Graduate Thesis Or Dissertation
 

The potential role of aliphatic gamma- and delta-lactones in beer fruit aroma

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  • This work set out to examine the potential contribution of five aliphatic lactones, γ-nonalactone, γ-decalactone, γ-dodecalactone, δ-decalactone and δ-dodecalactone to stone fruit aroma in beer. This work consists of three related studies; lactone olfaction thresholds, additive/synergistic aroma effects and a gas-chromatography-mass-spectrophometry method of analysis. First was the determination of these lactone's thresholds in an unhopped pale ale beer base. This same base was used for the second investigation, which assessed the influence of these lactones on overall fruit aroma in combination with hop-derived esters, a terpene alcohol and a norisoprenoid in descriptive analysis. Lastly, the third body of work consisted of developing a simple and accessible instrumental method for the detection of lactones in a beer matrix. The olfaction detection threshold of five aliphatic lactones were determined in an unhopped pale ale using the ASTM E679 "best estimate threshold" standard methodology. Twenty-five to twenty-nine panelists assessed the sets of 3-alternative forced choice tests and the group’s geometric mean calculated from each panelist's individual threshold served as the olfaction detection threshold in this base. The calculated thresholds in unhopped pale ale were above published thresholds previously reported in water and ranged from 238 - 750 μg/L. To assess the additive or synergistic effects of lactones (γ-nona and deca lactone, and δ-decalactone) in combination with hop-derived esters (ethyl 2- and ethyl 3-methylbutanoate) and oxygenated terpenes (linalool and β-damascenone) descriptive analysis was performed with a trained panel with a final ballot possessing stone fruit/peach, coconut/oily, red berry and melon plus overall fruity intensity as descriptors. All compounds were spiked into unhopped pale ale at published and commercially realistic levels detected in beers. Lactones individually yielded low average scores in all categories and only significantly differed from the base on coconut/oily and overall intensity. However, when mixed with ethyl esters and oxygenated terpenes, overall fruity intensity significantly increased, as did the stone fruit/peach descriptor. The development of the Headspace Solid Phase Microextraction (HS-SPME) coupled with gas chromatography and mass spectrometery (GC-MS) method for lactones in a beer matrix was adapted from multiple methods developed for the detection of lactones in wine. A model system (5% ABV ethanol, pH 4.5) was utilized to determine GC-MS identification parameters for Selected Ion Monitoring (SIM) mode. All subsequent calibration curves were performed in an American light lager base. The developed method was adequate at detecting spiked lactones in beers at trace levels (<5 μg/L). Analysis of all lactones in OSU research dry-hopped beers and a sampling of commercially produced beers were below the calculated olfaction thresholds and the limits of quantitation for the GC method thus providing evidence that lactones are found at trace levels in beer. Further studies into optimal extraction techniques of lactones from beer are required.
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Déclaration de droits
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