Freezing is the best method of storing food, although the blanching of food can reduce the thiamin and vitamin C content - but this is less than the loss that takes place in vegetables in a box during transport to and from a shop. Frozen foods should be kept below -18 C (0 F) until required for use.
Food that is processed for storage in tins, cans or glass jars will lose nutrients such as thiamin, folate and vitamin C as a result of the heat treatment. Other nutrients may be lost if a glass jar of food is stored in daylight.
Sulphur dioxide which is used as a preservative completely destroys all thiamin but helps to preserve vitamin C.
Prolonged drying in bright sunshine also destroys many of the vitamins in the food. Dried foods should be stored in sealed containers to exclude both oxygen and light.