Consider the rotten strawberry. Sitting there in your fridge, it suffers a cascading trifecta of maladies: For one, it dehydrates. Two, oxygen seeps in. And three, with the berry thus weakened, mold invades. Eventually, the strawberry turns to goop, a messy reminder of our own mortality.
Rotting produce is an inevitability—I for one wouldn’t trust fruit that lasts forever—but that doesn’t mean we have to give in to the forces of decay so quickly. To that end, a company called Apeel says it has formulated a coating that doubles the ripeness window of avocados, which it deployed in Costco this week (citrus and asparagus suppliers have also been using Apeel’s coatings). How? By supercharging the defenses that evolution crafted all on its own.
When plants made the jump from water to land hundreds of millions of years ago, they found themselves to be less, well, wet. Earth’s atmosphere has a habit of desiccating things, after all, so plants evolved something called cutin, a waxy barrier against the elements. It's made of fatty acids that link together to form a seal around the plant, helping keep moisture in.
The cutin was such a grand strategy that today you’ll find it encapsulating edibles across the plant kingdom, from strawberries to limes to avocados. Not that it’s exactly the same solution across the board: A lime can last longer than a strawberry not so much because of the thickness of its skin, but because of the variation of cutin it employs. “It's the same molecular building blocks that are being used in both situations,” says James Rogers, CEO of Apeel. “It's just a difference in the arrangement of those molecules on the surface.” Call it synergy: A molecule ain’t nothin’ without its friends. The denser the arrangement, the longer the fruit can resist rot.
Apeel’s challenge was first identifying what components of the cutin are water soluble, because they somehow had to apply the stuff to fruits. What they landed on was lipids, which are amphiphilic, meaning they’re both water-loving and oil-loving. “Part of it really likes water, and part of it really doesn't like water, which means you can get some limited solubility of that material in water,” says Rogers. “Once they dry, then they have the ability to block water.”
When dissolved in water, the lipid molecules are outnumbered by water molecules. But once that water starts evaporating, those lipid molecules start finding one another, joining into a structure.
As they do so, they build a kind of film that locks in moisture and repels oxygen. So Apeel has developed a substance, which they either spray on fruit or dip the fruit in, that exploits this relationship between lipid molecules you find naturally in fruits. “When we deposit them on a piece of produce and it dries, the result is that we form this special structure, this special barrier, which mimics that structure which is employed by longer shelf life produce,” says Rogers. Apeel isn’t inventing a newfangled substance. It's using the plant kingdom’s own evolved defense against our trifecta of maladies. By coating produce with interacting molecules, they create a microclimate within the fruit to keep good actors in and bad actors out.
Good actor number one: water. “If you don't deal with the water loss, forget about dealing with any other problems,” says Rogers. “It's just like us: If you're dehydrated, that's what's going to kill you, it's not running out of food.”
So the coating locks in the moisture and helps keep out air, a bad actor. Oxygen molecules are bouncing all around the atmosphere, working their way into fruit. Oxygen means increased chemical reactions inside the fruit, which doesn’t know it’s now disembodied. “It's not like it goes, ‘Oh, I've been picked. Time for me to do something different,’” Rogers says. “It's still a living, breathing thing.”
The fruit burns through nutrients to perform cellular functions, and as those nutrients deplete, the fruit gets stressed. Then it starts looking for more metabolites to consume—it’s self-cannibalizing.
The rate of this metabolism is a function, in part, of oxygen supply: Reduce the availability of oxygen and you slow down the rate at which the fruit is respiring. “With the oxidation barrier properties, you're slowing down the overall rate of the chemical reactions that are happening inside the produce,” says Rogers, “and so that gets you over the second hurdle.”
Keep the fruit relatively stress free like this for as long as possible and you help it ward off the third hurdle: those damned molds. Fruits fight off nasties with an immune system, recognizing molecular signals of pathogens and producing antimicrobials to fight the infection. So if you can help it resist abiotic stressors like dehydration and oxidation, you’ll help the fruit mount a stronger defense against biotic ones like mold.
“The thing is, mold is lazy,” Rogers says. “It's got almost this infinite time horizon over which it can grow. You can send spores into outer space bring them back down and they'll still germinate. They just wait.” Meaning, you can’t stop mold from eventually conquering a fruit. But with its coating, Apeel can use the plant kingdom’s own evolved defense to bolster produce that happen to have shorter shelf lives.
What makes the coating special is that it addresses the causes of spoilage, not the symptoms. You can coat a fruit in wax all you like, and it may look nice for a while, but you’re not tackling the dehydration and oxidation that comes with rotting, because Apeel picked out those specific water-soluble lipids from fruits, lipids that not only form up their own structure, but lie nicely over the cutin already on the fruit. With wax, you’re just delaying the inevitable.
Which, true, Apeel is doing too. But in addition to extending the lifespan of an avocado by almost a week and doubling the ripeness window from two to four days, the company says it can reduce water loss by 30 percent compared to untreated avocados, and the softening rate by 60 percent. And it claims a fivefold reduction in damage to its treated avocados.
A fancy lab-developed coating, though, isn’t going to revolutionize food production on its own. Because if you screw up the handling of your produce, no amount of coating is going to save you. Roughly handle a crop and you’ll pierce the produce, compromising its natural cutin barrier. “Now that product is very vulnerable to contaminants, or it can just simply dehydrate and you have an ugly damaged area,” says UC Davis postharvest specialist Marita Cantwell. Consumers don’t like ugly damaged areas, by the way. “But more problematic is the decay.”
In addition to careful handling, refrigeration is of paramount importance. “The general idea is to move it into a less extreme, less drying environment—a cooler, fresher environment,” Cantwell says. “That's a key strategy that we apply to products.” And it’s going to stay that way.
Coatings—for instance, substances that act as vehicles for fungicide—haven’t been tremendously common. “That doesn't mean that it's not useful under certain scenarios,” says Cantwell. “But it is not a magic treatment we can apply to products.”
Sure, Apeel can make your avocados last longer. But for produce in general, you still need sound refrigeration and handling techniques. You’ll never beat rot, because death and decay comes for us all, strawberry or otherwise.
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