Milk
and Milk products comprise of several different nutrient content it serves as
an excellent growth medium for all of the organism particularly bacteria. Thus
numerous preservation techniques are applied to eliminate the growth of Pathogenic
and spoilage causing (Non Pathogenic) bacteria and maintaining the nutritive
properties of milk and its product.
Many
different type of milk preservation techniques are there to increase the shelf
life of milk & milk products. Amongst several type of preservation
techniques. Preservative are often added in milk with different purposes.
However, it may be emphasized that addition of preservative is strictly
prohibited under FSS Rule 2011. This rule does not allow the addition of any
external substance to milk and is punishable under law. Preservatives are also
prohibited in market milk except during sampling for analytical point of view.
Milk
Preservation:
The
technique by which various type of microorganisms present in milk and/or its
products are destroyed or get inactive by any means for enhancing its self-life
is called preservation.
Techniques:
The
various technique of milk preservation are as follows:
Physical
Preservation
1. By heating: This
method is commonly adopted in India. Three procedure are adopted under this
method.
(a) Pasteurization Process: The technique by which the milk is
heated for definite period of time at certain temperature and is cooled
immediately so that all the pathogenic and bulk of non-pathogenic organism are
destroyed thus to increase the keeping quality. The temperature time relationship
are two : In LTLT method 145°F/30 min. and cooled
at 50°F temp. In HTST method 161°F/15
seconds and cooled at 50°F temp.
(b) Sterilization Process: Milk is heated at 115°C
which is high temperature and cooled at 50°F temperature. In the
process milk is heated at such high temperature so that all the microorganism
present in milk alongwith their spores are completely destroyed as a result
milk may be stored or preserved safe comparatively for long time.
(c) Removal of Water from Milk by Heating: The milk is heated
for a long time resulted a portion of water which is 25-30% vaporizes and milk
is condensed so as check the microbial growth due to lack of moisture. Now
sugar is added into milk to increase the osmatic pressure and remaining
microorganism became inactive and the milk can be stored for a long duration
eq. condensed milk and evaporated milk.
2. By cooling: This technique is comparatively more
expensive so it is not commonly followed in India but it is very common is
advanced countries such as U.S.A., England, Denmark etc. All micro-organism
found in milk including lactose fermenting bacteria get inactive if milk and
milk products are kept at below 10°C temperature.
3. By irradiation: Dairy scientist decided to explore this
method of preserving the milk which would be less expensive in means of both
money and labour also in consonance with health aspect. They occurred that some
rays ionizing have bactericidal properties. They irradiated the milk with
various types of rays which caused microorganism especially bacteria to become
inactive and enhance the shelf life of milk.
EFFECT
OF IRRADIATION ON THE NUTRITIVE VALUE OF MILK:
1. There
is no adverse effect on the acidity and pH of milk.
2. The
solubility of Phosphorus, citric acid and Ca + Mg is increased but citric acid
content of milk is decreased.
3. Content
of vitamin A and its precursor carotene in milk are decreased.
4. Some
enzymes of milk are destroyed by irradiation.
Types of Rays
(i) Non-ionizing
Radiation – Infra-red rays, Hertzian rays, Ultraviolet rays.
(ii) Ionizing
Radiation – X-rays, R-rays, Cathode rays, Micro Waves, Ultrasonic Laser rays
and Radio Waves.
Milk
Preservatives
Milk
preservatives are chemical substances which are added into milk is a very
little quantity to check the growth or to destroy the micro organism present in
milk and thus to prevent souring or decomposition and after all enhance the
keeping quality of milk.
Desirable
Properties of A Good Preservative
1. It
should be easily available in the market.
2. It
should not be expensive.
3. It
should be tasteless, odorless, colourless and non-toxic in nature.
4. It
should not be react with any constituents.
5. It
should not be interfere with physical properties of milk.
6. It
should have no adverse effect on the quality of the dairy product.
7. It
should be easily miscible and detectable.
8. It
should easily added to milk and milk products.
9. It
should be such that it may be isolated or separated from the milk before human
being consumption.
10. It
should not cause biting or caustic, itching, irritant any other harm to the
body.
11. It
should not create any type of disorder in the digestive tract if consumed.
Why
Addition Of Preservatives Should Be Discouraged:
1. All
preservative are toxic in nature, even some are more toxic and some are less
toxic.
2. They
create disorder in the digestive system and also leave the adverse effect on
digestion which is more serve in infants.
3. They
create loss of appetite and disturbed metabolism process.
4. They
affect the manufacturing of fermented products and fat rich product like
butter, cream and cheese also.
5. They
interfere the physio-chemical properties of milk.
6. They
adversely affect the acceptability of milk because when added to milk. They
change the colour taste and flavour etc.
7. In
some countries it is illegal to add in milk when milk to be consumed.
Detection
Of Some Common Preservatives:
Legal
Preservatives: Legal
or official preservatives are added to milk for analytical purposes.
1. Formalin: 40% solution of formaldehyde is known as
formalin. It is very efficient and widely accepted preservative for milk ment
for analytical purposes. 2 drop of formalin are sufficient amount to preserve
100 ml of milk.
