Effect of processing on mineral content of foods
Minerals are comparatively stable under processing conditions such as heat, light, use of oxidizing agents and extremes in pH. But, minerals can be removed from foods by leaching or physical separation. It has been reported that milling of cereals causes considerable mineral loss. Minerals are mainly concentrated in the bran layers and the germ. Thus, removal of bran and germ during milling leaves pure endosperm, which is mineral poor. For example, when wheat is milled to obtain refined flour, the losses in mineral content are 76% (iron); 78% (Zinc); 86% (manganese); 68% (copper); and 16% (selenium). Similar losses occur during milling of rice and other cereals. Cooking in water would result in some losses of minerals since many minerals have significant solubility in water.
In general, boiling in water causes greater loss of minerals from vegetables as against steaming. Canned foods may take up metals from the container: tin and iron from the tin plate, and tin and lead from the solder. For example, this occurs in canned acid foods such as fruit juices; canned foods having sulphur containing amino acids.