How do fruits ripen? – The Hindu

An assortment of fruits lie in a basket.
| Photo Credit: Jonas Kakaroto/Unsplash

A1: Ripening of fruits is associated with the process of senescence or aging in plants. It involves changes in colour, texture, flavour, sugar content, and acidity, and is influenced by the ripening hormone ethylene.

As ripening begins, there is a corresponding increase in respiration, which is followed by increased ethylene production. It triggers a series of biochemical changes such as lateral growth and loosening of cell walls, resulting in more intercellular spaces, the conversion of starch and organic acids into sugars, hydrolysis of stored materials, decrease in chlorophyll content, with corresponding increase in colouring pigments, and emission of characteristic volatile oils.

— T. Nagendra Pillai of Guruvayoor

A2: Colour changes occur due to synthesis of carotenoids (yellow and red) and phenolic compounds like anthocyanins (red and blue). Changes in texture occur by limited degradation of cell walls followed by an increase in polygalacturonase and pectinesterase activity. In bananas and apples, the enzymes phosphorylase and in mangoes amylase break the starch into glucose and sucrose, leading to their sweet taste. Volatile compounds such as ethyl-2-methyl butrate (in apples) also elicit a sweet smell.

Acidity of fruits is due to the presence of malic acid (in apples, apricots, bananas, cheery, and plums), citric acid (in gooseberry, tomatoes, and peaches), and malic acid and tartaric acid (in grapes).

Ripening is a prerequisite for the development of embryos after fertilisation and for better dispersal of seeds for survival.

— P.S. Dheenadayalan, Coimbatore