One bad apple...and ethylene
Updated: Apr 28, 2021
Many people, often on social media, are talking about "a few bad apples." Let's take a moment to look at this phrase and the science behind it.
The entire statement is "a bad apple spoils the barrel" (or apple container of your choice). Benjamin Franklin's version is "The rotten apple spoils his companions." It's an old saying, so there are variations, but the meaning is clear; the presence of one "bad apple" can ruin the whole group. Recent use however often leaves off the second part, claiming that the presence of "a few bad apples" doesn't mean the whole group is bad.
Time to talk about science! One rotten apple can, in fact, cause the whole storage unit to go rotten. Ethylene is a plant hormone that is produced as part of the fruit ripening process and in response to stress such as infection or environmental conditions. Ethylene is involved in the signaling pathways for many important plant mechanisms. If a seedling runs into a barrier (like a rock in the soil), ethylene induces a change in the direction of stem growth. Ethylene is also involved in apoptosis (cell death) that occurs during processes like seasonal leaf change.
Ripening makes fruit (a seed containing structure) more enticing to herbivores and assists in seed dispersal. During ripening, the fruit becomes softer and starches are converted to sugar, making the fruit sweeter. Ethylene triggers ripening, and ripening triggers more ethylene production, accelerating the process. This is a classic example of a positive feedback mechanism. Ethylene, a gas, can spread to nearby fruit, triggering more ripening and more ethylene production. Over time, exposure to ethylene will make the fruit overripe and lead to rotting. Another factor in fruit degradation (and ruining storage neighbors) is the growth of various organisms, including bacteria and fungi. A fungal infestation, for example, can spread to nearby fruit, which will lead to a bunch of moldy apples.
Summary: If you have a "bad" (overripe) apple, it can help ripen the apples around it faster, but if you leave it there, they'll all end up rotting. Not to sound like a 19th-century preacher, but...if you have bad apples in your bunch, get rid of them.
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Ethylene and ripening -