Role of ethylene in fruit ripening

Changes during ripening, commercial use of ethylene, ethylene inhibitors
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1. FSC-692 Doctoral seminar on Mechanism of Fruit Ripening Submitted by Debashish Hota Ph.D. 1 st year Submitted to Dr Prabhakar Singh Professor and Head 1

2. CHANGES DURING RIPENING 1. Structural changes 2. Physical changes 3. Biochemical changes 2

3. 1. Structural changes Cell wall: Cellulose fibre starts breaking and middle lamella dissolves which leads to softening of fruits. Cell membrane: Becomes permeable. Intercellular space: Porosity reduced. Chloroplast: Changes into chromoplast . Cuticle: Deposits of cuticle and wax e.g. grape and pear. Epidermal hair: Number reduced or disappeared e.g. Rambutan . Lenticels and stomata: Number increased as a result fruits shriveled, shorter storage life. Sclerenchyma and vascular bundle: Become lignified. 3

4. 2. Physical changes Colour: Loss of chlorophyll which is accompanied by synthesis of anthocyanin, carotenoid, xanthophyll giving the fruits characteristic colour. Water content Dry matter Fruit firmness Specific gravity Fruit Shape (Angularity in Banana) 4

5. 3. Biochemical changes Hormonal change- Ethylene Change in pigments Increase in activity of enzyme Change in pectic substances Change in phenols Synthesis of volatile compounds Change in acid Change in carbohydrate 5

6. Conventional method for ripening of fruits Mango ripening in air tight rice bin Mango ripening using paddy straw 6

7. Smoking Most common methods adopted to induce ripening. Fruits intended for ripening are exposed to smoke generated by burning kerosene stove inside the air tight chamber. Temperature increases Smoke emanates ethylene gas Mostly followed in mango and banana Drawback fruits do not attain uniform colour and flavour. persistence of smoke odour on the product impairs its quality. 7

8. Artificial ripening agents Chemicals or agents which are used to ripe fruits artificially. Used during pre-harvest, post-harvest, storage and transports. Induce colour changes and accelerate ripening . Some of most commonly used artificial ripeners : Calcium carbide Ethephon / Ethrel Ethylene glycol Ethylene 8

9. Calcium carbide (CaC 2 ) Calcium Carbide is widely used chemical to hasten the ripening. Calcium Carbide reacts with moisture in the air to produce acetylene gas. It contain traces of arsenic and phosphorus which are toxic and may be hazardous to health. It is carcinogenic and believed to affect the nervous system by reducing supply of oxygen to the brain. It is banned under Rule 44-A of PFA (Prevention of Food Adulteration) Rules, 1955. 9

10. Ethephon ( Ethrel ) Ethephon is 2-chloroethyl phosphonic acid, which penetrates into the fruit and decomposes to ethylene. It is a commercially available plant growth regulator which is a source of ethylene similar to that produced during ripening process. The government of India has allowed the use of ethephon for ripening of fruits as it is less harmful. Fruits ripened with ethrel have more acceptability and more shelf life than fruits ripened with CaC 2 . 10

11. Used to treat fruits either by dipping or fumes. In Tamil Nadu, a solution has been developed for ripening. A mixture of water (5 l), Ethephon (10 ml), NaOH (2g) kept in a wide mouthed vessel. This vessel is placed inside the ripening chamber near the fruits and the room is sealed air tight would release ethylene gas, which naturally facilitate ripening of fruits without any harmful effects. Ethephon is sold under commercial names as Floral, Cepa . 11

12. Aspects Calcium carbide Ethylene Legal Banned. Punishable under law. WHO, FDA approved Internationally preferred Health Hazardous and Carcinogenic, Affecting all vital organs Completely safe and Natural Quality of produce Dry skin, Less aroma, Possible Green patches Uniform appearance, soft skin, Natural Aroma Weight Loss More (13%) Less (7%) Transport losses Comparatively more Less, Transport Friendly Shelf-Life Less (5 Days More prone to Rot (12%) More Less prone to rot(3%) Market demand Decreasing Increasing with Growing awareness 12

13. Optimum ripening condition for different fruits with ethylene gas Parameters Value Temperature 18 to 25 C RH 90 to 95 % Ethylene concentration 10 to 100 ppm Duration of treatment 24 to 72 hrs. depending on fruit kind and Maturity stage Air circulation Sufficient to ensure uniform distribution of ethylene,high amount reduces effectiveness of ethylene. Carbon dioxide Less than 1% (Reid, 1992) 13

14. Conditions for controlled ripening of fruits at RH of 85-90% Commodities C2H4 (ppm ) Temperature (°C) Treatment time (hr.) Avocado 10-100 15-18 12-48 Banana 100-150 15-18 24 Kiwifruit 10-100 0-20 12-24 Mango 100-150 20-22 12-24 Stone fruits 10-100 13-25 12-72 Honeydew melon 100-150 20-25 18-24 14

15. Typical banana ripening process 15 Batch/shot process: Trickle/flow process: Induction of ethylene gas at once Ventilated in 24 hour Room should be sealed Induction of ethylene slowly in the stream continuously. Ventilated in each 6 hour Sealed room is not necessary Minimum air flow : 0.34 L/sec/kg of fruits A RH range of 85-90% has been recommended at stage 2(green, trace of yellow) B ut this should be reduced to 70-75% during the later colouring stages to avoid the skin splitting

16. 16 Methods to provide proper ethylene concentration in the ripening room Large Gas Cylinders Ethylene is available in large steel cylinders where it is stored under pressure Use of large cylinders of the pure gas is discouraged as ethylene is highly flammable Diluted with nitrogen or other inert gases (mixture of 95% nitrogen and 5% ethylene) Application: Measured quantities of ethylene are introduced in ripening room at regular intervals or continuously and the flow is regulated through metering device or flow meter.

