Everything you need to know about banana plant cultivation, growth and production. Learn about:- 1. Introduction to Banana 2. Climate and Soil Required for Cultivating Banana 3. Cultivation Practices 4. Propagation 5. Manuring and Fertilization 6. Water Management 7. Weed Management 8. Harvesting and Postharvest Management 9. Varieties 10. Grades, Sizes and Packaging.
Contents:
- Introduction to Banana
- Climate and Soil Required for Cultivating Banana
- Cultivation Practices of Banana
- Propagation of Banana
- Manuring and Fertilization of Banana
- Water Management of Banana
- Weed Management of Banana
- Harvesting and Postharvest Management of Banana
- Varieties of Banana
- Grades, Sizes and Packaging of Banana
1. Introduction to Banana:
Musa acuminata and Musa balbisiana, most cultivars of edible bananas and plantains derive from these two members of the family Musaceae. Before the 1940’s the cultivar ‘Gros Michel’ dominated the international banana trade, until it succumbed to Fusarium wilt (Panama disease). Since the 1940’s the trade has adopted cultivars of the Cavendish subgroup. Bananas are eaten mainly raw as a dessert fruit because they are sweet when ripe.
Plantains or cooking bananas are rich in starch and can be eaten either ripe or unripe. The edible cultivars of bananas and plantains are seedless. The two obvious tissues that constitute the fruit are the pulp and the peel. The peel is the ovary wall.
The pulp originates from cell division of the innermost layers of the pericarp. The growth of the peel begins to slow down as the fruit matures but the growth of the pulp continues, consequently peel splitting often occurs in very mature green fruit.
In India, banana and plantain (Musa sp.) are widely grown. It has great socio-economic and cultural heritage significance. It is an important food crop for farmers. It is also a desert fruit for millions apart from a staple food owing to its rich and easily digestible carbohydrates with a calorific value of 67- 137/100 g fruit. It is a rich source of vitamin C and minerals.
In India, banana contributes to 31.72% of the total fruit production. It is widely grown in States like Andhra Pradesh, Assam, Bihar, Gujarat, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Orissa and West Bengal. Maharashtra grows 52.18 tonnes/ha followed by Gujarat (40 tonnes/ha). In north-eastern region banana’s productivity is quite low.
2. Climate and Soil Required for Cultivating Banana
:
It is usually grown in humid subtropical to semi-arid subtropics areas up to 2,000 m above mean sea-level that is from 8°N to 28°N latitudes with a temperature of 15°-35°C and a rainfall of 500-2,000 mm/year. The restricted varieties of Hill bananas are grown at higher altitudes without any deterioration of quality and specific aroma. Bananas grown under mid- subtropical conditions have better-quality fruits, as they develop better aroma with crisp pulp.
The optimum mean temperature required for banana ranges from 20°- 30 °C. The plants are temperature sensitive because with increase or decrease in mean temperature growth is decline. If bunch emergence coincides with low temperature, it results in inflorescence emerging through pseudo-stem. Chilling temperature gives similar results. Temperature above 36°-38°C results in scorching effect due to increase in transpiration rate.
High temperature, water stress and stagnation in poorly-drained soils conditions negatively affect the growth and the plants collapse in extreme cases. High wind also causes major constraint in banana production and results in uprooting and collapse of plants.
Banana can be cultivated in all kinds of soils with good drainage. The sandy loam soil is most suitable as compared to vertisol or clay loam soil with soil pH of 6.5-7.5. Though, banana can be grown in soils having a pH up to 8.5 with suitable amendments. Organic amendments are required for sandy as well as heavy soils.
3. Cultivation Practices
of Banana:
The cultivation practices depend on available resources, cultivars, traditions and marketing.
i. Homestead or Backyard Cultivation:
Homestead farming is needs improper spacing, inadequate use of fertilizer and pesticides, high productivity and longer crop duration. In Indian tradition, banana homestead cultivation is common. The choice depends on family requirements and quality preference of the household. Backyard cultivation is easy to establish with a minimum capital investment. The monitoring and sharing of labour among family members are also easy.
Banana cultivated as a shade crop for coffee in Palney and Shevaroy hills. In coastal regions (Karnataka, Kerala and Andhra Pradesh) banana is grown in coconut and arecanut plantations with tall cultivars. Banana is also grown with ginger, turmeric, elephant-foot yam, cotton, gourd and other vegetables to exploit maximum income/unit area.
