In most Countries the production of many perishable crops is seasonal, this making them to be available only during short period of time within a year. During this short time they are produced in greater quantity than the market capacity, so the surplus of these crops must be processed and preserved to avoid wastage of food and income to the producer.
The surplus of many seasonal local crops can be preserved for later use by various processing methods requiring only simple, inexpensive equipment.
Processing and Preservation Methods.
>To process and preserve the fresh products successfully, the spoilage agents must be destroyed without ruining the nutritional value or palatability of the produces itself.
The best methods for small scale processing are; Drying, Chemical Preservation, and heat processing.
•Drying of produces.
The aim of drying is to reduce water content of the produce to a level insufficient for enzymes activity or the growth of microorganisms.
The critical moisture level is about 10-15% moisture content, depending on the commodity( if too much water is removed the product becomes brittle and easily shattered)
Produces can be dried using solar driying, and Artificial heart.
Solar drying is cheap but is not so easily controlled as drying by more sophisticated artificial methods. It can be done by using direct sun drying or using solar driers
The cons of using direct sun drying are as follows;
> Exposure of produces to dust and atmospheric contamination.
>Interference from animals and humans.
>Insect infestation.
> No control of Conditions.
Types of solar driers: Direct exposure driers, Indirect exposure driers , A combination of direct and indirect solar drier.
Certain treatments may be given to certain types of produces before drying to maintain the quality of commodity.
Fruits and Vegetables should be treated with sulpur dioxide before drying inorder to prevent enzymatic browning, It also slows breakdown of vitamin C and kills some microorganisms
Most vegetables except onions and Garlic are blanched by dipping them into hot water for a few minutes before drying; this stops the action of enzymes which may not be killed by sun drying process.
Green Vegetables retain their color better during drying, if about 0.25% of bicarbonate of soda is added to the blanching water (* but this can speed up the loss of vitamin C)
Dried vegetables products are subjected to severe insect infestation, and some may be affected by exposure to light during storage; therefore dried products must be stored in a very dry atmosphere in insect proof containers that is away from light.
• Chemical Preservation
Chemicals used in preservation includes Sugar, salt , Vinegar, and sodium meta- bisulphate
Preservation with sugar
This is based on using high concentration of sugar with fruit pulp or juices to create a product in which it is difficult for moulds and yeast to grow
Jams and Jellies. In these products acidified fruit pulp is boiled with sugar untill the cell pectin of the fruits form a gel. The hot preserve is sealed in sterilized jars to prevent contamination during storage.
An Example of strawberries Jams.
Apple Jams.
Fruits Chees. Pulped fruits is sieved and mixed with an equal weight of sugar. The mixture is then heated to remove most of the water. It is then spreaded on trays to cool and dry, then can be cut into cubes and stored under very dry conditions.
Fruits drink concentrates ( Squashes): Juice is extracted from heated fruit pulp and made into syrup with high sugar concentration. The syrup is then put into sterilized bottles, which are heated in a water bath at 88°C for 20 minutes. The bottles are closed with sterile caps for storage. Drinks are prepared by dilluting the concentrates with water.
Preservation with Vinegar ( pickled vegetables)
Young Fresh vegetables of many types as well as some fruits can be preserved by pickling in vinegar. The prepared vegetables or fruits are first soacked for few days in a strong salt solution ( brine ) and then packed into jars, which are then filled cold vinegar. The Vinegar is ussually flavored by steeping desired spices in it for one or two months. The jars are then covered with plastic lined cover.
Preservation with Salts
This method is usually used for preserving green beans, young green beans and salts are placed in alternative layers being of salt the jars are closed with moisture proof covers and then stored on stands.
* Fermented Products
Vegetables are subjected to lactic acid fermentation in brine glass of earthenware jars.
•Preservation using heat treatment.
For many years fruits and vegetables have been preserved by heat, using canning or bottling methods. The objective is to kill the enzymes and micro-ogarnisms by heating the produce in liquid in cans or jars. The containers are then sealed while still hot to prevent contamination of the sterilized contents.
Although moist heat Inactivates enzymes and kill most micro - organisms some bacteria such as clostridium and staphylococcus are heat resistant and are capable of growing and producing poisons in canned or bottled foods.
Acid foods such as fruits inhibit the growth of clostridium and prevent formation of poison. Non acid foods such as peas, beans and almost all vegetables can only be preserved by heat at high temperatures achieved in steam pressure vessels. For this reason, heat processing methods are not recommended for processing any vegetables under small scale local Conditions.
Thanks you so much for following me In my Blog.. The next Topic to be uploaded few days to come, will be Grains Storage and Handling...
Regards, Brogger Kihombo.
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