Freezing has very little effect on the nutrient content of foods. Some fruits and vegetables are blanched (immersed in boiling water for a short period) before freezing to inactivate enzymes and yeasts that would continue to cause food spoilage, even in the freezer.
As long as the food was grown in a high-quality way (for example, organically grown) and was fairly fresh at the time of freezing, the overall nutrient retention in a frozen food can be quite high. In other words, many of the vitamins and minerals will keep fairly well in frozen foods. Some of the phytonutrients found in food may also keep fairly well. For example, we have seen research showing that anthocyanin flavonoids can be well preserved during freezing. It's important to remember that these percentages of nutrient loss are very general and can be different with different foods. Nevertheless, as you can see from the numbers above, the freezing-connected loss of these water-soluble vitamins never comes close to outweighing the amount of vitamins retained. The question arises whether the opposite extreme, freezing, likewise alters the chemical and organic structure of foods. Let’s pursue this method of food preservation. First, we should note that freezing does not affect foods of little water content—nuts, seeds, dried legumes and dried fruits lose nothing by freezing. In nature, seeds and nuts remain fertile no matter how cold it gets. The more water a food contains, the more it is adversely affected by freezing. When a food is frozen, its water expands. This causes two immediately destructive occurrences: 1  The cell walls burst and the cell contents are spilled due to the internal water expansion; hence the cell’s life is lost. There's another problem with freezing. Fresh produce contains enzymes which are very good news to raw food people. However, these very enzymes will cause browning, loss of nutrients, flavor changes and color changes in frozen fruits and vegetables. Produce such as fruits and vegetables mostly consists of water. Water makes up over 90 percent of the weight of most fruits and vegetables. First, we should note that freezing does not affect foods with low water content—nuts, seeds, dried legumes and dried fruits. Freezing will not improve inferior foods. If the food is fresh, of top quality, and frozen using proper procedures, the effect on quality will be minimized as long as the food remains solidly frozen at a constant temperature at or below 0 degrees F. One of the main concerns for nutrient loss associated with freezing seems to be related to the blanching process that oftentimes occurs prior to freezing. About 25% of the vitamin C and a greater percentage of folate are lost during the blanching process that occurs before foods are frozen. It's important to remember that these percentages of nutrient loss are very general and can be different with different foods. Nevertheless, as you can see from the numbers above, the freezing-connected loss of these water-soluble vitamins never comes close to outweighing the amount of vitamins retained. Frozen food can be no better than the food was before it was frozen. Freezing does not sterilize foods as canning does. It simply retards the growth of microorganisms and slows down chemical changes that affect quality or cause food spoilage. Enzymes Freezing, heating and chemical compounds can control enzyme actions.  Fresh produce contains chemical compounds called enzymes which cause the loss of color, loss of nutrients, flavor changes, and color changes in frozen fruits and vegetables. These enzymes must be inactivated to prevent such reactions from taking place. William Schafer, Food technologist — Department of Food Science and Nutrition. Reviewed 2014 by Suzanne Driessen, Extension Educator — Food Safety. Freezing is a quick and convenient way to preserve fruits and vegetables at home. It is a popular method of home food preservation throughout Minnesota. Freezing is one of the easiest methods of preserving foods. The extreme cold of freezing vegetables retards the growth of microorganisms and slows down chemical changes that affect the quality. By following the directions for freezing foods, the quality and nutrition is maintained. Freezing has very little effect on the nutrient content of foods. Some fruits and vegetables are blanched (immersed in boiling water for a short period) before freezing to inactivate enzymes and yeasts that would continue to cause food spoilage, even in the freezer. This process can cause some of the vitamin C (15 to 20%) to be lost. Examples of foods that do not tolerate freezing well include salad vegetables, mushrooms and soft fruits. Foods with higher fat contents, such as cream and some sauces, tend to separate when frozen. Commercial freezing rapidly freezes foods so that smaller ice crystals are formed.
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how does freezing affect the nutrients in food