Introduction

• Banana is one of the oldest tropical fruits cultivated by man from prehistoric time in India with great socio-economic significance.

• A banana is an edible fruit, produced by several kinds of large herbaceous flowering plants. In some countries, bananas used for cooking may be called plantains. Banana var. ‘Robusta’ is one of the important tropical fruits grown commercially in India and is produced in large quantities throughout the year.

• India, banana contributes 31.72% of the total fruit production. India is the largest producer of banana in the world, producing around 20% of the worldwide crop of 145 million metric tones.

• Banana is indigenous to Asia, probably originated some where in the mountainous region of Assam, Burma, Thailand or Indo-China. From there it has spread to tropical parts of America, Africa, Australia, Philippines and Hawaii. 

 

Identification and Classification:

• Banana is classified as major tropical zone fruit according to growing regions & environmental conditions.

• It comes under climacteric fruits type i.e., can be harvested mature & ripened off plant. That increases the post harvest life.

• Botanically the Banana is a Berry.

 

Maturity at harvest and harvesting methods

Harvesting of banana:

•The trunk is lopped with a sickle or hatchet over half-way through the stem.

•The bunch will not fall to the ground but hang on, and injury is avoided. The bunch is held and its peduncle is served.

 •About 30 cm of the stalk must be left to make handling easy.

-Selection of right stage of maturity for harvest is an important aspect, which has considerable influence on storage life and quality and final acceptance by the consumer.

Signs of maturity:

1.The fruits are harvested when top leaves start drying. It usually happens in 120 to 140 days after flowering.

2. Shedding of floral ends of the fruits with slightest touch of the end.

3. The color of the fruits changes from deep green to lighter green.

4.The angles or ridges of the fruits become less prominent or they become round.

5.The dwarf bananas are ready for harvest within 11 to 14 months after planting while tall varieties take about 14 to 16 months to harvest.

Post Harvesting

•  After harvesting, banana is subjected to either storage or ripening. The fruits can be stored at a temperature of 13-14°C and relative humidity of 85-95 % for about 3 weeks.

•  Storage life can be prolonged by keeping the fruit in relatively high concentration of CO2 and low concentration of O2.

•  Ripening of banana fruits can easily be related for 10-12 days at ambient temperature held in sealed polythene bags.

•  Mature green banana fruits after harvesting resulted in reducing ripening without affecting fruit quality when they are immersed in hot water at 50°C for 10 minutes.                   

Ripening of Banana:

• The method is very simple. In this, bunches of banana are heaped in dry and clean air-tight room and covered with leaves. The fruits are ready within 4 days.

• Further, this period can be reduced to half by enhancing ripening if room is provided with smokes, which are produced with straw, leaves etc in a corner of the room. After that, they are placed in a wellventilated room for development of color. 

• Certain chemicals are also used, Ethrel solution @ 5000 ppm with 5 gm of NaOH pellets kept in a beaker in the ripening room ripened the banana fruits within 48 hours.

 

Chemical changes In Banana during ripening

1. Carbohydrates:

• Sugar is a major carbohydrate in mature unripe banana. During ripening, the starch is hydrolysed, only 1-2% remaining in a fully ripe fruit. Sugar normally 1-2% in the pulp of green fruits, increases to 15-20% in ripe pulp.

• Sucrose, Glucose and fructose are major sugars in banana pulp. These sugars increases during ripening, maintaining a constant proportion of 66% sucrose, 14% fructose and 20% glucose.

• Insoluble protopectin decreases from 0.5 to 0.3% and soluble pectin a corresponding increase during ripening. Cellulose decreases slightly during ripening.The hemicellulose makes up 8-10% of fresh banana pulp in green fruit, decreasing to about 1% in the ripe fruit.

2. Phenolic Compounds:

• Dopamine was reported to occur in high concentration (700 µg/g fresh weight) in bananas peel and to be present in pulp (8 µg/g fresh weight). It is the primary substrate in enzymatic browning. It is further confirmed that Dopamine is the only major phenolic constituent in banana peel.

• Loss of astringency during ripening of banana results from increased polymerization of the tannins.

3. Flavor Constituents:

• Several volatile compounds have been isolated and identified in banana.

• A banana like flavour was assigned to the amyl and isoamyl esters of acetic, propionic and butyric acids whereas alcohols and carbonyls gave odours described as green, woody or musty.

• Ripe banana aroma was due to a mixture of some 20 saturated acetates, propionates and butyrates together with n-hexane.

4. Organic Acids:

• Malic acid has been identified as the main acid in banana with substantial quantities of oxalic and citric acid in the pulp. The malic acid increases substantially upon ripening, whereas the oxalic acid is metabolized and decreased.

