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It was recently claimed that microwave heating of reconstituted formulas for infants could induce racemisation of amino acids, in particular, of proline. In the present work we investigated the presence of D-amino acids in different samples of a reconstituted infant formula heated by a conventional heattransfer way (oil bath), in a commercially available domestic microwave oven and in a wave-guide device. The analyses were carried out both by gas chromatography and by high performance liquid chromatography. The presence of D-enantiomers was determined both in proteins after hydrolysis (6 M HCl at 100°C for 6 h) and in the free amino acid pool. Regarding protein-bound amino acids, there is no evidence of racemisation in all samples examined under the different experimental conditions (conventionally and microwave-treated samples). In particular, D-proline was not detected at least above 1 mglitre-I in proteins and above 20 pg litre-' in free amino acids. Although small percentages (D/D+L %) of D-glu and D-asp and higher percentages of D-ala were detected among free amino acids, in all samples, no significant differences could be found between untreated and treated samples.

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