In States like Karnataka and Kerala the crops are planted with different canopy levels (Multistorey system). Coconut and arecanut plantation form the upper storey followed by middle story of banana and lower story with tapioca and lower-most storey with colocasia, turmeric, ginger and garlic. Semi-tall banana of Poovan and Ney Poovan varieties are suitable for this type of cultivation.
4. Propagation
of Banana:
Banana is propagated through suckers or corms. Sword-suckers with a well- developed rhizome, conical in shape with lanceolate leaves and actively growing central buds, weighing 500-750 g are generally used. In western and central Maharashtra, well-developed rhizomes with dormant lateral buds and dead central bud are used. Apart from these, cut rhizomes called ‘Bits’ and ‘Peppers’ are also used successfully.
Disease-free plants through micro-propagation using tissue culture technique, shoot-tips have been prepared but their use is cost-effective for production. In vitro propagated banana is becoming popular. It has been preferred over conventional propagation owing to its faster multiplication, uniformity in planting material and disease-free material from transmissible pests and diseases. In vitro propagated plants are becoming a commercial reality along with fertigation.
Time of planting depends on the choice of cultivar, agro-climatic conditions and market demand of the area.
Tamil Nadu:
The banana Dwarf Cavandish and Nendran are planted from February to April, while Poovan and Karpuravalli in November-December.
Maharashtra:
Banana are planted in two distinct seasons – September- October and June-July.
Tall-Growing Varieties:
They are planted 2.0-2.5 m apart and wider spacing is also followed in plantations identified for leaf purposes.
Commercial Banana:
The Poovan, Reasthali, Nendran and Robust varieties are planted maintaining the space of 2.1 m x 2.1 m. The while dwarf cultivars Dwarf Cavendish, Kullan and Jawari Bale varieties are planted with a spacing of 1.8 m x 1.8 m.
The planting method depends on the tradition, resource availability and existing constraints. It varies from region to region.
It is commonly used for garden land. The pits of 60 cm x 60 cm x 60 cm sizes are dug, filled with a mixture of soil, sand and farmyard manure in a 1:1:1 ratio. Suckers are planted in the centre of the pit and soil around is compacted. This is mostly followed in biennial plantations of Dwarf Cavendish, Rasthali, Robusta, Poovan and Karpuravalli banana.
It is common in Gujarat and Maharashtra States. Deep furrows after land preparation of 30 to 40 cm are prepared and suckers are placed at required spacing. The farmyard manure is applied around furrows mixed with soil and tightly packed round the suckers. This will reduce the cost of pit opening which is to be incurred every year. Furrow planting is practised in annual planting system.
This kind of planting is common wet land cultivation specially of Cauvery delta (Tamil Nadu). Land is prepared like paddy using plenty of water and gauge wheel then water is drained from the field allowing to sets the land for a day. Planting is done by pressing the suckers into the wet field. After a week 15 cm deep trenches are opened both ways maintaining 4 or 6 plants in each block.
Deepening of trenches by 20-25 cm is taken up every month after planting till suckers put forth 1-3 leaves. In the third month after planting the trenches are broadened and deepened to 60 cm. Trenches are used for draining out excess water in rainy season and for dumping cut plants, suckers and leaves for decaying under anaerobic conditions.
Two months after that the trenches are cleaned and decayed manure is used for plants. This will recycle the organic matter.
5. Manuring and Fertilization
of Banana:
Banana needs large quantity of nutrients for growth and yield. Manuring and fertilization cost may be about 20-30% of the total cost of production. The choice and quantum of manuring and fertilization depends on the time, frequency and mode of application, type of cultivar, production system and agro-climatic conditions.
i. Nitrogen:
Banana crop needs 100 to 250 g of N/plant. Urea is commonly used as a source of N. It is applied in 3-4 splits. At vegetative stage 150 g N and at reproductive phase 50 g N will help to enhance the yield and delay the leaf senescence. Nitrogen @ 25% as farmyard manure and 1 kg neem cake is beneficial for plant growth. The application of 25% N in organic form, 75% N in inorganic form along with growing of green manure crops like Crotalaria is ideal.
