Microbe-Fighting Plastic Wrap Keeps Fruits Fresher for a Week

In the case of rotting food, microbes are not our friends. Now, scientists have developed a new food wrap coated with tiny clay tubes packed with an antibacterial essential oil that can extend the shelf life of perishable food, so we can waste less and eat more.

"While companies can already make many films that prevent fruit and vegetables from drying out, incorporating additional properties in the same film is a challenge," researcher Hayriye Ünal, from Sabanci University in Turkey, said in a press release from the American Chemical Society.

It looks like Ünal's team has bested that challenge, though. They found a way to incorporate antibacterial agents into their innovative food wrap and published their results in the online version of Food Bioprocess Technology in January 2017. Their newest research, presented August 21 at the 254th National Meeting & Exposition of the American Chemical Society, described a novel way to coat their food wrap and the results of bacterial testing of chicken wrapped in the packaging.

The Food Waste Epidemic

Researchers estimate that we waste 40% of all food produced in the US. That number includes both retail and consumer sources, like restaurants, stores, and personal waste. The waste amounted to about 133 billion pounds and $161 billion worth of food in 2010.

Finding that green furry object in the refrigerator that is no longer recognizable as a vegetable means we've wasted money and food. Besides bacteria and mold, air can also help food turn the corner from fresh to spoiled. We wrap, and we seal, and we hope the food is still fresh when we want to use it.

Food spoils because of air, microbes, moisture, light, temperature, and enzymes. All these factors interact to cause a perfect food-spoiling storm. Microbes — landing on food from humans, garden, production sources, or the air itself — like fungus and bacteria uses our food for their nutrition and growth. As they infest the food, the microbial by-products smell bad and cause rot. Enzymes naturally present in food can speed up chemical reactions between oxygen and food, causing spoilage and increasing oxidation, the browning we associate with aging and rotting food. Refrigerated food often lasts longer because the cold slows microbial growth and enzyme activity. Fungus, the colorful furry growth that can grow on most foods, loves warmth, dark, and moisture.

The Environmental Protection Agency suggests that we can reduce food waste at home by planning meals in advance, so only food planned to be used is purchased, storing to increase life of foods, freezing foods that are not immediately needed, and planning to use leftovers. Of those tips, finding good storage methods that prevent spoilage is the one with the least predictable outcome.

We can put cut ends of asparagus in water so they won't wilt, wash greens and put them in breathable bags, wrestle with plastic wrap, and even wash with or store some fruits and vegetables in vinegar to discourage bacterial growth. The more time required to try to prevent spoilage, the more apt we are to skip it altogether, throw it in the refrigerator, and hope for the best.

The food wrap developed by Ünal and his team is a great way to prevent many foods from rotting by combining a product that protects food from air and moisture with an agent to prevent microbial growth.

A Better Food Wrap

One problem the researchers had to overcome in developing their food wrap was the ethylene gas naturally released by fruits and vegetables. Normally, it enhances the ripening process, but when it's trapped underneath food wrapping film, it can cause food rot, instead.

In their paper from Janurary, the team used polyethylene — the main component in plastic food wrap — as a base for their wrap. To suck up the ethylene gas and to provide a gas barrier over the food, they incorporated tiny hollow clay cylindrical tubes, called "halloysite" nanotubes, into the wrap. The nanotubes keep oxygen from entering the film, prevent moisture from escaping, and keep ethylene from building up by absorbing it. The team tested their wrap on tomatoes, bananas, and strawberries in the film and waited different times to compare freshness with food wrapped in polyethylene.

Microbe-Fighting Plastic Wrap Keeps Fruits Fresher for a Week — Halloysite nanotubes. *Image via VA Vinokurov et al., Sci. and Tech. of Ad. Mat., 2017*

The researchers wrapped sets of five bananas, five tomatoes, and five strawberries in the nanocomposite, along with control sets wrapped in normal plastic wrap. Another set of bananas were left unwrapped. All bananas were photographed daily to document and compare changes in their appearance until the bananas in the control set looked overripe. The tomatoes were observed daily until the control set seemed to lose their firmness, which was tested with a probe that measured it. Strawberries were weighed daily as a measure of degradation.

After 10 days, tomatoes wrapped with the new film were fresher than the ones wrapped in plastic wrap. Bananas wrapped in the new film were firmer and yellower after six days compared to the control fruit.

In their newest research, the researchers added an extra preventative measure against spoilage. They added a natural antibacterial essential oil from thyme and oregano called carvacrol to the nanotubes. They coated the inner surface of the plastic film with layers of carvacrol-loaded nanotubes. Layering the nanotubes eliminated the need to use heat to coat the polyethylene film, which would have reduced the activity of the antibacterial oils.

They tested the new antibacterial permeated clay nanotube wrap on chicken breast. Bacteria on the surface of the chicken was measured to see how well the carvacrol worked to control microbial growth. Chicken covered with the new film and refrigerated for 24 hours showed significantly less bacterial growth than chicken in plain polyethylene.

The study authors say their nanocomposite films can greatly contribute to food safety while improving the quality and shelf life of fresh food products. The product needs to be tested for safety and to make sure it's non-toxic before it reaches our store shelves. Until then, we are back to wrestling plastic wrap and hoping our food won't be rotten when we need it.