OVER VIEW LACTATION PHYSIOLOGY MAMMARY SYSTEM Mammary Gland • Mammary glands are modified skin glands • Characteristic of all mammals • Present both in males and females • Degree of development and position varies – Duckbill platypus – Porcupine anteater – Marsupials (Kangaroo) – Domestic mammals • Synthesis of milk to nourish young one EXTERNAL FEATURES OF THE MAMMARY GLAND • Udder of the dairy cow is comprised of four separate mammary glands • demarcated into right and left halves by a longitudinal furrow called the intermediary or intermammary groove • Sometimes, but not always a transverse furrow is seen between the front and rear halves; a characteristic not desired • Weight 10-25 kg • Rear: Front 60:40 • 1/3 increase between milking SKIN • Covering of the Gland • Little supportive action • Protects from abrasives and bacteria • Prevents excessive swaying • Retains fluids TEATS • Associated with each gland • Exit for secretion • Should be of sufficient size • Well placed • Large enough opening • Cows with funnel shape produce more than with Cylindrical teats • Supernumerary teat May not be associated with secretory tissue • is not uncommon to find one or two supernumerary teats on the udder. These small teats are commonly imperforate and are not harmful but on occasion they leak during milking and they can also become infected from time-to-time • Pseudo teat No gland, no streak canal Internal Structure of MG • Supportive Structures • The Vascular System – Arterial System – Venous System • Lymphatic System • Nervous System • Connective Tissue • Fatty pad (Stroma) • Secretory Tissue (Parenchyma) – Secretory cells – Alveoli – Lobules – Lobes • Collection System – Lumen – Terminal ducts – Lobular ducts – Lobar ducts – Gland Cistern – Teat Cistern Supportive Structure • Distance between udder and ground • Select against pendulus udders • Skin Stabilizes --- minor role – Skin to udder – Udder to abdominal wall • Lateral Suspensory Ligaments – Mainly fibrous --- non – elastic – Arise from sub-pubic & pre-pubic tendons (not part of suspensory apparatus) • Median Suspensory Ligament – Elastic connective tissue – Originates from abdominal wall – Two sheets of tissue – a double septum – Divides the udder in half Vascular System • Arterial System – Dorsal aorta – Internal illiac • Perineal – External illiac • Femoral • Prepubic • External pudendal • Mammary –Cranial –Caudal –Arteriols Vascular System (Venous) • Many more veins than arteries • Two Main Routes – 2-3 times larger in diameter Reverse of arterial System – Sub cutaneous abdominal vein (milk veins) • emerges from anterior basal border of udder • Enters abdominal wall opposite the xiphoid cartilage • Anterior vena cava • Perineal vein – flow towards udder Vascular System Arteries to the udder Venous Circle Lymphatic System • Consists of lymph vessels & lymph nodes • Lymph – tissue fluid drained from extra- cellular spaces through lymph vessels • Lymph vessel opens in anterior vena cava • Lymph composition – same as of plasma • Except – ½ the protein and no RBCs • Capillaries: lymph vessels 100:1 Lymphatic System • Thoracic lymph duct • Lacteals • Internal illiac lymph gland • External illiac lymph gland • Pre-femoral lymph gland • Deep inguinal lymph gland • Supra-mammary lymph gland Lymph Nodes • Form lymphocytes which produce antibodies • Deleterious matter/bacteria filtered out and destroyed Lymphatic System Nervous System • Neuron --- structural & functional unit • Sensory fibres --- afferent nerves – Impulses from body to the brain • Motor fibres --- efferent nerves – Impulses from body to the brain • CNS ---- Brain and spinal cord 12 pairs • Peripheral nervous system 37 pairs (cervical 8, thoracic 13, lumber 6, sacral 5 & coccygeal 5) Secretory Structure of Mammary Gland Synthesis of Milk Milk Letdown Milk Letdown Inhibition Proper Milking Give ‘em a Break Dairy Hygiene Effect of keeping temperature of raw milk on its count after 24 h Milk held at Count after 24h Keeping Quality (oC) (ml-1) (h) 4 2.5x103 >100 10 1.2x104 89 15 1.3x105 35 20 4.5x106 19 30 1.4x109 11 Initial count: 2.3x103/ml Milk suitable for Processing: not exceeding 1x106/ml 09.01.2013 04:45 49 Sources of Contamination Exterior of udder and adjacent areas Manure, soil and water Hand milking vs machine milking Hands and arms of milker/dairy worker Air of barn or milking parlor and flies Water used for cleaning and rinsing or utensils 09.01.2013 04:45 50 Control Measures Clipping the cow especially flanks and udder Grooming the cow Washing the udder with water or germicidal solution before milking Paving and draining barn yards Keeping away cow from stagnant pools Cleaning manure from barns from barns and milking parlors 09.01.2013 04:45 51 Micro