Several structural analogues of proline have been shown to be incorporated into proteins in place of proline. As a consequence, the proliferation of cells in culture and the extracellular deposition of collagen in animal systems are reduced.
Aqueous solutions of commercial preparations of an enzymatic partial hydrolysate of gelatin and 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 and investigated for the presence of eight possible stereoisomers of 3- and 4-hydroxyproline 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-Hydroxy-L-proline nor cis-4-Hydroxy-L-proline 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.