Fruit Ripening

V. Siva Shankar12-541-009

TNAU

Ripening• Ripening is a process in fruits that makes it

acceptable for consumption. The fruit becomes sweeter, and softer.

• During ripening starch is converted to sugar.• The fruit is said to be ripe when it attains its full

flavour and aroma (watada et al., 1984).• Ripening causes colour change in the fruit.• Based on ripening behaviour, fruits are classified as:

–Climacteric–Non Climacteric

Fruits show dramatic increase in the rate of respiration

during ripening and well respond to ethylene for ripening

Climacteric Fruits

Eg. Apple, Banana, Mango, Tomato

Fruits do not show dramatic increase in the rate of

Respiration during ripening and do not respond to

Ethylene for ripening

Non - Climacteric Fruits

Eg. Citrus, Grapes, Pineapple & Watermelon

produces

H2C=CH2(ethylene)

induces/turns on

genesenzymes (for enzyme

synthesis)

producing

degrade

parts of fruit resulting in

increasing

(chlorophyll, acids, starches, pectin, proteins, etc.)

BIO SYNTHESIS -- ETHYLENE

Methionine Adenosyl Methionine

ACC

Ethylene

ACC Synthase

ACC OxidaseO2

Amino Cyclopropane Carboxylic acid

AdoMet Synthetase

ATP

Changes during ripening• Cell wall• Starch• Organic acids• Pigments• Flavouring compounds• Ascorbic acid• Phenolics• Amino acids and proteins• Respiration• Transpiration• Ethylene evolution rate

Cell wall changes• It is rich in polysaccharides are degraded and

solubilised during ripening (Jona and Foa, 1979).

• Loss of neutral sugars such as galactose and arabinose (Tuker et al., 1987).

• Enzymes responsible for cell wall hydrolases• Pectineasterase• Polygalacturonase• Cellulase• β -galactosidase (Tuker, 1993)

Starch• Amylase degrades starch to sugar, hence

the mealy quality to juiciness.• Thus the starch is fully hydrolysed into

sugars is known as characteristic event for fruit ripening (Hulme, 1978).

• Starch degrading enzymes in fruits are• α-amylase• β- amylase• Phosphorylase• α- 1, 6-glucosidase (Garcia et al.,

1988)

Organic acids• The total organic acids(malic + citric +quinic) is

decreased with ripening of fruits (Wang et al 1993).• The decline in the content of organic acids during

ripening is the result of an increase in membrane permeability (kliewer, 1971).

Pigments• Degradation of chlorophyll pigment results in

anthocyanins or carotenoids.• Phenylalanine ammonia lyase and flavone synthase

are the key enzymes for synthesis of anthocyanins (Tucker, 1993).

• Biosynthesis of carotenoids lycopene acts as the precursor of β- carotene.

Flavouring Compounds• Interaction of sugars, organic acids,

phenolics and volatile compounds.• Esters, alcohols, aldehydes and

ketones.Ascorbic acid• Ascorbic acid is increase with fruit

growth in pome, pear etc• Thereafter the levels declined with

the advancement of maturity and onset of fruit ripening (Sharma, 1995).

Respiration• Respiration is the process by which stored

organic materials (carbohydrates, proteins, fats) are broken down into simple end products with a release of energy.

• Respiration involves degradation of food reserves, especially sugars, in order to produce chemical energy (in the form of ATP and NADH) needed to maintain cellular metabolic activity.

Transpiration• Water loss is a main cause for direct

quantitative loss, appearance, textural quality, and nutritional quality.

• Transpiration is physical process that can be controlled by applying some treatments to the commodity. (like waxes and other surface coating or wrapping with plastic films).

Current Ripening Methods

• Calcium Carbide is widely using chemical to hasten the ripening.

• It contain traces of arsenic and phosphorus, these are toxic and may be hazardous to health.

• Calcium Carbide reacts with moisture in the air to produce acetylene gas. Acetylene gas acts as a ripening agent, but is believed to affect the nervous system by reducing supply of oxygen to the brain.

• It is banned under Rule 44-AA of PFA (Prevention of Food Adulteration) Rules, 1955.

Ripening with Artificial Ethylene

• Scientific and safe ripening method accepted worldwide.• Ethylene is a natural plant hormone that the fruit itself emits

as it ripens.• Ethrel or ethaphon (2-chloroethane phosphonic acid).• Exposure of unripe fruit to a miniscule dose of ethylene is

sufficient to stimulate the natural ripening process until the fruit itself starts producing ethylene in large quantities.

• The use ethylene to promote ripening is permitted under FDA regulation 120,1016.

Ripe Fruit

chemical cause

The hormone ethylene initiates the ripening response:

Unripe Fruit

physical condition

Green

Hard

Sour

Mealy

chlorophyll

pectin

acid

starch

chemical cause

red

soft

neutral

sweet + juicy

physical condition

anthocyanin

less pectin

neutral

sugar

hydrolase

pectinase

kinase

amylase

Enzyme Produced

H2C=CH2

The four major factors for commercial ripening

• Temperature control.• RH control.• Ethylene gas.• Adequate air circulation.

Commercial Use of Ethylene• Methods of application – cylinders of

ethylene or banana gas (C2H4 in CO2) with flow meters.

