D-aspartate and D-glutamate in microwaved versus conventionally heated milk.

Abstract

It has been reported that microwave heating of infant formulae can isomerize and racemize amino acids in the milk proteins, causing toxicity or affecting the nutritional value of the milk formulae. Therefore, we investigated whether microwave heating vs conventional heating would produce any D- enantiomers of aspartic acid (Asp) and glutamic acid (Glu) in milk. Whole and skim milk samples were heated for 10 minutes in either a microwave oven at medium power or on a hot water bath at 80 degrees C. D-Asp and D-Glu were determined by high performance liquid chromatography. Unheated (control) samples were found to contain 0.40-0.45% D-Asp and D-Glu, inherent from the original pasteurizing process. Both conventional heating and microwave heating induce < 0.25% more racemization when compared to the control samples. Within experimental error, there is no significant difference in the levels of these D-amino acids between the conventionally heated and microwave heated milks, thus having no significant effect on the nutritional value of the milk proteins.