ii. Phosphate:
Banana requires comparatively low amount of phosphate. Superphosphate is the major source of P followed by the application of rock phosphate 50 to 95 g/plant at planting. For acidic soils, triple superphosphate or diammonium phosphate is recommended. Phosphorus is applied in single dose at the time of planting. The amount of quantity of P2O5 depends upon type of soil and type of variety (20 to 40 g/plant).
iii. Potassium:
This element has important role in vital functioning of a plant. It is not stored in plant. Its continuous supply is needed up to finger-filling stage. Hundred g of K in two splits is required during vegetative phase and 100 g in two splits during reproductive phase are recommended. Muriate of potash is also used as source of potassium. Potassium sulphate is recommended for the soils having pH above 7.5.
iv. Calcium:
This element is required to obtain proper yield of banana crop. It is used as soil amendments specially for acidic soils. The dolomite (MgSO4) and limestone (CaCO3) are used for this purpose.
v. Magnesium:
This element is the key component of chlorophyll. In acute deficiencies foliar spray of MgSO4 is found suitable in de-greening leaves.
vi. Sulphur:
Sulphur uptake by banana is active during sucker to shooting stage but after shooting, sulphur supply comes from leaves and pseudo-stem.
2. Micronutrients:
Zn, Fe, B, Cu and Mn are important micronutrients and play an important role in normal growth and development of banana. The application of Zn (0.1%), B (0.005%) and Mn (0.1%) improves yield.
6. Water Management
of Banana:
Banana is grown either as rainfed or irrigated or wetland crop. AAA and AAB clones are grown under irrigated conditions, while ABB clones are grown as rainfed crop. For commercial cultivation irrigation is the major source of water supply. Water requirement of banana depends on type of variety. It varies from 1,800 to 2,200 mm.
1. Nendrna, Robusta and Dwarf Cavendish – Needs origination at 20-40 cumulative pan evaporation (CPE).
2. Poovan – It needs at 60 CPE.
3. Karpuravalli – It needs at 80 CPE.
For banana cultivation normal furrow and basin and trench systems are used. The furrow or basin system is useful if water availability is not a constraint. Trench method is followed especially in wetland system of cultivation. Drip irrigation system is common in Maharashtra and many other states due to shortage of water supply.
The fertigation is also popular, wherein required quantity of nutrients is given through soluble fertilizer or liquid fertilizer. Flood irrigation is followed in garden land cultivation, where plenty of water is available. Temporary bunds are made around a block of 10-20 plants for convenience and irrigation is carried out block-wise.
7. Weed Management
of Banana:
Regular hand-weeding is essential. In wetland cultivation, turning of top soil to bury the weeds after complete wetting the field followed by no irrigation for 15-20 days is commonly followed to check weed growth for 2-3 months. Chemical control of weeds is also recommended. Glycel spray @ 0.4% is effective and economical.
Surplus and unwanted suckers should be kept under control for better growth and yield of the mother plant. De-suckering once in 45 days is recommended. The small suckers are headed back with a sharp knife. In later stages, removal along with their rhizomes is a must. Setting a suckers for rationing is important to maintain higher productivity of the orchard.
When three-fourths of the plants in the orchard are in flowering, one sucker is allowed and set for ratooning. In south India, the set suckers of biennial and perennial plantations are headed back once at 2-month stage to arrest apical growth and allow rhizome enlargement.
Mulching helps conserve soil moisture and suppress weed growth. Organic mulching also improves soil health. Sugarcane trash, paddy straw, dried leaves and Pongamia leaves are used for mulching purpose.
For maximum yield, a minimum of 10-12 leaves are required to be retained on the mother plant. Banana crop needs protection from strong wind therefore, propping is essential for tall cultivars. Removal of male bud after completion of the female phase is referred to as denavelling.
It serves the dual purpose of saving movement of food into unwanted sink and also earns additional income as it is used as vegetable. Bunch covering is practised for Cavendish and Silk groups of bananas to get attractive colour.
8. Harvesting and Postharvest Management
of Banana:
Harvesting of banana has no definite yardstick. In a polyclonal condition, harvest index varies a lot depending on the variety, proximity to the market and mode of transportation.
Quality Characteristics and Criteria:
A premium quality banana is very clean (free from defects such as scars, physical damage, insect injury, and latex staining), free from decay, has an adequate finger length and diameter, does not have excess curvature, and upon ripening has the desired uniform bright yellow color and sensory attributes in flavor (sweetness, acidity) and aroma. Attributes are defined by consumer preference.
