The ripening process is the last stage of fruit & vegetable development that brings about various biochemical changes rendering the fresh produce more attractive for consumption and helping in seed release and dispersal. Ethylene is particularly associated with the 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. ‘Non-climacteric’ fruit does not exhibit such a burst in respiration and ethylene production but rather displays a pattern of steadily declining respiration rates throughout ripening.

Significance of Ethylene Production in Climacteric and Non-Climacteric Fruits & Vegetables

Two unrelated ethylene biosynthesis mechanisms have been described. The first method corresponds to low ethylene making in the pre-climacteric era of climacteric fruit and is present all through the growth of non-climacteric fruit. The second method refers to an auto aroused huge ethylene production known as “autocatalytic synthesis” and is particular to climacteric fruit. Therefore, the most important ethylene-connected disparity among climacteric and non-climacteric fruit is the attendance or nonattendance of autocatalytic ethylene manufacture. Ethylene biosynthetic alleyway is now well established.

Ripening occurs when enzymes such as pectinase and amylase break down starches and pectin, which softens and sweetens the fruit. Another factor that is essential in fruit ripening is ethylene, a naturally occurring gas that triggers and promotes the ripening process.

Climacteric fruits — those that can ripen after being picked — produce much more ethylene than non-climacteric, which cannot ripen once removed from the plant. Some fruits, such as apples and bananas, produce even more ethylene gas than other climacteric fruits. If you find yourself impatiently waiting for a climacteric fruit to ripen, you can speed up the process by placing the fruit in a brown paper bag to concentrate the ethylene, or even position it near an apple or banana.

Fruits such as pears and peaches are climacteric, so you don’t have to worry about buying a hard peach because it will ripen given enough time. On the other hand, non-climacteric fruit, such as strawberries, have already done most of their ripening on the plant and will slowly begin to rot after they’re picked. Knowing which fruits will ripen or which may be in danger of rotting can help you determine when to eat them.

Controlling Ethylene Production in Climacteric and Non-Climacteric Fruits & Vegetables

Within the cold chain, there are three main application areas for Ethylene control over both Climacteric and Non-climacteric fresh produce and they are as follows:

  • controlled atmosphere storage

  • fruit/vegetables ripening rooms

  • shipping/transportation of stock

Advantages of Ethylene Control

  • Extends the life cycle of the fruit/ vegetable after plucking

  • Warehouse owners can easily preserve freshness and reduce spoilage of fruits and vegetables

  • They are able to meet increasing demands of non-seasonal fruits and vegetables

Controlled Atmosphere Storage (CA) is a facility built around the concept of controlling the reduction in produce respiration rates and the delay of ethylene-triggered changes, two major factors affecting fresh produce ageing.

This involves the use of increased levels of carbon dioxide (CO2), decreased levels of oxygen (O2) in the atmosphere, low storage temperatures, and lastly, preventing the build-up of internally generated ethylene to threshold levels.

Controlling ethylene gas will maintain the quality and extend the life of horticultural products, allowing them to be stored for a much longer period of time. While refrigeration and humidity control will slow ripening and decay, they will not halt ethylene control.

Ripening Rooms are used in accordance with the general practice of picking Fruits and Vegetables when they are still “green” so that there is ample time between harvesting and distribution. The “green” produce is then allowed to ripen – on occasion naturally depending on timelines, but most are assisted in the ripening process by exposure to elevated levels of ethylene.

Ripening rooms are often in buildings separate from traditional cold storage buildings or controlled atmosphere storage for obvious reasons. Otherwise, they are within storage areas with specific ventilation and exhaust protocols in place.

However, because of temperature and humidity concerns, makeup (dilution) air is typically drawn from the refrigerated area surrounding the ripening room. Even after venting, the ethylene levels may still be high enough to continue the ripening process and cause damage to the product. Thus a “recirculating air scrubber (Air & Gas Purification System)”, with special media should be employed to reduce the ethylene concentration below threshold levels.

Shipping of Produce is often overlooked for what lasting effects it can have on a product, but the distribution aspect of the cold chain often is the most unstable leg of the fresh produce journey, as most forms of distribution vehicles often rely on temperature control or speedy deliveries in order to maintain product quality.

Yet, these transport environments, unable to be airtight, often allow for small amounts of ethylene gas during shipping and storage causing fresh produce to deteriorate faster. This often flies under the radar for industry stakeholders as the fresh produce often arrives at retailers without blemish, yet the damage had unknowingly already been done, with both retailers and consumers purchasing a product that has a smaller shelf-life than what was predicted.