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Food and Nutrition


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4 June 2018

Adulterated Turmeric

Detecting Metanil Yellow

Turmeric is a popular ingredient extensively used in everyday Indian cooking. Because of its potential health benefit, turmeric is in high demand. It is, therefore, frequently adulterated with toxic chemicals. Metanil yellow, a carcinogenic azo dye, is often found in adulterated turmeric.


Turmeric,  Simon A. Eugster, via Wikimedia Commons

Traditional methods to detect metanil yellow adulteration, FTIR and FT-Raman spectroscopy, involve cumbersome and sophisticated processes. The high operational cost involved makes them unsuitable for field applications.

Researchers from Kolkata now report a simple and convenient method to detect metanil yellow in turmeric: Near Infrared Spectroscopy with chemometrics.

“This method uses real time samples. And the samples are easy to make”, says Saumita Kar, Jadhavpur University. The team prepared pure and adulterated turmeric samples and tested the reflectance spectra at the near infrared region using a spectrometer.

“Since the chemical composition of metanil yellow and turmeric are not the same, the spectra of the pure and adulterated turmeric were easily distinguishable”, says Anil Bag, Heritage Institute of Technology, Kolkata.

“Accuracy is better with NIR spectroscopy than with FTIR and FT-Raman instruments”, says Bipan Tudu, Jadhavpur University.

Moreover, Near Infrared Spectroscopy provides chemical-free and fast detection of metanil yellow in turmeric. It is a non-destructive method and does not require sophisticated laboratory equipment and skilled personnel for analysis.

“The lower costs involved make it a technology of choice to detect adulterants in food”, says Rajib Bandyopadhyay, ITMO University, Russia.

One more tool in the armamentarium of future food inspectors.

Food Analytical Methods, 11 (5): 1291-1302

R. Nagarajan

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