RIPENING OF CLIMACTERIC AND NON CLIMACTERIC

FRUITS

RIPENING Ripening - final stage of development of fruit, which involves series of physiological and biochemical events

Ripening induces changes that are structural, physical, chemical, nutritional, biochemical, or enzymatic. These changes are degradative, and synthetic.

The changes occurring are: thickening of cell wall and adhesion, increased permeability of plasmalemma, changes in color, loss of texture, thickening of cuticle etc

CLIMACTERIC VS NON-CLIMACTERIC

Climacteric: fruits are defined as fruits that enter ‘climacteric phase’ after harvest i.e. they continue to ripen. During the ripening process the fruits emit ethylene along with increased rate of respiration. These fruits are harvested hard and green, but are fully mature and ripened near consumption areas as fully ripe fruit are too delicate to withstand transportation over long distances. Small dose of ethylene is used to induce ripening process under controlled conditions of temperature and humidity. Climacteric fruits are: Mango, Banana, Papaya, Guava, Sapota, Kiwi, Fig, Apple, Passion fruit, Apricot, Plum,  Pear. 

Non-Climacteric: Non-climacteric fruits once harvested do not ripen further. They produce very small amount of ethylene and do not respond to ethylene treatment. There is no characteristic increased rate of respiration or production of carbon dioxide. Nonclimacteric, in which respiration shows no dramatic change and ethylene production remains at a very low level. Non-climacteric fruits are: Orange, Mousambi, Kinnow, Grapefruit, Grapes, Pomegranate, Litchi, Watermelon, Cherry, Raspberry, Blackberry, Strawberry, Carambola, Rambutan, Cashew.

Normally, the number of days taken for edible ripening varies for different fruits for instance, it takes about 5 to 6 days for mangoes and 6 to 7 days for sapotas to ripen. Under natural conditions, ethylene plays a major physiological role in the ripening process.

TECHNOLOGIES FOR RIPENING OF FRUITS (Artificial fruit ripening techniques)

Fruit ripening using calcium carbide •Most climacteric fruits in India are ripened with industrial grade calcium carbide. It contains traces of arsenic and phosphorus (are toxic and exposure may cause severe health hazards), and, thus use of this chemical for this purpose is illegal in most countries. •In India too, use of calcium carbide is strictly banned as per PoFA (Prevention of Food Adultration) Act [Section 44AA]. •Calcium carbide, once dissolved in water, produces acetylene which acts as an artificial ripening agent. Acetylene is believed to affect the nervous system by reducing oxygen supply to brain.

Workers at a fruit market using calcium carbide to ripen raw mangoes

The only safe and worldwide accepted method is using ethylene, which is a natural hormone for ripening when done under controlled temperature and relative humidity conditions.

Ethylene being a natural hormone does not pose any health hazard for consumers of the fruits. It is a de-greening agent, which can turn the peel from green to perfect yellow (in the case of bananas) and maintain the sweetness and aroma of the fruit. METHODS OF APPLYING ETHYLENE

Trickle method involves trickling ethylene gas into room so as to maintain a concentration of 10 µl per litre, usually for a period of 24 hours.

Room is then ventilated after 24 hours to prevent carbon dioxide exceeding 1% concentration, which would retard ripening.

Rooms that are poorly sealed are packed in vented cartons stacked on pallets, and fruit temperature is controlled by forced air circulation as in a cooling facility.

A small fan can be used to ensure a uniform continuous flow of ethylene into and through the room. Forced-air ripening provides more uniform temperature and ethylene concentration throughout ripening room.

Ripening can also be initiated using ethylene generated by passing ethanol over a bed of activated alumina. •This method is safer than using pure ethylene gas. •Ethylene releasing compounds such as ethephon (2-chloroethy1 phosphonic acid) are sometimes used to ripen tomatoes destined for processing. •When using ethephon as spray, amount of ethylene released will increase as pH and/or relative humidity increase.

Commodity  Ethylene conc.(ppm) 

 

Ethylene exposure time (hr.) 

