Ripening Behaviors and Harvest Indexes of Watermelons, Cantaloupes and Honeydew Melons
By Bruktawit Tsehay, B.S. Student in Bioengineering and Macarena Farcuh, Ph.D., Assistant Professor and Extension Specialist, University of Maryland, College Park.
Ethylene is a plant hormone that is naturally produced and plays an important role in regulating the ripening of fruits. The ripening of fruits can be categorized into two groups based on their pattern of respiration and ethylene production: Climacteric and nonclimacteric.
Climacteric fruits have an increased respiration and ethylene production during ripening. In climacteric fruits ethylene triggers multiple quality characteristics such as changes in texture, color, aroma, sugar, and acid content.
Non climacteric fruits do not show a high rise in respiration or ethylene production during ripening. The fruits must remain attached to the plant to fully ripen. Ripening generally takes more time to happen in these fruits, and they maintain their quality longer in the plant. Non climacteric fruits can still respond to external ethylene.
In the case of watermelons and melons, we can find different types of ripening behaviors. Understanding the ripening behavior of the fruit you are growing is key in order to maintain their quality and increase consumer acceptability.
Watermelons
Watermelons are classified as non-climacteric which means that once they are harvested they will not ripen any further. Therefore, harvesting them at the right time is critical. In order to define the maturity of watermelons, different maturity indices are used, which include: (a) the color of the area where the watermelon touches the ground typically changes its color from white to yellow, (b) tendril withering: the tendril that is closest to the stem of the fruit will dry and turn brown when the watermelon has reached its maturity, (c) small changes in the glossiness and reflectiveness of the rind of the fruit, but this is specific to only certain varieties, and (d) when tapped ripe watermelons will make a dull hollow sound. A secondary maturity index refers to the assessment of the color of the flesh: watermelons that are ripe will have a deep red flesh and immature watermelons will have a pink/white flesh (Fig. 1). Additionally, it is important to mention that watermelons will not reach a “full slip” (referring to the timing in which a watermelon can be easily slipped from the vine).
In addition, watermelons, although non climacteric, can be sensitive to the presence of ethylene in the environment or storage chambers. Thus, it is of crucial importance to avoid storing them near other products that produce ethylene such as apples, bananas, mangos, pears, peaches tomatoes, which could possibly shorten their shelf life.
Melons
The species called Cucumis melo subspecies melo L. which is most commonly known as melon is a very diverse species. Melons can be both climacteric and non climacteric. This diversity in melons differs depending on the rind type, flesh, color, texture and sweetness. The most commonly known varieties of melons are cantaloupes and honeydews.
Cantaloupes are climacteric type-melons that are well known for their generally netted rinds (which is not the case always, as they can vary from netted to smooth) and sweet aroma. Cantaloupes ripen very quickly after they are harvested and also have a very short shelf life.
Some maturity indices used for cantaloupes include color changes, aroma and stem detachment (also known as slip). One of the usual first changes that indicate an advancement of maturity is the change in color under the netting. The skin color changes from a green to a yellowish solar suggesting ripening. A cantaloupe that is ripe often has a sweet aroma especially around the stem. The presence of this aroma is an indicator that the fruit is ready to be harvested. Besides, the stem of an unripe cantaloupe will be firmly attached to the fruit. As the fruit ripens the stem will rise slightly from the surface of the fruit and when it is completely ripe the stem will slip off the fruit easily (Fig. 2). Usually, a fully ripe cantaloupe will even detach from the stem on its own, what is commonly referred to as “full slip”. Cantaloupes should be harvested earlier than when reaching the “full slip” stage, as they might be overripe at this point. Finally, the skin of the cantaloupe will become softer as it ripens.
Honeydews are non climacteric melons that have a very waxy and smooth skin with a sweet flesh, with even higher sugar contests than cantaloupes. They do not produce significant amounts of ethylene while ripening which suggests that they ripen slowly giving them a long shelf life and making them more ideal for storage. Furthermore, as they are non climacteric, they will not continue to ripen after detached from the vine and they will also not increase their sweetness after harvest (Fig. 3). Some maturity indices used for honeydew melons include rind color changes, from being greenish to white, as well as the presence of a sweet aroma. Honeydews, as well as described for watermelons, will not reach a “full slip”, so this should not be used as a maturity indicator.
This article is featured in the Vegetable and Fruit News, Vol. 16, Issue 1.
Vegetable and Fruit News is a statewide publication for the commercial vegetable and fruit industries and is published monthly during the growing season (April through October). Subscribers will receive an email with the latest edition.
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