What is Ethylene and how does it help Fruit & Vegetable development?

Mitch Denton   |   February 10, 2020
Ethylene Title Image

We’ve all at one point or another heard the idiom “One bad apple, ruins the bunch”. This particular saying is directly related to the effect that one overripe apple can have on the accompanying apples, as it continues to emit ethylene into the surrounding atmosphere, accelerating the ripening and senescence of the entire bunch in the process.

So, what exactly is Ethylene and how is it being utilised to maximise the outgoings of fruits & vegetables across global supply chains?

What is Ethylene?

Ethylene is the most commercially produced organic compound in the world and is used in many industrial applications.

Without scent and invisible to the eye, Ethylene (C2H4) is a small hydrocarbon gas and a natural plant hormone produced to organically aid in the ripening and ageing process of fresh produce. Fruits such as apples and pears emit a greater amount of ethylene gas, which as a result accelerates their ripening process. Other fruits, like cherries or blueberries, produce very little ethylene gas, therefore, not greatly impacting upon the ripening process.

Due to ethylene being so important for the ripening of some fruits and vegetables, it is sometimes used by commercial agribusinesses to speed up the ripening process of crops.

Ethylene is particularly associated with ripening of fruit such as bananas, mangoes and tomatoes. These fruits fall under the category known as ‘climacteric’ due to the large amounts of ethylene, and marked increase in respiration, that occurs during ripening. Ripening of climacteric fruit can be triggered by treating with ethylene during storage. Fruits that follow the pattern of steadily declining respiration rates through ripening are classified as ‘non-climacteric’.

What’s Ethylene’s effect on Fruits and Vegetables?

While ethylene is invaluable due to its ability to initiate the ripening process in several fruits and vegetables, it can also be very harmful to many fruits, vegetables, flowers, and plants by accelerating the ageing process and decreasing the product quality and shelf life. The degree of damage depends upon the concentration of ethylene, length of exposure time, and product temperature.

Minimising fruit exposure to external sources of ethylene and treatments in order to manage the internal ethylene concentration is the key to commercial optimisation of the storage life and edible quality of many fruits. Understanding the fundamental relationship between ethylene and fresh produce respiration rates during fruit ripening is necessary in order to manage the harvesting, storage and distribution processes. 

When fresh produce is exposed to the chemical, it will respond to ethylene when it latches on to their ethylene receptors and stimulates the maturing stages of the produce. The chemical reaction within fruits and vegetables then brings forth the development of flavours, vitamins, firmness, aroma, texture, and colour in the produce. However, too much ethylene exposure before shipments of fresh produce meet their required timelines and destinations, can lead to overripeness, a decline in product quality and an increase in Volatile Organic Compounds (VOCs) throughout the stock.

Different vegetables vary in their sensitivity to ethylene, yet all the effects of ethylene on vegetables are negative. Ethylene exposure increases breakdown of chlorophyll (causing yellowing), reduces storage life, increases sensitivity to chilling injury and can help spread decay. A concentration of 0.1ml/L (0.0001%) can be enough to cause undesirable changes in products such as leafy vegetables.

Fruits and vegetables play a vital role in human nutrition. One of the limiting factors that influence their economic value is the relatively short ripening period and reduced postharvest life. Overripe fruits and vegetables lead to excessive softening which results in spoilage and damage during the shipping and handling aspects of the cold chain system. Slowing the process of ripening and quality deterioration extends the storage and shelf life of fresh fruits and vegetables. Monitoring the shelf life of fresh produce not only helps the grower to save on postharvest losses but consumers are also benefited in terms of retained fresh­ness for longer periods and thus results in value addition to the fruits and vegetables.

One of the biggest contributors to mass amounts of waste within the fresh produce sector is directly linked to cases of overexposure to ethylene during the ripening and storage process. On a global scale, the main contributor to food waste is fruits and vegetables with an astounding 45-50% of all harvested fresh produce being lost or wasted within the food supply chain. This is roughly 1.3 billion tonnes of food, which equates to $680 Billion US Dollars of wasted fresh produce each year.