Horticultural Maturity Indices:
Bananas are harvested mature-green and ripened upon arrival at destination markets since fruits ripened on the plant often split and have poor texture.
Commercially, bananas and plantains must be harvested while mature green and transported to destination markets where they are ripened under controlled conditions (bananas), and controlled or natural conditions (plantains). Fruits ripened on the plant often split and have poor texture. Harvest time represents a compromise between leaving the fruit on the plant long enough to maximize yield, but harvesting it soon enough so that sufficient green life remains to market fruit with acceptable quality.
The stage of maturity for harvesting the fruit depends on the market for which is intended and is determined in terms of the marketable life required. Plantains tend to mature more prematurely than bananas when harvested at the same age.
One very useful criteria for harvesting fruit that is used commercially is age of the bunch after emergence from the pseudo-stem (emergence can be defined as the day on which the first complete hand of fruit is visible). Because bananas are growing rapidly when harvested, fruit size (finger diameter, and length), and finger fullness (angularity) are suitable measures of harvest maturity.
At a given age, the maturity of hands in a stem varies, those hands at the proximal end of the stem being more mature than those at the distal end. An estimate of maturity of the entire stem is then assessed using the second hand from the proximal end. It is usual to measure length/diameter (caliper grade or calibration) of the middle finger on outer whorls of the second hand on the stem before running fruit through packing plant processes.
9. Varieties
of Banana:
Following are the important varieties which are grown in India:
1. Dwarf Cavendish (AAA):
(syn. Basrai, Vhusawal, Jahaji, Kabuli, Pacha,
Vazhai, Mauritius, Morris, Kuzhi Vazhai, Sindhurni, Singapuri and Vamanakeli) is the leading commercial cultivar contributing to 58% of the total production owing to its high yield, ability to withstand strong winds, short crop cycle, good response to micro-irrigation and high economic returns/unit area. Other superior clones are under advanced stage of evaluation.
2. Gandevi:
This selection known as Hanuman or Padarse is gaining popularity despite having longer crop duration. The selection produces bunches weighing 55-60 kg and performs better under light soil condition with higher inputs.
3. Grand Naine (AAA):
It is a tall mutant of Dwarf Cavendish and is popular among the growers in Maharashtra and Karnataka. It resembles with Dwarf Cavendish except for its robustness, well-spaced hands, fingers of bigger size and heavy bunches. The bunches are 25-30 kg with uniform long fingers throughout the bunch.
4. Hill Banana (Pome, AAB):
(syn. Virupakshi, Sirumalai, Mala Vazhai, Vannan, Marabali and Ladan) is considered as elite banana of south India (hills of Tamil Nadu and Karnataka) because the fruits have unique aroma and taste. It is tall structured, small bunched and curved fruit crop and takes long duration for maturation. Each bunch weight varies from 11-13 kg with an average of 60 stout fruits per bunch. Fruits have good keeping quality, pulp is not juicy, dry and sweet.
5. Karpuravalli (ABB):
(syn. Kanthali, Jammulapalem Collection, Pisang Awak, Bharat Moni, Chinali, Pey Kunnan, Kosta Bontha and Jhurmani Kanthali) is cultivated in Tamil Nadu and other states of India. It is a hardy crop and can grow well in marginal soils. It is tolerant to drought, salt and wind. The cultivation is easy and productivity is quite high.
The plants are about 3.0 m tall with light pink-streaked pseudo-stem. It takes about 16 month to harvest. The weight of each bunch varies from 25 to 35 kg. Fruits are sweet and conspicuously ash coated, beaked and do not drop off when ripe. These are suitable for long-distance transportation. Juice and wine are prepared from this variety.
6. Monthan (ABB):
(syn. Bontha, Karibale, Bontha, Kachakel and Madhuranga Bale) is cultivated in Tamil Nadu, Kerala, Andhra Pradesh and Orissa. The plant is of fairly tall and robust size. It can grow to a height of 2.5- 3.0 m. Stem is yellowish-green without pigmentation but very shiny. Weight of each bunch varies from 18 to 20 kg with 60-70 fruits. The fruits are bold, stocky, knobbed and pale-green and are suitable for preparing chips.
