The reader will be able to:

o   Describe various ways of preserving and storing foods

o   Explain the biological bases of the methods of preserving and storing foods.

o   Explain what food additives are.

o   Identify categories of food additives.

o   Explain the biological principles upon which successful agriculture depends.

o   Explain how fertilizer use increases productivity of a farm land. 

o   Explain the biological importance of pesticides to boost agricultural productivity.

o   Explain the biological principles underlying successful animal husbandry.


Preservation and Storage of Food

Food preservation usually involves preventing the growth of bacteria or other micro-organisms, as well as retarding the oxidation of fats that cause rancidity.

Maintaining or creating nutritional value, texture and flavor is an important aspect of food preservation.

Food can be preserved by removing one or more of the factors that bacteria and fungi need to survive.

The basic idea behind all forms of food preservation is either:

o   To slow down the activity of disease-causing bacteria

o   To kill the bacteria altogether

o   To destroy enzymes found in a food that cause it to spoil or discolor quickly.


Food preservation

Methods of Food Preservation


Canning is the process of applying heat to food sealed in a container in order to destroy any microorganisms that can cause food spoilage. During the canning process, air is driven from the container.



Refrigeration preserves foods by slowing down the growth and reproduction of micro-organisms and the action of enzymes that cause food to rot. Fresh vegetables, meats and fish, breads and cakes are preserved in Refrigerators.



Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or sugar.

Methods of Food Preservation


This is achieved by exposing the food to smoke from burning plant materials such as wood. Smoke deposits a number of pyrolysis products such as phenols onto the food. The compounds aid in the drying and preservation of meats and other foods. 

smoking of food


Drying is the oldest method known for preserving food. Drying expose, the food to a temperature, high enough to remove the moisture but it does not cook.

Methods of Food Preservation


Pasteurization is a process for preservation of liquid food such as milk, wine, beer etc. In this method, food is heated at about 70 °C for 15 to 30 seconds to kill the bacteria present in it and cooling it quickly to 10 °C to prevent the remaining bacteria from growing.

Food preservation


Food is exposed to either gamma rays or x-rays. This treatment has a range of effects, including killing bacteria, reducing the ripening and spoiling of fruits.


Food Additives

Food additives are chemicals added to food in small quantities to preserve flavor or enhance its taste and appearance.

Examples are salts, yeast, baking powder, anti-caking agents (calcium silicate, magnesium stearate) to help retain moisture in breads and cakes, emulsifiers (yolk, lecithin, monoglycerides) binds oil and water to improve uniformity and smoothness of foods and stabilizers and thickeners (guar gum, gelatin).



o   To make food look and taste better

o   Maintain or improve nutritive value

o   Maintain freshness

o   Help in processing or preparation

o   Preserve food


Categories of Food Additives

1. Preservatives 

Preservatives prevent or inhibit the growth of microorganisms that might cause spoilage or food poisoning. Three natural preservatives are salt, sugar, and vinegar. But there are many more artificial preservatives in use today, such as nitrates and nitrites found in meats.   

2. Sweeteners

Sweeteners: are added to foods for flavoring. Sweeteners other than sugar are added to keep the food energy (calories) low, or because they have beneficial effects for diabetes mellitus and tooth decay.

3. Anti-Caking Agents

Anti-Caking Agents: keep powders such as milk powder from caking or sticking. Anti-caking agents are added to allow them to flow and mix evenly during processing.

4. Acidulants

Acidulants: are additives that give a sharp taste to foods. They also act as preservatives and antioxidants. Common food acids include vinegar, citric acid, malic acid, fumaric acid, and lactic acid.


Antioxidants such as vitamin C act as preservatives by inhibiting the effects of oxygen on food, and can be beneficial to health. They enhanced the nutritional value of food to which they are added.


Colorings: are added to food to replace colors lost during preparation, or to make food look more attractive. A range of organic, synthetic chemicals and other naturally occurring plant pigments are added to food to enhance the color.


Emulsifiers allow water and oils to remain mixed together in an emulsion, as in ice cream, and homogenized milk. Example of emulsifiers include sodium phosphates, lecithin, and diglycerides,


Stabilizers, thickeners and gelling agents, like agar or pectin (used in jam and jellies for example) give foods a firmer texture. While they are not true emulsifiers, they help to stabilize emulsions.


Flavors are additives that give food a particular taste or smell, and may be derived from natural ingredients or created artificially.


Health Implication in the Use of Food Additives

·   Some flavor-enhancer and preservative promote the growth and spread of cancer cells within the body. E.g.  mono-sodium glutamate.