The effect of ethylene on vegetables can be avoided or reduced by:

  • Low temperature storage. Below 5°C the effects of ethylene are greatly reduced.
  • Keeping the storage area ventilated to avoid accumulation of ethylene inside.
  • Removing ethylene from storage rooms by reacting it with potassium permanganate (KMnO3).
  • Oxidising ethylene by reacting it with ozone (O3). 
  • Storage in an atmosphere with high CO2.
  • Air scrubber systems for storage cleansing.

What Ethylene countermeasures are in place across the supply chain?

Current industry solutions involve invasive handling and inaccurate practices that are more data reactive than proactive when it comes to the conservation of produce across the cold chain journey. One of the most effective ways for cold chain operators to counteract ethylene levels around fresh produce is for the introduction of 1-MCP (1-methylenecyclopropene) into the atmosphere.

With a structural build of ions and molecules, 1-MCP treatments suppress Ethylene production in an effort to prevent the ripening of fruits. The mechanism of action for 1-MCP involves tightly binding to the ethylene receptors in fresh produce, acting as an inhibitor for ethylene’s stimulating qualities.

AVG (Aminoethoxyvinylglycine) and AOA (aminooxyacetic acid) are compounds that inhibit the synthesis of ethylene within the fruit.  Pre-harvest applications of these chemicals enable fruit to reach greater maturity and colour development on the tree prior to harvest.  They do this by inhibiting the ACC (1-aminocyclopropane-1-carboxylic acid) synthase enzyme. ACC synthase is thought to be the rate-limiting step in fruit for the production of internal ethylene - ACC being the precursor molecule to ethylene in the ethylene biosynthesis pathway.

Ozone generators when used in coolrooms are also alleged to react with and ‘scrub’ ethylene in the storage atmosphere. While ozone will destroy ethylene on contact, its use in coolrooms carries other risks to worker safety with 0.1 µL/L ozone being the limit of exposure.

Ethylene action has also been noted to slow at lower temperatures, in fact, at their minimum temperature levels, fruit is basically inactive and does not respond well to externally supplied ethylene.

While these methods have been proven to be effective countermeasures for the effects of ethylene on fresh produce, the biggest challenge supply chains have faced when using 1-MCP is knowing when to deploy the chemical and at what quantity in order to get the best results, or for how long they should keep produce in heavily refrigerated conditions. An industry that is strongly dependent upon guess work and loose monitoring methods is doomed to have large wastage & loss numbers.

What are the current methods for monitoring Ethylene levels?

Monitoring and controlling ripeness is becoming a very important issue in the fruit industry since the state of ripeness during harvest, storage and market distribution determines the quality of the final product measured in terms of customer satisfaction. Many methods to moni­tor the ripeness of fruits and vegetables have already been proposed. The main disadvantage of the majority of these technologies & techniques is that they are not practical for cultivars or storage stations. Moreover, most of them require the destruction of the samples used for analysis. This is why, nowadays, optimal harvest dates and predictions of storage life are mainly based on previous experiences with specific fruits and vegetables. Leaving these criti­cal decisions to subjective interpretation implies that large quantities of fruit are harvested too soon or too late and reach consumer markets in poor condition.

How RipeTime helps optimise Ethylene levels across supply chains

RipeTime has developed a form of amplification technology, which allows for users to accurately measure and forecast optimal delivery times, maximise outgoings and minimise food loss within supply chains. RipeTime’s amplification technology allows for atmospheric reads in the form of parts per billion (PPB), this measurement is often used to describe concentrations of contaminants found within an atmosphere in its most precise and finite form (currently an unmatched industry standard).

RipeTime’s Environmental Sensor is a wall mounted device that sits within storage facilities as it continuously captures ethylene samples, along with other chemical compounds from within the controlled atmosphere of a cold chain operation, providing the most accurate ripeness readings in the industry. This data provides conditioning & health reports to help cool store operators forecast their processes and supplies for a more optimised output.

If you’d like to know more about how RipeTime is helping cold chain stakeholders effectively monitor their Ethylene usage, you can read more at ripetime.co or contact our friendly staff today.

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