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Friday, 1 January 2016

Chemistry of milk

                 Chemistry of milk
Milk Components
  A.  Water  87.0%
  B.  Fat    4.0%
  C.  Proteins    3.5%  Average
  D.  Lactose    4.7%
  E.  Minerals    0.8%
.  Other Substances in Trace Amounts
  1.  Pigments
  2.  Enzymes
  3.  Vitamins
  4.  Phospholipids
  5.  Gases
.Basic Chemical Concepts
  A.  Atoms
       1.  An atom is the smallest building block of all matter in                                                                          nature and cannot be divided chemically.
       2.  A substance in which all the atoms are the same is                                        called an element.
       3.  Most natural occurring substances are composed of            
         several elements.  i.e.:  H2O = Water  
    4.  Are comprised of:
  a.  Protons – Positively charged particles
  b.  Neutrons – Neutrally charged particles
  c.  Electrons – Negatively charged particles
      5.  An Atom will have an overall neutral because it will                        have equal numbers Protons + and Electrons -
Ions
       1.  Ions are atoms that have lost or gained additional                electrons and are therefore no longer electrically             neutral.
         a.  Cations (positively charge ions) have lost          electrons
  b.  Anions (negatively charged ions) have gained                    electrons
       2.  Positive and negative ions will always be present              together in liquid solutions or in solid form as salts
Molecules
        1.  Atoms can combine into larger units which are              called molecules
        2.  Molecules can then form:
  a.  Solids – Sand   SiO2
  b.  Liquids – Water  H2O
  c.  Gases – Hydrogen  H2
        3.  Molecules that consist primarily of Carbon,              Hydrogen and Oxygen atoms are referred to as              organic.
      4.  Lactic Acid is an example of an organic compound              and has the formula C3H6O3.
Emulsion is a suspension of droplets of one liquid in             another.
        1.  Milk is an emulsion of fat in water
        2.  Butter is an emulsion of water in fat
  B.  Colloidal Solution is when matter exists in a state of        division intermediate to true solution (e.g. sugar in water)        and suspension (e.g. chalk in water) it is said to be in           colloidal solution or colloidal suspension.
1.  Characteristics of a colloid are:
              a.  Small particle size
              b.  Electrical charge and
              c.  Affinity of the particles for water molecules
  2.  In milk the whey proteins are in colloidal solution        and the casein in colloidal suspension.
  C.  True Solutions Matter which, when mixed with water or         other liquids, forms true solutions divided into:
        1.  Non-ionic solutions.  When lactose is dissolved in              water, no important changes occur in the molecular              structure of the lactose.
        2.  Ionic solutions. When common salt is dissolved in              water cations (Na+) and anions (Cl-) are dispersed in                the water forming an electrolyte.
Acidity of Solutions
        1.  When an acid (e.g. hydrochloric acid, HCl) is mixed   with water it releases hydrogen ions (protons) with a   positive charge (H+).  These quickly attach themselves   to water molecules, forming hydronium (H3O+) ions.
         2.  When a base (a metal oxide or hydroxide) is added to   water, it forms a basic or alkaline solution.  When the   base dissolves it releases hydroxide (OH-) ions
a.  A solution that contain equal        numbers of hydroxide and        hydronium ions is neutral
  b.  A solution that contains more                    hydroxide ions that hydronium ions        is alkaline
  c.  A solution that contains more        hydronium ions than hydroxide        ions is acid
pH
       1.    The acidity of a solution is determined as the   concentration of hydronium ions.
       2.  The symbol pH is used to denote the hydronium ion   concentration.
       3.  Mathematically pH is defined as the negative   logarithm to the base 10 of the hydronium ion   concentration expressed in molarity,                                       I.e. pH = -log(H+)
pH > 7  - Alkaline Solution
pH = 7  - Neutral Solution
pH < 7  - Acid Solution
  F.  Neutralization
       1.  Mix an acid with an alkali the hydronium and             hydroxide ions react with each other to form water.
       2.  If mixed equally with the same number of hydronium             ions and hydroxide ions the solution will be neutral. 
        H3O+ + OH-   H2O + H2O
Diffusion: is the migration or movement of particles from         an area of high concentration to an area of lower            concentration.
        1.  The diffusion process will continue until an entire               solution of homogeneous (the same concentration       throughout).
        2.  Rate of diffusion depends upon:
  a.  Particle velocity
  b.  Temperature
  c.  Size of particles
  d.  Concentration differences within a solution
Reverse Osmosis (RO)
        1.  When a pressure higher than the osmotic pressure is   applied to the sugar solution, water molecules diffuse   and the solution becomes more concentrated.
        2.  This process is used commercially to concentrate   solutions.
   I.  Dialysis
        1.  Is used to separate large particles from small ones in   solution, i.e.:  proteins from salts.

