Question

To prevent damage and facilitate easy shipping, many fruits such as bananas, mangoes, pineapples, etc. And some vegetables such as tomatoes are often plucked before they are ripe. Before the fruit or the vegetable is brought to the market, it is exposed to some chemicals which accelerates the ripening process. If, however, the fruit or the vegetable is allowed to stay on the plant, natural ripening process starts. 

Now answer the following questions. 

(i) What happens during natural ripening process? 

(ii) Name two chemicals which are used to ripen the fruits/vegetables artificially. 

(iii) Do the artificially ripen fruits/vegetables safe to use? Do they taste the same as naturally ripen fruits? 

Answer 1

(i) Ethylene is an important plant hormone. The plant emits ethylene which promotes the ripening process. 

(ii) The two chemicals commonly used are: ethylene and calcium carbide. Prior to sending the fruits/vegetables to the market, they are exposed to ethylene gas. Alternatively, the fruits/vegetables are placed on the floor and calcium carbide is place in between them. They are then covered with a tarpaulin and water is sprinkled on it. Calcium carbide reacts with water to give acetylene gas which like ethylene accelerates the ripening process. 

Commercial calcium carbide has impurities of calcium arsenide and calcium phosphide. These also react with water producing arsine (AsH₃) and phosphine (PH₃).

Ca₃As₂ + 6H₂O → 3Ca(OH)₂ + 2AsH₃ 

Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃ 

Since both arsine and phosphine are poisonous gases, therefore, it is not always safe to use artificially ripen fruits. Since the process of artificial ripening cannot be banned, therefore, fruits/vegetables must be properly washed before using. Further, it is a common observation that artificially ripen fruits/vegetables do not taste the same as naturally ripen fruits/vegetables. The reason is however not well understood.