Animal Husbandry, Dairy & Fisheries Sector – Pashudhan Sanjivani, E- Pashudhan Haat, etc

A paper sensor that can detect freshness of milk


Mains Paper 3: Science & Technology | Achievement of Indians in science & technology

From UPSC perspective, the following things are important:

Prelims level: ALP test

Mains level: Working and utility of the quality test


  • Scientists at IIT Guwahati have developed a simple paper kit that can test freshness of milk and tell how well it has been pasteurized.

Why such move?

  1. Milk is highly perishable and prone to action of enzymes and microorganisms inherently present in it.
  2. Although pasteurization, freezing and preservation using additives are widely used to prevent spoilage, perishability of milk is still a concern.
  3. There is no easy way to know if milk is fresh or stale or how effective is the pasteurization.
  4. Being a widely consumed food, the safety of milk is of prime concern to consumers.
  5. Tests used in dairies and dairy industries are time consuming and need sophisticated equipment like spectrophotometers.
  6. The new detection kit could make testing easy and fast.

Paper Kit

  1. A milk enzyme, Alkaline Phosphatase (ALP), is considered to be an indicator of milk quality because its presence even after pasteurization indicates presence of microbes that may not have been rendered inactive with pasteurization.
  2. Researchers used ordinary filter paper to prepare the detector.
  3. The filter paper was cut into small discs using office punch and impregnated with chemical probes that preferentially react with ALP.
  4. The ‘probes’ used are antibodies that specifically bind to ALP.
  5. When ALP comes into contact with the probe, it turns white paper disc into a coloured one.

How it works?

  1. The paper discs are soaked in 4-carboxybenzene diazonium solution and then chemically treated to expose-COOH groups on the diazonium.
  2. The -COOH groups then attach to NH2 groups on anti-ALP probe molecules.
  3. Thus the anti-ALP probes are fixed on paper.
  4. When a drop of milk is poured on the tiny paper disc, the ALP in milk reacts with probes, resulting in change of colour.
  5. The colour change on paper discs is then photographed by a smartphone camera and images processed to obtain corresponding colour values.
  6. These values are then compared with standard data stored in the phone.  Thus not only the presence of ALP could be detected but the amount of it in milk could also be measured.
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