Cooking food in a microwave oven induced high rates of change in food proteins that are not observed after conventional cooking. D-proline* and cis-D-hydroxyproline were found in significant quantities in microwave-heated infant milk formulas, whereas only L-proline* is normally found in biological material.

Lubec and his colleagues warned that “the conversion of trans to cis forms could be hazardous because when cis-amino acids are incorporated into peptides and proteins instead of their transisomers, this can lead to structural, functional, and immunological changes”.

* ‘L’ stands for ‘laevo-rotary’, ‘D‘ for ‘dextro-rotary’, referring to the direction electrons rotate in their plane of optical polarisation.

Ed.- Another study found that microwaving infant formula could produce molecular changes in the amino acids in the milk proteins it contained, either causing toxicity or affecting the nutritional value of the milk formula. The degree of protein change, however, was very small (American College of Nutrition 1994;13:209-10).