Chemistry of milk
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January 01, 2016 |
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Chemistry of milk
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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.
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.
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 B1 Water
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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