As heat is not required, this process impacts less on the vitamin content, flavour and colour of foods. This method has been used in foods such as fruit juices. This alternative preservation method subjects a food to elevated pressures, with or without the use of heat to kill micro-organisms. In the case of pasteurised fruit juices, some losses of vitamin C can occur. The nutrient value of milk is generally unaffected. Pasteurisation involves heating liquid foods such as milk and fruit juices to specific temperatures to destroy micro-organisms. Any nutrient losses are due to the processing prior to freezing and the cooking once the frozen food is thawed. The nutrient value of a food is retained when it is frozen. Many people believe that canned foods are not as nutritious as their fresh counterparts, but this is not always the case, as fresh food often deteriorates more rapidly than canned foods. Water-soluble vitamins are particularly sensitive to high temperatures.

Preservatives are generally not needed or used in canned foods.

Some types of micro-organisms require severe heat treatment and this may affect the taste and texture of the food, making it less appealing. CanningДЇood is heated inside the can to kill any dangerous micro-organisms and extend the foodвЂ™s shelf life. The water-soluble vitamins, including vitamin C and B-complex, are sensitive and easily destroyed by blanching. BlanchingД«efore a food is canned or frozen, it is usually heated very quickly with steam or water. The вЂfibreвЂ™ that is added back to some products is often in the form of resistant starch, which may not be as beneficial as the fibre removed. It is impossible to add back everything that is taken out, especially the phytochemicals. That is why products such as white bread are less nutritious than wholemeal varieties, even if they have been artificially fortified with some of the nutrients that were lost after milling. The husks contain most of the plantвЂ™s dietary fibre, B-group vitamins, phytochemicals and some minerals. MillingД¬ereals such as wheat can be ground to remove the fibrous husks.

It does not seem to make any difference to the plantвЂ™s nutrient value whether the fertiliser is organic or not. High use of nitrogen fertilisers tends to reduce the vitamin C content in many fruit and vegetable crops. Most plant crops are produced with the aid of fertilised soils. Processes that expose foods to high levels of heat, light or oxygen cause the greatest nutrient loss. Processes affecting food nutrient contentДЄ variety of things can happen during the growing, harvesting, storage and preparing of food that can affect its nutritional content. Water-soluble vitamins (B-group and C) are more unstable than fat-soluble vitamins (K, A, D and E) during food processing and storage. Some vitamins are more stable (less affected by processing) than others. Effects of processing and storage of food Whatever the case, the nutrient value of any food is often altered by the processing. Simply cooking or combining a food with other foodstuffs to create a recipe is also considered a form of food processing. Commercially, the main reasons to process food are to eliminate micro-organisms (which may cause disease) and to extend shelf life. Almost all food is processed in some way before it is eaten.

Food processing methods