Evidence for the absence of amino acid isomerization in microwave-heated milk and infant formulas

According to a recent paper (Lubec et al., 1989), microwave heating of milk or reconstituted infant formulas could induce the inversion of amino acid residues to a significantly higher extent than conventional heating. In this study, UHT milk and three different infant formulas were heated under two sets of conditions: 600 W for 3 min and 70 W for 20 min. When the proportions of D-amino acids were measured after acid hydrolysis, no significant differences could be found between untreated and treated samples. On the basis of these results, it is concluded that heating of milk or infant formula in a microwave oven under conditions corresponding to those normally applied for heating food does not induce significant inversion of protein-bound amino acids