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Fruit Ripening Conditions


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A reporting on the fruit ripening conditions relating to post harvest handlng conditions

Published in: Food
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Fruit Ripening Conditions

  1. 1. FRUIT RIPENING CONDITIONS Ilyana Causing & Sharmaine Ylanan
  2. 2. Introduction • Fruits can be classified into two groups: • Climacteric and Non-climacteric • Biale and Barcus published measurements of the respiration rate of some fruits • They classified them into Climacteric, Non-climacteric and Indeterminate • Respiration rate of non-climacteric fruit and vegetables tends to decrease during development • Ripening involves physical and chemical changes in the fruit • This occur after the fruit is at full maturity
  3. 3. Introduction • Immature fruit may be harvested and exposed to postharvest conditions that are conductive to ripening • Temperature, Gas content in the atmosphere, and Humidity • Initiation of ripening occurs when the threshold level of ethylene reached the cells of the fruit • Can occur naturally during maturity or if the fruit undergoes stress
  4. 4. Changes During Fruit Ripening • Color • Texture • Carbohydrates • Acids • Phenolic Compounds • Flavor and Aroma • Toxicity
  5. 5. Color • External Color – most change in fruit ripening • Change in color in fruit ripening is associated with breakdown of chlorophyll with carotenoid levels remains constant • Color changes is used as a rough guide to the stage of ripeness • Used in Bananas • Used commercially in the form of color-matching charts
  6. 6. Examples: Color In Cherry Tomatoes • Total chlorophyll level was reduced from 5490 μg per 100 g fresh weight in green fruit to 119 μg per 100 g fresh weight in dark-red fruit • At the same time - degradation process, lycopene, carotenes and xanthophylls are synthesized • giving the fruit its characteristic color, usually red • The optimum temperature for color development is 24°C • 30°C and above lycopene is not formed
  7. 7. In Banana and Plantains • The pigments in the peel of are chlorophylls, carotenoids and xanthophylls • Cavendish banana fail to de-green completely when they are ripened at 25°C and above • Result: bananas are ripe in every other respect but remains green • Physiological disorder of Cavendish bananas called ‘pulpa crema’ or ‘yellow pulp’ where chlorophyll in the skin is not fully broken down • In Plantains - chlorophyll destruction can occur even at 35°C Examples: Color
  8. 8. Texture • Fruits soften during ripening • Softening is due to the breakdown of starch and other non-pectic polysaccharides in the pulp • This reduce cellular rigidity • Change in the moisture status contributes to the ease with the detaching of the peel from the pulp • There are changes in pectic polymers during ripening
  9. 9. Texture • There are major changes in pectic polymers during ripening • Neutral sugars (Galactose) • Some loss of arabinose – major components of the cell wall neutral pectin • Losses of acidic pectin • Solubility of these polyuronides increases and hav shown to depolymerized • Solubilization of non-soluble pection to water-soluble pectin influence the texture of Japanese pears.
