Plantain is a climacteric fruit. During their growth, there is an increase in size of the fruits and accumulation of starch. This increase in size stops when the fruits reach total physiological maturity.
Theoretical determination of the harvesting stage of Cavendish banana (Ganry, 1978) showed that increased fruit diameter in the absence of limiting soil factors is a function of the total daily temperature from the appearance of the last hand of the bunch up to the harvest stage (3/4 full or 34 mm grade). The total daily temperature is defined from a 14 ºC threshold, which represents the minimum temperature permitting the growth of bananas. The total daily temperature is equal to [(0,4 x T max) + (0,6 x T min)]-14. In optimal conditions without constraints other than temperature, a total cumulative temperature of 900º C is required to obtain the theoretical optimum harvest stage of dessert bananas. The same growth model applied to French Sombre plantain (N'da Adopo, 1992) confirms that bunches of this plantain cultivar at the 3/4 filling stage are obtained at total cumulative temperature between 900 and 1000ºC. Bunches harvested at full maturity (bunches with well filled fingers and some few ripe fingers) correspond to a total cumulative temperature of 1200ºC. In practice, this model is not apparent to most plantain producers who usually don't work in optimal farming conditions.
In practice, harvest maturity of fruits will depend mostly on the target market. Plantains for local markets are harvested at a more advanced stage of maturity than those for exportation. The maturity indices are based on the age of the bunch, the interval between flowering and harvesting (IFH), the filling of the fingers or the colour of the skin and pulp. The filling of the fingers is the criterion mostly used. This standard is typically completed by other visual criteria like the evolution of the peel colour of the fruits. Most of these criteria depend on the cultivar. If the filling of the fingers was combined with the colour of the pulp, evaluating harvest maturity could become more objective (Marchal, 1993). This leads to the definition of three stages of fruit maturity: non-angular fruits with pale and whitish pulp (stage 1), rounded fruits with well-coloured pulp (stage 3), and stage 2 between stage 1 and 3. The interval between flowering and harvesting (IFH) is also an objective criterion, which can be grounds for harvest decision. Using the practical IFH and the evolution of average temperature, it is possible to define in each ecological zone an IFH chart according to the seasons and cultivars.
Other maturity indices like pulp to peel ratio, fruit firmness, diameter and length of the fruits reported by Thompson and Burden (1993) are less useful for traditional plantain producers.
Investigations on the best standards to address yield requirement, bunch quality and the conservation of green mature plantain by analysing stages of harvesting remains a priority in producing countries.
The usual method of harvesting plantains is to partly cut through the pseudostem approximately 2 m from the ground or at upper thirds with a machete. This allows the plant to bend over under the weight of the bunch. The bunch is then cut off and taken away while the pseudostem is left in the plot. The pseudostem is then cut into pieces to reconstitute the organic matter. The stages involved in harvesting a bunch of plantain are shown in Figure 2. This mode of harvesting exposes the fruits to mechanical damage, especially when no precautions are taken to prevent the bunch from falling on the ground (Wainwright and Burdon, 1991; Dadzie, 1994). In the case of dwarf types, bunches can directly be cut off and removed from the pseudostem without cutting it into sections.
Figure 2a-2d:
Stages involved in harvesting a bunch of plantain without mechanical damage (photo J. Tchango Tchango)
The use of plastic forms is recommended to protect bunches of plantain during harvesting and transportation to the packaging site in the same manner as exportation from industrial plantations. This reduces mechanical damage and avoids reduction of fruit quality of plantains for exportation.
The handling techniques of plantains before marketing are generally less adapted to the fragile and perishable nature of the product. In the producing countries of central and west Africa, hands or entire bunches of plantains are combined with other agricultural products in baskets and pans and carried on top of a person's head home or to sell by the roadside. Hands or single fingers can also be packed with other agricultural products in bags to facilitate transportation. Generally in Cameroon, men transport plantains on their heads, behind their bicycles or motorbikes or in rickshaws to their houses or to be sold. Packages of 2 to 3 bunches of plantain are jointed to each other. Women in certain regions of Cameroon carry bunches of plantains in baskets hung on their backs from the plantation to their homes or selling points (Figure 3).
Figure 3:
Transportation of bunches of plantains to the market by women in the region of mile 20 in the South West province of Cameroon (photo J. Tchango Tchango)
In markets located in the production zones, the bunches of plantains bought from the villages are piled up on one another (Figure 4), then loaded in bulk in trucks (Figure 5) or vans for travel to big distribution and consumption centres situated at times hundreds of kilometres away. The bunches are piled up to maximise loading and to expedite transportation. They are unloaded without caution at the destination. These different modes of packaging and transportation expose the fruits to damage and low market quality (Marchal, 1990; Wainwright and Burdon, 1991; Dadzie, 1994; N'da Adopo et al, 1996).
