The packaging of fruit and vegetables also produces massive amounts of plastic waste. With a newly developed process for a plastic-free coating, the problem of keeping food fresh could be solved in the future. It already works with avocados.
An eco-friendly, plastic-free casing can keep fruits and vegetables, such as avocados, fresher for longer. To do this, fine threads of pullulan, which consists of sugar molecules and is edible, are applied to the food. The pullulan is enriched with natural substances that are effective against microorganisms, as a group led by Philip Demokritou and Kevin Kit Parker from Harvard University in the US writes in the journal “Nature Food”.
In trials, avocados wrapped in this way lasted significantly longer than unwrapped fruit. After seven days of storage at 22 degrees Celsius, 90 percent of the untreated fruit showed visibly rotten spots, with the coated specimens it was only half. According to the researchers, pullulan can be easily washed off and is broken down in the earth in three days.
To date, it has mainly been packaging made from petroleum-based plastics that is used to keep fruit and vegetables fresh. However, because such plastic is not degraded in nature, a major environmental problem has now arisen. “We knew we had to get rid of the petroleum-based food packaging that’s out there and replace it with something more sustainable, biodegradable and non-toxic,” Demokritou is quoted as saying in a statement from Rutgers University in New Brunswick, New Jersey, where Demokritou is also active.
The researchers added thyme oil, citric acid and nisin, a natural antibiotic produced by lactic acid bacteria, to the sugar polymer pullulan dissolved in water, which is also used for drug capsules, for example. All three substances are effective against microorganisms such as the bacteria Escherichia coli and Listeria innocua and the mold Aspergillus fumigatus. These occur naturally on the skins of fruit and vegetables and are largely responsible for fresh food rotting. By inhibiting the growth of microorganisms, coated foods remain edible for longer.
To apply it to the fruit, the scientists used a special method in which a hair dryer-like device heats the pullulan dissolved in water with the antimicrobial substances. Most of the water evaporates and the pullulan is expelled from the apparatus in tiny threads, wrapping itself around the fruit. This currently takes two to four minutes. The researchers state the costs as a few cents per fruit. But improvements are still possible. “I’m not against plastic, but I’m against petroleum-based plastics, which we keep throwing away because only a tiny fraction of them can be recycled,” says Demokritou.