March 27, 2020
March 19, 2020
Post-harvest fruit ripening is a complicated process. It can produce fruits that don’t just look good but are also tasty and nutritional. Ripening rooms are even more misunderstood than the process itself. Cold storage rooms are not the right places for ripening, and, while fruits will ripen on their own, a ripening room can produce the desired taste and appearance as needed, bringing customers back again for more. Understanding ripening rooms and the ripening process can give suppliers an edge over their competition, improving profits.
Ripening rooms are facilities used to ripen fruits. Modern facilities are designed so that specific environmental conditions can be modified and fine-tuned to control the ripening process. It is possible to produce fruits with a specified ripeness and standardised taste to ensure consumer satisfaction.
There are several systems used around the world, depending on climate and fruit types. Transport ripening facilities are also currently available.
However, the principle of ripening rooms remains the same: use ethylene, a natural hormone at warmer temperatures, to ripen fruits without impacting later storage time.
Figure 1. Image credits: Zeroni and Shalom (1973) doi/pdf/10.1111/j.1469-8137.1973.tb02089.x
There are variations in the conditions that influence ripening in different fruits; however, the parameters remain the same. The important conditions that are regulated in ripening rooms are as follows:
Temperature - Ripening occurs faster at higher temperatures and slows down at low temperatures.
Relative humidity - The best level will vary with the species. However, it will lie within a range of 85-95%.
Supply of ethylene gas - It is advisable to keep ethylene levels below 100 ppm for ripening all fruits and at 3-5 ppm for degreening citrus fruits. There are various sources of ethylene, such as generators, gas cylinders, and lecture bottles. Staff should be trained in the use of the equipment to avoid risks.
Carbon dioxide (CO2) - Carbon dioxide, which is produced as a result of respiration, can slow down ripening. Therefore, its levels should be maintained at less than 0.5% by ventilating the room.
Oxygen (O2) - Since fruits need O2 to ripen, it is important to maintain an optimal level during the process. As O2 decreases, CO2 increases, so the right balance of these two gases is necessary (See Figure 1).
Three procedures that are important during ripening are air circulation, ventilation, and monitoring:
Another aspect of ripening that determines the success of the operations is the length of time that fruits are treated. In some cases, the ripening is split into various stages where the conditions provided can be different. Duration depends not only on the species but also its
For example, in the case of avocados ripened with ethylene,
Less mature fruits with DM <26% need 18-200C for 2-3 days.
Mature avocados with DM > 26% need lower temperatures of 16 -200C for only 1-2 days.
There are two types of fruits: climacteric and non-climacteric. Ripening rooms are not suitable for all of them.
Climacteric: These fruits can be harvested when they are mature and ripened later. They ripen due to a spike in ethylene, the ripening hormone. It is, therefore, only this category of fruits that benefit from ripening rooms. Some examples are mango, banana, fig, apricot, apple, pear, plum, sapota, papaya, kiwis, passion fruits, etc. (See Figure 2).
Non-climacteric: Some fruits have to be allowed to ripen on the tree, as the process stops once they are harvested. Moreover, ethylene is not important during the ripening, and these fruits do not respond to its applications. Ripening rooms are, therefore, not useful for non-climacteric fruits. Citrus such as orange, lemon, tangerine, and grapefruit are the only fruits in this category which are held in ripening rooms, but only to degreen their skin colour. Examples of non-climacteric fruits are strawberry, blackberry, raspberry, grapes, pomegranate, watermelon, cherry, litchi, and citrus.
Figure 2. Uniform ripening with ethylene. (Image credits: http://agritech.tnau.ac.in/horticulture/fruit_ripening.pdf)
Fruits can be stored for a short time even after ripening. This storage is outside the ripening rooms, and once again, the time of storage will depend on:
For example, Haas avocados are stored at 5-70C and Shepherd at 6-80C for three to seven days.
There are simple, traditional, and advanced methods of ripening that are used.
There are several innovations which improve different aspects of ripening. All new technology is aimed at providing a better ripening environment. Some important developments are mentioned below.
Ethylene is the only hormone/compound that is recommended for use in ripening. Precise amounts can be supplied through several techniques:
Venting systems control levels of CO2, O2, and ethylene. Since ventilation is a frequent and important practice, several methods are available
These systems control temperatures. Their efficiency depends on the stacking system so that air can move easily within and between pallets.
Ripening room such as those fabricated by Dutch-maker Interko (https://interko.com/) and instruments such as the Felix AccuRipe system and hand-held line of gas analyzers can enable users to monitor and control CO2, O2, and ethylene leves in real time. These systems are programmable for any commodity so users can enter their ripening "recipe" and the system does the heavy lifting for them.
It is important to know that systems and combinations of parameters will differ between temperate and tropical countries. There have been cases reported where people have purchased the wrong ripening room system. Knowledge of modern ripening processes is not widespread, so using an expert to choose the correct system is one easy way to avoid costly mistakes. Besides improving profit margins, modern ripening rooms can save fruit waste due to inefficient handling.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
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