Organisms (MO) of Udder Healthy cow/buffalo No MO in alveoli, ducts cistern and teat cistern MO present in teat canal and sphincter of teat Micrococcus, Staphylococcus sp, Corynebacterium bovis Count after milking is 15000/ml Aseptically drawn is <100/ml Defense system of Cow/Buffalo Sphincter of teat have circular muscles Bacteriostatic and bacteriocidal agents of teat canal Leukocytes in milk Rinsing effect due to discharge of milk 09.01.2013 04:45 52 Sources of Contamination of Raw Milk Source of Estimate of the contribution contamination to count (ml-1) Udder of a healthy cow Up to several thousand Udder of a mastitic cow Up to a several millions Skin of cow A hundred up to several thousand Milking parlor (soil, dung, dust, air) Up to a thousand Feed Up to a thousand Milking unit A thousand up to a several million Water for cleaning, rinsing Up to a several thousand Good milker Generally negligible 09.01.2013 04:45 53 Protection of the Consumer Against Pathogenic Micro-organisms 1. During microbial growth in raw milk, toxins may be formed. Some toxins are fairly heat resistant. 2. Some pathogens survive heat treatment such as pasteurization. 3. Higher count in raw milk, greater the number of organism that may survive heat treatment 4. Heavier the contamination of raw milk by pathogens, the greater the risk of recontamination of heated milk. 09.01.2013 04:45 54 Protection of the Consumer Against Pathogenic Micro-organisms Control measure Prevent growth of spoilage organisms Stop the growth of pathogenic bacteria that produce heat resistant toxins Pasteurized milk is the safest product 09.01.2013 04:45 55 Milk Processing Changes in Milk and its Constituents Changes during Storage Fat and Protein may undergo chemical changes during storage These changes are normally of two kinds: Oxidation and Lipolysis The resulting reaction products can cause off-flavours, principally in milk and butter Oxidation of Fat Oxidation of fat in milk results in a metallic flavour, While in butter it gives an oily, tallowy taste Oxidation occurs at the double bonds of the unsaturated fatty acids The presence of iron and copper salts accelerates, As does the presence of dissolved oxygen Oxidation of Protein Another type of off-flavour is sun taste Which occurs when milk is exposed to strong light Even a few minutes irradiation by direct sunlight is enough Which is due to oxidation of an amino acid in milk protein The reaction forms a substance which gives a sweetish flavour Lipolysis The breakdown of fat into glycerol and free fatty acids is called Lipolysis Lipolyzed fat has a rancid taste and smell Caused by the presence of low molecular free fatty acids (butyric and Caproic acid) Effect of Heat Treatment Milk is heat treated to kill off any pathogenic micro-organisms Heat treatment also causes changes in the constituents of milk The higher the temperature and The longer the exposure to heat, the greater the changes Fat Fatis not affected by temp. below 100 oC Cream separation is, however, impaired somewhat if the milk is heated to 75 oC or above Proteins Casein does not undergo any detectable changes at temperatures below 100 oC But the rate of coagulation of milk by rennet diminishes with increasing pasteurization temp. The reason for this is that the casein loses its calcium when heated Ifmilk is heated to above 140 oC for 5 minutes, the casein is precipitated as a brownish mass β-lactglobulin and albumin begin to precipitate at temperatures as low as 70 oC Enzymes Enzymes can be inactivated by heating The temperature of inactivation varies according to the type of enzyme Lactose Lactose undergoes changes more readily in milk than in the dry state At temperature above 100 oC a reaction takes place between lactose and protein, giving rise to a brownish colour Vitamins Vitamin C is the most sensitive to heat, especially in the presence of air and certain metals HTST pasteurization in a plate heat exchanger can, however, be accomplished with virtually no loss of Vitamin C Minerals Theminerals in milk are not affected to any significant degree by heat treatment Minerals Theminerals in milk are not affected to any significant degree by heat treatment CHEMICAL PROPERTIES/ COMPOSITION OF MILK MAJOR COMPONENTS Total solids – fat, protein, lactose and minerals. Total Solids – fat and solids not fat (SNF). The SNF contents of milk refer to all solid constituents – (protein, lactose and ash) except fat Milk Composition Water 86.60 % Fat 4.15 % Protein 3.58 % Lactose 4.96 % Minerals 0.71 % Total Solids 13.40 % Species-wise Milk Composition Sp. Water Fat Prot. Lact. Ash T.S Cattle 86.60 4.15 3.58 4.96 0.71 13.40 Buff 82.76 7.38 3.60 5.48 0.78 17.24 Goat 87.00 4.25 3.52 4.27 0.86 13.00 Sheep 80.71 