Agricultural processing refers to activities performed to maintain or improve the quality or to change the form or characteristics of agricultural products. These processing operations add value to agricultural materials after production.
The primary purpose of agricultural processing is to minimize both qualitative and quantitative deterioration of materials after harvest. High post-harvest food losses, mainly due to limited food preservation capacity, significantly constrain food and nutrition security in developing West African countries. Seasonal food shortages and nutritional deficiency diseases remain major concerns in this region.
Simple, low-cost traditional food processing techniques form the foundation of small-scale food processing enterprises essential to rural development in West Africa. It is estimated that about 50% of perishable food commodities including fruits, vegetables, roots, and tubers and about 30% of food grains such as maize, sorghum, millet, rice, and cowpeas are lost after harvest.
Factors responsible for these high post-harvest food losses include ineffective or inappropriate food processing technologies, careless harvesting, inefficient post-harvest handling, poor road and rail infrastructure, bad market practices, and lack of adequate storage facilities, packing houses, and market infrastructures.
Definition and Importance of Food Processing in Agriculture
Food processing is the transformation of plant, animal, or other materials used for food to improve acceptability and ensure availability throughout the year.
It includes food preparation, which makes food ready for immediate consumption, and food preservation, which keeps food for future use. Food processing may sometimes cause the loss of certain desirable qualities in food.
Reasons for Food Processing in Agricultural Products
1. Improve digestibility by making food easier to break down in the stomach.
2. Enhance sanitary quality by killing harmful microorganisms.
3. Create desirable flavors that are pleasant to the taste.
4. Preserve food to allow longer storage, saving time and energy.
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Basic Principles of Agricultural Food Processing and Preservation
Food preservation targets either short-term or long-term storage. Short-term preservation applies to horticultural commodities consumed soon after harvest, where keeping the product alive and respiring is best.
This method does not destroy microorganisms or enzymes, so deterioration continues, often faster due to stresses during harvesting and handling.
Long-term preservation involves inactivating or controlling microorganisms and enzymes, and reducing or eliminating chemical reactions causing food deterioration.
Microorganisms are controlled through heat, cold, dehydration, acid, sugar, salt, smoke, atmospheric composition, and radiation.
Mild heat (82°C to 93°C) kills bacteria in low-acid foods, but to destroy spores, 121°C wet heat for at least 15 minutes is required. Refrigeration and freezing slow microbial growth but do not kill all bacteria.
Dehydration removes water necessary for microbial growth, preserving crops against spoilage. Sugar and salt act as preservatives by causing osmotic dehydration of microbial cells, leading to cell death.
Controlling moisture or relative humidity in storage is vital for maintaining crop life and preventing microbial growth.
Common Methods Used in Preparation and Processing of Agricultural Foods
1. Separation and sub-division
2. Combination or mixing
3. Heating
4. Cooling
5. Use of chemical compounds
6. Use of microorganisms
Separation and Sub-Division in Agricultural Food Processing
Separation and subdivision improve food palatability or eating quality. Separation removes undesirable parts that are distasteful, coarse, or unattractive.
For example, peeling cassava removes the outer layer, which is unpalatable and coarse. Paring yams removes the coarse cortex. Subdivision removes parts that cause fast spoilage.
Methods of Separation and Sub-Division
1. Cutting: Reducing food into small pieces using knives or machetes.
2. Grinding: Crushing food like tomatoes and peppers into mash using wooden tools or machines.
3. Pounding: Reducing food into coarse or smooth paste using a mortar and pestle.
4. Grating: Rubbing food against a rough surface (e.g., cassava or coconut).
5. Peeling: Removing outer layers of fruits or vegetables, sometimes aided by hot water, steam, or chemicals.
6. Paring: Removing surface layers with a knife (e.g., yams, potatoes).
7. Scraping: Removing surface layers by applying pressure with a knife edge (e.g., fish scales).
8. Cracking: Breaking hard nuts or kernels with stones or rods (e.g., palm kernel, coconut).
9. Milling: Crushing and sifting grains into flour using machines.
Other methods include filtering, flotation, pressing, refining, skimming, steeping, evaporation, and centrifugation.
Combination or Mixing in Food Preparation
Combination or mixing joins food materials or ingredients to improve palatability, texture, and flavor control.
Methods of Combination or Mixing
1. Beating: Lifting and dropping food briskly with tools to incorporate air (e.g., whipping eggs or cowpea mash).
2. Stirring: Mixing in a circular motion with a spoon (e.g., stirring porridge).
3. Blending: Thorough mixing of ingredients (e.g., mixing corn dough with spices).
4. Stir-pressing: Pressing and turning thick paste to prevent lumps during cooking (e.g., tuwo preparation).
5. Kneading: Folding and stretching dough to develop texture (e.g., bread dough).
6. Cutting: Incorporating fat into flour for pastry preparation.
7. Folding: Gently mixing ingredients to retain air (e.g., folding whipped cowpea in akra).
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Other techniques include creaming, marinating, and emulsification.
Heating as a Method in Agricultural Food Preparation
Heat causes temperature rise in food by absorption from the environment or direct contact with a heat source. Heating is used for cooking (affecting the whole food mass) or toasting (primarily affecting the surface).
Examples include boiling yams (cooking) and roasting plantain (toasting).
Factors affecting heating include:
1. Method of heat transfer
2. Duration of heating
3. Temperature at the food surface and center
4. Type of food being heated
Common cooking media include air, water, sand, fat, or combinations of these.
Types of Agricultural Food Processing
Agricultural processing is carried out to maintain or improve quality or change the form of products, minimizing post-harvest deterioration. Processing types include:
1. Primary Processing: Purification and grading of raw materials, removing foreign matter and immature grains to prepare for further processing.
2. Secondary Processing: Converting primary processed raw materials into food suitable for consumption after cooking, roasting, or frying.
3. Tertiary Processing: Converting secondary processed materials into ready-to-eat forms.
Farmers usually sell produce immediately after harvest, keeping some for consumption and seed. Food processing has gained importance due to consumer demand for ready-to-cook (RTC) and ready-to-eat (RTE) foods, as well as snacks and beverages.
Sector-wise Agricultural Food Processing
Food processing transforms raw ingredients into consumable food products for humans or animals, either at home or by industries. It uses harvested crops or butchered animal products to produce marketable, often shelf-stable food and animal feed.
Fruits and Vegetable Processing
Processed products include beverages, jams, jellies, candies, preserves, canned and dehydrated fruits and vegetables, pickles, soup mixes, sauces, and ketchups.
Processing involves washing, grading, treating, storage, dehydration, peeling, slicing, crushing, extraction, bleaching, sterilizing, filling, sealing, and packaging.
Although fresh fruits and vegetables are preferred in Nigeria due to seasonal abundance and low prices, processed forms like canned pineapples, mango slices, and juices have increased significantly in recent years.
Examples of Common Agricultural Processing Industries
1. Gari Processing: Cottage industries processing raw cassava into gari.
2. Rice Milling: Modern rice mills separate dehusking and polishing processes. Husk is used for energy and industrial products, while bran is used for oil extraction. These mills offer better recovery and energy efficiency than traditional hullers.
3. Wheat Milling: Roller mills produce flour sold to bakers and confectionery companies. The demand for soy-blended and branded wheat flour is increasing due to better quality, expanding organized wheat milling.
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