This document discusses fruit ripening conditions and factors that influence the ripening process. It describes how climacteric and non-climacteric fruits differ in their respiration rates during ripening. Ripening involves physical and chemical changes in the fruit brought about by ethylene exposure and environmental conditions like temperature and humidity. Key changes during ripening include softening of texture, changes in color, sugar content, acidity, and the development of flavor and aroma compounds. The role of ethylene and controlled atmosphere storage conditions in modulating the ripening process is also covered.

1. FRUIT RIPENING CONDITIONS
Ilyana Causing & Sharmaine Ylanan

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. 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. Changes During Fruit Ripening
• Color
• Texture
• Carbohydrates
• Acids
• Phenolic Compounds
• Flavor and Aroma
• Toxicity

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. 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. 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

9. 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

10. 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.

11. 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

12. 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

13. • 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. Toxicity
• Toxins may exist in unripe fruit which reduce in ripening

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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)

32. Sources of Ethylene
• Ethylene Application Methods
• Liquid
• Large Gas Cylinders
• Small Gas Cylinders
• Ethylene Generators

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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.

39. Simple Methods: Fruit Ripening
•Smoke
•Damage
•Fruit Generation

40. Smoke
• Smoky fire is lit in the ripening room
• Produce various gases, including acetylene, ethylene and carbon
monoxide – initiate ripening

41. 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

42. 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)