7. Nendran (AAB):
(syn. French Plantain, Rajeli and Bhorot) is a cooking variety of Kerala and Tamil Nadu because their products are exported till date to the Gulf countries. Plant is slender has prominent pigmentation in younger leaves and pink shade on the pseudo-stem. Each bunch weight varies from 8 to 15 kg with 30-50 fingers/bunch.
The fruits remain starchy even on ripening. The important ecotypes of Nendran are Zanzibar, Otta Moongil, Moongil, Kali Ethan, Valiettan, Manjeri Nendran, Chengalikodan, Nedu Nendran, Chenganacheri Nendran, Attu Nendran, Myndoli and Padali Murian.
8. Ney Poovan (AB):
(syn. Njali Poovan, Elakki Bale, Ney Kadali, Hoobale, Vadakkan Kadali, Deva Bale, Putta Sugantha and Safed Velchi) is mainly grown in Elakki Bale (Karnataka). It is commercially grown as monoclonal crop. The plants are medium-tall banana and takes about 12-13 months for its cycle.
The bunch are oriented horizontally and weight as each bunch varies from 18 to 20 kg. The fruits are small and packed closely. The pulp is ivory-coloured, firm, sweet, having good aroma with good-keeping quality. It fetches double the price than other cultivars.
9. Poovan (Mysore AAB):
(syn. Alpan, Champa, Chini Champa, Dora Vazhai, Karpura Chakkarakeli and Palayankodan) variety is grown in southern and north-eastern states of India in a perennial cropping system. The fruits have pink pigmentation on the ventral side of the midrib when young. The weight of each bunch (fruit each bunch 150-300) varies from 20-24 kg.
The fruit are closely packed, short and stout with prominent beak. The fruits are slightly acidic. Crop duration is 16- 17 months. The plants are affected by banana-streak virus.
10. Rasthali (AAB):
(syn. Amrithpani, Malbhog, Mortman, Rasabale, Kulfiait, Sabri, Salsikola and Poovan) is most successful table banana. The fruits are tasty, crisp, good sour-sweet blended and with pleasant flavour. Plant is medium structured. The crop is of about 13-15 months and each bunch weight is 15-18 kg. It has about 6-7 hands with bold, stout fruits, turning golden- yellow on ripening. The major physiological disorders are hard lumps and fruit cracking.
11. Red Banana (AAA):
(syn. Lal Kela, Chenkadali, chewazhai, Yerra Arati, Anupam, Chandrabale, Kembale and Agniswar) is a red-skinned, delicious fruits. It is cultivated commercially in Kerala and Tamil Nadu. The pseudo-stem is bold, robust and 2.5-3.0 m tall. Each bunch weight varies from 20 to 22 kg with 70-90 fruits each bunch. The crop has long duration (16 months).
12. Robusta (AAA):
(syn. Bombay Green, Pedda Pacha Arati and Harichal Borjahaji are the semi-tall sport of Dwarf Cavendish) is the successful variety for Karnataka, Andhra Pradesh and parts of Maharashtra. The plants bear bunches weighing 25-30 kg each with good-sized slightly curved fruits. Plants complete their life-cycle in a year. It is highly susceptible to sigatoka leaf spot limiting its cultivation in humid areas but is resistant to Panama wilt.
13. Promising Hybrids:
A few hybrids have also been developed in banana. Of these, H 1, H 2, CO 1, FHIA 1 and FHIA 3 are promising hybrid varieties of banana.
10. Grades, Sizes and Packaging
of Banana:
Maturity (the more mature the better the quality when ripe); finger length (depending on intended use and demand for various sizes); freedom from defects, such as insect injury, physical damage, scars, and decay. As bananas ripen their starch content is converted into sugars (increased sweetness). Other constituents that influence flavor include acids and volatiles.
Minimum acceptable size (length and diameter) grade standards for export markets vary depending on banana and plantain cultivar and market specifications. Hands, clusters, or single fingers not meeting these fresh market grades are used for processing products or discarded.
Bananas are packed in corrugated fiberboard boxes as whole hands, clusters or individual fingers holding an average weight, for premium fruit, between 13 and 18 kg depending on market preference. Plantains are packed as individual fingers in 18 kg boxes. Most exporters use polyethylene film liners and paper pads to reduce moisture loss and provide protection to fruit from physical damage during handling and transport.
Pre-cooling of bananas or plantains is not generally done. Adequate cooling is not initiated until fruit are loaded into containers or cargo holds onboard ships.
