Simple Paper Kit to Test Freshness of Milk

A research team that was led by Dr Pranjal Chandra, Assistant Professor at the Department of Biosciences & Bioengineering, IIT Guwahati and Kuldeep Mahato, research scholar have made a simple visual detection technique that can detect the quality of milk, without the need for special equipment or instruments.

The quality as well as freshness of milk is decided by the invasion & presence of microbes in milk. Bacteria and other microbes that can grow in milk can not only affect the taste and freshness but can also result in health issues. Pasteurization is mainly used to kill the microbes in milk and various tests are used to ensure the effectiveness of pasteurization.

India is the world’s largest milk producer and consumer in the world with the values amounting to 176.35 and 160 million tonne respectively for 2017-18. The annual demand for milk by 2022 is estimated to be 210-220 million metric tonne. Adulteration is more common in north India.

“It would be useful if the quality of milk can be tested at the point of collection of milk or even in the home kitchen,” said Dr. Chandra, adding that such testing needs easy-to-operate & portable detection kits.

Explaining about the research, Dr Chandra added, “Alkaline Phosphatase (ALP) is a metalloprotein found naturally in raw milk samples & is considered an important biomarker in quality control of milk”. It is found in raw milk and is destroyed during pasteurization. ALP is also found in higher amounts in the case of milk derived from animals with infection in the mammary glands. Detection of ALP in milk can thus point to inadequate pasteurization and perhaps contamination.

“Despite ALP’s recognizable detection potential in native milk, the multistep nature & requirement of sophisticated bulky analytical instruments & trained personnel, to detect ALP, limit their use as a sensor of milk quality in remote settings and in home kitchens,” said Dr Chandra, justifying the scope as well as need for developing better ALP detection kits.

 The researchers have used simple filter paper, chemically modified it & loaded it with a recognition element anti-ALP that captures the ALP present in the milk. Upon treatment of colour forming compound BCIP to the captured complex of ALP forms a blue-green colored precipitate, that otherwise does not gives any colour in the absence of ALP. The intensity of the colour indicates the amount of ALP present. The group used a smartphone to capture the image of colour and used Red Green Blue filter in the phone to profile the colour obtained that could be co-related to the concentration of ALP present in the test sample.

Dr. Chandra also said “Our sensor takes merely 13 min to detect ALP, and hence it can be applied for quick onsite analysis”.

The researchers successfully tested milk obtained from villages & commercially available milk samples using their paper-based sensor kit & found that they could detect down to 0.87 units of ALP / milliliter of milk to about 91 to 100 percent accuracy. This detection limit & accuracy make it possible to discriminate raw milk from pasteurized or boiled milk that contains ALP in ultra-trace amount.

Based on principle of detection, they developed a miniaturized detection kit & demonstrated the instrument-free, in-kitchen applicability of the kit for milk monitoring. “We plan to extend the sensing principle we have developed for ALP towards the detection of various molecules in different matrices. In fact, we have made another sensor for ALP detection using a label-free bio-electronic chip. This new sensor has been developed by Buddhadev Purohit, Kuldeep Mahato and Ashutosh Kumar. The developed bio-electronic chip is an advanced version of the paper-based kit with improved accuracy”, told Dr Chandra.