7.90 5.23 4.81 0.90 19.29 Camel 87.61 5.38 2.98 3.26 0.70 12.39 Mare 89.04 1.59 2.69 6.14 0.51 10.96 Ass 89.03 2.53 2.01 6.07 0.41 10.97 From a processing view, – fat, – protein and – carbohydrate are important. MILK FAT Fat in milk consists of – Lipids and Associated Substances Lipids consist of >98% Triacylglycerides Triacylglycerides – esters of fatty acids and glycerol. Chemical properties vary with – fatty acid chain length, – degree and nature of unsaturation. These factors also affect the nature of taints and off flavours associated with lipolysis. Fat in milk exists as – Milk fat globule (MFG). This consists of a core of pure triacylglyceride surrounded by a membrane (the milk fat globule membrane, MFGM) The MFGM prevents coagulation of the MFGs, and protects against enzymatic action. Composition of the MFGM phospholipids, protein fractions, cholesterol, fat soluble vitamins, enzymes and some trace metals (Fe, Co). The MFGM thickness may vary as result of lipoproteins present. It is also “hairy” due to the presence of hydrophilic glycoprotein chain protruding into the plasma. Agitation – rupture of MFGM, leading to coagulation of fat, and increased susceptibility of lipolysis Heating – causing denaturizing of whey proteins in MFGM Acidification – absorption of casein onto MFG surface Fat soluble vitamins Include A, D, E and K. Lie close to the surface of fat globules, forming part of the coating Importance beyond nutritional consideration – Vitamin E, particularly, serves as an antioxidant. Inhibits oxidized flavours Milk PROTEIN Milk protein consists of around 80% Casein The remaining proteins are referred to as Whey Proteins. This latter group of proteins is a wide-ranging family. Casein Fractions are α, β, γ, and κ. Casein in milk as micelles – Roughly spherical, – 0.02 to 0.30mm in diameter – Contain Calcium Phosphate – Spongy in texture and can therefore accommodate more water than casein. Micelle consists of sub-micelles, containing different casein molecules Majority of the κ casein exists on the surface of the micelles The stability of the casein micelles is dependent on environment, and can be utilized in processing. Different treatments will lead to destabilization and subsequent aggregation of casein micelles Whey Proteins Whey proteins will not precipitate upon acidification Most of the whey proteins are susceptible to heat denaturation CARBOHYDRATES Lactose or Milk Sugar Main carbohydrate in milk nearly 30 percent of total solids. A disaccharide (Glu & Galac) in the form of true solution in milk On hydrolysis it yields galactose and glucose. Lactose Not as readily soluble in water as other sugars such as cane sugar, dextrose. Less sweet than other sugars. MINERALS, SALTS AND ASH OF MILK Minerals of milk Relatively in small amounts. Significance in dairy processing Some are required at much higher levels for good health These are macro (major) minerals – include calcium, phosphorus, magnesium, sodium, potassium and sulfur. Others required by the body only in trace amounts, and called micro (minor) minerals – include zinc. Copper, manganese, iodine iron etc. Minerals have a direct bearing on – formation of curd during cheese making – storage stability of concentrated/ evaporated and UHT milk, and – stability of lipids. Salts in milk Salts of milk are chlorides phosphates and citrates of potassium, sodium, calcium and magnesium Salts in milk exist in two major forms. – Soluble (dissolved) form – Colloidal dispersion. Colloidal salts are associated with casein and consist mainly of calcium and phosphorous integrated into the casein micelle as colloidal calcium phosphate. Some small amount of citrate is also associated with casein . Salts play a role in – physical structure of casein micelle – coagulation of casein in presence of rennin – stability of casein milk to heat – curd tension of milk – colour of milk In mastitic milk There is increase in chloride, sodium and sulphates Decrease in lactose & potassium resulting in to “Salt Milk” Ash in milk If solids are heated (incinerated) to a dull red heat, all that part, which can be converted to volatile substances by oxidation, will be driven off and non-volatile part will be left as white residue This is the ash The composition of ash does not represent the state of salts as they occur in milk (dissolved, suspended and attached to proteins and fat globule membrane). There is considerable alteration due to chemical reaction taking place during incineration. Factors Affecting Milk Production and Composition MILK Milk is physiological secretion of normally functioning mammary gland 15 days before and 5 days after parturition. Factors Affecting Milk Yield and Composition Genetic Physiological Environmental