholipids **Image:** A slide presentation with the title "Important terms" * **Creaming:** Creaming is the upward movement of dispersed oil droplets in an o/w emulsion due to the density difference. This can be reversed by shaking. * **Coalescence and flocculation:** Coalescence and flocculation both involve the aggregation or clustering of fat globules. * **Flocculation:** A reversible agglomeration/clustering of fat globules with no loss of identity of the globules in the floc. **Image:** A slide presentation showing the changes in fat droplets during the following processes: * **Partial Coalescence of Fat Globules:** fat globules are partially clumped together, but not completely fused. * **Gravitational Separation:** The fat globules are shown to be moving upwards (creaming) or downwards (sedimentation) under the influence of gravity. * **Aggregation:** the fat globules shown to be clumped together in two ways: Flocculation (the fat globules are loosely clumped) and Coalescence (the fat globules are completely fused). **Image:** A slide presentation showing the changes in fat droplets during the following processes: * **Creaming:** The fat globules are shown to be moving upward into a separate layer. * **Aggregation:** The fat globules are shown to be coming together into clusters. * **Coalescence:** The fat globules are shown to be fusing together. * **Partial Coalescence:** The fat globules are shown to be partially fused together. **Image:** A slide presentation with the title "Heat induced changes in MF contd." * These interactions are stronger than the agglutinin-mediated mechanism thus a harder and less soluble cream layer is formed. * This layer does not dissolve upon shaking and visual solid fat lumps are present, leading to consumer rejection. * Milk fat is composed of various triglycerides, which melt at different temperatures. As milk is heated, these fats begin to melt, leading to a separation of fat from the aqueous phase of milk. * Heating sometimes induces the lipolysis and autoxidation of milk fat. * The C14:0 and C16:0 B-hydroxy fatty acids spontaneously form lactones upon heating which enhance the flavor of butter. **Image:** A slide presentation with the title "Lipolysis of milk fat" * Milk lipids are susceptible to lipolysis. Natural milk lipase is the primary responsible agent for this degradation reaction. * Lipolysis increases the concentration of short-chain fatty acids in free form and can cause an unpleasant taste and aroma (rancidity) in milk and dairy products. * Butyric acid is specific for milk fat of ruminant animals and is responsible for the rancid flavor when it cleaves from glycerol by lipase action. * However, in some cheeses, such as Blue cheese and Provolone, a small amount of lipolysis is needed to achieve the characteristic flavor. **Image:** A slide presentation with the title "Commercial use of MFGM" * Adding an appropriate amount of MFGM and MFGM protein in whipping cream increases the foaming rate. * Because of its high water-holding capacity, MFGM may prevent moisture loss and migration in the bread core, which reduces the problem of bread aging and hardening. * It can also be used as a bread improver to increase the nutritional value the quality of bread. * Adding MFGM to infant formula as an natural emulsifier showed better cognitive development in infants **Image:** A slide presentation with the title "Important terms" * Such a crystal can, upon collision with another globule, thereby making oil-oil contact. * Temperature dependent, once the crystals melt, the cluster coalesces. * **Breaking:** Breaking (or phase separation) is the ultimate failure of the emulsion where the dispersed phase separates completely from the continuous phase. * This process is often irreversible without re-emulsification.