FLAVOR CONTRIBUTION AND FORMATION OF THE INTENSE ROAST-SMELLING ODORANTS 2-PROPIONYL-1-PYRROLINE AND 2-PROPIONYLTETRAHYDROPYRIDINE IN MAILLARD-TYPE REACTIONS

Application of aroma extract dilution analysis on two different model mixtures of proline and glucose, reacted under aqueous or dry-heating conditions, revealed 2-propionyl-1-pyrroline (PP) and 2-propionyltetra hydropyridine (PTHP; occurring in two tautomers), besides 2-acetyl-1-p yrroline and 2-acetyltetrahydropyridine, as important roast-smelling o dorants in both mixtures. A comparison of the isotope distribution in PP and PTHP formed from either C-13(6)-labeled or unlabeled glucose su ggested a formation pathway for both odorants from the same intermedia te, l-pyrroline, when reacted with either 2-oxobutanal (yielding PP) o r 1-hydroxy-2-butanone (yielding PTHP). 2-Oxobutanal, a possible precu rsor of 1-hydroxy-2-butanone, was shown to be formed in high yields (2 9 mol %) by reacting acetaldehyde and glycolaldehyde, two well-known d egradation products of carbohydrates.