What makes fruits ripen

See Subscription Options. Go Paperless with Digital. Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Climacteric fruits continue to ripen after being picked due to a process accelerated by a gaseous plant hormone called ethylene. Bananas, apples, kiwi fruit, figs, pears, mangoes, peaches, plums, tomatoes, avocadoes and some other fruits respond to ethylene in their environment and begin the ripening process.

Non-climacteric fruit produce little or no ethylene gas and therefore do not ripen once picked; these fruits include citrus fruits, raspberries, blueberries, strawberries, watermelons, cherries, grapes and grapefruit. Bananas are very sensitive fruits — they react quickly to extreme temperatures!

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. However, once fruits are ripe, they tend to spoil quickly, as you might have noticed in your own experience.

This article provides an insight into two of the changes that are associated with fruit ripening: 1 softness; and 2 flavor, in particular, sweetness, and the role of ethylene gas in controlling fruit ripening. As fruit-bearing plants grow, the fruits accumulate water and nutrients from the plant and they use these nutrients to create their flesh and seeds. Most growing fruits initially provide protection to the developing seeds. At this stage, fruits are generally hard and unattractive to predators—including us!

After seed development and fruit growth, the properties of the fruit change to make the fruit more attractive to potential consumers, such as animals, birds, and humans [ 1 ]. These changes include the most common ways by which we judge whether a fruit is ripe or not, including external features, such as softness to the touch, and internal features, such as sweetness.

Fruits also change color as they ripen. This happens because of the breakdown of a green pigment called chlorophyll, along with the creation and accumulation of other pigments responsible for red, purple, or blue hues anthocyanin , or bright red, yellow, and orange hues carotenoids , to name a few.

First, how is fruit softness regulated? The softness or firmness of a fruit is determined by the state of its cell walls. The three main polysaccharide of the cell wall are cellulose , hemicellulose and pectin.

Cellulose is made up of hundreds of glucose sugars joined together to form a long chaiin; hemicelluloses are also long chains of sugars, but unlike cellulose, these can include many different types of sugar, such as glucose, xylose, galactose, and mannose and instead of being linear are branched structures; pectins are also long branched chains of sugars, but in this case the sugars are galacturonic acid, rhamnose, galactose, and arabinose. As the cell wall begins to break down, the fruit starts to get softer [ 2 ].

Cell wall breakdown happens when proteins called enzymes dissolve these important cell wall polysaccharides. The activity of these enzymes is directly linked to the shelf life and texture of the fruit [ 2 ].

Fruit softness is also affected by the fluid pressure inside the plasma membrane called turgor pressure. Turgor pressure keeps the fruit firm, just like air pressure inside a balloon keeps the balloon firm. After maturation or harvest, fruits lose fluid water , causing a decrease in turgor pressure, so the fruits shrivel. During ripening, there is an increase in the breakdown of starch inside the fruit, and a corresponding increase in the amount of simple sugars which taste sweet, such as sucrose, glucose, and fructose.

This process is particularly obvious in bananas as they ripen. Green bananas do not taste sweet at all, and the riper they get, the sweeter they taste.

There is also a decrease in acidity as the fruit ripens and a decrease in bitter plant substances, such as alkaloids. This produce makeover is accomplished by a group of enzymes that are made on cue. They take their cue from a ripening signal — a burst of a gas called ethylene. Ethylene is a simple hydrocarbon gas produced when a fruit ripens. Ethylene flips the switch to trigger the genes that in turn make the enzymes that cause ripening. Plants send signals all the time using hormones.

This ripening signal is unique, though, because it involves an airborne hormone the ethylene.