Ripening temp. oC 

Storage Temp oC 

Avocado 10-100 12-48 15-18 4.4-13Banana 100-150 24 15-18 13-14

Honey dew melon

100-150 18-24 20-25 7-10

Kiwifruit 10-100 12-24 0-20 0.5-0Mango 100-150 12-24 20-22 13-14Orange

degreening1-10 24-72 20-22 5-9

Stone fruit 10-100 12-72 13-25 -0.5-0

DEGREENINGIn order to improve external skin colour and market acceptance, citrus like orange, lemon, Mousambi can be treated with ethylene, as a de-greening agent. Ethylene treatment breaks down the green chlorophyll pigment in the exterior part of the peel and allows the yellow or orange carotenoid pigments to be expressed. Degreening is carried out in ripening rooms and this process takes 2 to 3 days. It is again necessary to ventilate daily to ensure that CO2 levels do not exceed 1%. The most rapid degreening occurs at temperatures of 25 to 30ºC but the best colour (concentration of peel carotenoids) occurs at 15oC to 25oC.

Ripening chambers

Catalytic generator for ethylene production in ripening rooms

DELAY IN RIPENING Gibberellins: Post harvest treatment of gibberellins markedly retards ripening of tomatoes, guava and banana. The delay in ripening was indicated by lowered respiratory rate, retarded climacteric and delayed colour change.

Pre-harvest sprays of gibberellins were shown by Kitagawa to have a striking effect in decreasing the rate of development, maturation and ripening of lemons.

Some of the effects are firmness, delayed accumulation of cartoenoids on ‘Navala orange’, higher TSS and Ascorbic acid in lemons.

Auxins (CIPA and NOA) :Pre-harvest application of CIPA and NOA at 25 ppm each delayed the physiochemical deterioration of ‘Coorg’ mandarins in storage.The improved marketable condition of treated fruits after storage was due to reduced weights loss and retention of Vitamin-C.

Ethylene Oxide:Mangoes treated with ethylene oxide also show a definite delay in ripening.

Ethylene Absorbents:Waxing, low O2, High CO2, and ripening inhibitors are sometimes combined to prolong storage life. Banana is packed in film bag containing KmnO4 ( to absorb C2H4).

The ethylene control strategy includes prevention of exposure of plants to biologically active levels of ethylene, reducing the tissue perception of atmospheric ethylene, and preventing the tissue response to perceived ethylene.

Ethylene damage can be reduced by (i) adequate ventilation, (ii) reduction of O2 and increase in CO2 levels, (iii) reducing temperature, (iv) avoiding storage and transportation of ethylene producers and sensitive produce, and (v) reduction of ethylene by forcing air through filters of activated charcoal, potassium permanganate (KMnO4) or purafil and oxidation by UV light.

Potassium permanganate, the most accepted ethylene remover used commercially, oxidizes ethylene into ethylene glycol and often is incorporated into different carrier materials such as activated alumina and silica gel.

It is applied in sachets, tubes and blankets in storage and transportation of fresh fruits and vegetables. When used in conjunction with modified-atmosphere packaging, the use of KMnO4 increases the shelf life of banana to 21 days from 7 days in air.

The fading distinctions between classical patterns of ripening in climacteric and non-climacteric fruit and the ubiquity of ethylene—An overviewVijay Paul, Rakesh Pandey, and Girish C. Srivastava

The process of fruit ripening is normally viewed distinctly in climacteric and non-climacteric fruits. But, many fruits such as guava, melon, Japanese plum, Asian pear and pepper show climacteric as well as non-climacteric behaviour depending on the cultivar or genotype. 

Guava

Ethylene was found to be necessary for skin colour changes and firmness loss during ripening. These characteristics classify guava as a climacteric fruit. The exogenous application of ethylene to these fruits at the mature-light green stage had no effect on the ripening process. This evidence contradicts classification of ‘Pedro Sato’ guava as a traditional climacteric fruit.

Based on these findings, Azzolini et al. (2005) concluded that classification of guava fruit as climacteric or non-climacteric varies with cultivars

Pepper

Capsicum fruits are classified as non-climacteric based on the patterns of CO2 and ethylene production (Saltveit 1977; Lurie et al. 1986; Lu et al. 1990; Biles et al. 1993).

However, some hot pepper cultivars are climacteric (Gross et al. 1986), indicating that classification of capsicum as non-climacteric may be inconclusive.

Further, some cultivars seem to be ethylene insensitive, while in others continuous treatment with exogenous ethylene has been shown to accelerate ripening (Armitage 1989) and to up-regulate the expression of ripening specific genes

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