melamine in milk

A new handheld device to detect melamine in milk R. Prasad

Detecting melamine in milk has become extremely easy, quick and
inexpensive thanks to a handheld melamine detector developed by
researchers at the Indian Institute of Science (IISc), Bangalore. Leaf
extract of a commonly seen weed parthenium along with silver nitrate is
used for detecting the presence of melamine in milk. The results were
published in the journal Sensors and Actuators B: Chemical.

"The presence of melamine in milk can be detected at room temperature
within a few seconds through a change in colour," says S.C.G. Kiruba
Daniel from the Department of Instrumentation and Applied Physics, IISc
and the first author of the paper.

"Our sensor has a very high sensitivity as it can detect melamine even
at a low concentration of 0.5 ppm in raw milk." Melamine content of more
than 1 ppm in infant formula and more than 2.5 ppm in other foods should
be viewed with suspicion of adulteration, says the Food Safety and
Standards Authority of India.

In 2008, at least four babies in China died and around 100,000 became
sick after consuming powdered milk baby food laced with melamine. Due to
the presence of nitrogen, the addition of melamine to milk makes it look
protein-rich.

Prior to melamine detection, the milk is processed to remove fat and
proteins as they tend to interfere with detection. While most
researchers had used already prepared silver nanoparticles for melamine
detection, the IISc team added silver nitrate and the leaf extract in a
particular ratio and at a particular pH to the preprocessed milk to
synthesise silver nanoparticles.

"If melamine is present then it interferes with the synthesis and there
is abrupt formation of nanoparticles leading to colour change," says Dr.
Daniel.

The change in colour depends on the amount of melamine present and,
therefore, the extent of its interference with the synthesis of silver
nanoparticles. "The colour change can be directly observed by the naked
eye and also recorded by spectral change," he says.

The silver nanoparticles are reddish yellow in the absence of melamine,
while it becomes nearly colourless when melamine is present. Light
absorption at 414 nm wavelength is a signature of silver nanopartciles.
But when melamine is present the absorption of light is reduced as
nanoparticle formation decreases.

"Currently, milk samples have to be brought to a central testing
facility, so very less testing gets done. But all this can change with
our handheld device," Dr. Daniel says. As little as 1 ml of milk is
sufficient for carrying out melamine detection.

The team is in the process of commercialising the product through a
start-up that is incubated at the Society for Innovation & Development
Centre at IISc.


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