The purpose of the experiment is to determine whether the amount of ethylene would affect the rate of ripeness of Musa acuminata. It is hypothesized that the amount of ethylene does affect the rate of ripeness of M. acuminata. The more the ethylene, the faster M. acuminata will ripen. This is because it stimulates plant response when it gets to the plant tissue. It is hypothesized that the banana with two slices of apple will ripen the fastest, followed by the banana with one slice of apple, and finally the control group, which consists of only a banana and no apples.
Ethylene, also known as ethene, is a naturally occurring gas that is produced by ripening fruits. The chemical formula for ethylene is C2H4. Ethylene, which is shown in Figure 1, is a member of the alkene family, which includes any chemical that contains two carbons connected by a double bond and two other single bonds can be formed for each carbon (1, 2, 3).
Ethylene can be used intentionally to ripen fruits. Some characteristics of ethylene are that its vapors from a boiling liquid are lighter than air and thus can rise easily, that it can easily be ignited, that it is not toxic at all (4).
Ethylene affects plants by influencing plants’ growth, development, and how long they can be stored. External sources of ethylene can also have similar influence on fruits. A fruit produces significantly more ethylene during some stages of its development and when there are abiotic or biotic changes happening to it. A plant is affected and influenced when it is exposed to ethylene in the environment surrounding it or when it is close to a fruit that is producing excessive amounts of ethylene. The main purpose of having external sources of ethylene is to ripen fruits (1).
Ethylene can only be produced under a condition where there is enough oxygen and not too much of carbon dioxide. The same condition must happen for ethylene to influence the fruits. Ethylene is spread throughout the fruit by diffusion. The rate of the production and diffusion depends what the stage of plant development that the plant is going through (1).
Climacteric fruits, such as tomato, apple, pear, and melon, are those that increase the amount of ethylene significantly during the process of ripening. On the other hand, non-climacteric fruits, such as grape, orange, and pineapple, are those fruits that do not produce an excessive amount of ethylene during the process of ripening (1).
Ethylene can only affect nearby tissue when it is produced in climacteric fruits or fruits that are “injured.” Examples of “injured” fruits or vegetables are when they are peeled, sliced, cut, or any kind of preparation or processing actions. For non-climacteric fruits that are not ripening yet, ethylene can reduce or slow down the production of itself. That means that when it is not ripening, a fruit that follows that criteria will not ripen so fast since the production of ethylene is stopped by ethylene itself. When climacteric fruits start to ripen, the ethylene leads to its own synthesis and a lot more of ethylene is produced. Because of this, the concentration of ethylene in the fruit increases rapidly and reaches such a high level that external ethylene source no longer has effects on the fruit (1).
There is little effect when the external source of ethylene for fruits like apples and bananas is reduced, because the fruit itself has the ability to resist the diffusion and the fruit can produce ethylene at a very fast rate that exceeds the rate of diffusion of ethylene leaving the fruit to the surrounding (1).
External ethylene source includes other plants, smoke, compressed ethylene gas, and chemicals that release ethylene. When a fruit is has just started to ripen, the concentration of ethylene in the fruit is low. At this time, reducing external ethylene source helps to slow down or delay the process of ripening significantly. When a fruit is wounded, which means that it is damaged, the rate of the production of ethylene increases. This leads to the fruit ripening earlier than normal or at a faster rate. The interactions between ethylene and the plant’s environment is also shown in Figure 2 (1).
Ethylene production can be accelerated when there is external influence, such as injuries or wounds on the fruit. This causes the fruit to ripen faster since more ethylene was being produced. However, the result of external influence and internal development ultimately results in the same thing – causing the fruit to ripen faster. As a result, it is difficult to tell if the fruit was ripening at a faster rate because it was damaged or if it was at that stage of plant development (5).
External and internal ethylene sources like pollution, ethylene in the surrounding, ethylene production, and stress, both abiotic and biotic, all affect the plant tissue. When the plant tissue is influenced, it stimulates plant responses, such as producing excessive amounts of ethylene to start the ripening process (1).
One way that this plant response can be delayed or slowed down is to store the fruit in a place like the refrigerator, where the temperature would be low so that the quality of the fruit can be preserved. Since ethylene can only be produced under a condition where there is enough oxygen and not too much carbon dioxide, lowering the amount of oxygen around the fruit can also slow down the process of ripening. In addition, the rate of the process of ripening can also be reduced by increasing the amount of carbon dioxide around the area so that ethylene cannot be produced as effectively (1).
Ethylene in bananas causes the banana to lose chlorophyll and turn into a yellow color from a green color. When ethylene is removed or reduced, the color changes can be delayed and the fruit can be stored for a longer period of time (1).
Ethylene can cause a fruit to be softened and produce a different or stronger aroma, texture, and taste. Usually, ripened fruits become sweeter than unripe fruits. In addition, the difference of the amount of ascorbic acid between ripened fruits and unripe fruits is not very significant (1).
Figure 1: Ethylene
Figure 2: Ethylene interactions with plants and environment