Hehner Test: Take about 10 ml of
milk in a test tube, add 0.5 ml of 0% Fcl3 solution add thereafter
carefully 5ml of conc. H2SO4 down the side of test tube
in such a way that it forms a separate layer at the bottom of test tube without
mixing the sample milk. Presence of violet coloured ring formed at the junction
of the two liquids shows the presence of formalin.
2. Potassium Chromate: Prepare ash from 50ml of milk sample
by drying on boiling water bath and then heating it in a muffle furnace at 550°C
for 2 hours add to ash with 4ml dil. HCl and mixing by warming. Take 1ml ash
solution add 2N. NaOH solution dropwise till the solution is alkaline which
testing by pH paper add 1 ml acetic acid and then add 0.5 ml Barium Chloride
(BaCl2) solution and mix. Formation of a yellow precipitate shows
the presence of dichromate in milk as preservative.
3. Mercuric Chloride: It is a heavy metal salt and is also highly
toxic. Mercuric Chloride is detected from milk by adding stannous chloride
solution. A white precipitate is formed in the presence of Mercuric Chloride.
Illegal
Preservatives: Illegal
preservative are added to milk or milk products principally to remove the
defects:
1. Sodium Carbonate: Rasolic acid Test– 9.1 grams of sodium
carbonate or sodium bicarbonate are sufficient amount to prepare 100ml of milk.
Take about 5ml sample of milk in a Test Tube. Add 5ml of alcohol and few drop
of aqueous 1% rosalic acid solution. Formation of rose red colour shows addition
of sodium carbonate.
2. Sodium bicarbonate: Take 5ml of sample of milk in a silica
dish evaporated to dryness and ignite to ash. Titrate against standard N/10
acid to neutralize the base (alkali) present in ash. If more than 0.3ml of N/0
acid is required to neutralize the soluble alkali present then it is possible
that NaHCO3 has been added.
3. Hydrogen Peroxide (H2O2):5 drop of H2O2
are sufficient amount to preserve 100 ml of milk for analysis.
Warther's test: Take 10ml sample of
milk in Test tube add 10 drop of 10% solution of sodium arthovana date and few
drop of 10% solution of H2SO4. Observe the red colour
conforms the presence of H2O2 present in milk.
Paraphenylene diamine
test: Take
5ml of sample milk in test tube, add 5 drop of 2% aqueous solution of Paraphenylene
diamine mixed. Adulterated milk sample gives intense Blue colour thus indicating
the H2O2 is added.
4. Boric acid (H3PO3): 0.1 gram per 100 ml
of milk is necessary to preserve sample.
Take 5ml of mil in a
test tube, add 1ml Conc. HCl and mix well. Dip a strip or piece of turmeric
paper in the milk. Dry the paper quickly and note the change in colour. Observe
turmeric paper turns red. If boric acid present. Developed red colour turning
to dark green with ammonium hydroxide indicate the presence of Boric acid
confirmed.
5. Benzoic acid and Salicylic acid: 0.1gm per 100 ml milk
is capable of preserving milk.
Take 5ml sample of
milk in a Test tube, add 3-4 drop of Ferric chloride (FeCl3)
solution. Appearances of Beef-colour indicate the presence of Benzoic acid in
milk as preservative if violet colour develops it shows the presence of
salicylic acid.
6. Potassium Nitrites: 0.1gm per 100 ml of milk used as
preservative.
Take 10ml milk in a
Test tube and 5ml Griess-llosvay reagent after 10 minutes develops pink colour
indicating the presence of Nitrites.
7. Potassium Nitrates: 0.1gm per 100ml of milk is sufficient
as preservative.
Take 10ml milk sample
in a Test tube add 1ml acetic acid resulted fat and protein coagulated then
filter. Take 1ml filtrate in a clean test tube, add carefully 4ml Diphenyal
amine prepared in conc. H2SO4 down the side of test tube
for form a separate layer without mixing. Presence of blue coloured ring at the
junction of the liquid indicates the presence of nitrates.
8. b. naphthol: 0.1 gram of b.
naphthol are sufficient amount to preserve 100 ml of milk.
Sample milk is
extracted with chloroform and heated with KOH for a few minute, the formation
of deep blue coloures shows the presence of b. naphthol in milk.
References:
1. Mathur,
M.P., Datta Roy, D. and Dinakar (1999). Text Book of Dairy Chemistry, ICAR New
Delhi.
2. Singh,
Rama Shankar & Saraswat, B.L. (2008). Dairy Chemistry and Animal Nutrition,
Kushal Publication & Distributors, Varansi, ISBN-81-86099-64-6.
3. Singh,
T.B. & Shukla, S.G. (2014). Dairy Chemistry & Animal Nutrition, Rama
Publishing House, Meerut.
4. Singh,
Jain – Dairying, Nidhi Prakashan, Baraut.
5. Bhati,
S.S. and Lavana, G.S. (2000). Dairy Science, V.K. Prakashan, Baraut.
6. Chaudhary,
A.C. (1959). Practical Dairy Science & Laboratory Method, Scientific Book
Agency, Calcutta.
