How are nutrients retained during cooking?

Feb 23, 2017
Studies of the effects of cooking and other methods of processing report no significant alterations in the protein value of meat. However, cooking at too high a temperature for long periods of time can slightly decrease the biological value of meat proteins.

Fat, and consequently the caloric value of meat can change substantially depending on cooking method and time. Methods such as broiling will reduce final fat content because the meat is cooked on a rack, which allows the fat in the meat to drip off as it melts. Methods such as frying increase final fat content because the meat is cooked in added fat and the fat naturally present in the meat does not drip away as it does in broiling.

Thiamin is one of the least stable vitamins and reported retentions are from 90 percent to about 30 percent. The average retention of thiamin in cooked meat is about 65 percent. Values stated in food composition tables reflect the thiamin is retained in meat cooked by dry heat, rather than by moist heat methods because being water-soluble, it tends to leach into the cooking liquid.

The longer cooking time needed for moist heat methods also increases the amount of thiamin lost. However, if the meat drippings are consumed with the meat, the total amount of thiamin is about the same as before cooking. Meat cooked to lower internal temperatures usually retains more thiamin than meat cooked to higher internal temperatures.

Other B-vitamins are fairly heat-stable, but may also be transferred to the drippings or cooking liquids during preparation. Niacin is the most stable of the B-vitamins. It is relatively unaffected by heat, light, oxygen, acids or alkalis.

Because minerals such as iron and zinc are heat-stable, cooking temperatures do not appear to reduce the quantity or availability of minerals in meat. However, methods of food preparation can affect the iron content of food both positively and negatively. Research findings suggest a five-fold increase in the iron content of foods, particularly acidic foods, cooked in cast-iron pots. Using iron cookware could be a simple and practical way of increasing dietary iron. However, fewer and fewer consumers are using iron cookware.

The major cause for the loss of iron during food preparation is cooking in liquid because iron will dissolve in the liquid. If cooking meat in liquid is the chosen method, the liquid should be simmering, not boiling, the pieces should be relatively large, the amount of liquid should be small, and the meat should not be over cooked. However, if the cooking liquid is consumed, the dissolved iron is not lost. As mentioned above, temperature does not appear to affect iron content since this mineral is relatively heat stable.

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