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3.  Fat globules range in size from 0.1 to 20 µm (1 µm =        0.001mm with an average size of 3 – 4 µm.
  4.  There may be up to 15 billion globules per ml of milk.
  5.  Chemical Structure of Milk Fat
       a.  Milk fat is a mixture of difference fatty-acid esters             called triglycerides, which are composed of an alcohol             called glycerol and various fatty acids.
       b.  Fatty acids make up about 90% of milk fat.
    c.  Saturated fatty acids the carbon atoms are linked by               single bonds.
      d.  Unsaturated fatty acids the carbon atoms are linked by            one or more double bonds.
  6.  Melting Point of Fat
       a.  The melting points of the fatty acids vary considerably             from –7.9 C to 62.6 C.
       b.  Therefore milk fat with a greater content of high-            melting point fatty acids will be harder and fat with a             high content of low-melting point fatty acids will be                    softer, at room temperature.
7.  Iodine Value
       a.  Iodine Value is an indicator of the relative softness or             firmness of a fat as a percentage of Iodine bonded to a             fat sample.
       b.  Iodine is taken up by the double bonds of the fatty                 acids.
       c.  Since the unsaturated fats, primarily Oleic acid, are the             lower melting point fats the Iodine value is primarily a             measure of the relative softness of a fat.
       d.  Iodine value of butter fat varies between 24 – 46 with             32 – 37 being ideal for butter manufacturing.
8.  Refractive Index
       a.  The different fatty acids in fat also affects the way it             refracts light.  Therefore it is a common practice to             determine the refractive index of fat, which can then be             used to calculate the Iodine Value.
       b.  The Refractive index of fat normally ranges from 40 –             46.
  9.  Nuclear Magnetic Resonance (NMR)
       a.  Is another way to determine the relative softness /             hardness of milk fat.  This value varies between 30 –             41.
 10.  Fat Crystallization
         a.  Milk fat crystallization is an exothermic reaction,               which means that the chemical reaction is                 accompanied by evolution of heat.
         b.  During this process the fat globules are very unstable   and may rupture releasing liquid fat into the milk   serum.
         c.  The crystallization process is important in the   production of cream for various purposes.
B.Proteins in Milk
1.Amino Acids
      a.  Amino Acids are the referred to as the ‘Building Blocks     of Protein’
  b.  Amino Acids will always contain Carbon, Hydrogen,   Oxygen, Nitrogen, and either/or Sulfur, Potassium,   and/or Phosphorus
  c.  A single Amino Acid molecule will generally consist of   an amino group (NH2) and a carboxyl (COOH)   group bound to the same carbon atom
    d.  Essential Amino acids are those which cannot be       synthesized by humans and therefore must be added to   the diet.
      e.  Milk contains all of the Essential Amino Acids
      f.  They are: 
  Arginine  Lysine
  Histidine  Methionine
  Isoleucine  Phenylalanine
  Leucine  Tryptophan
  Threonine  Valine
.  Amino Acids emit hydronium ions in alkaline solutions            and absorb hydronium ions in acid solutions hence the            term amphotery electrolytes or ampholytes.
      h.  Therefore Amino Acids can appear in three states:
  1)  Negatively charged in alkaline solutions
  2)  Neutral at equal + and – charges
  3)  Positively charge in acid solutions
       i.  Most proteins will be a combination of 100 – 200 of            approximately 18 different amino acids
.  Classes of Milk Proteins
a.There are literally 100’s of types of milk proteins, most in very small amounts.
b.Milk proteins used to be grouped according into three major categories:
  1) Casein  2) Albumin  3) Globulin
c.Today they are grouped into the major groups:
