The tendency to produce excess crops, especially fruits and vegetables during the rainy season and their perishable nature underscore the need to preserve them. Being living tissues they respire rapidly and so deteriorate easily after harvest. However, advanced preservation methods are too sophisticated and expensive for the rural farmers. More so, they lack steady electric power supply at the farm centers and most rural settlements. Yet, they have to store the excess and transport them to markets especially at urban centres. This process may take some days.
In the course of transportation, the desirable attributes and qualities of colour, flavour, texture and nutritional values maybe impaired or lost. To prevent these, agriculturists and food technologists have designed local methods to extend their shelf lives. They are easy-to-do-it-yourself methods, which farmers can take full advantage of. Be that as it may, each has its advantages and disadvantages. The relevant ministries should organized seminars and work-shops to sensitise farmers on these methods.
Let us start with vegetables
The HESSIAN/POT method involves the preservation of wet, leafy vegetables inside earthen pots. The open top of the pot is covered with a wire mesh, above which a wet jute bag is laid. The humid nature of the surrounding atmosphere keeps the leaves fresh due to reduced water loss. The advantages include the local availability and cheap source of the materials. The vegetables so stored can remain fresh for between 6 to 7 days. There are no major disadvantages. This method is therefore, highly recommended to the rural farmers.
THE MOIST STEM CUNCH method involves the keeping of leafy vegetables inside a polythene bag, within a basket with a jute bag covering the top. A rectangular plastic container with vertical baffles on the opposite, narrower sides would confer similar keeping qualities on the vegetables, which can remain fresh for upward of 6 days. It has similar advantages as the Hessian/Pot method.
The PRE-STORAGE DRYING method can be done using a multi-purpose dryer. The diced vegetables are kept on top of the wire mesh, with the source of heat a few centimeters below. Cutting the vegetables into pieces increases the surface exposed to heat, and therefore the dehydration effect. This lowers the water activity or its availability to spoilage micro-organisms. Such vegetables can be stored for weeks.
The desirable food values such as colour, flaour, texture and nutritional qualities are largely retained when cooked. Its disadvantages include its loss of freshness and the need for special techniques on drying which may vary from one type of vegetable to another. For instance, amaranths should be dried at 39oC plus or minus 1oCelcius.
For those with access to a refrigerator, fresh vegetables can be kept inside freezers to be cut into pieces, wrapped with newspapers and covered with polythene. This method prevents freeze-drying.
Similar to this is the BLANCHED/FROZEN method. The vegetables are first blanched before keeping them inside polythene bags and kept in the freezer compartment. Blanching involves bringing the vegetables in contact with hot water (93.7oC – 99.2oC), or Steam (100oC), for some minutes, or even an hour. Blanching has many advantages. Oxygen is driven out. This prevents oxidation, browning and other enzymatic deterioration. The heat prevents microbial growth on the surface. Blanching prevents the toughness of the texture while retaining its colour, flavour and nutritional values.
The subsequent freezing further enhances the keeping qualities, since it slows down the growth of both bacteria and fungi. Despite the obvious disadvantage of the need for a refrigerator, this is one of the best methods of preserving vegetables.
THE EVAPORATOR COOLANT STRUCTURE method includes the pot-in-pot, tin-in-tin or metal-in-metal preservation techniques. The leafy vegetables are kept inside the inner container but are kept moist always with constant addition of water. The advantages are that they can be used by anybody anywhere because the materials are available locally and need no supply of electricity.
PRESEVERVATION OF FRUITS
Preservation of fruits is a slightly different ball game. To start with, the saying that “one bad apple spoils the bunch” holds true for fruits. It is therefore, imperative to remove the injured, spoilt or diseased ones from the rest, from onset. Fruits respire more rapidly than vegetables and are more susceptible to spoilage, as their stored nutrients are partly used up, after harvesting.
Climacteric fruits which exhibit such sharp rise in respiration include bananas, plantains, African mango, apples, pears and oranges. However, several methods can be used to inhibit their ripening. These include their storage in low ethylene atmosphere, within polythene bags, the use of candle wax and controlled atmosphere.
The latter which requires low oxygen tension and higher concentration of carbon dioxide above their natural atmospheric concentrations, may not be readily made available to rural farmers. Some do keep freshly harvest fruits inside ash to stimulate this.
DIRECT PACKAGING OF FRUITS IN BASKETS is cheap and easy to construct. They are easy to pack since the baskets are light in weight. However, they have low tensile strength. As such they should not be stacked during loading. The disadvantage is that the baskets are difficult to clean, making the fruits susceptible to contamination with spoilage micro-organisms. More so, the fruits have soft outer covering or epicarp which can be easily bruised by the sharp ends of the raffia basket.
THE DELAYED RIPENING TECHNIQUE is the packaging of fruits like oranges, mangoes, bananas and plantains inside polythene bags containing ethylene absorbent. This method extends the shelf life of fruits and delays the onset of storage deterioration. It allows the transportation of fruits in wholesome conditions, and ensures regulated ripening for use. The disadvantage is that if too many fruits are used at once, some may fail to ripen afterwards.
FRUIT WAXINGTREATMENT method involves the rubbing of fruit cover with candle wax, bee wax or a combination of both. This is best for enhancing fruit keeping qualities. The advantages include the reduction of moisture loss and prevention of its deterioration. It allows its transpiration and retention of its wholesome condition.
The DUFAYLITE CELL packaging method uses circular plastic compartments, joined together, with each containing a fruit. This physical separation prevents contact and contamination. It allows for aeration, but raises extra costs and labour during transportation.
Fruit packaging in PERFORATED CARTON is as its name suggests. The holes at the sides of the carton encourage aeration or ventilation. The carton used is light, cheap and can be locally constructed. However, they cannot be packed when empty. They soak easily and disintegrate. The fruits so packaged, therefore have short shelf life.
VENTILATED PLASTIC CRATES used for packaging fruits are strong, and yet relatively light. They are easy to stack when loaded, easy to pack when empty and can be cleaned after use. They are also adequately ventilated. Therefore, the fruits have appreciable long shelf life. The disadvantage is that of being expensive and cannot be locally constructed.
SLATED WOODEN BOXES used for packaging fruits are made of strong, wooden slabs. They are separated vertically, but bound one above the other with iron straps. They can be constructed by an average carpenter. They have high tensile strength and can be stacked when loaded. The boxes ensure long shelf life for fruits.
But the advantages include the facts that they cannot be packaged when empty, are not easily cleaned and are heavy and expensive.
The major considerations for packaging vegetables and fruits locally should be the availability and affordability of packaging materials. All these would ensure that they maintain the keeping qualities of colour, flavor, texture and nutritional values for the eventual consumer.
Ayo Oyoze Baje
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