Presenting author: Bethany Hausch

Co-authors: Keith Cadwallader

Department of Food Science and Human Nutrition

2-Acetyl-1-pyrroline (2AP) is the characterizing odorant in foods such as aromatic rice and popcorn and is an important odorant in many other foods including corn, crustaceans, cooked meat and roasted nuts (1,2). 2AP is a potent odorant with a detection threshold of 0.1 ppb and contributes a roasted, cracker-like or popcorn-like aroma character. As such, 2AP would be appealing as an added flavoring but this poses a challenge due to the molecule’s unstable nature. This molecule was first discovered in 1982 by Ron Buttery and his group, who noted its unstable nature in their first report (3). When 2AP is neat or in a concentrated aqueous solution, the color will rapidly change from colorless to red as 2AP reacts. Mass spectral data from our lab show a decline in a 25 mg/mL aqueous solution of 2AP in only 5 minutes. Buttery et al. hypothesized in 1983 that this molecule undergoes a polymerization process (4). Yet, little information is available in the literature to support this hypothesis. Conversely, the literature is rich with reports on 2AP’s biological formation, its formation via the Maillard reaction, synthetic routes to generate 2AP, its occurrence in various foods and methods for quantitation. Therefore, the significance of this compound is clear, but knowledge about its loss/degradation is lacking. Our research has probed 2AP loss in water by high resolution mass spectrometry (HR-MS) and NMR (1D and 2D) and confirmed that 2AP undergoes a polymerization reaction. We have observed that 2AP polymerization is a complex process, generating many unstable intermediates. The intermediates are highly unsaturated molecules which contain increasing numbers of 2AP moieties, accompanied by the loss of water. NMR showed an increase of other small molecules in the first 2-6 hours of reaction. We have assembled a list of structural features of the polymeric species via 2D NMR and MS2. The research presented will focus on the insights gained about 2AP’s reactions products. Stabilization strategies for 2AP will also be briefly mentioned. References: (1) Adams, A.; De Kimpe, N. Chemistry of 2-Acetyl-1-Pyrroline, 6-Acetyl-1,2,3,4-Tetrahydropyridine, 2-Acetyl-2-Thiazoline, and 5-Acetyl-2,3-Dihydro-4H-Thiazine:  Extraordinary Maillard Flavor Compounds. Chem. Rev. 2006, 106, 2299–2319. (2) Cadwallader, K.; Hausch, B.; Yun, Y. Quest for Stability of 2-Acetyl-1-Pyrroline: The Key Odorant in Aromatic Rice and Pandan. In Proceedings: Food Innovation Asia Conference 2015 “Innovative ASEAN Food Research towards the World,” Bangkok, Thailand, June 18-19, 2015; pp. 560-567. (3) Buttery, R. G.; Ling, L. C.; Juliano, B. O. 2-Acetyl-1-Pyrroline: An Important Aroma Component of Cooked Rice. Chem. Ind. 1982, 958–959. (4) Buttery, R. G.; Ling, L. C.; Juliano, B. O.; Turnbaugh, J. G. Cooked Rice Aroma and 2-Acetyl-1-Pyrroline. J. Agric. Food Chem. 1983, 31, 823–826.