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Scientists 'envisage' carton tag that changes color when milk is spoiled

By Mark Astley+

04-Apr-2014
Last updated the 07-Apr-2014 at 11:09 GMT

Chinese scientists have developed a “smart tag” they say can indicate - by changing from red to green - when the contents of a milk carton are spoiled.

Researchers from Peking University in Beijing have developed a time-temperature indicator (TTIs) using silver and gold nanorods, that can be “generally employed to track, mimic, and indicate the deterioration processes of numerous perishables.”

The tags contain vitamin C, acetic and lactic acids, and agar, which react with the gold and silver nanorods over time to change the color of the tag. This mimics the length of time it typically takes microbes to grow in food, but also takes into account temperature fluctuations that could spoil a product.

When the product is 100% fresh, the tag is red or reddish orange. As the packaged product ages, it changes to orange, yellow and when it is completely off, green.

The Peking University team detailed their research in the study, Time-Temperature Indicator for Perishable Products Based on Kinetically Programmable Ag Overgrowth on Au Nanorods.

In their report, the researchers presented “proof of principle demonstrations” that the tag can be tailored to “track perishables, dynamically mimic deteriorate processes therein, and indicate product quality through sharp-contrast multicolor changes.”

To date, it has so far been tested using E.coli in lysogeny broth, which was used to mimic milk. 

Based on the garnered results, the all-Chinese team are confident their TTI concept can be used commercially.

“The basic design is simple,” said the study, published in the journal ACS Nano.

“As a typical class of perishables, dairy products spoil easily owing to bacterial growth, and the growth rate of bacteria is strongly dependent on temperature.”

“We therefore can envisage the design of a smart tracking tag based on the chemical reaction for dairy products,” it said.

“The tag is attached to the product package to ensure that it undergoes the same temperature history. The tag can then, in principle, serve as an indicator for the product quality because now the magnitude of microbial growth is correlated to and indicated by how much the chemical system has evolved.”

The report added that the “flexible programmability” of the tag means that “general applicability to each single packed item of a plethora of perishable products.”

“We believe that it holds the promise to be further developed into a unified and standardized protocol generally applicable to a vast number of perishable products and has great potential to revolutionize the current food/beverage/pharmaceutical/cosmetics industries,” said the report.

The study was presented at the National Meeting and Exposition of the American Chemical Society (ACS) in Dallas last month. 

Source: American Chemistry Society (ACS) Nano 10.1021/nn401266u

Title: Time-Temperature Indicator for Perishable Products Based on Kinetically Programmable Ag Overgrowth on Au Nanorods.
Authors: Chao Zhang, An-Xiang Yin, Ruibin Jiang, Jie Rong, Lu Dong, Tian Zhao, Ling-Dong Sun, Jianfang Wang, Xing Chen, and Chun-Hua Yan.

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