Introduction
Milk is a highly nutritious and perishable food product that serves as an excellent medium for microbial growth. To extend its shelf life and maintain quality during storage and transportation, various preservatives are added to milk. However, the use of certain preservatives in milk is regulated and some are completely prohibited due to health concerns. Understanding these preservatives and their detection methods is crucial for food safety and quality control.
Common Preservatives and Adulterants in Milk
1. Formalin (Formaldehyde)
Chemical Formula: HCHO
Nature: Formalin is a 37-40% aqueous solution of formaldehyde gas. It is a highly toxic chemical primarily used as a disinfectant and preservative for biological specimens.
Why it's added: Illegally added to milk to increase shelf life and prevent spoilage, especially in areas with poor refrigeration facilities.
Health effects: Carcinogenic, causes gastric irritation, nausea, vomiting, and can lead to serious organ damage.
Legal status: Completely banned for use in food products.
2. Hydrogen Peroxide
Chemical Formula: H₂O₂
Nature: A strong oxidizing agent that appears as a colorless liquid.
Why it's added: Used illegally to extend shelf life by killing bacteria and other microorganisms.
Health effects: Can cause gastric irritation, ulcers, and in high concentrations, can be toxic to cells.
Legal status: Prohibited in milk and dairy products.
3. Boric Acid and Borax
Chemical Formula: H₃BO₃ (Boric Acid), Na₂B₄O₇ (Borax)
Nature: White crystalline compounds with antiseptic properties.
Why it's added: Illegally used to preserve milk and prevent curdling.
Health effects: Can cause nausea, vomiting, skin rashes, and affect the nervous system with prolonged exposure.
Legal status: Banned for use in food products.
4. Salicylic Acid
Chemical Formula: C₇H₆O₃
Nature: A white crystalline organic acid with antimicrobial properties.
Why it's added: Sometimes illegally added as a preservative to prevent bacterial growth.
Health effects: Can cause gastric irritation and allergic reactions in sensitive individuals.
Legal status: Not permitted in milk.
Detection Methods
Detection of Formalin
Method 1: Schiff's Reagent Test
1Take 5 ml of milk sample in a test tube.
2Add 2-3 drops of Schiff's reagent (colorless solution).
3Mix gently and observe for color change.
Positive Result: Pink to violet color indicates presence of formalin.
Negative Result: No color change indicates absence of formalin.
Method 2: Milk and HCl Test
1Take 10 ml of milk in a test tube.
2Add 5 ml of concentrated HCl slowly along the sides.
3Allow to stand without mixing.
Positive Result: Violet ring at the junction indicates formalin.
Negative Result: No colored ring formation.
Detection of Hydrogen Peroxide
Potassium Iodide-Starch Test
1Take 5 ml of milk sample.
2Add 2-3 drops of freshly prepared starch solution.
3Add 2-3 drops of potassium iodide solution.
4Mix and observe immediately.
Positive Result: Blue color development indicates H₂O₂.
Negative Result: No blue color indicates absence.
Detection of Boric Acid/Borax
Turmeric Paper Test
1Prepare turmeric paper by dipping filter paper in turmeric solution and drying.
2Take 5 ml of milk and add few drops of HCl.
3Dip the turmeric paper in the acidified milk.
4Remove and dry the paper.
5Moisten the paper with dilute NaOH.
Positive Result: Reddish-brown color indicates presence of boric acid/borax.
Negative Result: Yellow color remains unchanged.
Detection of Salicylic Acid
Ferric Chloride Test
1Take 5 ml of milk sample.
2Add 5 ml of distilled water and mix.
3Add 2-3 drops of neutral ferric chloride solution.
4Mix and observe color change.
Positive Result: Violet color indicates presence of salicylic acid.
Negative Result: No color change or pale yellow color.
Summary Table of Detection Methods
| Preservative | Detection Method | Reagent Used | Positive Result |
|---|---|---|---|
| Formalin | Schiff's Reagent Test | Schiff's Reagent | Pink to violet color |
| Formalin | HCl Test | Concentrated HCl | Violet ring at junction |
| Hydrogen Peroxide | Starch-KI Test | Starch + KI solution | Blue color |
| Boric Acid/Borax | Turmeric Paper Test | Turmeric paper + NaOH | Reddish-brown color |
| Salicylic Acid | Ferric Chloride Test | Neutral FeCl₃ | Violet color |
Precautions and Safety Measures
Laboratory Safety:
- Always wear safety goggles and gloves when handling chemicals
- Work in a well-ventilated area or under a fume hood
- Handle concentrated acids with extreme care
- Dispose of chemical waste properly according to institutional guidelines
- Never taste or consume any test samples
Conclusion
The detection of preservatives and adulterants in milk is crucial for ensuring food safety and protecting public health. The methods described above are simple, cost-effective, and can be easily performed in basic laboratory settings. Regular monitoring and testing of milk samples help maintain quality standards and prevent the consumption of harmful substances.
As future scientists and food technologists, it is important to understand that while preservation is necessary for food safety, the use of harmful chemicals is never justified. Proper pasteurization, refrigeration, and hygienic handling remain the best methods for ensuring milk safety and quality.