Figure 4:
Bunches of plantains piled on one another while awaiting loading in truck at the Mile 20 market in the South West province of Cameroon (photo J. Tchango Tchango)
Figure 5:
Loading bunches of plantains in bulk in trucks at the Mile 20 market in the Southwest province of Cameroon for transportation to urban centres (photo R. Achard)
Figure 6:
Reusable plastic cages, which could be used for packaging and transportation of plantain hands (photo J. Tchango Tchango)
Dehanding plantains in the field and packaging the hands in reusable plastic cages reduce mechanical damage and preserve the fruit quality during transportation. An example of reusable plastic cages, which could be used, is shown in Figure 6. The utility of this packaging is not obvious in many producing countries as peasants and intermediate wholesalers are accustomed to bunches. In addition, they are not prepared to bear additional costs or extra investment to buy plastic cages for local sales.
Bunches of plantains exported by ship from Cameroon to Gabon are transported in bulk by ship, without any particular care similar to those sold locally since the trip is about 48 hours.
Plantains exported to Europe and North America are superior quality compared to those sold locally. A high grade of false horn type plantains is in great demand in these countries. In Cameroon, plantains exported to Europe by air are harvested at normal maturity and packed under perforated plastic film in well-ventilated cartons. This method is used to export dessert bananas. Plantain exported by ship in containers or in refrigerated docks (12-14_ C) should be harvested much earlier to avoid ripening during transportation (about 15 days). They are handpacked under perforated plastic film in cartons after soaking them in a solution to avoid the development of fungi during transportation. Studies are underway at the CRBP bananas and plantains regional research centre in Cameroon to determine the optimal harvest period of fruits for plantain cultivars (Big Ebanga, Bâtard and French Clair). This study intends to ensure crop conservation at 12-14_C in the mature green stage during transportation to Europe. Export by ship would enable participants:
To compete with the higher costs of transportation by plane in Cameroon and in other producing countries;
To increase the profit margin;
Promote the development of the production of plantains to ensure high export tonnage.
In Central America, the false horn Cuerno and the bâtard Dominico-harton are the most exported cultivars to North America (United States) and Europe (FHIA, 1993; Lescot, 1993). Single fruits are packed in normalised cartons after soaking in a fungicide solution containing 35 ppm of thiabendazole (0.0035 percentage) and 1000 ppm of imazalil (0.1 percentage). Afterwards the cartons are placed into pallets and transported in refrigerated containers (8 to 9_C) to North America and Europe (FHIA, 1993). In the European market, plantains from Latin America seem to be of inferior quality since they ripen poorly during marketing compared to those transported by plane or by ship in optimal conservation conditions (12 to 14_C and 85 to 95 percentage HR).
In producing zones and at the local distribution market, bunches of plantains are generally stockpiled in bulk (Figure 4). However, simple methods intended to reduce the desiccation and the evapotranspiration rate of fruits are occasionally used within the traditional distribution channel to maintain a certain level of freshness and an acceptable quality for a number of days. These measures include precautions to limit mechanical damage to fruits, stocking bunches under shades shielded from the sun and protection of piles of plantains with leaves of banana or bags regularly moistened with water.
Studies carried out in Côte-d'Ivoire have shown that bunches of plantains (Offoto and Orishele cultivars) harvested at normal maturity stage can be kept green in peasant farms for 14 to 20 days at 302_C and 24 to 27 days at 202_C. This assumes that bunches are harvested when fingers are well filled or rounded and wrapped in plastic bags (8/100 mm) mixed with powder of dry cocoa leaves or rice husk. They will be preserved without remarkable modifications of their organoleptic characteristics (Agbo et al, 1996)
Traders who want to sell their plantains at the ripe stage generally induce the ripening process by stocking them in baskets, drums or other containers covered with plastic bags or jute bags to maintain heat among fruits. These containers are ventilated by removing the covers after 2 to 4 days.
Studies carried out on the conservation of plantains recommend that they be packaged in suitable plastic bags to reduce air circulation. In addition, the use of low temperatures (12 to 14_C) to extend the green life span and maintain the fresh quality of fruits is advised (Hernandez, 1973; Ngalani, 1986; Marchal, 1990; Collin, 1991). These modern techniques of conservation require an investment (purchase of appropriate plastic bags and storage equipment, installation of positive cold store, electricity bills, etc.). Traditional plantain producers and traders would hardly adopt them. All storage attempt to prolong the shelf life of mature green plantain should be preceded by an economic analysis of the system in place: network type, stage of harvest, market value and price after conservation (N'da Adopo et al; 1996). The use of refrigerators or appropriate plastic bags would then be necessary only in the long distribution channel to great distances to supply the non producing zones where selling plantains at a higher price will justify the establishment of such a technology.