Rapid Inspection Technology for Fresh Milk Adulteration
Han Qiwen 1, Qin Lihu 2, Sun Wubin 3
(1. Baoji Huimin Dairy Group Co., Ltd., Baoji 721305, Shaanxi, China; 2. Xi'an Dongfang Dairy Product Factory, Xi'an 710065, Shaanxi, China; 3. Shanghai Heshaoyu Chemical Co., Ltd., Shanghai 210000, China)
Abstract: This article introduces several rapid technical methods for detecting adulteration in fresh milk, including the detection of alkaline substances, nitrite, glucose, starch, urea, sucrose, hydrolyzed protein, powdered oils, antibiotics, preservatives, and mastitis milk. These techniques have been applied in actual production practices to ensure milk quality and safety.
Keywords: Fresh cow (goat) milk; Adulteration; Inspection
Rapid Methods for Detecting Adulterants in Milk
Han Qiwen 1, Qin Lihu 2, Sun Wubin 3
(1. Baoji Huiming Dairy Group Corp, Baoji 721305, China; 2. Xi'an Oriental Dairy Factory, Xi'an 710065, China; 3. Shanghai Hesibi Chemistry Corp, Shanghai 210000, China)
Abstract: This paper presents rapid technological methods for identifying basic substances, nitrite, starch, bactericides, preservatives, carbamide, and sugar in adulterated milk. These techniques are essential for ensuring the quality and safety of dairy products.
Keywords: Milk; Adulteration; Detection
0 Introduction
In today's competitive dairy market, companies are increasingly focused on securing high-quality milk resources. Unfortunately, some dairy farmers add water or other substances to fresh milk to increase volume, which can negatively impact product quality and consumer health. As an experienced professional in the dairy industry, I have developed and tested various methods to detect milk adulteration. This article shares practical insights and techniques for monitoring the quality of fresh milk during procurement.
1 Measuring Specific Gravity
1.1 Purpose
The primary purpose of measuring specific gravity is to determine whether fresh milk has been diluted with water. The specific gravity of normal milk typically ranges from 1.028 to 1.032. If the measured value is below 1.028, it may indicate adulteration.
1.2 Detection Method
1.2.1 Equipment: Hydrometer (20°C/4°C), thermometer (100°C, mercury rod), and a 250 mL graduated glass cylinder.
1.2.2 Procedure: Mix the milk thoroughly, take 400–500 mL, pour slowly into the cylinder, insert the hydrometer, and wait until it stabilizes. Measure the temperature and calculate the specific gravity.
1.3 Explanation
Although this method does not directly measure the freezing point, it is simple and effective for checking water dilution. It is widely used in dairy processing to maintain powder extraction efficiency.
2 Alkaline Substances
2.1 Purpose
Common alkaline substances like soda or lye are often added to mask spoilage, especially in summer. Detecting these helps identify abnormal milk.
2.2 Detection Method
2.2.1 Principle: Bromothymol blue changes color in alkaline conditions (pH 6.0–7.6).
2.2.2 Reagent: 0.04% bromothymol blue ethanol solution.
2.2.3 Procedure: Add 0.6 mL of reagent to 2 mL of milk in a test tube, mix gently, and observe the color change after 2 minutes.
2.3 Results Interpretation
- Yellow: No alkali, qualified milk
- Yellow-green: 0.03% alkali, abnormal milk
- Light green: 0.05% alkali, abnormal milk
- Green: ≥0.1% alkali, severely abnormal milk
Another method uses rhododendron acid, which turns red in the presence of alkali. This method is also quick and easy to perform.
3 Nitrite and Nitrate Detection
3.1 Purpose
Nitrite and nitrate are common preservatives but can be harmful in excess. Monitoring their levels is crucial to ensure milk safety.
3.2 Nitrite Detection
3.2.1 Principle: Nitrite reacts with sulfanilic acid and α-naphthylamine under acidic conditions to form a purple-red dye.
3.2.2 Reagent: A mixture of α-naphthol, α-naphthylamine, and sulfanilic acid in acetic acid.
3.2.3 Procedure: Add 1.5 mL of reagent to 2 mL of milk and observe color changes.
3.3 Results Interpretation
- White: No nitrite, qualified milk
- Pink: 0.2 mg/kg nitrite, abnormal milk
- Pink water: 0.3 mg/kg nitrite, abnormal milk
- Deep pink: ≥0.4 mg/kg nitrite, severely abnormal milk
3.4 Nitrate Detection
3.4.1 Principle: Nitrates are reduced to nitrites, then react to form a red azo compound.
3.4.2 Reagents: A reducing agent (barium nitrate, manganese sulfate, cadmium acetate) and a color reagent.
3.4.3 Procedure: Add reducing agent and color reagent to 2 mL of milk and observe the color.
3.5 Results Interpretation
- Milky: No nitrite/nitrate, qualified milk
- Pink: 0.2 mg/kg, abnormal milk
- Pink water: 0.3 mg/kg, abnormal milk
- Red: ≥0.5 mg/kg, severely abnormal milk
These methods are efficient, accurate, and widely used in dairy quality control. They help ensure that only safe and high-quality milk is processed and sold. By applying these tests, dairy producers can protect both their business and consumers.
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