Genetic Species Breed Individual variation Physiological Age of the Animal Stage of Lactation (normal lactation curve) Animal Health Milking Frequency (Interval) Physiological Dry period and Body condition Body weight/size Gestation Calving interval Environmental Feeding and Nutrition –Ingredient composition –Nutrient composition –Concentrate to roughage ratio –Moisture contents –Physical form of ingredients –Treatment of ingredients –Processing Environmental Weather (Temperature and Humidity) Season Climate Day to day variation Morning and evening milking Exercise Change of milker and milking procedure Lactation Lactationimplies the secreting and giving of milk (removable) by the mammary glands. It is also used to denote the period of milk production commencing from calving and ending when cow ceases to be milked Milk Secretion Synthesis of milk by the epithelial cells passage of milk from the cytoplasm into the alveolar lumen Rate of secretion remains constant for the first ½ hours after milking and declines slowly thereafter due to back pressure of the synthesized Mammogenesis Growth of mammary gland Lactogenesis Initiation of milk secretion Galactopoiesis Maintenance of lactation Milk Ejection (Milk let-down) Milk secretion --- a continuous process, Most of the milk secured at any milking is already present A small amount is in the teat and gland cisterns, but most of it is in the alveoli and ducts to the gland cisterns Removed by either hand milking or Involution Shrinking of an organ to its normal size after enlargement i.e., of alveolar cells. As lactation processes, there is a gradual decrease in – number of active alveoli and – in efficiency of activity lossof secretory activity with increase of connective tissue stroma Hormonal Regulation of Lactation Initiation of Lactation (Lactogenesis) At parturition sudden loss of estrogen and progesterone secretion by the placenta removes any inhibitory effects and allows marked production of prolactin, Enzymes within the epithelial cells are essential to the activate the cells to convert blood constituents into milk Prolactin stimulates increased enzymes activity which in turn stimulates secretion milk secretion requires in addition to prolactin an adequate background secretion of both growth hormones and the adrenocorticosteroids. Maintenance of Lactation (Galactopoiesis) Along with prolactin STH (growth hormone), ACTH adrenocorticotropic hormone), TSH (thyroid stimulating hormone), and oxytocin from pituitary Non-pituitary origin, parathyroid, placental lactogen and insulin Maintenance of Lactation (Galactopoiesis) TSH stimulates thyroid gland to secrete thyroxin which regulates metabolic process of the body. It increases the appetite, heart rate, flow of blood to the udder and rate of milk secretion. Thyroxin secretion rates show seasonable trends, with increase in winter and decline in summer. This partially explains why milk secretion slows in hot weather Growth hormone (Somatotrapin) Thishormone appears to influence substances from which milk is made, e.g., by increasing the availability of blood amino acids, fats, and sugar for use by the mammary gland cell in milk synthesis Parathyroid hormone regulates blood level of Calcium and Phosphorus. Feeding high levels of vitamin D (20million 1U for 3 to 7 days prepartum) will significantly reduce the incidence of parturient paresis (milk fever) in cows. Adrenals Adrenal corticoids are essential for milk secretion, but excess amount inhibits lactation Oxytocin secreted from the posterior pituitary gland and is a must for the ejection (milk let-down) of milk Placental lactogen has got the properties of both growth hormone and prolactin but is identical with neither Since the source of bPL is lost when the placenta is expelled, its effect must occur prior to peak milk secretion in the subsequent lactation. Insulin promotes mammary cell growth and cell division during gestation and lactation but alone is incapable of inducing synthesis of milk proteins by the cells. MILK SECRETION RATE Thedaily milk yield is dependent upon –the number of secretory cells –Supply of nutrients –Efficiency of epithelial cells –pressure in the alveolar lumina due to the accumulation of milk. Residual Milk The residual milk is the amount of milk left in the udder after a normal milking. It can be obtained only after the injection of oxytocin and remilking the animal. The amount of residual milk is proportional to the amount of milk presenting the udder at the beginning of the milking. Residual Milk On an average it is about 14 18 per cent for a cow Older cows have high percentages of residual milk than first-calf heifers Cows with high percentages of residual milk have a lower persistency of