– ethylene generators (liquid ethanol plus catalyst produces C2H4)

– ethylene-releasing chemicals (e.g. Ethephon = 2-chloroethanephosphonic acid)

Commercial Use of Ethylene• Ethylene concentration and duration

of treatment:– physiological responses saturated at

100 ppm.– mature climacteric fruit should

initiate endogenous ethylene production within no more than 72 hours.

– degreening should continue for no more than 72 hours or risk increased peel senescence and decay.

Commercial Use of Ethylene• Ripening of climacteric fruits:– Banana– Tomato– Avocado– Mango– Papaya– Persimmon– Honeydew melon

Banana ripening

Commercial Use of EthyleneRipening of climacteric fruits:

• Recommended conditions (tomatoes):– 20 to 21°C– 90 to 95% RH– 100 to 150 ppm C2H4

– Air circulation = 1 m3 per ton of product– Ventilation = 1 air change per 6 hours or open room for 0.5 h

twice per day

Undesirable Ethylene Effects• Undesired ripening and softening of

fruits in storage.• Accelerated senescence and loss of

green color in immature fruit. • Sprouting (stimulation or retardation)

Overcoming Ethylene’s undesirable effects

• Eliminating sources of ethylene• Ventilation• Chemical removal

Control of Ripening

Measure to control ripening helps to increase the shelf life of fruits.

Temperature Regulation

• Rate of ripening increases with the increase in temperature.

• Storage at low temperature immediately after harvest reduces the rate of respiration and ethylene production.

• Storing in low temperature below optimum level results in cold injury and spoilage of fruit quality.

Regulation of storage atmosphere

The natural atmospheric air is conductive for the synthesis of ethylene.

Lowering oxygen content or increasing carbon-di-

oxide concentration in the air within the storage cabinet retards ethylene production.

Decreasing O2 concentration below 5 per cent and increasing CO2 concentration between 3 to 10 per cent delayed ripening by inhibiting ethylene. The shelf-life of fruits can thus be increased.

Chemical Regulators Potassium permanganate is a good ethylene absorbent.

Using KMnO4 coated newspaper as packing materials in the bottom delays ripening.

Ethylene synthesis inhibitors (block synthesis of SAM→ ACC)

AVG - Aminoethoxy Vinyl GlycineMVG - Methoxy Vinyl GlycineAOA - Amino Oxyacetic Acid

Avoiding Exposure to Ethylene

• Removal of ethylene from storage rooms:– use of adequate ventilation (air exchange)– use of ethylene absorbers• potassium permanganate (alkaline KMnO4 on

inert pellets “Ethysorb,” etc.)• Activated and brominated charcoal +/- KMnO4 =

“Stayfresh” absorbers

Avoiding Exposure to Ethylene

• Removal of ethylene from storage rooms:– use of ozone or UV radiation to oxidize ethylene:1. O2 + UV → O3

2. C2H4 + [O] → → CO2 + H2O– must remove excess O3 to avoid injury to fruits & vegetables

Inhibiting Ethylene Biosynthesis & Action

Biosynthesis inhibition: • AVG - Aminoethoxy Vinyl Glycine• MVG - Methoxy Vinyl Glycine• AOA - Amino Oxyacetic Acid

Inhibits ACS (i.e., SAM → ACC)• Action inhibition– 1-MCP (1-methylcyclopropene)• Irreversibly binds to ethylene receptors• “EthylBloc” and “SmartFresh”

1-MCP (1-Methylcyclopropene)

Cyclopropane derivative (Cyclodextrin powder)Gaseous ethylene action inhibitorNon- toxicOdourless gasBinds irreversibly to ethylene receptorSimple organic compound(C4H6)

(Sisler and Serek, 1999)

Ethylene Action Blocker (ethylene→ block action)

1-MCP Mode of Action

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• Works by tightly binding to the ethylene receptor site in fruit tissues, thereby blocking the effects of ethylene.

• Once ethylene production is prevented, It no longer promotes ripening and senescence .

• Blocking of ethylene receptor by 1-MCP gas causes fruits to be ripen and soften more slowly.

Application of 1-MCP• 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.

Commercial products of 1-MCP

EthyBloc® – for use with ornamentalsSmartFresh® – for use with fruit and vegetables

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• Chemical :1-MCP (0.6 µl l−1 )

• Cultivars :‘Cortland’ and ‘Empire’ apple

• Duration of exposure to of 1-MCP :0, 3, 6, 9, 12, 16, 24,

or 48 h

• Temperature :3, 13, or 23 °C

Fruit firmness of ‘Cortland’ (A) and ‘Empire’ (B) apples exposed to 0.6 µl l−1 1-MCP for 0, 3, 6, 9, 12, 16, 24, or 48 h at 3, 13, or 23 °C, and stored 120 days in air at 0–1 °C.

Incidence of severe superficial scald development in ‘Cortland’ apples exposed to µl l−1 1-MCP for 0, 3, 6, 9,12, 16, 24, or 48 h at 3, 13, or 23 °C, and stored 120 days in air at 0–1 °C plus 7 days at 20 °C.

Conclusion• The treatment temperature and duration are

important factors that affect the effectiveness of 1-MCP on apple quality and different cultivars respond differently to 1-MCP treatment

• 1-MCP has tremendous potential for maintaining apple quality during storage, but its efficacy can be affected by treatment temperature and duration as well as by apple cultivar

• Ethylene induced ionic leakage and water loss and peroxidase activity.

References