  1) Casein – 79.5%  2) Whey Proteins – 19.3%
  3) Globule Membrane Proteins – 1.2%
1)  Casein
       a)  Casein is the most prominent protein found in milk and             there are three primary types:
  * ά-casein  38.6%
  * κ-casein, and   30.8%
  * β-casein  10.1%
       b)  Casein Micelles
             *  Are groups of casein submicelle’s bonded together      to form somewhat of a network that allows curd to      form in cheese making.
     c.  Precipitation of Casein
           1)  Precipitation by Acid
    * Added acid or acid from acid-producing bacteria                    will cause precipitation (coagulation) of the milk.
    * The range for optimum precipitation is pH 4.5 to         4.9.  Ideal pH for Casein precipitation is 4.7
            2)  Precipitation by Enzymes
      * κ-casein are easily split by proteolytic enzymes
      * κ-casein consists of 169 amino acids
      * The enzyme splits the molecule at A.A. 105-106
    * κ-casein A.A.’s 106 to 169 are soluble amino          acids and are released into the whey in          cheese making
      * The remaining part of the κ-casein, A.A.’s 1 to          105 are insoluble and remains in the curd           together with ά-casein and β-casein
      * This splitting of the 105-106 bond in the κ-casein           molecule referred to as the primary phase of the          rennet action
      *  The Phase of coagulation and syneresis follows.
2.  Whey Proteins
        a.  Whey protein is the name commonly applied to milk   serum proteins and consist primarily of:
          1)  ά-lactalbumin  - 3.7% of milk protein
  2)  β-lactoglobulin  - 9.8% of milk protein
         b.  They are very high quality proteins with an Amino   Acid profile that is regarded as a biological optimum.
         c.  Responsible for the cooked flavor and odor of milk               and milk products
     d.  Immunoglobulins
  1)  Immune related proteins
  3.  Membrane Proteins
       a)  Membrane proteins are a group of proteins that form a             protective layer around fat globules to stabilize the                     emulsion.
  4.  Denatured Proteins
       a)  Biological function is lost due to:
  1)  Heat  2)  Acidity  3)  Alkali  4) Radiation  5)  Violent Agita
C. Enzymes in Milk
  1. Enzymes are a group of proteins produced by living      organisms.
  2. They trigger chemical reactions and affect the course and speed of such reactions
  3. Enzymes do this without being consumed.
  4. They are referred to as ‘Biocatalysts
  5. Enzymes action is very specific; each type of enzyme catalyses only one type of reaction
  6. Temperature and pH strongly influence enzyme action
7.  Primary Enzymes found in milk are:
       a.  Peroxidase
       b.  Catalase
       c.  Phosphatase
       d.  Lipase
D.Lactose (Milk Sugar)
  1.   Lactose is a disaccharide (sugar) found only in milk.
  2.   It is a carbohydrate made up of two molecules of simple     sugars (glucose – galactose)
  3.   Lactose content of milk varies between 3.6% to 5.5%
  4.   Lactose can be attacked by lactic acid bacteria which produce an enzyme call lactase which splits the lactose molecule into glucose and galactose which then forms into lactic acid through a fermentation process.  This is what has happened to sour milk
E.Vitamins in Milk
   1.  Vitamins are organic substances which occur in very small concentrations in both plants and animals
   2.  Milk contains many vitamins.  However the primary vitamins found in milk are:
  a.  Vitamin A  Fat Soluble
  b.  Vitamin BWater Soluble
  c.  Vitamin B2  Water Soluble
  d.  Vitamin C  Water Soluble
  e.  Vitamin D  Fat Soluble
F.Minerals and Salts in Milk
  1.  The total concentration of Minerals in milk is less than   1%
  2.  Mineral salts occur in solution in milk serum or in casein     compounds.
  3.  Primary mineral salts include calcium, sodium,   potassium and magnesium

   Other Constituents of Milk
      1.  Somatic Cells (White Blood Cells/Leucocytes)
      2.  Gases – Carbon Dioxide, Nitrogen and Oxygen




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