Adulterants and Contaminants in Milk
Physicochemical Properties of Milk and their Importance
Milk Quality Evaluation/Analysis
Parameters for Milk Analysis
“It is not possible to produce good quality market milk and milk products from bad quality raw milk.”
Any company works for profit which is measured in terms of money earned by company. This success is indicated by 'repeat buys' of the product-means consumer's satisfaction-a measure goal of a manufacturer.
In order to increase 'repeat buys' the manufacturer must identify consumers requirements in terms of characteristics or attributes of the product. This combination of attributes/characteristics that contribute to the acceptability of the product , is defined as 'Quality'.
Quality of a product/milk is the sum of the following kind of attributes.
Ř Physico-chemical attributes-nutritive elements, pH, acidity, Boiling point, freezing point etc.
Ř Microbiological attributes-spoilage causing or pathogenic/toxin producing microorganisms.
Ř Sensory attributes-colour, texture, odour, taste
Adulterants and Contaminants
ADULTERANTS are Substances, addition of which makes the food poorer in quality.
CONTAMINANTS are Dangerous or disease-carrying substances, addition of which makes the food impure.
Industrial waste/ chemicals – Heavy metals (lead, mercury, cadmium, arsenic)
Aflatoxin- from Aspergillus flavus & A. parasiticus
Physical contaminants- metal fragments, glass, stones, dirt, plastics, insects & others.
Physicochemical Properties of milk
Acidity & pH
Density & specific gravity
Importance of properties:
Ř Helps in detection of adulteration.
Ř Helps in determining quality of milk.
Ř Helps in processing of milk & milk products.
Ř Helps in evaluating physical changes in milk & milk products during processing
Organoleptic / Sensory analysis – taste, flavour, aroma etc.
Physical analysis – boiling point, specific gravity etc.
Chemical analysis – fat %, lactic acid %, protein %, etc.
Parameters for Milk Analysis
Efficiency of pasteurization
Protein, lactose, lactic acid, citric acid, calcium, chloride, copper, ash
Adulterants and Contaminants :Dirt, added dyes, urea, starch, can sugar, animal (tissue) or vegetable fat, preservatives, detergents, antibiotics and others
Methyl blue test and bacteriological examination
Lact ometer reading
Lactometer reading is required to determine the per cent water or solids present in milk. The addition of water in milk result in the lowering of lactometer reading. Hence this test is applied to detect the adulteration of milk with water.
Lactometer: Lactometer consists of a long cylinder stem connected to the body, which is a large air chamber. This chamber causes the instrument to float, attached to the lower end of the body is the bulb which is filled with mercury to cause the lactometer to sink up to the proper level and to float in and up right position in the milk. Inside the lactometer there may be a thermometer extending from the bulb up into the upper part of the stem where the scale is located. This thermometer does not record temperature above 380C thus this liquid does not put into the milk above this temperature. Just below the thermometer is the lactometer scale, with the graduation ranging from 15 at the top to 45 at the bottom. Each division is known as the lactometer degree. The average reading of normal whale milk is 32.
Reading the lactometer: In taking the lactometer reading of milk, sample of the milk is thoroughly mixed, and pour the milk into a glass measuring cylinder which is large enough to float the lactometer freely, then the lactometer is inserted as soon as the instrument comes to the rest ,read the division at the top of the meniscus film and on a level with the milk. The reading should be taken with a little delay as possible, as the fat globules soon rise and there fore the lower part of the lactometer would be resting in partially skimmed milk. Note the temp of the milk when reading the lactometer and correct the lactometer degrees to standard temperature.
Materials: Butyrometer, Sulphuric acid, Amyl alcohol, Gerber centrifuge, Standard pipette for milk
1. Take 10ml of Sulphuric acid(sp.gravity 1.82) in butyrometer
2. Add 11 ml (11.33g) of milk
3. Add 1 ml amyl of alcohol
4. Insert stopper
5. Invert & shake
6. Centrifugation ( 5 min. in Gerber Centrifuge)
7. Remove and read fat content in %
Total solids: (milk constituents excluding water)
Hehner and Richmond formula
LR( at 60 0F) X 0.29
TS= ------------------------- +1.2 F + 0.14
TS= % Total solids
LR= Lactometer reading
F = % Fat
Solids Not Fat (SNF): (milk constituents excluding fat and water)
% SNF = % TS - % Fat
Modified Lane & Eynon Method, Ranganna, 1986
10 gm of the sample is deproteinized by adding 20ml of 2.7 % barium hydroxide solution slowly with agitation followed by 20 ml of zinc sulphate solution.
The contents are allowed to stand for 10min and than transffered to 100ml volumetric flask.
After making up the volume to 100 ml with distilled water, the contents are filtered through watman # 4 filter paper.
The supernatant thus obtained is used to determine lactose content by titrating against Fehling solution using methylene blue as indicator.
The lactose content in the sample is calculated according to the following expression
% lactose = [(mg of invert sugar x dilution )/(titre value x wt of sample) x 1000]
where, mg of invert sugar represents thefactor for Fehling's solution.
standard solution of lactose (2.5 mg/ml)is used to determine factor for Fehling's solution.
In 100 ml volumetric flask, 20 ml milk,12 ml 10% sodium tungstate and 15 ml 2/3 N H2SO4 are added and make upto 100 ml with water. It is filtered.
The filtrate is titrated with 25 ml benedict's solution until it changes to white colour.
% Lactose = (0.067 X 100 X 100)/(TV X 20 X sp. gr.)
Protein & Casein Estimation
Formal Titration Method
Pipette out 10ml of milk into a 100 ml flask.
Add 5 drops of Phenolphthalein indicator.
