March 18, 2014
Color-Coded Tags Tell When Food Is Spoiled In Unopened Containers
[ Watch the Video: Knowing Whether Food Has Spoiled ]
Lawrence LeBlond for redOrbit.com - Your Universe OnlineDetermining if the food you’re about to consume is spoiled or not is often times an unpleasant experience. It is not always easy to tell if something is bad by the way it smells, often leaving taste the only other option. More often than not, people will just toss food out instead of taking a risk. And many likely toss food out as soon as the expiration date has been reached without even opening the package.
But now, thanks to a Chinese research team, there is a new way to tell if that food you are concerned about is still consumable or past it’s prime. And what’s more, the new method can determine a food’s freshness without ever opening the package and without regard to the expiration date, suggesting that many foods may have been discarded prematurely in the past or needed to hit the trash bin sooner than expected.
This new method involves using a color-coded smart tag that can be placed on the outer packaging of products such as milk cartons, tin cans and plastic bags, and can determine if the contents therein are still in good standing. The researchers said the tags can even be used to tell if medications and other perishable products are still active or fresh.
The study’s lead author, Chao Zhang, PhD, of Peking University in Beijing, China, presented the findings today at the 247th National Meeting & Exposition of the American Chemical Society (ACS) at the Dallas Convention Center in Dallas, Texas.
"This tag, which has a gel-like consistency, is really inexpensive and safe, and can be widely programmed to mimic almost all ambient-temperature deterioration processes in foods," said Zhang, adding that these tags could potentially solve the problem of knowing how fresh packaged, perishable foods remain over time.
Zhang noted the real advantage of these tags would be for when manufacturers, grocery-store owners and consumers do not know if the food has been exposed to higher temperatures, which can speed up spoilage in many products – “the tag still gives a reliable indication of the quality of the product.”
The tags, which are about the size of a kernel of corn, appear in various color codes on packaging.
“In our configuration, red, or reddish orange, would mean fresh,” explained Zhang. "Over time, the tag changes its color to orange, yellow and later green, which indicates the food is spoiled."
The colors signify a range between 100 percent fresh and 100 percent spoiled. An example would be for a food product that is labeled to remain fresh for 14 days under refrigeration, but the tag shows up orange, which means the product is only half as fresh as it should be. In this case, the consumer would know the food is good for about another seven days in the fridge, Zhang explained.
To test the tags, the research team used E. coli in milk as a reference model.
"We successfully synchronized, at multiple temperatures, the chemical evolution process in the smart tag with microbial growth processes in the milk," said Zhang, noting that the tags can be customized for a variety of foods and beverages.
The tags contain tiny metallic nanorods that can have a variety of colors: red, orange, yellow, green, blue and violet.
"The gold nanorods we used are inherently red, which dictates the initial tag color," Zhang said. "Silver chloride and vitamin C are also in the tags, reacting slowly and controllably. Over time, the metallic silver gradually deposits on each gold nanorod, forming a silver shell layer. That changes the particle's chemical composition and shape, so the tag color now would be different. Therefore, as the silver layer thickens over time, the tag color evolves from the initial red to orange, yellow, and green, and even blue and violet."
Although these tags use gold and silver nanorods, they are very inexpensive. Zhang said that all the chemicals in the tiny tag cost much less than one cent -- $0.002.
"In addition, all of the reagents in the tags are nontoxic, and some of them (such as vitamin C, acetic acid, lactic acid and agar) are even edible," he explained.
Zhang, noting that the technique is patented in China and initial results published in the journal ACS Nano, said that the next step is to contact manufacturers and explain how the tag would be useful for them and their customers.