Microwave treatment of dietary gelatin does not generate cis-4-hydroxy-L-proline, an inhibitor of collagen biosynthesis

Aqueous solutions (5 g/100 ml) of commercial preparations of (a) an enzymatic partial hydrolysate of gelatin and (b) type A gelatin were subjected to threefold heating to boiling in a domestic microwave oven at 750 W and to conventional heating. Then samples were totally hydrolyzed (6 M hydrochloric acid, 110 degrees C, 24 h) and investigated for the presence of eight possible stereoisomers of 3- and 4-hydroxyproline (Hyp) using capillary gas chromatography. Amino acids were analyzed as N(O)-trifluoroacetyl 2-propyl esters on Chirasil-L-Val and detected by selected ion monitoring mass spectrometry. Blanks of (a) and (b) were analyzed in parallel. Relative amounts of 5.0+/-0.2% cis-4-D-Hyp were generated from native trans-4-L-Hyp as a result of total hydrolysis in all samples and independent of previous treatment. Notably, neither cis-3-L-Hyp nor cis-4-L-Hyp could be detected in either of the gelatin samples. Thus a report on the generation of antifibrotic and therefore potentially hazardous cis-3-L-Hyp and cis-4-L-Hyp from protein-bonded native trans-3-L-Hyp and trans-4-L-Hyp on microwave heating of infant formulae could not be confirmed.