What happens when methylene blue is added to milk?
The test relies on the fact that methylene blue solution is blue in the presence of oxygen, but will lose color as oxygen is depleted. Bacteria in milk ferment lactose (milk sugar) to form lactic acid. During this process oxygen is used up and electrons are released, which react with methylene blue.
What is the function of methylene blue in the reductase test for milk quality?
Aim of Methylene Blue Reduction Test This test is performed to check the bacteria contamination in milk. It will visually indicate the presence of bacteria in a given milk sample, and it will indicate the level of milk quality.
Why would milk turn blue?
The lactic acid sours the milk and curdles (coagulates) the milk protein. Yeasts and molds grow well in this acid environment, and they convert acid into non-acid products. Adding methylene blue to milk will turn it a blue color, and it will remain blue as long as oxygen is present inside the milk.
What is the bacterial content of milk?
The initial bacterial count of milk may range from less than 1000 cells/ml to 106/ml. High counts (more than 105/ml) are evidence of poor production hygiene. Rapid tests are available for estimating the bacterial quality of milk. Pasteurisation is the process used to destroy bacteria in milk.
How is methylene blue reduced in milk?
Because methylene blue is a redox indicator, which loses its colour when it comes under the effect of lack of oxygen. Bacterial metabolism causes decrease of oxygen in the milk due to formation of reducing substances.
Why does methylene blue turn clear in the milk?
The dissolved oxygen oxidizes the methylene blue (which begins colorless when reduced) turning it blue (oxidized). 3) The removal of the oxygen from milk during bacterial metabolism causes the oxidized methylene blue color to disappear.
What is methylene blue used to test for?
The methylene blue test is a test to determine the type or to treat methemoglobinemia, a blood disorder.
Which microorganism is responsible for blue discoloration of milk?
The species Pseudomonas koreensis has been found along the production chain of the dairy plant during a period of 8 months: pre-milk pasteurization, buffer surface water of the charger and the finished product, including a sampled mozzarella showing blue discoloration.
What is the microbiology of milk?
In addition to being a nutritious food for humans, milk provides a favorable environment for the growth of microorganisms. Yeasts, moulds and a broad spectrum of bacteria can grow in milk, particularly at temperatures above 16°C….Milk microbiology.
| Pseudomonas | Spoilage |
|---|---|
| Mycobacterium tuberculosis | Pathogenic |
What are the microbial standards for milk?
TABLE F-1European Commission Overview of Microbiological Criteria for Dairy Products
| Food Category | Microorganisms | Limit |
|---|---|---|
| Raw milk intended to processing (Directive 92/46/EEC) | Plate count at 30°C | 105 cfu/mL |
| 5 × 105 or 1.5 × 106 cfu/mL | ||
| Staphylococcus aureus |
How is the speed of reduction of methylene blue dye in milk an indicator of microbial load?
Because methylene blue is a redox indicator, which loses its colour when it comes under the effect of lack of oxygen. The time taken by the dye to get reduced determines the amount of microbes in the milk and the metabolic reactions in the microorganism.