lactation. The percentage residual is also higher in low producers than high PHYSICAL PROPERTIES OF MILK FLAVOUR AND TASTE: Fresh milk that has been produced under ideal conditions will have no pronounced flavour. The natural flavour of milk is hardly discernable, yet it Is slightly sweet and pleasant in taste. This is primarily due the relationship of the lactose and chloride contents. If this relationship is disturbed so that the chloride becomes relatively greater, as in late lactation or in mastic conditions, the flavors is adversely affected. The fat the protein contents primarily concerned with the taste of milk, give too the flavour. Milks with low fats and low solids not fat will taste some what fat, while the milks with higher percentage of a these constituents will have a fuller flavor. The pleasing flavor of milk fat cannot be entirely duplicated by other fats. COLOUR: The white of milk results from the dispersion of reflected light by the fat globules and the colloidal particles of casein and calcium phosphate. The yellow color is due the pigment Carotene, which is fat-soluble. The deeper color of Guernsey and jersey cow milk as compared to that of the lower testing breeds is due to the greater amount of carotene present in the fat. All milks have a deeper color during pasture feeding compared to barn feeding due to high carotene content present in such grass. This pigment is readily transferred from the feed to the fat in the milk or to the body fat, of the animal. Feeding carrots will have the same effect, as these roots are very high in carotene content. Xanthophylls another fat-soluble pigment also gives some REACTOIN OF MILK The reaction of fresh normal milk is rather peculiar. It will turn blue litmus red and red litmus blue, the so-called amphoteric reaction. The acidic as well alkaline reaction at a time shown by milk is due to amino acids of milk protein. These acids have NH2, terminal which is alkaline and COOH carboxyl terminal which is acidic. The milk from carnivores is more acidic than herbivores. While humien milk is alkaline. ACIDITY OF MILK Acidity is one of the most important factors controlling various processes in dairy industry. Freshly drawn milk has “natural” or “apparent” acidity and caused by the presence of casein acid phosphates, citrates etc, in milk. The natural acidity of individual milk varies considerably depending on species, breed, individually, stage of lactation, physiological condition of the udder, etc. but the natural acidity of fresh milk is much more uniform. The higher the solids not fat content in milk, the higher the natural acidity (N.A) and vice versa. It is determined by titration against an alkali NaOH. The titrable acidity of cow milk varies on an average from 0.13 t o 0.14 present and buffalo milk from 0.14 to 0.15 percent. Developed or real acidity is due to lactic acid form as a result of bacterial action on lactose in the milk. Hence the titrable acidity of stored milk is equal to the sum of natural acidity and developed acidity. The titrable acidity is usually expressed as it a percentage of lactic acid. The action of bacteria on lactose may be undesirable as it occurs by contaminating bacteria or it may desirable when it occurs during dahi, cheese and butter making by deliberately adding (culture of bacteria). In both the case slow conversion of lactose into lactic acid takes place, and acidity is increased pH OF MILK -: Ph may be defined as the log to the reciprocal of the hydrogen ion concentration. Milk contains acids and alkalies, which dissociate or ionize producing H (Hydrogen ions) and OIT (hydroxyl ions), PH of milk is a measure of “H “ions by an instrument called PH meter. PH scale is from 1 to 14 where pH 7 is neutral point i.e. both types of ions are exactly equal. Below 7 is the increasing acid range where where as above 7 to 14 is increasing alkaline range. This is one of the most important properties to check during various stages of cheese–making. The pH value of milk ranges from 6.5 to 6.7 pH values above 6.8 indicate the evidence of mastitis while samples giving reading below 6.4 showed apartment THE SPECIFIC GRAVITY OF MILK : The density of substances is its mass (mass) per unit volume. Specific gravity is the ratio of density of a substance to density of a standard substance (water). Since the density of a substance varies with temperature, it is necessary to specify the temperature when reporting densities or specific gravities. The specific gravity of milk is usually expressed at 5.6 0C to 20.oC. Milk is heavier than water. The average specific gravity ranges at 15.5 oC from 1.028 to 1.30 for cow milk, 1.032 for buffalo milk and 1.035to 1.037 for skim milk. The specific gravity of