  10. 10. Texture • Stow and Genge measured the cell wall strength of apples using osmotic techniques • They found that cell walls do not weaken during fruit softening • Softening results from loss of cell-to-cell cohesion • Soluble pectin content of the apples do not correlate with fruit firmness • They also suggested removal of ethylene from store could slow softening once started • Cellulase is involved in softening during ripening of avocado fruit
  11. 11. Texture • Genetic engineering – produced fruit that do not soften normally but market was restricted • In ripening of bananas and plantains • Ratio of mass of pulp – mass of peel increases which makes the peel easily detach from the pulp • This could be used to measure the fruit’s ripeness
  12. 12. • Softening of bananas during ripening appears to be associated with two or three processes 1. Breakdown of starch to form sugars since starch granules could have a structural function in the cells 2. Breakdown of the cell walls due to the solubilization of pectic substances and even the breakdown of cellulose • increased activity of cellulase during banana ripening 3. Movement of water from the peel of the banana to its pulp during ripening • affect the turgidity of the skin - enhanced by transpirational losses Examples: Texture
  13. 13. Carbohydrates • In Climacteric fruit there is increase in starch content during development • Hydrolysis of starch to simple sugars is a chemical change during ripening • Early part of ripening – Sucrose is the predominant sugar • Later stage – Glucose and Fructose predominates • Proportion of different sugars is related to the stage in the respiratory climacteric of the fruit
  14. 14. Carbohydrates • Starch is broken down to sucrose – by action of sucrose phosphate synthetase • Non-reducing sugar from sucrose – by acid hydrolysis • Starch-sugar conversion is influenced by harvest maturity
  15. 15. Avocados • Starch occurs in the plastids of unripe avocados but reduces to undetectable levels when ripe Kiwi • Starch was hydrolyzed to glucose and fructose and to a lesser degree to sucrose during ripening Mangoes • Starch content was completely hydrolyzed to sugar during ripening • glucose, fructose and sucrose • reduction in the level of sucrose is due to it being used by the fruit for metabolic activity after all the starch had been hydrolyzed Examples: Carbohydrate
  16. 16. Acids • Organic acids also influence the overall fruit flavor • Acids help form the desirable sugar-acid balance – for pleasant taste • Acidity of fruit decreases during ripening • The most common organic acids: Malate and Citrate • But vary with different fruits
  17. 17. Banana and Plantains • Acidic in with a pulp pH below 4.5 • Main acids in bananas were citric, malic and oxalic acid • Levels of these acids normally increase during ripening • Titratable acidity in bananas increased during ripening at 20°C and then decreased Examples: Acids
  18. 18. Phenolic Compounds • Phenolic (i.e. Tannins) are polymerized to insoluble compounds • It reduce astringency in the ripe banana fruit • Tannins most important phenolic compound • give fruit an astringency taste • As fruit ripens astringency decreases • Tannins form polymers due to change in structure • Phenolics are responsible for the oxidative browning reaction in immature fruit • Polyphenol oxidase – responsible for this reaction
  19. 19. Bananas and Plantain • Can contain high levels of phenolic compounds, especially in the peel • Tannins are polymerized to insoluble compounds - reduction in astringency in the ripe banana fruit Carabao Mango • Decrease in total phenolic content during ripening Examples: Phenolic Compounds
  20. 20. Flavor and Aroma • Flavor – a subtle and complex perception • Combination of taste, smell, and texture/mouth feel • Ripening • Increase in simple sugars – give sweetness • Decrease in organic acids • Decrease in phenolics – minimize astringency • Increase in volatiles – produce characteristic flacor • Aroma – in ripe fruit is due to production of a complex mixture of individual volatile components
  21. 21. Apples and Pears • butyl ethanoate, 2-methylbutyl ethanoate and hexyl ethanoate • typical flavor and aroma compounds synthesized during ripening Tomatoes • More than 400 substances have been shown to contribute to the odor of tomatoes Examples: Flavor and Aroma
  22. 22. Toxicity • Toxins may exist in unripe fruit which reduce in ripening
  23. 23. Tomatoes • at the green stage of maturity contain a toxic alkaloid called solanine • Decreases during ripening Ackee fruit • contain the toxin hypoglycin in the arils • reduces as the fruit matures Examples: Toxicity
  24. 24. Controlled Atmosphere Storage • Levels of CO2 and O2 in the environment of climacteric fruit can affect ripening rate • Controlled Atmosphere – suppress production of ethylene in fruit
  25. 25. Banana • High CO2 and low O2 delayed the high production of ethylene associated with the initiation of ripening • application of exogenous ethylene reverse this effect • Bananas could be ripened in atmospheres of reduced O2 (low as 1%) but peel failed to de-green
  26. 26. Design of Ripening Rooms • Primary requirements • Have good temperature control system • Have good and effective air circulation • Gas tight • Have good system for introducing fresh air
