With these suppressed-climacteric types, fruit may remain under-ripe if harvested too early. Other plum varieties such as Early Golden ripen very rapidly. In this case, harvest should be timed more precisely so that fruit are not over-ripe when they reach the consumer.
To measure ethylene, expensive instruments are needed. The methods we described above for slowing down ripening work in this way, because, in general, low temperatures reduce metabolism in fruit. Controlled atmospheres limit the amount of oxygen around the fruit, and oxygen is needed to make ethylene.
Ethylene action is inhibited by carbon dioxide and by 1-MCP. Another method for slowing down ripening is to remove ethylene from the storage environment by using materials that absorb ethylene, such as potassium permanganate. Once the fruit reaches its destination, it can be ripened by exposure to ethylene gas. The effect of ethylene on ripening is dependent on many factors.
The fruits need to be mature enough to be able to respond effectively to ethylene. In highly sensitive species, like cantaloupes or bananas, ripening is immediately stimulated by ethylene, but the more immature the fruit, the greater the concentration of ethylene required to cause ripening. In the less sensitive species, like tomatoes or apples, ethylene treatment reduces the time before ripening occurs.
Some fruits, such as avocados, do not ripen while attached to the tree and gradually increase their sensitivity to ethylene with time after harvest [ 6 ]. All plants produce some ethylene during their life cycle. Ethylene production can increase up to fold or more during particular stages—for instance in response to a wound [ 1 ]. Ancient Egyptians used to cut figs to enhance their ripening, since ethylene produced by the injured fruit tissue triggered the ripening response.
Similarly, the ancient Chinese used to burn incense in closed rooms with stored pears, because ethylene was released as a by-product of the burning incense.
Ethylene gas is commercially used to ripen fruits after they have been picked. Fruits, such as tomato, banana, and pear are harvested just before ripening has started typically in a hard, green, but mature stage. This allows time for the fruit to be stored and transported to distant places. Once the fruit reaches its destination, ripening is conducted under controlled conditions. This is usually carried out in specially constructed ripening rooms, with optimum ripening temperature, humidity, and ethylene concentration.
These special conditions cause the fruit to ripen at a consistent rate. By the time the ethylene-treated fruit reaches the consumer, the commercially applied ethylene is gone, and the fruit is producing its own ethylene.
Both ethylene and another widely used ripening agent, methyl jasmonate, are reported to be non-toxic to humans; however, they are relatively expensive. Understanding the effects of ethylene on fresh produce can be helpful in ripening fruits in our own kitchen. This kind of plant is so interested in seed dispersal that it creates fruit intended to tempt some animal to come along and carry it off. Many things happen as fruit ripens. Unripe fruit is often green, sour, odorless, hard and mealy.
The ripening process makes the fruit more appealing — the color of the skin changes as chlorophyll the green stuff in plants is broken down and in some cases new pigments are made, the acids that make the fruit sour are broken down, the mealy starches are converted into sugar, hard pectin is softened, and larger molecules are made into smaller ones that then evaporate as aroma.
Suddenly, we have a soft, juicy, sweet, fragrant, colorful animal-attractor. This produce makeover is accomplished by a group of enzymes that are made on cue.
Green bananas, or any unripe fruit for that matter, is a test of faith. Ripening fruit gives off ethylene gas, and putting the fruit in a paper bag traps the gas near the fruit, causing it to ripen faster. Place bananas in a brown paper bag and close loosely. Ethylene will build up and circulate within the bag, speeding up the ripening process. Check now and again so you can take them out at your desired ripeness.
This usually takes about 3 days depending on room temperature. To ripen the bananas faster, place a ripe fruit such as an apple or tomato in the bag as well. If you store bananas in the fridge they will turn black! Remember to only refrigerate bananas once they are ripe. Occasionally this discolouration can happen to our bananas on very cold delivery days, although we do our utmost to keep them warm by wrapping them in blankets — exposure to extreme cold even for a short period, may turn the bananas dark grey in colour.
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