17. 17 Ethylene Generators Portable and placed inside ripening room. Ethyl alcohol is filled into the tank with ethylene generator and connected to electric power. Ethyl alcohol is heated in a controlled manner in the presence of catalyst that produces ethylene gas. Gas is maintained inside the ripening room until colour break occurs in the fruits.

18. 18 ETHYLENE MANAGEMENT Potassium permanganate Celite-KMnO 4 Silica gel-KMnO 4 Alumina silicates-KMnO 4 Activated charcoal Zeolites Sodium Permanganate AVG= Aminoethoxy-vinyl-glycine AOA= Amino oxyacetic acid 1-MCP= 1-methyl cyclo propane AgNO 3 = Silver Nitrate Ag(S 2 O 3 ) 2 3- =Silver thiosulphate Co 2+ = Cobalt ion Ethylene inhibitor Ethylene absorbant

19. 1-MCP (1-Methylcyclopropane ) Cyclopropane derivative ( Cyclodextrin powder) Gaseous ethylene action inhibitor Non- toxic, Odourless gas Binds irreversibly to ethylene receptor Simple organic compound (C 4 H 6 ) 19 1-MCP Mode of Action Works by tightly binding to the ethylene receptor site in fruit tissues, thereby blocking the effects of ethylene . Application of 1-MCP: Available in the market in the name of EthylBloc ®(0.14%), SmartFresh ™(3.3%), SmartTabs ™(0.63%). When the product is mixed with water or a buffer solution, it releases the gas 1-MCP. Formulation Type: Powder Timing: Immediately after harvest.

20. 20 These products remove unwanted ethylene gas mainly through the process of oxidation. 3CH 2 CH 2 + 2KMnO 4 + H 2 O 2MnO 2 + 3CH 3 CHO + 2KOH 3CH 3 CHO + 2KMnO 4 + H 2 O 3CH 3 COOH + 2MnO 2 + 2KOH 3CH 3 COOH+ 8KMnO 4 6CO 2 + 8MnO 2 + 8KOH + 2H 2 O KMnO 4 reacts with the ethylene gas and form MnO 2 Which is not harmful for the fruits. Principle of ethylene absorbent

21. 21 TMC ethylene absorbents The Magic Cube is a Ethylene absorbing tubes and sachets which are used worldwide for the safe transportation and storage of fresh fruits, flowers and vegetables. TMC Ethylene absorbers have proven to be 2,3 times more effective than other ethylene adsorbing products that are currently used. This is due to the fact that TMC is based upon unique formula of Sodium Permanganate pellets instead of the more common Potassium Permanganate. It reduces the ethylene at a faster rate. 

22. 22 HOW DOES IT WORK? TMC pellets are made out of micro structure, impregnated with sodium permanganate. Relatively large amount of the Sodium Permanganate is distributed deep into the pore structure of the pellets. Before use, TMC pellets have a deep purple color , but after interaction with ethylene the color will change to dark brown . In the final stages what will be left is black manganese, an environmentally safe residue that can be disposed off.

23. 23 Ethylene Absorbing Screen functions similarly to Ethylene absorbing sachets. These screens are ideally applicable in places such as in refrigerated trucks. These are mainly helpful for delaying ripening during transportation. ETHYLENE ABSORBING SCREENS

24. 24 Application of apple as ripening agent for Banana ( Singal et.al ., 2012) Indian journal of natural product and resources, 3 (1) :61-64

25. 25 Fig 1. Banana fruits after exposure to different ripening agents for varying number of days

26. 26 Fig.2. Number of days taken for ripening different batches of banana Singal et.al ., 2012

27. Effect of ethephon and ethylene gas on total soluble solids (TSS%) during ripening in pear. Treatments Temperature Storage days Mean 4 8 12 16 Ethephone 500 ppm 20 degree 12.83 13.55 12.05 11.14 12.39 Ambient 12.15 12.33 11.65 11.05 11.79 Ethephone 1000 ppm 20 degree 13.12 14.02 12.08 11.73 12.73 Ambient 12.62 12.77 10.73 11.08 11.80 Ethephone 1500 ppm 20 degree 13.05 14.04 11.94 11.55 12.65 Ambient 12.87 12.70 11.83 11.84 12.31 Ethylene gas 100 ppm 20 degree 13.68 14.04 11.90 11.20 12.71 Ambient 12.13 11.56 10.93 11.00 11.40 Control 20 degree 11.08 11.90 10.73 9.05 10.69 Ambient 11.00 11.10 10.23 8.95 10.32 Mean 12.45 12.80 11.41 10.86 27 Dhillon and Mahajan , 2011

28. Conclusion The irreversible ripening process can be regulated by different chemical mean. Use of ethylene absorbent and ethylene inhibitor has been successfully applied for delayed the ripening process. Other methods to delay ripening involve use of ionizing radiation, calcium application and application of growth regulators. As calcium carbide is hazardous to ecosystem so use of ethrel is advisable for commercial fruit ripening. 28

29. Thank You 29