Some additives are manufactured from natural sources such as soybeans, which provide lecithin to maintain product consistency, or beetroot, which provides beet powder used as food colouring. Other useful additives are not found in nature and must be made. Artificial additives can be produced more economically, with greater purity than some of their natural counterparts. Whether an additive is natural or artificial has no bearing on its safety.

Are sulphites safe?

Sulphiting agents are sometimes used to preserve the colour of foods such as dried fruits and vegetables, and to inhibit the growth of microorganisms in fermented foods such as wine. They may also be used in fruit juices, soft drinks, and sausages.

Why so many additives?

Choice and variety are important in our enjoyment of food. The nature and purpose of a food and how it is processed determine which additives may be needed. Additives differ from one another in a number of important respects. Some examples are given below:

• Sweeteners

  Consumer's demand for 'sweetness without calories' has led to the development of a range of low-calorie sweeteners. One sweetener however cannot satisfactorily replace another. Each has a different stability to heat and a different flavour profile. For example, a blend of a quickly perceived sweetener with one that has a more lingering aftertaste will provide a more rounded and balanced sensation of sweetness. Blends of sweeteners, with each other and with sugars, also provide enhancement of taste with an overall reduction in sweetener concentration.

• Acidulants

  Food acids or acidulates, have different taste profiles. Citric acid, the most commonly used, is "lemony" and acetic acid has the familiar vinegar taste. Tartaric acid has a sharp taste of very short duration. Malic acid has a sharp taste but with a slower build up than citric acid. The taste of lactic acid is relatively mild and lingering.

• Emulsifiers

  Emulsifiers depend for their action upon the presence of both water-attracting and oil-attracting groups in the molecule. Different emulsifiers have different molecular structures and are therefore suitable only for specific applications.

  Emulsifiers also perform other important functions in food. They interact with fats to modify their crystal structure and thereby reduce viscosity (chocolate) or increase aeration (whipped cream). They interact with starch to reduce stickiness (for instance when making potato granules) and to retard firming or staling of bread. They interact with gluten and thereby improve the baking quality of wheat flour resulting in better texture and volume in packed goods.

• Stabilisers, thickeners, gelling agents

  Different foods have different consistencies and textures. No two stabilizers, thickeners, or gelling agents are exactly the same and one will generally be more effective in a particular application than another. For example, gelatin produces a soft elastic texture, whereas agar produces a short brittle texture.

  Processing conditions also vary widely from one food to another. For example some foods require a hot setting gelling agent, e.g. pectin; others a cold setting agent, e.g. alginate. Gums will also interact with other food components which will make them suitable for certain applications. Carrageenan, for example will react uniquely with milk proteins to form a soft gel, effective in preventing cocoa particles settling out in chocolate milk. In acidic milk products, pectin and carboxymethylcellulose will stabilise the milk proteins during pasteurisation. A mixture of stabilisers is frequently more effective than any one used alone, especially in ice cream manufacture.

• Colours

  Firstly, colours have different stabilities, For reasons of safety certain foods are subjected to high temperature, sometimes for a considerable period, and some colours will not withstand such treatment. Others will fade so quickly that even the mildest form of heat will destroy them in a very short space of time. Then again some colours are suited only to acidic foods and will simply vanish under the wrong conditions.

  Secondly, specific types of colour are needed for different types of food. Oil soluble colours are required for margarine and processed cheese, though certain other cheeses need water-soluble colours.

• Antioxidants

  Vegetable oils contain alpha-tocopherols, natural antioxidants that preserve the oil in the plant. While effective for their purpose in nature, they are not completely adequate to protect the extracted oil during storage or in cooking, though blends of tocopherols with products such as ascorbyl palmitate have been found to be appreciably more effective.

• Preservatives

  The selection of a preservative will depend on the process condition, in particular the ph (acidity), the water activity (water is essential for microbial growth) and the type of organism that may be present in the food. It is only when one stops to consider their specific properties and subtle differences, their often synergistic effects, as well as their particular uses, that the need for a wide variety of additives becomes evident.