Respiration can be reduced, and hence storage life increased, by modifying atmospheric composition within the storage area. However, this method can be costly, and therefore is less used.
Normal atmospheric composition is approximately 21% oxygen, 78% nitrogen, and 0.03% carbon dioxide. By reducing the proportion of oxygen and raising the carbon dioxide, the rate of respiration is reduced, and plantain and banana ripening is delayed. For example, bananas stored in 5% carbon dioxide and 3% oxygen at 20 °C have been stored for more than 6 months.
Control of atmospheric composition requires a sealed environment. Sealed storage rooms, where levels of atmospheric gases can be monitored and adjusted, are expensive. A cheaper alternative is a plastic tent. Plastic tents are used in Malaysia and the Philippines to extend the storage life of Pisang Mas (Golden banana).
A simple and cheaper method is to seal fruit in polythene (polyethylene) bags. Plantains sealed in polythene bags remain green for a longer period than fruits stored in perforated polythene bags, paper bags, or wet coir. As the fruits respire, the atmosphere within the bag decreases in oxygen and increases in carbon dioxide. Respiration is then inhibited because of the reduced oxygen.
Plantain and banana may be sealed individually, or several fruits may be bagged together. When several plantains or bananas are stored together in a bag, the first fruit that ripens produces ethylene, and this causes other fruit to ripen. Therefore, only bag together fruit of the same maturity.
In one study, storing bananas in polythene bags at 20 °C delayed ripening by up to 6 days. Also, weight loss was reduced and there was less mechanical damage. High humidity develops in polythene bags. This reduces water loss from fruit, and also has a lubricating effect, which protects fruit from physical damage.
Although polythene bags can extend storage life, there are a number of problems associated with their use. High humidity within bags can result in development of crown rots, caused by Gleosporium musarum. These rots are controlled with fungicides such as benomyl and TBZ.
'Green soft' or 'boiling' may also occur in fruit stored in polythene bags. The peel remains green, but the pulp becomes soft and develops an off-flavor and odor. This disorder results from storing fruit in high levels of ethylene and carbon dioxide, with low oxygen. 'Green soft' can be avoided by including an ethylene absorber in the bag (see below), or using semipermeable polythene.
Polythene bags are now widely used in Australia to extend storage life of fruit. Studies in Sudan and Ghana confirmed the advantage of using polythene bags to extend storage life, but the technology has not been adopted in these countries. Reasons may be lack of information or unavailability of materials. However, it is more likely that polythene bags were not suited to the current system of handling, or that the extra investment in materials and time was not rewarded by higher profit at the market.
Storing perishable produce in bags to extend storage life has also proven successful with cassava. To avoid high costs, cheap and easily available materials, such as moist jute bags, can also be used.
Ethylene removal. Reducing ethylene levels delays ripening. Using chemical ethylene absorbents or oxidizers, to reduce ethylene inside polythene bags, is a feasible method for extending storage life.
Ethylene can be absorbed by activated carbon, or oxidized by potassium permanganate, ozone, ultraviolet light, or the use of catalysts.
The simplest ethylene absorber consists of an inert carrier, such as vermiculite or rice hulm and ash, impregnated with potassium permanganate. Potassium permanganate absorbs free ethylene. Recently, Japanese researchers have made plastic bags coated with zeolites, which absorb both oxygen and ethylene. Zeolite use is at an early stage, but may eventually result in an appropriate technology for extending storage life of plantain and banana.
|Objectives, Study materials, Practicals|
|1||Storing plantain and banana|
|2||Improving storage life|
|3||Temperature, humidity and ventilation|
|5||Treatment of fruit|
|6||Improving postharvest handling|
|8||Suggestions for trainers|