This document discusses milk quality testing techniques. It introduces the Methylene Blue Dye Reduction (MBRT) test, Resazurin test, and Litmus test. The MBRT test measures microbiological quality by detecting how quickly a blue dye is decolorized by microbial activity. The Resazurin test checks quality by noting color changes from blue based on bacterial levels. The Litmus test differentiates microbes by how they metabolize the litmus milk medium, noting reactions like acid production or clotting. Procedures for each test are provided.

1. DEPARTMENT OF MICROBIOLOGY
VIVEKANANDHA ARTS AND SCIENCE COLLEGE FOR WOMEN
SANKARI,SALEM
SUBJECT : FOOD MICROBIOLOGY
Submitted by
Nandhini Sekar
III-B.SC Microbiology
Department of microbiology
Vivekanandha arts and science college for women
Sankari Salem.
Tamilnadu, India.
MILK QUALITY TEST

2. CONTENT :
● INTRODUCTION
● MILK CAN BE TESTED FOR :
● MBRT TEST
● RESAZURIN TEST
● LITMUS TEST

3. INTRODUCTION :
● Milk quality is the most important factor in
dairy production. It affects milk’s
nutritional value, taste, and safety. As such,
milk quality control tests are important to
ensure quality and safety. But quality
control in the dairy industry is a relatively
complex process that requires a lot of time
and resources.

4. Milk testing and quality control should be carried out at all stages of the dairy chain.
Milk can be tested for:
● Quantity – measured in volume or weight;
● Organoleptic characteristics – appearance, taste and
smell;
● Compositional characteristics – especially fat, solid and
protein contents;
● Physical and chemical characteristics;
● Hygienic characteristics – hygienic conditions, cleanliness
and quality;
● Adulteration – with water, preservatives, added solids, etc;
● Drug residues.

5. COMMON MILK GRADING TECHNIQUES
● MBRT TEST
● RESAZURIN TEST
● LITMUS TEST

6. ● Methylene Blue Dye Reduction Test, commonly known as
MBRT test is used as a quick method to assess the
microbiological quality of raw and pasteurized milk. This test
is based on the fact that the blue colour of the dye solution
added to the milk get decolourized when the oxygen present
in the milk get exhausted due to microbial activity. The
sooner the decolourization, more inferior is the
bacteriological quality of milk assumed to be.
MBRT TEST

7. PROCEDURE
● The test has to be done under sterile conditions. Take 10 ml milk sample in
sterile MBRT test tube. Add 1 ml MBRT dye solution
● Stopper the tubes with sterilized rubber stopper and carefully place them in a
test tube stand dipped in a serological water bath maintained at 37±1⁰C.
● Record this time as the beginning of the incubation period. Decolorization is
considered complete when only a faint blue ring (about 5mm) persists at the
top.

8. RESAZURIN TEST
● Resazurin is a kind of test that is done to check the quality of the milk and its
consistency.
● The milk that is contained in a bulk has been tested through this test because
it is not possible for the test if the quantity of the milk is less.
● Through this test, the milk has been given a bluish color to its character.
Initially, the test is based on the bacteria that are present in the milk
● It is a rapid test of three hours that suggests the milk whether is all good
or bad for us.
● The resazurin test gives the bluish characteristic color to the milk that is all based
on the quality of the milk. The milk quality is considered by only noting the color
change degree of the milk.

9. PROCEDURE :
● Mix the Milk sample thoroughly by inverting from one to another container.
● Take 10 ml of milk into a test tube and add 1 ml of working solution of Resazurin solution.
● Put air tight closure to prevent oxygen entry.Invert the test tubes to mix the milk and
Resazurin solution.
● Place the test tubes in a thermostatically maintained water bath at 37.5 °C for 10
minutes.Immediately match the colour of the milk with the Lovibond colour standards
for Resazurin discs.

10. LITMUS TEST :
● Litmus milk is an undefined milk-based medium consisting of skim milk and the pH
indicator azolitmin
● Litmus milk medium differentiates microorganisms based on their ability to
metabolize litmus milk. Four essential reactions in litmus milk are; lactose
fermentation, reduction of litmus, casein coagulation, and casein hydrolysis.
● It is especially useful in the species differentiation within the genus Clostridium.
● Litmus Milk is a differential medium used to determine different metabolicfunctions.
Litmus Milk is also useful in the maintenance and propagation of lactic acid bacteria

11. PROCEDURE
1. Inoculate with 4 drops of a 24-hour broth culture.
2. Incubate at 35°-37°C in ambient air.
3. Observe daily for seven days for alkaline reaction (litmus turns blue),
indicator reduction, acid clot, acid reaction (litmus turns pink), rennet clot,
and peptonization.
4. Record all changes.

12. THE APPEARANCE OF LITMUS INDICATOR

13. THANK
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