One of our member has raised a very good topic in his group - Ethylene and Fruit ripening. This topic was discussed in our earlier forum. So thought to bring it back to all ....
1. Sources of Ethylene for artificial ripening
The change in physiology of climacteric fruit from maturation to ripening is initiated when cellular quantities of ethylene reach a threshold level. The metabolic pathway within the cells of the plant that result in ethylene production is complex. (For detail refer FST 4714). The threshold level can also be achieved by exposing the fruit, for a sufficient period, to a threshold concentration of ethylene in a gas-tight room. This is the principle used in most commercial fruit ripening rooms
1.1. Ethylene application method
With bananas, very low concentrations of ethylene are sufficient for mature fruit at 14-19 ºC (the temperature commonly used commercially). These are in the range of 1-10 ppm for 24 hrs. However, in commercial practice 1000 ppm is commonly used to ensure ripening. This is partly because many ripening rooms are not fully gas tight and the concentration may be rapidly reduced through leakage. There are several sources of ethylene that can be used in fruit ripening and degreening. The source and the method selected for applying ethylene to fruit depend on cost, convenience and safety factors.
Compounds that decompose in or on the crop to release ethylene can have the advantage of easy application. Etacekasil [2-chloroethyltris (ethoxymethoxy) silane] or ACC (1-aminocyclopropane-1-carboxylic acid), which is the immediate precursor of ethylene biosynthesis in plants, have not been used practically for the application of ethylene to crops. However, 2-Chloroethylphosphonic acid, which is commonly called ‘Ethrel’ or ‘Ethephon’, has been used as a source of ethylene for decades. Ethrel is hydrolyzed in plant tissue to produce ethylene, phosphate and chloride
Cl-CH2- CH2-PHO¬ 3 ¯ OH ¯ CH2=CH2 + PH2O4¯ + Cl¯
Ethylene can be released from Ethrel by mixing it with a base such as sodium hydroxide.
1.3. Large gas cylinders
Ethylene is available in large steel cylinders where it is stored under pressure. Typical cylinders are number 1, which is 1520 mm high and 230 mm in diameter, and number 3, which is 940 m high and 140 in diameter. The former contains 15 kg of ethylene and the latter 3 kg. Because ethylene is highly flammable, the use of large cylinders of the pure gas is discouraged. In order to allow some margin for error it is usually used diluted with nitrogen. Typical mixture of 95% nitrogen and 5% ethylene or 95.5% nitrogen and 4.5% ethylene. The method of application is to meter the gas into the ripening room containing the fruit through a pipe. The volume of room should have been previously calculated and the volume of ethylene introduced calculated with a flow meter and a stop watch.
1.4. Small gas cylinders
These are steel cylinders, also called lecture tubes, and commonly contain 35 litres of ethylene. Two types are available. One type has a cover which, when it is punctured, releases all the gas inside. The second types can be fitted with a metering device to allow for slow and controlled release of the gas. The former is the type commonly used for initiating fruit to ripen commercially. The way it is applied is to calculate the volume of the ripening room and release the gas from the correct number of cylinders to achieve the correct concentration of ethylene required for ripening or degreening.
1.5. Ethylene generators
These are devices that are placed in ripening room. A liquid is poured into them and they are connected to an electrical power source, and they produce ethylene over a protracted period. The manufacturers of these generators do not provide information on exactly what the liquid is which they supply for use in the generators or the process by which the ethylene is generated. A possible way of generating ethylene is would be to heat ethanol in a controlled way in the presence of a copper catalyst.
2. Some of the other simple methods are compiled as follows
Another simple method of initiating ripening is to light a smoky fire in the ripening room. This can produce various gases, including acetylene, ethylene and carbon monoxide, which will initiate ripening. It is used in many developing countries.
Wounding the banana bunch stalks or even the fruit may produce ethylene in response to the wound. A simple technique used in Southeast Asia where a stick is inserted into the stalk of jackfruit, which not only makes a convenient handle for carrying the fruit but also initiates it to ripen. Other methods are cutting, scraping or ‘pinching’ papaya, or avocado, which can hasten ripening.
2.3. Fruit generation
Fruit that are ripening and thus giving out ethylene can be placed in an air-tight room with green fruit. A continuous system could be worked out for commercial application of this method. However, the room would need to be frequently ventilated to ensure there was no build up of CO¬2, which is known to inhibit the effect of ethylene.
Good evening sir..
I want to apply it for leaf degreening..............
What concentration should I put ?
A simple technology practiced in households to trigger ripening is to keep un-ripened and ripened fruits together inside an air tight container. Since the already ripened fruits release ethylene, ripening will be faster.
In yet another practice some farmers dip unripe mature fruits in 0.1 per cent ethrel solution (1 ml of ethrel solution in 1 litre of water) and wipe it dry.
The fruits are then spread over a newspaper without touching each other and a thin cotton cloth is covered over this. The fruits ripen in two days.
Spreading unripe fruits as layers over paddy husk or wheat straw for a week to ripen is another alternative.
But these conventional methods possess some disadvantages like longer duration for ripening, high degree of spoilage due to excessive handling and lack of uniformity in colour development. About one-fourth of the fruits are spoilt by these methods, according to him.
In one of the simple and harmless techniques, 10 ml of ethrel and 2 gm of sodium hydroxide pellets are mixed in five litres of water taken in a wide mouthed vessel.
This vessel is placed inside the ripening chamber near the fruits and the room is sealed air tight. About a third of the room is filled with fruits leaving the remaining area for air circulation. Ripening of fruits takes place in about 12 to 24 hours.
In order to reduce the cost of chemical, some ethylene releasing fruits such as papaya and banana can also kept in the same room. Since ethrel is a plant hormone and hastens the ripening process by the release of ethylene in the atmosphere this practice may be the safest method,” explains Dr. S.P. Thamaraiselvi, Assistant Professor of the Institute..
For more information contact Dr. M. Selvarajan, Professor and Head, Department of fruit crops, Horticultural college and research institute, Periyakulam, Tamil Nadu, email: email@example.com, mobile: 9003027732, phone: 04546-231726.
Thank you guys............
Your information is very important for me...............
Dept. of Food Eng and Tech.
Institute of Chemical Technology, Mumbai
Good morning Pravin..................
Here I want to put one more point, Ethylene is only natural ripening hormone which hastens various enzymatic processes and increases respiration rate. So we can't substitute ethylene but we can ensure uniform diffusion of ethylene through use of degreening chambers which also controls relative humidity and carbon dioxide conc which reduces the conc of ethylene needed (only upto 100 ppm) and for short time. When ethylene level inside the tissue reaches to Physiologically Active of Ethylene (PAE), fruit itself start producing ethylene invivo.
Dept. of Food Eng and Tech.
Institute of Chemical Technology, Mumbai