An article appearing on June 24, 2022, in Scientific American describes the nontoxic food coating as an important contributor in the fight to reduce plastic pollution. Win Cowger, Environmental Scientist at the Moore Institute for Plastic Pollution Research is quoted stating, “we can see globally that food packaging is the most abundant plastic material in the environment.” And although antimicrobial pullulan fibre (APF) cannot be used with every type of fruit and vegetable (I was having trouble visualizing it with grapes), it can certainly cover a wide range of produce.

The researchers note their reason for using APF which is a polymer fibre. They note that “fibrous materials are an attractive alternative to films for producing antimicrobial food packaging systems because their high surface-to-volume ratios allow for more efficient release of antimicrobial agents.” 

The APF is electrospun using a rotary jet spinning system (FRJS) with water as the only solvent. Pullulan fibre occurs naturally. It is an extracellular polysaccharide that is considered safe by the U.S. Food and Drug Administration. And as you can see from the two avocados pictured above, APF provides a uniform protective coating making the avocado on the right look a bit like a Monarch Butterfly chrysalis.

The FRJS applies the APF using a nozzle spray that focuses a stream on the target fruit or vegetable. It can be layered to produce the coating you see in the picture. The researchers added a green dye to the APF to make it visible so that you can tell the difference between coated and uncoated fruits and vegetables. Applying it took 2 to 4 minutes. Rinsing it off took a few seconds.

The antimicrobial agents integrated into the APF solution include tiny amounts of thyme oil, citric acid and nisin, the latter an antibacterial peptide produced by bacteria commonly used in food preservation. None of these antimicrobials altered the characteristics of the APF coating or negatively impacted the preserved avocado.

The researchers looked at changes in colour, firmness and pH levels externally and internally. An avocado changes colour rapidly as it ripens. The changes occur both externally and internally. The APF-coated produce, when compared to uncoated avocados, displayed less colour change and lighter acidity (pH). The researchers believed the small quantity of citric acid in the APF may have had something to do with the changes to pH.

The researchers exposed the test avocados for up to 24 hours to E. coli, Listeria, and Aspergillus fumigatus, the latter a fungal pathogen. They compared the coated with uncoated produce over a week. Results showed that the APF coating reduced spoiled produce from 90 to 50% after a week and retained most of their weight unlike the uncoated produce.

In their conclusions, the researchers stated, “The water-based synthesis process, the edible and washable nature of pullulan, and high-throughput fibre technology combine to present a promising method to package perishable food products to enhance food safety and quality while reducing food waste.” 

And then there are these other major added benefits: reducing the number of food poisoning cases currently at 600 million, the 420,000 deaths, and the $17.6 billion in the U.S. alone annually in spoilage.

Evaptainers use evaporative cooling, something you experience on a hot day when you splash water on your skin and experience a cooling effect as it evaporates.

How do you apply this phenomenon to preserving food?

It is really quite simple. You create a cooler-sized tub (see illustration below) that consists of an inner waterproof storage chamber and surround it with an outer chamber filled with a water-permeable substance. You then create a means to feed water to the outer chamber just enough so that the water can be absorbed and then evaporate. As it evaporates the cooling effect to the interior chamber produces a  temperature drop of about 20 Celsius (36 Fahrenheit) compared to the outside temperature.

The Evaptainers prototype holds 60 liters of food and uses one liter (a little more than a U.S. quart) of water every two days. Recently 25 Evaptainers were tested in Morocco successfully and the company has plans for a second field test involving 500 units this year. Half of these test units will be given away while the remainder will be sold at $25 US each. Commercial launch is yet to be announced.

What’s the immediate problem Evaptainers solves?

The United Nations Food and Agriculture Organization estimates $310 billion worth of food is wasted through spoilage annually in Developing World countries. Spoilage rates can be as high as 45% for fruit and vegetables. Lack of refrigeration is one reason. But poor post-harvest storage infrastructure, and inadequate transportation to bring food to local consumer markets contribute as well. For Developing World nations this problem of spoilage produces a significant drain on their economies and makes many of them food dependent on imports even for crops that they are already growing.

One of the key features that makes Evaptainer such an appropriate solution for its target market is its size. The picture above doesn’t give you a sense of its actual dimensions. But I found a picture online that shows this very well while demonstrating just how much produce a single Evaptainer can hold. It is surprisingly a lot. Everything displayed in the foreground of this picture was brought to market in the single Evaptainer being held up by the man in the picture.

Typical capacity, enough room to hold up to 150 apples and oranges and keeping them fresh for 12 hours, a long enough time to get the produce to market whether strapped to the back of a motorbike, or riding on the back of a mule. Seems Evaptainers are ideal for small farm holders who can daily harvest and deliver produce to local markets without spoilage.