• The enzymatic decarboxylation of oxalate may account for the disappearance of astringent taste during ripening.

5. Pigments:

• The change in colour of fruit from green to yellow is the most obvious change during ripening.

• The green banana peel contains about 50-100 µg/g fresh weight of chlorophyll, 5-7 µg/g fresh weight of xanthophyll and 1.5-3.5 µg/g fresh weight of carotene. During ripening, chlorophyll is lost and total yellow pigment remains approximately constant.

• Chlorophyllase activity in banana peels increases sharply at the onset of the climacteric rises to a peak which coincides with the climacteric peak and then falls to near zero in the post climacteric period.

6. Enzymes:

Banana fruits contain several hydrolytic and oxidative enzymes. The relative activities of alpha-amylase, starch phosphorylase, acid phosphatase, peroxidase and catalase increased considerably in three cultivars of banana fruits stored for 5 weeks at 200 C. A rise in the activities of all the enzymes, having a maximum about 1.2-19.1 times their initial level, was observed during ripening at 200C.

 

Post harvest factors:

Maturity Indices:

Degree of fullness of the fingers. Bananas are harvested mature-green and ripened since fruits ripened on the plant often split and have poor texture.

pH of fruit   Pulp to peel ratio Peel Color   Pulp Firmness Pulp Color Shape   Appearance Starch Content   Specific gravity Total Titrable Acidity   Total Soluble Solids Content

(5.2-5.6), Highest on the 12th week from harvesting. Decreases later. (2.7), More the ratio, more mature is the fruit. Dark Green to Light Green, then yellow to yellowish brown. Decreases as it matures. White-Creamy to Yellowish Creamy. Angular to round &  full notably with less visible angles. Rust like spots on the peel. Increases gradually as banana ripens. Highest in the 10th week from harvesting and again it decreases. Varied from 1.08 – 1.12 Increased from the 7th to 8th week and highest at 12th week from harvesting. Has no sugars till 12th week Initiation ripening process as a result of starch hydrolysis.

 

Post Harvest Management

Sequence of postharvest operations in banana

 

Factors Involved in Post Harvest Deterioration

Biological Factors

·         Respiration

·         Ethylene Production

·         Transpiration (Water loss)

·         Physiological Disorders

·         Physical Damage

·         Pathological Breakdown

Environmental Factors

·         Temperature

·         Relative Humidity

·         Atmospheric Composition

·         Ethylene

 

Biological Factors

Respiration:

• The process of respiration involves combining O2 in the air with organic molecules in the tissue to form CO2 and Water.

•  A major part of postharvest technology is devoted to reducing respiration because the storage life of commodities varies inversely with the rate of respiration.

•  Bananas, having higher rates of respiration tend to have shorter storage life than those with lower rates of respiration.

•  Once the respiration ends, senescence of the banana fruit starts thereby contaminating it with microorganisms and decaying of the fruit. 

•  Banana has moderate rate of respiration of around 10-20 mg CO2 kg^-1 h^-1 at 5°C

 

Ethylene Production

•  Ethylene (C2H4) is a gaseous plant hormone which determines the time between harvest and senescence. Ethylene shortens the preclimacteric period; at high concentrations, ethylene causes rapid initiation of the climacteric respiratory response and accelerates ripening.

•  During ripening, banana produces larger amounts of ethylene than nonclimacteric fruits.

•  When ethylene is applied to bananas, at a concentration as low as 0.1-1.0 ml/l, for 1 day, ripening starts. Once ripening starts, bananas ripen within 1-2 days.

•  When nonclimacteric fruits are exposed to ethylene, fruits show an increased rate of respiration. However, respiration rate falls when ethylene is removed. A rise in respiration rate may occur more than once in nonclimacteric fruits. However, for bananas, the climacteric is autocatalytic, that is, once started, the process cannot be stopped until the fruit is ripe.

• Poor storage methods allow a build up of ethylene, stimulate the climacteric response, and increase the ripening period.

•For example, plastic sheets placed over stacks of fruit for shade increase the level of ethylene within the plantain stack and increase the rate of ripening. Therefore, store plantain in thatched or ventilated areas to prevent the build up of ethylene.

•  Also, do not store unripe fruits with ripe fruits. During the preclimacteric period, fruits are less susceptible to physical damage and pathological attack. This is the best time for handling, transportation, and marketing.

 

Transpiration and Relative humidity

•  Where banana fruit is sold on a weight basis, loss of water means economic loss. Additionally, water loss reduces visual quality. Water loss causes plantain to lose its firmness, the peel becomes soft and shriveled, and ripening period reduces.