Optimum temperatures for storage and holding of green bananas are 13.3 to 14.4 °C (56 to 58 °F). Some banana cultivars can be handled at 12.8 °C (55 °F). Because marketing quality standards are more relaxed for plantains, and plantains are more prone to premature ripening during transit and storage, it is recommended that green plantains be held between 8.9 to 11.7 °C (48 to 53 °F).
Plantains grown during the warmer months tend to attain physiological maturity faster than fruit grown during the winter months, consequently green life potential varies during the year. Optimum RH for holding and transport fruit is 90 to 95%. Holding of ripe fruit should be kept to a minimum.
Controlled Atmosphere (CA) Considerations:
Bananas and plantains respond well to CA. CA is used commercially during ocean transport of green bananas. Modified atmosphere packaging using polyethylene bags (banavac) is used for both bananas and plantains, but plantain are physiologically more active than bananas and have higher respiration rates and could exhaust O2 more rapidly than bananas. Optimum gas levels for most cultivars range between 2 to 5% O2 and 2 to 5% CO2.
Main benefits of controlled atmospheres include delaying of ripening, reduction of crown rot incidence, and a much fresher condition (latex flowing through the vascular tissues) upon arrival at destination. Shelf-life can potentially be extended 2- to 3-fold by optimum CA.
O2 levels below 1 to 1.5 % may cause grayish or brown peel discoloration, failure to ripen properly, and off-flavor. CO2 levels greater than about 6 to 8% may cause pulp to soften while the peel is still green, and may confer undesirable texture and flavor.
Ripe fruit can tolerate higher levels of CO2. The beneficial and detrimental effects of reduced O2 and/or elevated CO2 are temperature and time-of- exposure dependent. Removal of ethylene gas can have an additional benefit on extending green-life of bananas and plantains, under both ambient and modified atmosphere conditions. CO2 inhibits the effect of ethylene on ripening, and higher levels of O2 than those under CA are necessary for adequate ripening.
Thus, bananas held under CA should be ventilated with fresh air for at least 18 to 24 h before ripening (gassing with ethylene) is initiated. An under-peel discoloration resembling chilling injury has been observed on green bananas when transported long distance under CA conditions at below 14 °C (57.5 °F), this disorder has also been associated with high temperatures of 33 to 35 °C (91 to 95 °F) in the field.
Responses to Controlled Atmospheres (CA):
1. 2-5% O2 and 2-5% CO2
2. CA delays ripening and reduces respiration and ethylene production rates.
3. Postharvest life potential of mature-green bananas – 2-4 weeks in air and 4- 6 weeks in CA at 14°C (58°F)
4. Exposure to <1% O2 and/or >7% CO2 may cause undesirable texture and flavor.
5. Use of CA during transport to delay ripening has facilitated picking bananas at the full mature stage.
Retail Outlet Display Considerations:
Fruit should be displayed at retail in non-refrigerated areas in the produce section. Existing refrigerated shelf space in supermarkets normally is below the minimum safe temperature for bananas and plantains and chilling injury can still occur in ripe fruit. Displaying surfaces should be cushioned in order to avoid physical damage to the fruit.
Chilling injury is an important disorder of bananas and plantains. Both green and ripe fruit are susceptible, with green fruit being slightly more sensitive than ripe fruit. Chilling injury results from exposing fruit to temperatures below about 13 °C (56 °F) for a few hours to a few days, depending on cultivar, maturity, condition of the fruit, temperature, and duration of exposure. Chilling injury is mainly a peel disorder.
Symptoms include sub-epidermal discoloration visible as brown to black streaks in a longitudinal cut, a dull or grayish (Smokey) cast on ripe fruit, failure to ripen, and in severe cases the peel turns dark brown or black, and even the flesh can turn brown and develop an off taste.
Chilled fruit are more sensitive to mechanical injury. Ripe fruit, if chilled, turn dull brown when later exposed to higher temperatures and are very susceptible to handling marks; the slightest pressure causes discoloration. Inflicted chill in green or ripe fruit may not become apparent until 18 to 24 h after actual damage has occurred.
ii. Ethylene Production and Sensitivity:
Bananas and plantains are sensitive to physiological levels of ethylene as low as 0.3 to 0.5 μL L-1 if the O2 and CO2 levels are similar to those found in outside fresh air. The three main factors affecting response to external ethylene are – fruit maturity; time from harvest when ethylene exposure began; and the length of exposure to ethylene.
iii. Responses to Ethylene:
Most commercial cultivars of bananas require exposure to 100-150 ppm ethylene 24-48 hours at 15-20°C (59-68 °F) and 90-95% relative humidity to induce uniform ripening. Carbon dioxide concentration should be kept below 1% to avoid its effect on delaying ethylene action. Use of a forced-air system in ripening rooms assures more uniform cooling or warming of bananas as needed and more uniform ethylene concentration throughout the ripening.
