Stabilization of the potent odorant 2-acetyl-1-pyrroline and structural analogues by complexation with zinc halides

2-Acetyl-1-pyrroline (2AP) and the structurally similar compounds 6-acetyl-2,3,4,5-tetrahydropyridine (ATHP, along with its tautomer 6-acetyl-1,2,3,4-tetrahydropyridine), 2-propionyl-1-pyrroline (2PP), and 2-acetyl-2-thiazoline (2A2T) are well-known potent odorants in various food products. However, due to the highly unstable nature of these compounds, especially 2AP and ATHP, they are scarcely used commercially in flavor formulations. A novel and attractive method for the stabilization of these potent odorants in dry powder form is presented. Coordination of 2AP, ATHP, 2PP, and 2A2T to zinc ions (ZnI2, ZnBr2, or ZnCl2) resulted in the formation in high yields of stable crystalline complexes, which upon hydration release the free odorant. Infrared spectroscopy was used to study the coordination complexes. 2AP contains donor atoms, which coordinate (with covalent character) through both the heterocyclic nitrogen and carbonyl oxygen atoms to the zinc ion. This is also the case for ATHP and 2PP, but not for 2A2T, because the sulfur group in 2A2T provides a third possible donor site. Stability studies showed that the 2AP-ZnI2 complex (with 14% loading) maintained >94% retention of 2AP after 3 months of storage at ambient temperature in a dry environment. Meanwhile, the ATHP-ZnI2 complex was similarly stable and retained 89% of the ATHP after 3 months of storage. This stabilization technology may enable the commercial use of this powerful aroma compound as a flavoring agent.