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Title:Synthesis and stabilization of selected heterocyclic aroma compounds
Author(s):Fang, Ming-Chih
Director of Research:Cadwallader, Keith R.
Doctoral Committee Chair(s):Schmidt, Shelly J.
Doctoral Committee Member(s):Cadwallader, Keith R.; Engeseth, Nicki J.; Lee, Youngsoo
Department / Program:Food Science & Human Nutrition
Discipline:Food Science & Human Nutrition
Degree Granting Institution:University of Illinois at Urbana-Champaign
stable isotope dilution assay
deuterated pyrazines
Abstract:Alkylpyrazines and alkanone substituted pyrrolines are heterocyclic compounds and are predominant odorants in various foods in which they provide pleasant nutty and roasty aroma characteristics. This study describes the development of technologies for the accurate and precise quantitation of flavor alkalypyrazines in foods and for the stabilization of some labile alkanone substituted pyrrolines for potential use in food flavoring applications. The synthesis of deuterium labeled alkylpyrazines was successfully carried out through a novel and convenient procedure which was achieved by reacting labeled alkyl Grignard reagents with chloro-alkylpyrazines. Twelve isotopes, namely [2H3]-2-methylpyrazine, [2H5]-2-ethylpyrazine, [2H3]-2,3(or 6)-dimethylpyrazine, [2H3]-2,[2H3]-6-dimethylpyrazine, [2H5]-2,[2H5]-6-diethylpyrazine, [2H5]-2-ethyl-3(or 6)-methylpyrazine, 2,[2H3]-3,5-trimethylpyrazine, [2H5]-2-ethyl-3,6-dimethylpyrazine, [2H5]-2-ethyl-3,5-dimethylpyrazine, and 2,3-diethyl-[2H3]-5-methylpyrazine were prepared in good yields (57-100%) and high purities (86-98%). Use of synthesized isotopes for SIDA was evaluated using two distinctly different volatile extraction/isolation methods: solvent-assisted flavor evaporation (SAFE), and solid-phase micro-extraction (SPME). Results showed that 2,3-diethyl-5-methylpyrazine and 2-ethyl-3,5-dimethylpyrazine had the highest odor-active values among the 13 pyrazines quantified in commercial peanut butter, cocoa powder, and instant coffee. Besides, the average difference and relative standard deviation (%RSD) between SAFE and SPME was less than 10% (4.9%) and 3.6% respectively. 2-Acetyl-1-pyrroline (2AP) which provides a rice-like and roasty aroma was reported as the primary odorant in various foods. However, due to the highly unstable nature of this compound, it is scarcely used commercially in flavor formulations. A novel and attractive method for stabilizing 2AP was successfully developed in this study. Coordination of 2AP to zinc ions (ZnI2, ZnBr2 or ZnCl2) resulted in the formation in high yields of stable crystalline complexes. Heterocyclic nitrogen and carbonyl oxygen atoms were possible binding sites to the zinc ion as indicated by infrared spectroscopy. Stable complexes of other structural homologues of 2AP, including 6-acetyltetrahydropyridine(s), 2-propionyl-1-pyrroline, 2-acetyl-2-thiazoline, 2-acetylpyrazine, 2-acetylpyridine, and 2-acetylthiazole could also be prepared by the same method. Stability studies showed that 2AP zinc iodide complex was stable at ambient temperature (only 6% reduction after 3 months of storage at 25°C). Meanwhile, the ATHP-ZnI2 complex was similarly stable and showed over 88% retention after 2 months of storage. The newly developed synthesis method for isotopically labeled alkylpyrazines is very important for other scientists who want to accurately and precisely quantitate pyrazines in foods. The discovery of the method for the complexation between 2AP and zinc ions may enable the practical use of the labile, yet powerful flavor compounds 2AP and its homologues as flavoring agents in foods. Among the zinc salts evaluated in this study, zinc chloride may be preferred for the complexation process since it has GRAS status. Temperature and moisture were found as primary factors that influence the stability of the 2AP-zine complex. This information suggest that it for practical use an appropriate package or encapsulation technology, such as dispersion in an edible oil or lipid, or wax encapsulation may be desired in order to protect the complex from moisture and interactions with other food components.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Ming-Chih Fang
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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