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Ethylene Management Breakthroughs
by Greg Pavett
The most recent report from the Food and Agriculture Organization of the United Nations estimates that a staggering 1.3 billion tons of food is wasted globally every year, resulting in direct, annual economic losses of $750 billion U.S. dollars. A projected 40 percent of food goes uneaten just in the U.S., according to the Natural Resources Defense Council.
The significance of these statistics takes on still more meaning when factoring in the environmental and social impacts of global food wastage. Some 3.3 billion tons of greenhouse gases are pumped into the planet’s atmosphere just to produce food that is eventually discarded into landfills, which, incidentally, further emit damaging methane gas. Amidst all of this waste, 870 million world citizens go hungry every day.
What’s responsible? The causes of food waste of course are varied, complex, and prevalent throughout the entire supply chain—overproduction, inadequate storage or packaging, inefficient stock management, consumer confusion about dating labels, and oversized portions to name some.
But there is also one simple culprit hidden within nature that’s responsible for much of the wasted food, yet often overlooked: Ethylene. Ethylene is the naturally occurring gas emitted by many kinds of fruit which acts as a ripening hormone.
For more than 80 years, it’s been known that ethylene is emitted by various kinds of produce when under stress or injured, such as when they are picked, peeled, pressed into packing containers, or bruised in consumers’ grocery bags. This begins occurring immediately upon being harvested, but accelerates as the fruit ages.
Ethylene can be thought of as a distress signal, sent to other fruit and vegetables to warn of imminent danger, and to communicate the need to ripen as fast as possible. The gas is responsible for changes in taste, texture, color, and other ripening processes. Chlorophyll is degraded, new pigments are produced, and the activity of many maturation-related enzymes intensifies. Starches, acids, and lipids convert to sugars while fruit pectins degrade. Consequently, produce items respire, abscise, soften, and grow mold to the point of spoiling—shortening the shelf life.
Slowing Down the Clock
Fortunately, there are certain best practices for managing ethylene exposure that can be used across the supply chain in order to slow the ripening process and reduce instances of premature rot, mold, and waste. Over the past 10 years, society has wised up to the significant impact ethylene can have on fresh produce. As a result, new processes, innovations, and technologies for produce supply chain players have become available that are far more effective at controlling ethylene than ever before.
The gas is responsible for changes in taste, texture, color, and other ripening processes.
For maximum shelf life and quality, certain climacteric fruits and vegetables (produce that rapidly ripen to a climax in response to ethylene) such as apples, mangos, tomatoes, peaches, and bananas should not be stored or shipped with non-climacteric produce like cherries, lemons, oranges, broccoli, or lettuce. In many ways, climacteric and non-climacteric fruits “speak” to one another, with ethylene being the common language. So for example, despite producing comparatively smaller amounts of ethylene on their own, strawberries exposed to more of the gas will take it as a sign to begin ripening more rapidly. Ethylene has a cumulative effect, so continuous exposure to even small amounts of ethylene can result in significantly shortened product lifespan. And overripe or rotting produce continue to emit ethylene, so should be removed promptly.
While most who work inside the production and distribution of fruits and vegetables are accustomed to this segregation of climacteric and non-climacteric produce, this comes as a surprise to most people. After all, in retail settings the majority of produce is stored in a single space and then displayed in close proximity as a convenience and enticement to shoppers.
It’s also interesting to note that ethylene gas is a byproduct of combustion engines, so using electric forklifts rather than gas-powered ones can help reduce the presence of the gas. Trucks and gas forklifts should not be left idling near fresh produce, and proper ventilation of storage areas is another important factor.
Turning to Materials Science Solutions
Beyond these process lessons and improvements, there have been several advances made in the field of ethylene management over the years.
Modified Atmosphere Packaging (MAP) is a technique in which fruits and vegetables are allowed to respire in a more enclosed environment, to slow their respiration rate. Membranes are used to allow some carbon dioxide to escape and some oxygen to enter. But for many ethylene-producing foods, MAP becomes a more tricky issue, as ethylene buildup can occur. Allowing the growth hormone to stay while lowering the oxygen is like breaking and accelerating a car at the same time. This generates confusion in the fruit’s metabolic processes. Some refer to this as “fruit freak-out” as the food exhibits dramatic respiration levels and rapid degradation upon being removed from its controlled atmosphere and forced to acclimate to new environments.
Ethylene inhibitor 1-methylcyclopropene (1-MCP) is a gaseous ethylene inhibitor used in enclosed commercial environments, such as inside truck trailers, coolers. and storage facilities. 1-MCP is a chemical application that binds to the ethylene receptors on fruit surfaces. The danger here is that in many cases 1-MCP can permanently stop fruits and vegetables from ripening. That may be good for crunchy apples, but it’s less desirable in the instance of hard avocados, for example. Blocking ethylene receptor sites also involves chemically spraying the produce, which can be unpopular with consumers. And it doesn’t stop ethylene peel damage, like scald on pear skin, nor does it halt ethylene’s involvement in the pathways of rots and molds in wounded fruit.
Ethylene-scrubbing filters, usually containing the inorganic (but toxic) compound Potassium permanganate, may also be used within cold chain storage areas as an oxidizing agent to convert ethylene into carbon dioxide and water. When using these filters, it’s crucial for the oxidizing process to be fully complete as incomplete oxidation may potentially result in undesirable byproducts. And while there are various scrubber solutions on the market—some use Potassium permanganate pellets, others have ozone-based systems, and still others offer photocatalytic oxidation where UV light is used as a catalyst to break down ethylene—it’s important to keep in mind that most all cannot be used in-store or at home, where more than 60 percent of waste occurs.
Recent materials science developments also provide new and effective deterrents against ethylene-induced ripening.
For example, It’sFresh! has developed an ethylene adsorption sheet capable of extending natural shelf life and the quality of fresh produce by up to three extra days in-store and at home. The paper-thin sheet, which can be inserted into fruit and vegetables crates and containers, includes a patented mixture of minerals and clay designed to capture ethylene and minimize ripening and other damaging effects. The sheet acts as a “scavenger”-type method that seeks out, adsorbs, and traps nearby ethylene molecules as they are released at any stage of the supply chain from immediately upon postharvest through to the consumer’s home. The technology is effective in all temperatures and atmospheres, and can be used in harmony with MAP.
The produce and retail industry’s efforts to extend shelf life will obviously have great commercial benefits. Shelf-life extension increases store availability of fresh produce, offering retailers more freedom to sell their stock, thereby reducing loss of inventory and increasing sales.
Ecological sustainability is another added benefit of using the latest materials science solutions to delay the ripening process. After all, less waste means greater efficiencies and an overall reduction of agricultural inputs, such as water usage and transport emissions, over time.
A Team Effort
Certainly, the problem of food waste will not be solved by any single technology, law or campaign. This global issue will require a multi-faceted, global solution with contributions from scientists, regulators, academics, businesses, and consumers.
However, proper ethylene management in the produce supply chain is one crucial step toward creating a more sustainable, efficient, high-quality food supply. In an era of rapid worldwide population growth alongside persistent hunger and waste, the improving technologies for combating this ripening agent are an encouraging and hopeful sign.
Pavett is president of It’sFresh!, Inc., part of the Food Freshness Technology group. Reach him at email@example.com.