Ascorbic acid, or vitamin C, is an extremely unstable water-soluble vitamin. The vitamin C content of foods can be reduced by exposure to extreme cold, heat, light, lengthy storage and water. All forms of cooking reduce vitamin C levels in foods. However, boiling foods destroys the highest percentage. In a study published in the August 2009 issue of the "Journal of Zhejiang University Science," researchers examined five methods of cooking broccoli. The methods were stir-frying, microwaving, steaming, boiling, and a combination of stir-frying and boiling. The study concluded that after five minutes of cooking broccoli florets, using each method, boiling destroyed the highest percentage of vitamin C. (5)
Pasteurisation of fruit juice
Pasteurization is the process of treating juice, milk and other foods to kill harmful germs, usually by heating.
Beta-carotene (which is converted into vitamin A by the body) is stable during mild heating, but losses occur at high temperatures. Vitamin C leaches out during cooking because it is water soluble and it is also heat sensitive, so some is destroyed. Water-soluble B vitamins are lost if the cooking water is discarded. Vitamin E is destroyed at high temperature. (6)
The sugars and minerals in juices are typically unchanged by pasteurization and remain present in high concentrations. Pasteurized apple, orange, grape, pomegranate, tomato and carrot juices contain substantial amounts of the minerals potassium, phosphorus and magnesium.
Vitamins are more vulnerable to heat destruction than are sugars and minerals. Pasteurization may cause low-level loss of some of these micronutrients. Fresh-squeezed orange juice contains approximately 124 milligrams of vitamin C per cup; pasteurized orange juice contains approximately 84 milligrams, nearly one-third less. (7)
Dairy products, alcoholic beverages and fruit juices are commonly pasteurized. The pasteurization process typically involves heating beverages up to 180 degrees Fahrenheit in order to kill bacteria, although many fungi and parasites are also destroyed by the heat. Flash pasteurization uses higher temperatures and only needs about 10 seconds to complete, whereas traditional pasteurization needs up to 30 minutes. Before pasteurizing the juice, the majority of inorganic fruit is irradiated with high-frequency gamma rays in order to kill insect larvae, parasites and other pathogens. This method destroys more nutrients than pasteurization. (8)
Bibliography
-
-
-
-
-
-
-