Tag Archives: fruit

Coat fruit with silk to keep it fresh

A May 6, 2016 news item on ScienceDaily describes a way to keep fruit fresh without refrigeration,

Half of the world’s fruit and vegetable crops are lost during the food supply chain, due mostly to premature deterioration of these perishable foods, according to the Food and Agriculture Organization (FAO) of the United Nations.

Tufts University biomedical engineers have demonstrated that fruits can stay fresh for more than a week without refrigeration if they are coated in an odorless, biocompatible silk solution so thin as to be virtually invisible. The approach is a promising alternative for preservation of delicate foods using a naturally derived material and a water-based manufacturing process.

A May 6, 2016 Tufts University news release (also on EurekAlert), which originated the news item, describes the work,

Silk’s unique crystalline structure makes it one of nature’s toughest materials. Fibroin, an insoluble protein found in silk, has a remarkable ability to stabilize and protect other materials while being fully biocompatible and biodegradable.

For the study, researchers dipped freshly picked strawberries in a solution of 1 percent silk fibroin protein; the coating process was repeated up to four times.  The silk fibroin-coated fruits were then treated for varying amounts of time with water vapor under vacuum (water annealed) to create varying percentages of crystalline beta-sheets in the coating. The longer the exposure, the higher the percentage of beta-sheets and the more robust the fibroin coating. The coating was 27 to 35 microns thick.

The strawberries were then stored at room temperature. Uncoated berries were compared over time with berries dipped in varying numbers of coats of silk that had been annealed for different periods of time. At seven days, the berries coated with the higher beta-sheet silk were still juicy and firm while the uncoated berries were dehydrated and discolored.

Tests showed that the silk coating prolonged the freshness of the fruits by slowing fruit respiration, extending fruit firmness and preventing decay.

“The beta-sheet content of the edible silk fibroin coatings made the strawberries less permeable to carbon dioxide and oxygen. We saw a statistically significant delay in the decay of the fruit,” said senior and corresponding study author Fiorenzo G. Omenetto, Ph.D. Omenetto is the Frank C. Doble Professor in the Department of Biomedical Engineering and also has appointments in the Department of Electrical Engineering and in the Department of Physics in the School of Arts and Sciences.

Similar experiments were performed on bananas, which, unlike strawberries, are able to ripen after they are harvested. The silk coating decreased the bananas’ ripening rate compared with uncoated controls and added firmness to the fruit by preventing softening of the peel.

The thin, odorless silk coating did not affect fruit texture.  Taste was not studied.

“Various therapeutic agents could be easily added to the water-based silk solution used for the coatings, so we could potentially both preserve and add therapeutic function to consumable goods without the need for complex chemistries,” said the study’s first author, Benedetto Marelli, Ph.D., formerly a post-doctoral associate in the Omenetto laboratory and now at MIT.

Here’s a link to and a citation for the paper,

Silk Fibroin as Edible Coating for Perishable Food Preservation by B. Marelli, M. A. Brenckle, D. L. Kaplan & F. G. Omenetto. Scientific Reports 6, Article number: 25263 (2016) doi:10.1038/srep25263 Published online: 06 May 2016

This is an open access paper.

Soldiers sniff overripe fruit

Technically speaking the soldiers are not sniffing the fruit, it’s the sensing technology developed at the Massachusetts Institute of Technology’s Institute for Soldier Nanotechnologies which is doing the ‘sniffing’. From the April 30, 2012 news item on Nanowerk (I have removed some links),

Every year, U.S. supermarkets lose roughly 10 percent of their fruits and vegetables to spoilage, according to the Department of Agriculture. To help combat those losses, MIT chemistry professor Timothy Swager and his students have built a new sensor that could help grocers and food distributors better monitor their produce.

The new sensors, described in the journal Angewandte Chemie (“Selective Detection of Ethylene Gas Using Carbon Nanotube-based Devices: Utility in Determination of Fruit Ripeness”), can detect tiny amounts of ethylene, a gas that promotes ripening in plants. Swager envisions the inexpensive sensors attached to cardboard boxes of produce and scanned with a handheld device that would reveal the contents’ ripeness.

Detecting gases to monitor the food supply is a new area of interest for Swager, whose previous research has focused on sensors to detect explosives or chemical and biological warfare agents.

Here’s how the technology works (from the April 30, 2012 news release by Anne Trafton for MIT News),

Funded by the U.S. Army Office of Research through MIT’s Institute for Soldier Nanotechnologies, the MIT team built a sensor consisting of an array of tens of thousands of carbon nanotubes: sheets of carbon atoms rolled into cylinders that act as “superhighways” for electron flow.

To modify the tubes to detect ethylene gas, the researchers added copper atoms, which serve as “speed bumps” to slow the flowing electrons. “Anytime you put something on these nanotubes, you’re making speed bumps, because you’re taking this perfect, pristine system and you’re putting something on it,” Swager says.

Copper atoms slow the electrons a little bit, but when ethylene is present, it binds to the copper atoms and slows the electrons even more. By measuring how much the electrons slow down — a property also known as resistance — the researchers can determine how much ethylene is present.

To make the device even more sensitive, the researchers added tiny beads of polystyrene, which absorbs ethylene and concentrates it near the carbon nanotubes. With their latest version, the researchers can detect concentrations of ethylene as low as 0.5 parts per million. The concentration required for fruit ripening is usually between 0.1 and one part per million.

The researchers tested their sensors on several types of fruit — banana, avocado, apple, pear and orange — and were able to accurately measure their ripeness by detecting how much ethylene the fruits secreted.

It looks like the technology will be commercialized in the not too distant future (from the Trafton news release) here’s why,

John Saffell, the technical director at Alphasense, a company that develops sensors, describes the MIT team’s approach as rigorous and focused. “This sensor, if designed and implemented correctly, could significantly reduce the level of fruit spoilage during shipping,” he says.

“At any given time, there are thousands of cargo containers on the seas, transporting fruit and hoping that they arrive at their destination with the correct degree of ripeness,” adds Saffell, who was not involved in this research. “Expensive analytical systems can monitor ethylene generation, but in the cost-sensitive shipping business, they are not economically viable for most of shipped fruit.”

Swager has filed for a patent on the technology and hopes to start a company to commercialize the sensors. In future work, he plans to add a radio-frequency identification (RFID) chip to the sensor so it can communicate wirelessly with a handheld device that would display ethylene levels. The system would be extremely cheap — about 25 cents for the carbon nanotube sensor plus another 75 cents for the RFID chip, Swager estimates.

“This could be done with absolutely dirt-cheap electronics, with almost no power,” he says.

I should mention that a couple of students were part of the MIT research team with Birgit Esser being the lead author and Jan Schnorr also contributing to the paper in Angewandte Chemie.