·   Aspartame, a well-known artificial sweetener, cause migraine headaches, dizziness. Its consumption over long periods of time, lead to breast cancer.

·    Artificial sweetener e.g., saccharin used in soft drinks causes cancer in the urinary tract, bladder and ovaries.

·   Food colorings, such as Blue No.1, Blue No.2, Yellow No.6 and Red No.3, have been found to contain cancer-causing properties.



Biological Principles underlying Successful Agriculture

Optimum or ideal soil conditions supply essential minerals, water and air in their right proportions for successful farming.

Plants grow and develop by absorbing water and nutrients from the soil. Their ability to do this depends on the nature of the soil. Depending on its location, a soil contains some combination of sand, silt, clay, and organic matter. Soil Texture (the amount of sand, silt, clay, and organic matter in the soil) affects how well nutrients and water are retained in the soil. An ideal soil contains equivalent portions of sand, silt, clay, and organic matter. Such soil holds right type and quantity of nutrients (macro nutrients and micronutrients) required for plant growth. Sometimes, the nutrients that plants need occur naturally in the soil. Other times, they must be added to the soil as lime or fertilizer.

For proper growth and development of plants, the right amount of water should be provided to the plants. Water provides oxygen and hydrogen molecules needed by plants for photosynthesis. Insufficient supply of water lead to poor agricultural productivity.  

Another important material for proper plant growth and development is soil air. The principal soil air available for plants is oxygen and nitrogen. Nitrogen often comes from fertilizer application, from the air (through nitrogen fixing bacteria) or from decomposition of dead organism. The oxygen in the air surrounding the soil particles are used by plant roots and other organisms for respiration. The oxygen is also used for the decomposition of organic matter to form humus.

Effect of Fertilizer Use on Productivity on a Farmland

Fertilizer is any material of natural or synthetic origin that is applied to soils to supply one or more nutrients essential to the growth of plants.


For plants to grow and thrive, it needs a number of different chemical elements. The most important are:

o   Carbon, hydrogen and oxygen available from air and water.

o   Nitrogen, phosphorus, potassium (a.k.a. potash); the three macronutrients found in most fertilizers. Sulfur, calcium, and magnesium are secondary nutrients.

o   Boron, cobalt, copper, iron, manganese, molybdenum and zinc – Micronutrients


The most important elements are nitrogen, phosphorus and potassium and needed by plant in large quantities.  Any missing of macronutrients, limit the growth rate of plant. To make plants grow faster, there is a need to supply the elements that the plants need in readily available forms. That is the goal of fertilizer.

To maximize productivity, soils need routine applications of organic matter (compost, manure etc.) or artificial (synthetic or chemical) fertilizers to improve soil nutrients.

Organic fertilizers provide required nutrients to plants while also feeding the soil organisms by providing nutrient sources for microorganisms and earthworms living in the soil. Soil structure relies on these organisms, which help a plant's ability to absorb nutrients.

Manufactured or chemical fertilizers are readily available to plants without decomposition, easy to apply, and generally provide a quick release of nutrients for plant growth. 


The use of Pesticides to Increase Agricultural Productivity

A pesticide is any substance or chemical meant for preventing, destroying or repelling pest. Pests are unwanted living organisms or organisms that cause damage to crops or humans or other animals. Examples include: insects, mice and other animals, unwanted plants (weeds), fungi, microorganisms such as bacteria and viruses.

Pesticides can be grouped according to the types of pests which they kill:

  • Insecticides - insects
  • Herbicides - weeds
  • Rodenticides - rodents (rats and mice)
  • Fungicides - fungi
  • Larvicides - larvae

Benefits of Pesticide Use

Large quantities of foods are destroyed both on the field and in storage by pests.

The use of pesticides

¨  increase agricultural productivity by killing non-crop plants, limiting damage by insects and nematode pest, and by eliminating disease caused by fungi.

¨      also kill organisms that attack or destroy food crops in storage.

This contributes to increase in agricultural productivity and guarantee food security.


Biological Principles of Animal Husbandry

The term can refer to the practice of selectively breeding and raising livestock to promote desirable traits in animals for utility, sport, pleasure, or research.

Good animal husbandry practices are beneficial to the farmers in the following ways

¨      Improvement of breeds of the domesticated animals

¨      Increasing the yield of foodstuff such as milk, eggs and meat

¨   Proper management of domestic animals in terms of shelter, feeding care and protection against disease.

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