Physicochemical and pharmacodynamic effects of ethanol, water type and proofing method on the perceived sensory properties of distilled spirits

Wang, Zhuzhu

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https://hdl.handle.net/2142/115676 Copy

Description

Title

Physicochemical and pharmacodynamic effects of ethanol, water type and proofing method on the perceived sensory properties of distilled spirits

Author(s)

Wang, Zhuzhu

Issue Date

2022-04-01

Director of Research (if dissertation) or Advisor (if thesis)

Cadwallader, Keith

Doctoral Committee Chair(s)

Schmidt, Shelly

Committee Member(s)

• Lee, Soo-Yeun
• Pepino, M.Yanina

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Ethanol
• water
• distilled spirits
• sensory

Abstract

Ethanol and water are the most sensory influential matrix components of distilled spirits. Despite their importance, analytical and sensory studies on how they affect the sensory perception of distilled spirits are lacking. Therefore, the goal of this study was to provide a deeper understanding of how these two components affect perceived aroma perception and taste/mouthfeel properties of distilled spirits. Specifically, for ethanol, we were interested in understanding its pharmacodynamic effect on odor perception; and for water we were interested in understanding if the mineral composition and proofing method affect the perceived taste/mouthfeel properties in aged and unaged spirits. Change of ethanol concentration in distilled spirits is known to change the odor detection thresholds (ODT) of odor-important volatile components. This is caused by the combined effects of ethanol that is present in both the liquid matrix and vapor (headspace) matrix. Ethanol in the liquid matrix affects an odorant’s solubility, thereby changing its headspace partition coefficient (ethanol’s physicochemical effect). Meanwhile, ethanol in the vapor matrix affects the function of olfactory receptor cells (ORCs) and is likely to suppresses olfactory signal transduction (ethanol’s pharmacodynamic effect). Changes in ethanol concentration in the liquid matrix influences these two factors simultaneously, and as a result affects the ODTs of the odor constituents. However, the observed increase in ODT caused by an increase in ethanol concentration in the spirits matrix has been most often asserted to be a consequence of ethanol’s physicochemical effect, whereas the influence of ethanol’s pharmacodynamic effect is scarcely mentioned or recognized. In the first part of this study, we demonstrated that ethanol’s pharmacodynamic effect suppresses olfactory detection (ODTs were increased) for all odorants tested, and the ODTs tend to increase with an increase in ethanol concentration in the vapor matrix. This was supported by the observations that when three panelists (panel 1) evaluated 34 odorants in different ethanolic vapor backgrounds (air, 20% ABVd.equiv., and 40% ABVd.equiv.), the ODTs increased with an increase in ethanol vapor concentration. We have also found that for all three panelists, some odorants underwent greater odor suppression than others. Based on the literature it is believed that the general suppression effect of ethanol on all odorants is a result of ethanol’s interaction at the lipid bilayer membrane in olfactory cilia. Furthermore, the differences in olfactory suppression across odorants is mostly attributed to the competitive binding affinity to the odorant-binding proteins (OBPs) and/or olfactory receptor antagonism between ethanol and the odorants. In the second part of this study, we demonstrated that ethanol’s pharmacodynamic effect is a more important factor than its physicochemical effect in causing an increase in ODTs as a function of an increase of ethanol concentration in the liquid matrix. This was supported by the observation that when four panelists (panel 2) evaluated 7 selected odorants in ethanolic solution matrix (water, 20% ABV, and 40% ABV), the degree of individual ODT change (R) followed a similar pattern as when they evaluated the same odorants in an ethanolic vapor background (air, 20% ABVd.equiv., and 40% ABVd.equiv.). In addition, for each odorant, the increase of ODTs in a high ethanol matrix solution (20% ABV and 40% ABV) was not in accordance with the reduction in their headspace partition coefficients. Using ethyl butyrate as an example, the headspace partition coefficients of this odorant in 20% and 40% ABV solutions were increased by 1.88 and 2 times, respectively, but its ODT in 20% ABV solution increased by 30 times, while its ODT in 40% ABV solution increased by 130 times. These observations are rationalized by ethanol’s pharmacodynamic