Add 0.4 ml of saturated potassium oxalate solution and keep it aside for 2-4 min without disturbing.
Titrate the milk against 0.1 N NaOH to end point.
Add 2 ml of neutral formalin and mix well.
Titrate the same to end point with 0.1 N NaOH.
Volume of NaOH in second titration is V.
Protein % = V x 1.7
Casein % = V x 1.38
Protein - Casein = Whey Proteins
Add 10 g milk, 25 ml H2SO4, 0.2 g CuSO4,and 10 g potassium oxalate to the Kjeldahl flask.
Heat the flask for 2-3 hrs.
Dilute it with 200 ml distilled water.
Distill the contents in Kjeldahl distillation apparatus after adding 50% NaOH until it gives pink colour with phenolphthalein.
Distill ammonia in 50 ml 0.1 N H2SO4.
Titrate the excess acid against 0.1 N NaOH using methyl red indicator.
Total N = (TV x 0.0014 x 100)/ wt of sample.
Protein = Total N x 6.38
15 ml of Silver nitrate (0.0291 N) solution is added to 10 ml milk.
Titrate it with Potassium thiocynate ( 0.0291 N ).
% Chloride = (15 -TV ) x 0.01
% Chloride = (% Chlorine x 58.45 )/35.5
Efficiency of pasteurization
measured by Alkaline phosphatase test
Alkaline phophatase is an enzyme present in raw milk. This enzyme is heat labile and destroyed by adequate pasteurization. If the milk is under pasteurized it gives positive reaction to phosphatase test.
Enzyme has the ability to liberate phenol from phenol phosphoric acid compounds. Free phenol gives a deep blue colour with certain organic compounds; this is the basis for the phosphatase test.
Disodium phenyl phosphate is used as the source of phenol and 2,6 dichloroquinone – chlorimide is the indicator reagent.
Milk is incubated with the DSPP and then indicator reagent is added. Blue colour indicates improper pasteurization
DSPP ---- alkaline phophatase------> free phenol
(phenol phosphoric + ------->indophenol(blue colour)
acid compound) 2,6 DCQC
(organic compound indicator reagent)
Amount of phenol liberated is proportional to the active enzyme present. Colour intensity is measured by colourimetry.
Natural or Apparent Acidity
Due to presence of already present natural constituents like casein, acid Phosphate, citrates, whey proteins, CO2 etc.
Developed Acidity or Real acidity
Due to lactic acid, formed as a result of growth of LAB in milk. Action of them on lactose is responsible for lactic acid production in milk.
Cow milk------- 0.13-0.14 %
Buffalo milk---- 0.14-0.15 %
Produced Lactic acid contributes a major part of the milk acidity and it can be measured by simple titration method. It is expressed as per cent Lactic acid.
Determination of Titratable Acidity
White porcelain dish
Phenolphthalein indicator (1.0% solution in 95 % alcohol)
Oxalic acid (for standardization of NaOH)
Measure accurately 10g/10ml of milk and take it into a porcelain dish/beaker.
Add equal volume of freshly boiled and cooled distilled water.
Add 0.5 ml /2-3 drops of phenolphalein indicator.
Titrate against 0.1 N NaOH till light pink colour appear for 10 seconds (time should not exceed 20 seconds).
% TA= [( V X 0.009)/W] х 100
V= volume of 0.1 N NaOH required for titration.
W=amount of milk taken for titration in gm.
Modes of adulteration:
Removal of fat by skimming
Addition of skim milk
Addition of water
Addition of starch and cane sugar for raising density
Addition of neutralizers and other preservatives to increase keeping quality
a) Detection of skim milk
a. Lower fat percentage
b. Higher density of milk
c. Higher ratio of SNF: fat
b) Detection of added water
a. Lower fat percentage
b. Lower density of milk
c. Lower SNF percentage
d. Depression in freezing point
c) Detection of starch
Reagent: 1% iodine solution
1.Take 3 ml milk in a test tube
2. Boil the content
3. Cool it and add a few drop of 1per cent iodine solution
4. Appearance of blue colour indicates the presence of starch.
5. Blue colour disappears when the sample is boiled.
d) Detection of cane sugar
Reagents: Resorcinol, concentrated HCl
1. Take 1 ml milk in test tube
2. Add 1ml HCl
3. Add 0.1g resorcinol and mix.
4. The test tube is then placed in boiling water for 5 minutes
5. Appearance of red colour indicate the presence of red colour indicate the presence of cane sugar.
e) Detection of neutralizers
Reagents: 1 per cent rosalic acid in alcohol, Alcohol.
1. Take 1 ml milk in test tube.
2. Add 5 ml alcohol.
3. Add a few drops of 1 percent rosalic acid and mix it.
4. The rose red colour indicates the presence of carbonate.
include all those tests which are performed to check the quality of the incoming milk on the receiving platform, so as to make a quick decision regarding its acceptance /rejection. They are performed on each can /tanker of milk with the object of detecting milk of inferior or doubtful quality so as to prevent it to be mixed with high-grade milk. Sometimes the term ‘Rapid platform test’ is used to refer mainly to the organoleptic or sensory tests which take very little time to perform.
Purpose is to determine final acceptance or rejection of milk.( on the basis of pre-determined level).
To determine heat stability of milk.
To determine both heat stability & pH.
To determine heat stability.
5 ml milk-----boiling-----clotting, indicates excess level of LA due to microbial activities.
Dye-reduction test( MBR or Resazurin)
To determine extent of bacterial contamination.
Milk + MB dye----( incubation at 370C)--------------Reduction time
Colour changes from Blue to White
If RT is more—less contamination and vice versa
To identify types of microorganisms present
Todetermine extent of bacterial contamination.
To detect adultration with water.