So you saw your mother brought home a bunch of green bananas. But seriously hard and green. Sounds inedible, right? And then after several days, they turned ripe and yellow. Awesome! But why is that? Why are there fruits that continue to ripen after harvest? The answer lies behind a little science.
During the ripening process, several physiological changes happen. Inside the fruit, the starch is broken down into simple sugars (such as sucrose, fructose and glucose) making the fruit sweet. The flavor and aroma form. The flesh gets softer and the color changes.
All these changes happen with the presence of ethylene. Ethylene is a natural plant hormone (and natural ripening agent) responsible for the ripening process. The amount of ethylene is low in young fruits. As they mature, they produce more ethylene that speeds up the ripening process.
This article discusses ethylene in more detail.
The climacteric fruits and non-climacteric fruits
While fruits are natural ethylene producers, there are many that produce more than the others. There are two classifications of fruits when it comes to ripening: climacteric and non-climacteric fruits. Climacteric fruits can continue it’s ripening process after harvest. That means picking fruits that haven’t reached maturity is totally fine. Here are some common climacteric fruits:
- Mangoes
- Bananas
- Avocados
- Tomatoes
- Papayas
- Guavas
- Peaches
Yes, there are fruits that produce more ethylene than others. The disadvantage of this though is they undergo deterioration faster. Apples, tomatoes and bananas are notorious for producing the most amount ethylene. But the ripening process can be slowed down using low temperature. Freezing has been the norm but be careful as the fruits may lose flavor and texture.
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Non-climacteric fruits, on the other hand, can only ripen on the plant—their ripening process stops after harvesting. And there is no beneficial effect when they are subjected to ethylene or another ripening agent. Because of this, Non-climacteric fruits have a shorter shelf life when harvested ripe. In short, handling of non-climacteric fruits are more delicate than climacteric ones. Here are some common non-climacteric fruits:
- Strawberries
- Grapes
- Pineapples
- Cherries
- Watermelon
- Lemons
What is artificial ripening
Most banana producers for example, harvest their bananas green and then ripen them during storage or delivery. Question is, why don’t they just wait for the fruits to ripen naturally? And what is artificial ripening?
One obvious reason here is to prevent bruising and other physical injuries that may occur in fruits during transit. Then, after arrival, the fruit handler may perform artificial ripening through the use of ripening agents.
These ripening agents are chemicals that hastens the ripening process in fruits. One most commonly used chemical is calcium carbide (CaC2) in banana ripening. CaC2 has the ability to produce acetylene gas, a gas that’s very similar in effect to ethylene during the ripening process. The use of CaC2 has been practiced for decades now because it helps in developing attractive surface. However, like most artificial processes, there are a few downsides to this practice. The use of CaC2 may not uniformly ripen the inside and adverse health effect may occur. CaC2 has trace amount of arsenic and phosphorous hydride, both of which are cancerous. This led to countries banning the chemical.
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Why should you know which fruits are climacteric and non-climacteric?
Fruit ripening is discussed frequently in post-harvest handling for its importance. You may go crazy for buying an unripe fruit and is actually climacteric, fortunately. You may mistakenly pick an unripe and non-climacteric fruit from your backyard. These are simple instances but for producers, it’s actually a big deal for them. Just determining which fruits are climacteric and which ones are not have saved many post-harvest handlers a huge sum of money.
