Characterization of "savory" aroma compounds in aged red wines via gas chromatography-olfactometry and descriptive analysis
Abstract
The practice of extended bottle aging to increase wine quality is traditionally carried out by both wine producers as well as wine collectors. Mainly red wines are anaerobically bottle-aged to increase the complexity of sensory characteristics. Past research on the evolution of red wine aroma during aging has mainly focused on wood-derived characters during barrel-aging, or those related to the release of grape-derived, sugar-bound precursors due to acid hydrolysis. The latter reactions may result in enhance fruity and floral aromas during post-fermentation aging in barrels or tanks plus bottle-aging ("bottle bouquet") notes such as leather, honey, or tobacco. This research investigated the origin of wine sensory characteristics generally described as "savory" or umami-type aromas. The most common savory aromas used to describe aged red wines in the scientific and consumer literature include beef broth (bouillon), cured, smoked and grilled meats, wild mushrooms, vegetables and herbs, roasted nuts, caramel, and soy sauce. It was postulated that Maillard reactions, a series of chemical reactions between reducing sugars and compounds with free amino groups, can occur under wine-like conditions (relatively low pH and storage temperature, aqueous solution) though at very slow reaction rates to produce savory aromas over the course of years or even decades of aging. In this study, professional wine judges were employed to select a range of commercial wines that display particular savory aromas. Subsequently, the use of a trained descriptive analysis panel was utilized to evaluate in detail a subset of the wines identified. The goal was to compare the tasting abilities of trained panelists to those of wine competition judges, and to generate savory aroma profiles for the wines. The wines with the highest intensity savory notes were analyzed via gas chromatography-olfactometry (GC-O) to identify contributing aroma compounds. Based on established Maillard reaction products in the enology literature, several compounds related to savory, umami-type aromas were screened for, including 2-acetylthiazole, 2-acetyl-2-thiazoline, 4-methylthiazole, 2,4-dimethylthiazole, 2,4,5,-trimethyloxazole, 2-methyl-3-furanthiol, and 2-furanmethanethiol. Although no thiazoles, oxazoles or furanthiols could be detected, other compounds were found to be of savory odor-impact including methionol (raw potato, cauliflower), γ-butyrolactone (caramel), γ-nonalactone (coconut), pantolactone (cotton candy), eugenol (cloves), isobutyric acid (cheese), and 5-methylfurfural (almond, burnt sugar), among others. It is hypothesized that these compounds act synergistically to create a savory sensory experience by nose, even if present in concentrations below threshold individually. This work helps to expand the specificity and detail, at which wines can be described, by wine researchers, producers and consumers. The information provides a basis for future work investigating optimum aging parameters to increase the formation of desirable savory aroma compounds that can increase the complexity and thereby the perceived quality and value of certain wine-styles.
Degree
M.S.
Advisors
Butzke, Purdue University.
Subject Area
Food Science
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