Ethylene gas – a safe aid for artificial ripening of fruit
Fruits are the best natural foods that provide essential nutrients. The consumption of fruits has increased in recent years due to the awareness of its benefits and their availability around the year. Fruit trade involves transporting of fruits to distant places. Highly perishable fruits such as mango, papaya, banana, etc. cannot be stored and transported long distance after ripening as they tend to spoil. Therefore, to avoid spoilage of fruit over long distances, traders generally harvest raw fruits and ripen them artificially at the destination market before sale. Considering the importance of artificial ripening in the supply chain of certain fruits, the FSSAI has permitted the use of ethylene gas for artificial ripening of fruits. Ethylene gas can be generated from various sources. Due to the high cost and scarce availability of ethylene gas, traders often use unsafe and banned chemicals like carbide gas as the aid for artificial ripening of fruits, which can be potentially harmful to health. This guidance note will help to spread awareness among FBOs/ traders/ consumers and food safety officials which is related to various aspects of artificial ripening of fruits. This guidance also includes Standard Operating Procedures (SOP) detailing all facets of artificial ripening of fruits using ethylene gas and the reliable sources available.
Fruit ripening is a combination of physiological, biochemical and molecular processes which lead to changes in colour, sugar content, acidity, texture, and aroma. In general, it is a physiological process which makes the fruit edible, palatable and nutritious. Fruits are classified into two categories according to ripening pattern
- Climacteric fruits; these fruits are generally harvested once they have reached their full maturity and can be further ripened during transit and storage. These include banana, guava, mango apple, pears, apricots, peach, and tomato.
- Non-climacteric fruits: these fruits do not ripen after harvest. So in order to attain full ripeness and flavour, these fruits are often harvested once they have fully matured and ripened in the orchard. These include fruits like lemons, oranges, grape, cherry, pineapple, and strawberry.
Need for artificial ripening
Artificial ripening is the process by which ripening is controlled to achieve desired characteristics intended for better consumer acceptance and improving sales. It is generally carried out on climacteric fruits so there is uniform ripening. Globally, artificially ripened fruits are considered safe for human consumption if safe ripening agents are used.
Provisions for artificial ripening of fruits under Food Safety and Standards Regulations 2011
Artificial ripening of fruits by acetylene gas, commonly known as carbide gas is prohibited as per the provisions in the sub-regulation 2.3.5 of the Food Safety and Standards (Prohibition and Restrictions on Sales) Regulation, 2011. The regulations permit the use of ethylene gas at a concentration up to 100ppm (100μ/L) depending upon the crop, variety, and maturity for artificial ripening of fruits.
Issues in artificial ripening
The industrial grade carbide gas popularly known as ‘masala’ is often used by some unscrupulous traders to release acetylene gas for artificial ripening of mango, banana, papaya, etc. Calcium carbide contains traces of arsenic and phosphorous which are harmful to humans and may cause dizziness, frequent thirst, weakness, difficulty in swallowing, vomiting, skin ulcers, etc. It is equally harmful to the handlers. There are also chances that calcium carbide may come in direct contact with fruits during application and leave arsenic residues and phosphorous on fruits and so the use of this chemical is banned in India.
In order to discourage the use of the banned calcium carbide and the non-availability of an alternative ripening agent, the FSSAI has permitted the use of ethylene gas for ripening of fruits in India to vide notification dated 23 August 2016.
Artificial Ripening using ethylene gas
Ethylene is a hormone naturally produced within the fruits and regulates the fruit ripening by initiating and controlling a series of chemical and biochemical activities. The treatment of unripe fruits with ethylene gas triggers the natural ripening until the fruit itself starts producing ethylene in large quantities.
Standard Operating Procedure (SOP)
- Any preparation containing calcium carbide or acetylene gas
- Any source of ethylene gas that comes into direct contact with the fruit
Requirements for Ethylene Ripening System/ chamber
- Airtight room, preferably insulated for better temperature control
- Temperature regulation system (cooling, heating)
- Humidity regulation system
- Proper air circulation and ventilation
- Ethylene gas generation/ injection system
- Ensured power supply (for ripening chambers)
- Display board including temperature, relative humidity, ethylene concentration, CO2 Concentration
Suggested handling conditions for stacking fruits and air circulation
Fruits should be kept in ventilated plastic crates or stackable fruit boxes inside the ripening chamber/ temporary structure. Stacking of boxes should be done keeping minimum 4 to 6 inch space from the walls and between adjacent crates. For uniform ripening, airflow throughout the chamber shall be maintained. Fruits should not occupy more than 75% of the volume of the chamber as well as crate during the treatment.
Requirements of exposure time and ripening temperature for different fruits
|Fruits||Ethylene Exposure time (hours||Ripening temperature (oC)*||Relative Humidity|
- Fruits should be transferred to the ripening chamber once the ripening temperature is attained after pre-cooling by the appropriate method
Sources of Ethylene Gas: Ethylene has obtained through the following systems may be used for artificial ripening
- For ripening chambers
- Ethylene gas cylinders
- Compressed ethylene gas (aerosol cans)
- Ethylene generators
- 2chloroethylphosphonic acid (ethephon/ethrel) and alkali
- For cartons and boxes
- 2chloroethylphosphonic acid (ethephon) in powder form
Protocol for application of Ethylene gas from various sources
Ethylene gas cylinders
- Maintain the temperatures and RH inside the chamber as per table 1 above
- When the desired temperature and RH has achieved place the fruit crates inside the ripening chamber. Temperatures must be as close as possible to those mentioned in Table 1 above
- Introduce the ethylene gas into the chamber (up to 100ppm) through the gas cylinders
- Monitor the CO2 inside the chamber and maintain it at below 5000ppm
- Maintain the temperature and RH concentration of ethylene gas and Carbon-dioxide levels as suggested in table 1 above.