suppression effect on this odorant due to competitive binding to OBPs. When ethanol concentration was increased in the headspace (from 20% ABVs.equiv to 40% ABVs.equiv), a much higher concentration of this odorant was required in the 40% ABV solution for its detection in the headspace. This is the first study to evaluate the ethanol’s pharmacodynamic effect on the ODT of odorants. Our results emphasize the considerable impact of ethanol’s pharmacodynamic suppression effect at the ORCs, and how the concentration of ethanol presented in the vapor matrix can change the olfactory sensitivity to odorants. These results help rationalize the industry practice of decreasing ethanol content by half (from 40% ABV to 20% ABV) or use of different shaped glass vessels during nosing (odor evaluation). Both practices decrease ethanol headspace concentration thereby decreasing its pharmacodynamic suppression effect on the ORCs and improving the odor detection sensitivity of panelists. Water type and proofing method are reputed to be critical to the perceived taste/mouthfeel quality of finished spirits products. However, there are no published sensory studies that substantiate these beliefs. According to the literature minerals in water are likely to strengthen the H-bonds between water and ethanol molecules, and dilution methods probably affect the amount of H-bonds broken and reformed between water and ethanol molecules through endothermic and exothermic processes. In distilled spirits, water-ethanol clusters formed through H-bonding are believed to have a significant influence on the development of “mellowing” mouthfeel and activity of flavor compounds. Therefore, it is possible that water type and proofing method may influence the water-ethanol clusters in spirits through their effects on H-bonding. But it is not clear if these changes are significant enough to give a rise to perceived sensory differences. In this study, both oak-aged spirits (barrel strength) and unaged spirits (95% ABV) were diluted to 40% ABV, and then were evaluated to determine if the choice of water type (limestone water, spring water, vs. distilled water) and proofing method (fast- vs. slow-proofing) affected the perceived taste/mouthfeel characteristics in the final spirits. In fast-proofing, water was rapidly poured into the spirits, and mixed by shaking. In slow-proofing, water was slowly added to the spirits at a flow rate of 0.6 ml/min and no further mixing was conducted. Results of an A-Not A difference test with a trained panel showed that water type and proofing method did not have a significant effect in the oak-aged spirits. However, proofing method but not water type, had a significant effect in the unaged spirits. The biggest difference between oak-aged and unaged spirits is the presence of maturation related polyphenolics and other nonvolatile congeners that are derived/extracted from the oak barrel during aging. These results suggested that mineral contents in water may have strengthened the H-bonding in the spirits matrix, but this effect was not significant enough to cause a change in the perceived sensory properties in both aged and unaged spirits. In aged spirits the effects of maturation related compounds appear to predominate over proofing water constituents or method with respect to their impact on the perceived taste/mouthfeel characteristics of the finished spirits. The dynamic sensory profiles of two unaged spirit products (fast- vs slow-proofed) were further characterized by the same panel using temporal check-all-that-apply (TCATA) method, and the sensory differences between these two products were investigated. Results showed that the slow-proofed unaged spirits were cited more often as sweet at the beginning, and with less burn throughout the entire evaluation period. Therefore, slow-proofing may be a better option over fast-proofing for dilution of unaged spirits. To our knowledge, this is the first study to evaluate the effects of proofing method on the perceived sensory properties of distilled spirits. This is also the first to demonstrate the use of the A-Not A test method to determine whether a perceived difference exists between two confusable high alcohol containing beverages. In addition, our findings are of particular importance to producers of unaged spirits (i.e., vodkas), as it illustrates the importance of proofing strategies and how they can affect and possibly improve the perceived taste/mouthfeel characteristics of the final products, especially when no other influential congeners are present.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Zhuzhu Wang

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