Paper Sensor to detect freshness of Milk

Scientists from the Indian Institute of Technology, Guwahati, have developed a paper kit to test the freshness of milk and determine how well the milk has been pasteurized. The kit can also aid in ensuring that milk is consumed before it turns too sour with the help of a smartphone app.

How does the Kit work?

The Kit uses an ordinary filter paper to prepare the detector. The filter paper which is cut into small pieces is impregnated with chemical probes that preferentially react with Alkaline Phosphatase, which is an indicator of the quality of the milk. When the filter paper impregnated with probes come in contact with the milk, its colour changes.

Alkaline Phosphatase or ALP is an indicator of milk quality. It’s presence even after pasteurization indicates presence of microbes that may not have been rendered inactive with pasteurization.

The colour change is photographed by a Smartphone. The images are then processed to obtain corresponding colour values. These values are then compared with standard data stored in the phone. This provides information about the quality of the Milk. Since the sensors used works in both qualitative and quantitative mode, the kit can also be used to measure the quantity of the milk.


The probe discs were attached to a 2 cm square transparent cellulose acetate film. Another layer cellulose acetate film is coated as cover on the probe. The milk is injected through the tiny hole on the cover. The colour change is photographed and processed using a smartphone to get the results.


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