  27. 27. Design of Ripening Rooms • Air circulation is important to prevent accumulation of CO2 • In bananas the boxes are lined with polyethylene film and stacked on pallets • Air circulation systems are largely convectional • Air is blown through the cooler and then across the top just below the ceiling • Cool air falls by convection through the boxes of the fruit and then recirculated • Inflatable air bags are used for better air circulation • Good ventilation – important for successful fruit ripening • During initiation of ripening (24 hours) no fresh air is introduced ony ethylene gas
  28. 28. Design of Ripening Rooms • If rooms are not frequently ventilated ripening can be delayed or abnormal ripening occur • Gas tight – ensure threshold levels of ethylene are maintained • The room is metal-lined with mastic between joints or use Gas-tight paint to ensure no gas can pass through • The room should have high humidity (90-95%) • Rooms are fitted with humidification device – spinning disc humidifier
  29. 29. Ethylene on Ripening • Change in physiology of climacteric fruit from maturation to ripening is initiated when cellular quantities of ethylene reach a threshold level • High levels of CO2 in stores could compete with ethylene for binding sites in fruits • CO2 accumulation in the intercellular spaces of fruit acts as an ethylene antagonist • Increase in ethylene synthesis is followed by changes in the fruits physiology, texture and composition
  30. 30. Ethylene on Ripening • Threshold levels of ethylene will be reached naturally at fruit maturity • Can also arise by the fruit being put under stress during production (water shortage, infection by disease-causing organisms, mechanical damage and exposing fruit to low humidity)
  31. 31. Sources of Ethylene • Ethylene Application Methods • Liquid • Large Gas Cylinders • Small Gas Cylinders • Ethylene Generators
  32. 32. Ethylene Application Method • There are several sources of ethylene that can be used in fruit ripening and de-greening • The source and the method selected for applying ethylene to fruit depends on: • cost • convenience • safety factors
  33. 33. Liquid • Ethrel or Etheph on (2- chloroethylphosphonic acid) is used as a source of ethylene. Ethrel is hydrolyzed in plant tissue to produce ethylene, phosphate and chloride • Ethylene can also be released from Ethrel by mixing it with a base such as sodium hydroxide • Ethrel ‘C’ - will release 93 g from 1 litre or 74.4 litres of ethylene gas per litre of Ethrel • Used initiate fruit to ripen by placing containers of Ethrel in a gas-tight room containing the fruit and then adding the base to the containers
  34. 34. 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 –Ethylene is highly flammable • Dilution with nitrogen – allow margin for error • Application: Volume of the room should have been previously calculated and the volume of ethylene introduced calculated with a flow meter and a stop-watch
  35. 35. Small Gas Cylinders • Lecture tubes – steel cylinders that contain 35 L of ethylene • Types • a. Has a cover which, when it is punctured, releases all the gas inside - commonly used for initiating fruit to ripen commercially b. Can be fitted with a metering device to allow for slow and controlled release of the gas • Application: Calculate the volume of the ripening room and the release the gas from the correct number of cylinders to achieve the correct concentration of ethylene required for ripening or de- greening
  36. 36. Ethylene Generators • Devices that are placed in ripening rooms • A liquid is poured into them and they are connected to an electrical power source, and they produce ethylene over a protracted period • Way of generating ethylene would be to heat ethanol in a controlled way in the presence of a copper catalyst • Application: Calculate the volume of the store and place the correct number of generators in the store to provide the required ethylene concentration
  37. 37. Alternative Gases: Acetylene • Produced in less developed countries throughout the world using calcium carbide • cheaper than ethylene sources and easier to apply in simple ripening rooms • Pure calcium carbide then 1 kg would produce 300 L of acetylene gas • gas is released when the calcium carbide is exposed to moisture • High humidity reacts with the calcium carbide, giving a slow release of acetylene • Large quantities of acetylene are required - small amounts of calcium carbide can be dropped carefully into large buckets of water.
  38. 38. Simple Methods: Fruit Ripening •Smoke •Damage •Fruit Generation
  39. 39. Smoke • Smoky fire is lit in the ripening room • Produce various gases, including acetylene, ethylene and carbon monoxide – initiate ripening
  40. 40. Damage • Wounding the banana bunch stalks or even the fruit may produce ethylene in response to the wound • Other methods, includes cutting, scraping or ‘pinching’ papaya, chico or avocado, which can hasten ripening
  41. 41. Fruit Generation • Fruit that are ripening and thus giving out ethylene can be placed in an air-tight room with green fruit • Room should need to be frequently ventilated to ensure there was no build-up of CO2 (inhibits the effect of ethylene)