milk is influenced by the proportion of its constituents (i.e. composition). Each of which has a different specific gravity approximately as fellow: water 1.000; fat 0.93;protein 1.346; lactose 1.666; and salts 4.12 (solids-not-fat-11.616). The specific gravity of milk is lowered by addition of water and cream, increased by addition of skim milk or removal of fat. Specific gravity of milk determined by lactometer pycnometer. Specific gravity of milk is used to determine the adulteration of water. By addition of water the specific gravity is lowered. However this is very rough test. This is evident from the following facts. Specific gravity of the mixed milk of a herd varies from 1.030 to 1.034. At least 10% water could be added to milk of 1.034 specific gravity before it would be suspected by this test. If all the cream from milk having 1.032 specific gravity is removed its specific gravity would be raised to 1.036 but an addition of 10% water AVERAGE SPECIFIC GRAVITY OF MILK OF DIFFERENT ANIMALS : 1. Cow 1.031 2. Cow colostrums 1.042 3. Buffalo 1.035 4. Sheep 1.032 5. Goat 1.030 6. Woman 1.029 SURFACE TENSION : The molecules in a liquid are attracted to each other, and this creates a pull from the surface. Beneath the surface the molecules are surrounded by other molecules and the attraction is equalized. But at the surface the balance is broken and a tension result. Surface tension may thus be defined as a state of stress of a liquid due to the attraction of the molecules for each other. It is expressed in dynes. A dyne is the force that acting The surface tension of water is 72 to 73 dynes. The surface tension of skim milk, whole milk and cream (30- 35%fat) is 57.4, 55.3 and 49.6 dynes, respectively proteins of milk are mainly responsible for the lowering of surface tension. Increase in fat content of milk also reduces the surface tension. Reduced surface tension by the fat in milk helps to VISCOSITY OR STICKNESS : The viscosity of a liquid is its internal friction or its resistance to adhcar, agitation or flow. Viscosity of milk is manifested by the adhesence of milk to the sides of glass vessel. Viscosity depends upon the milk solids, specially the casein. Dilution of milk with water reduces its viscosity, and creaming proceeds more rapidly. Further, shaking reduces viscosity and letting it stand undisturbed increases it. Cold milk has greater viscosity than warm milk. For engineering purposes, viscosity determines the amount of force that must be applied to move a given weight of product through various processing systems at some given speed. Similarly, viscosity determines the amount of force required to provide a given level of agitation to milk in a storage tank or ice cream mix in a freezer etc. Measuring viscosity : Viscosity can be measured using suitable techniques. This property is often expressed in terms of centipose(s). Centipoise is 1/100 of poise. Poise is unit of force. A poise is given as 1.0 dyne per second per cm2. One dyne is force required to produce an acceleration of 1.0 Relative viscosity : It is ratio of viscosity of any substance compared to the viscosity of standard (water). Viscosity of water is 1.005 centipoises at 20*C. Whole milk has viscosity of 1.75 centipoises at that temperature. Relative viscosity; Viscosity of substance/ viscosity of water FREEZING POINT OF MILK : The most constant physical property of milk is the temperature at which liquid milk is in equilibrium with solid ice. The freezing point of milk is slightly lower than water i.e. –0.54 to – 0.57*C. It is greatly influenced by the dissolved constituents (particularly salts and lactose) in milk. When water is added to milk, its freezing point rises due to this property even 5% added of water can be detected. Boiled milk has a lower freezing point than raw milk. The determination of freezing point of milk is called BOILING POINT : Since a dissolved substance in water will lower the freezing point of the mixture below that of the water itself, it will also act inversely, and increase the boiling point. Therefore milk with its dissolved substances will have a slightly higher boiling point than pure water. The average temperature of boiling point of milk is 100.17*C at sea level. Lowering the pressure, i.e. treatment under vacuum, can significantly reduce boiling point of milk. This is the principle behind use of vacuum processing of evaporated and condensed milk products. Under 20-inch vacuum. Milk boils at 57*C. SPECIFIC HEAT OF MILK One cal = the amount of heat required to raise the temperature of one gram of water to one degree (i.e. from 15 to 16*C) The specific heat of water is 1.0 cal / g/ºC, whole milk 0.93, skimmed milk 0.94, whey 0.98, butter 0.48, cream (60%) 0.75.