Ethylene is used

Ethylene is a gaseous plant growth hormone. Ethylene is highly effective in fruit ripening and in turn it increases the respiration rate during ripening of the fruits. It aids in breaking seed dormancy thus initiating germination. Thus ethylene acts as a ripening agent.

Ripening describes the change from physiological maturity of a plant to its senescence (ageing). During ripening, there's a change in the skin colour of the fruit, the internal flesh softens, the fruit sweetens, etc.