Mature bananas left to ripen naturally will eventually soften but the change in color will not be uniform and the peel will be dull, pale yellow and unattractive. In order for the fruit to attain a bright yellow peel color, a firm pulp texture, and good flavor, bananas are ripened by releasing ethylene into a sealed chamber or room and at controlled temperature and RH.
Plantains are being ripened by this controlled method in most markets but in some they still rely on natural ripening. Immediately after harvest bananas do not respond to ethylene treatment or, in the best scenario will initiate ripening but will never attain the characteristic bright yellow coloration. One main reason for controlled ripening is to provide retailers and wholesalers with fruit at a stage of ripeness desired by consumers.
Generally, very low concentrations of ethylene are sufficient to ripen the fruit, i.e., 10 to 50 μL L-1 In commercial practices however, 1000 μL L-1 is commonly used to ensure uniform ripening.
This is partly because many ripening rooms are not fully gas tight and the concentration may be rapidly reduced through leakage. Most commercial cultivars of bananas and plantains require exposure to ethylene for 24 to 48 h at 14.4 to 18 °C (58 to 64 °F). However, temperatures of up to 20 °C (68 °F) are sometimes necessary for bananas.
Optimum RH levels during ripening are 90 to 95% (after coloring is underway RH should be reduced to 85% to prevent peel splitting). High RH requirements for proper ripening can be attained when the fruit is being packed in partially-sealed polyethylene liners. Exposure of ripe bananas or plantains to temperatures higher than those in the ripening range hastens softening and decay, weakens the neck, can cause splitting of the peel, and may cause poor color development.
The color of the peel is used as an indicator of ripening. A scale of 1 to 7 is convenient where 1 is dark green, 2 is light green, 3 is more green than yellow, 4 is more yellow than green, 5 is yellow with green tips, 6 is fully yellow, and 7 is flecking.
Room ventilation after gassing with ethylene is essential to keep CO2 < 1% and avoid its effects on delaying ethylene action. Use of a forced-air system (pressurized) in ripening rooms assures more uniform cooling or warming of the fruit as needed and more uniform ethylene concentrations throughout the ripening.
When ripening is done in non-pressurized conventional rooms, open stacking of boxes is essential to allow adequate air circulation for uniform ripening. Many stacking patterns are used, the best pattern to be used depends upon pallet sizes and ripening facilities. Because heat rises, the amount of box top area exposed is most important for preventing heat build-up in the stack and controlling pulp temperature during ripening. Bananas are usually ripened to color stage 3 to 4 before delivery to distribution centers, retailers or wholesalers.
Within certain limits, the period required for ripening bananas can be shortened or extended to meet trade requirements by adjusting the temperature. Under average conditions, depending on initial temperatures chosen and condition of the fruit, the ripening cycle can be as short as 4 days (> 18 °C) or may be extended to 8 to 10 days (at 14 °C). If initial ripening temperatures are too high (> 25 °C), the pulp will soften but the peel will remain green (a condition described as ‘cooked’ or ‘boiled’ fruit).
Uneven ripening can be caused by low temperatures and insufficient ethylene. Ripening rates and characteristics of the fruit vary to some extent between lots depending on cultivar, country of origin, weather conditions during the growing of the fruit, temperatures during handling and transit, and maturity of the fruit. Hard-green fruit (less full), will take longer to ripen than more advanced and full fruit.
The lower value of the range is for mature-green fruit, and the higher value is for ripening fruit. Data were modified from Kader, 1998. To get mL kg-1 h-1, divide the mg kg-1 h-1 rate by 2.0 at 0 °C (32 °F), 1.9 at 10 °C (50 °F), and 1.8 at 20 °C (68 °F). To calculate heat production, multiply mg kg-1 h-1 by 220 to get BTU per ton per day or by 61 to get kcal per metric ton per day.