- Remove the fruits from the ripening chamber and store in another chamber at the optimum storage temperature till further use
- Avoid excess accumulation of ethylene in the chamber for desired results
Compressed ethylene gas (aerosol cylinders)
- Procedure is the same as above except step 3 as instead of introducing the ethylene gas cylinders the ethylene gas will be sprayed from the aerosol cans inside the chamber. The (ratio will be about 2.7 litres gas per can of 27m3 volume) this will result in maximum ethylene concentration of 100ppm
- Ethylene gas from aerosol cans will be sprayed in the ripening chamber and not directly on the fruits.
Steps same as for ethylene gas cylinders except 3 as in this method ethylene gas is generated using the catalytic converter from ethanol and is brought into the ripening chamber through calibrated gas regulator which will be up to 100ppm
2Chloroethylphosphonic acid (ethephon 39% SL) with alkali
All the same as ethylene gas cylinders except step 3 as in this method the ethylene gas is generated from 2Chloroethylphosphonic acid(ethephon 39% SL) 0.50g is added in 2 ml of ethephon 39% SL for every 1m3 airtight room/ ripening chamber. Gas formation will start immediately. The maximum concentration of ethylene gas generated will be 100ppm.
Sachet containing 2Chloroethylphosphonic acid (Ethephon) in powder form
Ethephonin powder form may be used for artificial ripening of fruits. It shall be packed in 40-60 micron cellulose membrane paper or its equivalent in the form of small sachets. The ripening mixture in the sachets should be as per the composition recommended below. This ripening method may be used where ripening chambers are not available or for in-transit ripening. The sachet must generate ethylene gas only and should not contain any traces of calcium carbide or acetylene gas.
Composition: 2Chloroethylphosphonic acid (Ethephon) and combination of alkali (oxides and carbonates of magnesium and calcium, sodium and potassium carbonates and bicarbonates magnesium silicates).
- Keep the boxes airtight or make them airtight with paper
- Take the ethylene forming sachets (1500mg containing 50 mg2Chloroethylphosphonic acid (Ethephon) and dip in water for 5 to 10 seconds.
- Place the water soaked sachets in perforated plastic box (approx. 5cmx5cmx5cm size)
- Place this small plastic box containing the sachet inside the centre of the fruit box/crate which has a volume of 2.7m3 which should be sufficient for 10 kg fruits. The ethylene gas generated will not exceed 100ppm
- Remove the small plastic box containing the sachet after 24 hours.
For Food Business Operators/ Traders
- Pre-treatment operations
- Harvest the fruits at optimum maturity
- Treatment with ethylene up to 100ppm concentration should be used for ripening. The concentration of ethylene may go up due to an autocatalytic production of ethylene once ripening is triggered by exogenous application of ethylene
- Procure ethylene cylinder, aerosol cans, ethephon, ethrel only from reputed companies
- Ensure the authenticity and purity of the sachet containing ethephon in powder form and other components
- Use well-labeled sachets mentioning details of manufacture composition, instructions for use etc.
- Ethylene releasing agents shall not come in direct contact with fruits
- For uniform ripening in chambers airflow through throughout the room shall be maintained. Fruits should not occupy more than 75% of the volume of the chamber as well as the crate during treatment
- Relative humidity, temperature and exposure time shall be maintained as prescribed in table 1 above during the period or ripening as that gives the best results
- Carbon-dioxide concentrations shall be maintained at below 5000ppm. It can be achieved by CO2 scrubbing devices or air exchange at intervals of 6 hours. High concentrations of CO2 will retard the ripening process.
- Post-treatment operations:
- Transfer the fruits to ventilated room with appropriate storage temperature and relative humidity for ripening after completion of the treatment.
- Remove the sachet out of the fruit boxes after completion of the treatment (24 hours)
- Guidelines for Safety
- Ethylene gas is inflammable. Cylinders should be used with caution. Ethylene concentrations of above 27000ppm are explosive
- Strictly prohibit smoking around the premises
- Electrical circuits must be properly maintained and monitored
- Install a gas leakage monitoring system in the commercial ripening chambers
- Purchase fruits and vegetables only from known vendors and reputed stores or dealers who know for sure that the fruits are not ripened by using harmful or banned chemicals
- Wash fruits thoroughly with running potable water before eating
- Avoid fruits with black blotches on the skin as these fruits are likely ripened by acetylene gas produced from calcium carbide
For Food Safety Officials
- The illegal use of calcium carbide in fruit mandis and shops shall be monitored
- Safety and purity of sources used for generating ethylene gas shall be monitored and regulated. Any source of ethylene gas should not come in direct contact with fruits
- Labeling on ethylene releasing sources must be checked for composition, mane of manufacturer, instructions for use, etc.
- Suspected sample of any source of ethylene gas shall be analysed for absence of calcium carbide by the authorised labs.
- The display units, if available in the ripening chambers may be checked for the concentration of ethylene gas used
- Capacity building of fruit traders/FBOs may be encouraged for the permitted source of ethylene gas and its use as a ripening agent as per the standard operating procedure mentioned in this document
- The fruit traders need to be made aware of the dangers of unsafe ripening agents like calcium carbide
Guidelines for Ripening Fruits Naturally
Fruits may be ripened naturally using the methods mentioned below. They will ripen within 4 to 6 days if kept at room temperature. These methods entrap ethylene around the fruit and facilitate faster ripening
- Harvest the fruits at optimum maturity
- Wrap the fruits individually with paper or place it in a paper bag
- Keep the unripe fruit layers over paddy husk or wheat straws
Keep the unripe fruits inside an airtight rice bin /container