In botany, fruits are the developed ovaries that usually bear the seed in the flowering plants, otherwise known as angiosperms. Apart from their role in the reproduction of plants, some fruits are one of the best natural food sources for humans because they include necessary nutrients. In general, fruits are typically sweet, sour, and the most common edible part of a plant. The process by which fruits obtain their ideal flavor, quality, color, agreeable character, and other textural features is known as ripening. In chemical terms, the change in composition, such as the conversion of starch to sugar, is associated with ripening. Fruit consumption has increased significantly in recent years as a result of increasing awareness of its health advantages. As a result, the fruit commerce that ranges from large-scale growth to delivery of fruits to far-flung locations has driven scientific communities around the world to find artificial ways to carry out the ripening process. In particular, fruits that spoil quickly, such as mango, papaya, and banana, cannot be stored or carried over long distances after they have ripened. To avoid fruit spoiling during transit, producers typically harvest raw fruits and artificially ripen them at the destination market before selling them. Artificial ripening is the process of controlling ripening to obtain desired qualities for increased consumer acceptance and sales. The chemicals that are involved in the artificial ripening processes are known as ripening agents. To understand how these agents work, let’s first understand the science behind ripening.
Ripening is a physiological phenomenon that includes many biochemical changes, including tissue softening, pigment changes, aroma and flavor production, reduction in astringency, and many others. Fruit-bearing plants gather water and nutrients from the environment, which they use to make their flesh and seeds. As the main role of fruits is to protect seeds, they are generally hard and unappealing to predators when the seed is underdeveloped; however, the fruit becomes more palatable after the seed is optimally developed. Throughout its existence, every fruit produces a particular amount of ethylene. When the seeds are optimally developed, the ethylene levels in some fruit can rise dramatically. Fruits can be divided into two types based on how they react to ethylene during maturation. The climacteric fruits are the ones whose ripening is accompanied by an ethylene burst. Examples may include tomatoes, avocados, apples, melon, peaches, kiwis, and bananas. The non-climacteric fruits are those whose ethylene production does not increase as the fruit ripens, e.g., grapes, lemons, and other citrus fruits. The artificial fruit ripening process is generally carried out for climacteric fruits, as they can be harvested before the optimal development of the seed, and ethylene burst can later be induced with the help of ripening agents. Let’s take a look at few examples of fruit ripening agents.
Examples of Fruit Ripening Agents
It may come as a surprise to many of us that one of the most common chemical precursors in the polymer industry is also the most commonly used fruit ripening agent. Apart from providing us with several plastic goods that make our daily life comfortable, ethylene also ensures the year-round supplies of fruits that carry some of the most essential nutrients for our well-being. Modern fruit ripening rooms are equipped with suitable ventilation, exhaust systems, and other techniques to control temperature, humidity, and ethylene gas concentration. In these rooms, fruits are meticulously packed and preserved, and ethylene is then delivered at the proper temperature and humidity. The amount of ethylene required to accelerate the ripening of the fruits varies according to the commodities. In commercial ripening rooms, ethylene is mostly generated by “catalytic generators.” The amount of ethylene required to accelerate the ripening of various commodities varies.
Ethephon, also known as 2-chloroethyl phosphonic acid, is not only a fruit ripening agent but also one of the most commonly used plant growth regulators. Although ethephon is an authorized chemical for preharvest processing of several fruits like tomatoes and table grapes, with a maximum allowed residue level of 2 ppm, it is not approved for postharvest use (direct spray or dipping) on bananas and other fruits to speed up ripening. On a limited scale, however, ethylene gas liberated by ethephon can be used to ripen climacteric fruits such as bananas if this is more cost-effective than using ethylene gas from ethylene generators or gas cylinders with flow controls. In practice, Ethephon sachets are dipped in water to produce ethylene gas that can be used as a fruit ripening agent.
Calcium carbide is a greyish black powder that is mostly used for welding purposes. When calcium carbide is dissolved in water, it produces acetylene, which is used as an artificial ripening agent. Calcium carbide-ripened fruits are soft and have good peel color development, but they have a dull flavor. Because it is inexpensive, vendors use it haphazardly in place of other approved methods of ripening, such as dipping fruits in an ethephon solution or exposing them to ethylene gas. Ethylene being a natural hormone does not pose any health hazard for consumers; however, acetylene gas produced by calcium carbide may affect the neurological system by inducing prolonged hypoxia gradually culminating in headaches, dizziness, mood disturbances, sleepiness, mental confusion, memory loss, cerebral edema, and seizures. Moreover, the treatment of fruits with calcium carbide is extremely hazardous because the chemical is known to contain traces of arsenic and phosphorous. The symptoms of arsenic or phosphorus poisoning are diarrhea, weakness, vomiting, burning sensation in the chest and abdomen, burning of skin and eyes, permanent eye damage, difficulty in swallowing, irritation in nose, mouth, and throat.