D-ASPARTATE AND D-GLUTAMATE IN MICROWAVED VERSUS CONVENTIONALLY HEATED MILK

Objective: It has been reported that microwave heating of infant formu lae can isomerize and racemize amino acids in the milk proteins, causi ng toxicity or affecting the nutritional value of the milk formulae. T herefore, we investigated whether microwave heating vs conventional he ating would produce any D- enantiomers of aspartic acid (Asp) and glut amic acid (Glu) in milk. Methods: Whole and skim milk samples were hea ted 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 hig h performance liquid chromatography. Results: Unheated (control) sampl es were found to contain 0.40-0.45% D-Asp and D-Glu, inherent from the original pasteurizing process. Both conventional heating and microwav e heating induce <0.25% more racemization when compared to the control samples. Conclusion: Within experimental error, there is no significa nt difference in the levels of these D-amino acids between the convent ionally heated and microwave heated milks, thus having no significant effect on the nutritional value of the milk proteins.