•  For a 2% change from 2% to 4% weight loss per day, ripening period reduced by 9 days or 50%. However, for the same 2% change from 8% to 10% per day, only a 1 day or 5% reduction in the ripening period occurred. Therefore, at a high rate of weight loss, a small increase in weight loss has a critical effect on ripening.

•  The rate of water loss depends on the ambient relative humidity (RH). RH is the amount of water vapor present in the air, relative to the maximum amount of water vapor that can be held in the air, at a given temperature, saturated air being 100% RH.

• When banana is placed in an enclosed space, for example, a sealed container, the water content of the air within the container increases or decreases until it is in equilibrium with the fruit.

•  The water equilibrium principle applies when fruit is stored. The rate of water loss depends on the ambient RH. At an ambient RH of 95-100%, fruit loses little or no moisture, and ripening period is unaffected. However, as humidity decreases, the rate of water loss increases, and ripening period reduces.

Physiological and Physical Disorders

Chilling injury:

Symptoms include surface discoloration, dull or smokey color, subepidermal tissues reveal dark-brown streaks, failure to ripen, and, in severe cases, flesh browning. Chilling injury results from exposing bananas to temperatures below 13°C (56°F) for a few hours to a few days, depending on cultivar, maturity, and temperature. For example, moderate chilling injury will result from exposing mature-green bananas to one hour at 10°C (50°F), 5 hours at 11.7°C (53°F), 24 hours at 12.2°C (54°F), or 72 hours at 12.8°C (55°F). Chilled fruits are more sensitive to mechanical injury.

Skin abrasions:  

Abrasions result from skin scuffing against other fruits or surfaces of handling equipment or shipping boxes. When exposed to low (<90%) relative humidity conditions, water loss from scuffed areas is accelerated and their color turns brown to black.

Impact bruising:

Dropping of bananas may induce browning of the flesh without damage to the skin.

 

Environmental factors

Temperature:

• Physiological studies on bananas show that storage life decreases as external temperature increases over the range 15-35ºC. A 1ºC reduction increases storage period by 1-2 days.

• However, at temperatures below 11ºC, fruits suffer chilling injury. Therefore, optimum storage temperature for plantain and banana fruits is 13-14ºC. This temperature will maintain fully mature, ripe and unripe fruits for 1-2 weeks. Storage period can extend to 4 weeks when plantain and banana are harvested up to 4 weeks before full maturity.

• The relationship between ripening period and temperature is due to fruit respiration. Fruit respiration depends on many enzymatic reactions, and the rate of these reactions increases exponentially with increase in temperature. Studies show that ripe fruits respire at approximately 4 times the rate of unripe fruits. Consequently, ripe fruits lose sugar resources at a higher rate than unripe fruits. This explains why ripe fruits deteriorate quickly.

 

Air Composition:

•  The atmospheric gases present can be desirable and undesirable. More CO2, lesser O2 is not good and very high concentrations of O2 ripens the banana rapidly.

Relative Humidity:

•  RH governs the water losses occurring in the fruit. More the water loss, lesser is the ripening period.                               

Ethylene:

•  At high concentration of Ethylene, it causes rapid initiation of the climacteric respiratory response and accelerates ripening. •  It’s effect on harvested fruit desirable (degreening & ripening) or undesirable (abbreviated storage, softening).

 

Recommendations for Maintaining Postharvest Quality

1.    Temperature & Controlled atmosphere:  

-Optimum Temperature                                        -Optimum Relative Humidity 

13-14°C (56-58°F) for storage and transport            90-95%  

15-20°C (59-68°F) for ripening

 

2.     Rates of Respiration Production                  

Temperature	ml Co2/kg-hr1,2
13oC (56oF) 15oC (59oF) 18oC (65oF) 20oC (68oF)	10-30 12-40 15-60 20-70

3.   Rates of Ethylene Production

Temperature	ul C2H4/kg-hr1
13oC (56oF) 15oC (59oF) 18oC (65oF) 20oC (68oF)	0.1-2 0.2-5 0.2-8 0.3-10

4.   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) 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 room.

 

5.    Responses to Controlled Atmospheres (CA)

·         Optimum: 2% O2 and Below 6-8% CO2 at 15.6°C

·         CA delays ripening and reduces respiration and ethylene production rates

·          Post-harvest life potential of mature-green bananas: 2-4 weeks in air and 4-6 weeks in CA at 14°C (58°F)

·         Exposure <2% O2 and/or >7% CO2 may cause undesirable texture and flavor

·         Use of CA during transport to delay ripening has facilitated picking bananas at the full mature stage.

 

Range of post harvest life of Banana

·       Upto 1(in months).

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