Overview Lactation.ppt

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					   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


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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.

				
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