B) Ripening Techniques
i) Ripening with ethephon / Ethrel : Ethephon (2-choloroethyl-phosphonic acid) is commercially available and is registered for pre-harvest use on a variety of crops for controlling developmental processes or inducing ripening. This chemical is approved for post-harvest use on fruits crops for enhancing ripening. For post-harvest treatments, the known quantity of ethephon is diluted in water and fruits are dipped in the solution for a specified period. This substance ensures that there is uniform ripening of fruits. This technique provides a safe and effective method of ripening of fruits compared to the conventional technique of using calcium carbide. ii) Ripening with Ethylene gas: In this technique, the fruits are exposed to low level of ethylene gas (10-100ppm) in an air-tight ripening chamber for 24 to 72 hours so as to induce ripening. The most important thing in this technique is temperature and relative humidity control inside the ripening chamber, which should range between 15-250C and 90-95% relative humidity, depending upon the fruit type. Several methods are used to provide proper ethylene concentration in the ripening room.
a) Gas Cylinders: Ethylene is available in large steel cylinders where it is stored under pressure. As it is highly flammable, the use of pure gas is discouraged. Therefore, it is usually used diluted with nitrogen or other inert gases. Typical mixtures are 95 per cent nitrogen and 5 per cent ethylene or 95.5 per cent nitrogen and 4.5 per cent ethylene. The measured quantities of ethylene are introduced in ripening room at regular intervals or continuously and the flow is regulated through metering devise or flow meter. Any piping leading into the ripening room should be grounded to prevent possible electrostatic ignition of ethylene gas.
b) Shot system: On small scale, commodities can be treated using shot method with ethylene liberated from ethephon. A calculated amount of ethephon in stainless steel bowl is placed around the room. The fruits are stacked in the room and sodium hydroxide is added to ethephon and all ventilation to the room is then blocked. When sodium hydroxide reacts with ethephon, ethylene gas is released that ripens the fruits, Precaution should be taken while handling sodium hydroxide and ethephon as these are corrosive. Safety glasses and rubber gloves should be used while their handling.
c) Ethylene generator: This is a device that is portable and placed inside the ripening room. A liquid (ethyl alcohol) is filled into the tank fitted with ethylene generator and it is connected to an electric power source. The ethyle alcohol gets heated in a controlled manner in the presence of a catalyst that produces ethylene gas. Gas is maintained inside the ripening room until colour break occurs in the fruits.
Table 7 : Ripening conditions for some fruits
Commodity Ethylene concentration (ppm) Ethylene exposure time Ripening temperature Predicted storage after treatment
Apple(Grany Smith) 10 ppm 6 days 25°C Less than 4 months at 0°C
Banana 100-150 ppm 24-48 hours 14-18°C Less than 7 days at 14°C
Mango 100 ppm 12-24 hours 15.5-25°C Less than 7 days at 1013°C
Tomato (mature green
stage) 100 ppm 3-3.5 days to reach breaker stage and 5-16 days, depending on temperature, to reach full red
stage 18°-20°C (65°68°F) with 9095% RH 7 days after reaching the red stage
(Source : Adel A. Kader, 2002 )