Food Processing
Before food is processed it often undergoes a range of procedures such as picking, sorting, washing, packing, and transporting and short term storage. All these procedures, before processing, affect vitamins and other nutrients. Washing, trimming and heat treatments affect nutrient content. Canning, evaporating, drying and freezing alter nutritional values, and the choices of times and temperatures in these operations frequently must be balanced between good bacterial destruction and minimal nutrient loss or destruction.
One of the most influential factors in nutrient loss from processing is the processing that occurs at home ie in preparation and cooking. Look at what happens to the nutritional value of spinach when it is cooked:
When fresh fruits and vegetables are harvested they continue to undergo chemical changes which can cause them to spoil and deteriorate. Food processors take a range of steps to make sure these changes - the ones consumers will see and therefore choose not buy the produce - are reduced. What results is an incomplete product that has been altered to make sure it is more appealing to consumers.
Fresh fruit and vegetables contain chemical compounds called enzymes that cause the loss of color, loss of nutrients, flavor changes, and color changes in frozen fruits and vegetables. The aim of food processors is to inactivate these enzymes to prevent these chemical changes from taking place.
Enzymes in vegetables are inactivated by the blanching process. That is, the vegetable is exposed to boiling water or steam for a brief period of time. It must then be rapidly cooled in ice water to stop it from cooking. This process renders the vegetable incomplete - by the destruction of the enzymes. Blanching also destroys bacteria from the surface of the vegetable. Blanching makes some vegetable, such as broccoli and spinach, more compact.
Because fruits are usually eaten raw, the enzymes in frozen fruit are controlled by using chemical compounds that interfere with deteriorative chemical reactions. The most common control chemical is ascorbic acid (vitamin C) that may be used in its pure form or in commercial mixtures with sugars.
Another group of chemical changes that can take place in frozen products is the development of rancid oxidative flavors through contact of the frozen product with air. This is overcome by using plastic wrapping material with its associated health problems.
The more a food is processed the less like real food it becomes.