Chemo-sensory characterization of aroma active compounds of native oak wood in relation to their geographical origins.

Oak wood contains aroma-active compounds that contribute significantly to the chemical structure, olfactory and gustatory qualities of alcoholic beverages and vinegars as by-products that have been either fermented and/or aged in oak barrels. The chemical composition of cooperage oak is highly variable, depending on the degree of toasting and natural seasoning. However, it is unclear whether the odor of oak varies according to different geographical regions and pedoclimatic conditions. Especially in view of the actual challenges in forestry in relation to climate change, the present study aimed at elucidating the odorous constituents of nine natural oak samples from Germany, Austria and Hungary with respect to these influencing parameters. The odor profiles of the oaks were compared, the potent odorants were determined, and selected odorants were quantified using stable isotope dilution assays (SIDA). The majority of the identified odorants in all samples were fatty acid degradation products, followed by a series of odorants with terpenoic structure and others resulting from the degradation of lignin. Several different odorants including 2-propenoic acid and cinnamaldehyde are reported here for the first time in oaks from different growth regions. Odor activity values (OAVs), calculated based on odor thresholds (OTs) in water, revealed hexanal, (E)-2-nonenal, (Z)-3-hexenal, eugenol, vanillin, and whiskey lactone as potent odorants for the oak odor. Principal component analysis of the data obtained from sensory evaluation, comparative aroma extract dilution analysis (cAEDA) and their corresponding quantified odorants showed that the highest separation rate was obtained for Hungarian oak, whereas Austrian and Bavarian oak samples were more similar. Recombination experiments by mixing the dominant odorants in their naturally occurring concentrations revealed a good agreement of the smell properties of the model mixture with the smell of the respective original sample. These findings aimat evaluating and establishing a better understanding of the distinctive smell of oak wood and demonstrated the prospects of new oak sources.

Molecular and sensory characterization of odorants in Cembran pine (Pinus cembra L.) from different geographic regions.

The wood of the Cembran pine (Pinus cembra L.), also known as Swiss pine, Arolla pine or Stone pine, has a prominent and long-lasting odor which has been reported to relieve stress in humans. However, the odorants responsible for this are unknown and it is also unclear whether the odor profile depends on the origin of the trees, namely different geographical regions and pedoclimatic conditions. Therefore, in this study human sensory analyses together with isolation and analysis of the target odorants via solvent-assisted flavor evaporation were performed. Afterwards, comparative odor extract dilution analysis (cOEDA) was applied to investigate the odorous constituents of pinewood samples from forests in Austria and Italy. Specific odorants were thereby identified using one-dimensional and two-dimensional gas chromatography-mass spectrometry/olfactometry using two capillary columns with different polarities (DB-5 and DB-FFAP). In total, 103 odorants were detected with successful identification of 98 of these substances. The identified odorants were predominately monoterpenes and sesquiterpenes as well as organic acids. Several compounds including germacrene D, thymol, carvacrol, rotundone, ß-caryophyllene, α-humulene, cinnamaldehyde, and ethyl cinnamate are reported here for the first time as odorous constituents of pinewood. Principal component analysis of the data obtained from sensory evaluation and cOEDA indicated that terpenes and sesquiterpenes were correlated with higher hedonic rates for the wood samples. Moreover, a Mantel test between the geographical distances of the trees and their sensory and cOEDA values demonstrated that the origin of the trees had a significant impact on the sensory characteristics of the wood, in agreement with the differences in the relative proportions of different volatile components. As such, the odor of Cembran pinewood is prone to variation but, yet, unique.

Identification of odorous compounds in oak wood using odor extract dilution analysis and two-dimensional gas chromatography-mass spectrometry/olfactometry.

Over the centuries, oak wood has been used in the maturation process of alcoholic beverages imparting aroma and flavor notes. Whereas several studies have dealt with the impact of oak wood on the chemical composition of, for example, wine aroma, only limited information is available on the odorant composition of unmodified and raw oak wood itself. To close this gap, a combination of human sensory and chemo-analytical techniques was applied for the elucidation of the chemical composition of oak odor, comprising extraction of the volatile fraction of oak wood by means of solvent-assisted flavor evaporation (SAFE) and subsequent mild concentration of the distillate. Odor extract dilution analysis (OEDA), which is based on gas chromatography-olfactometry (GC-O), was then applied for the targeted characterization of the odor-active compounds. Overall, a total of 97 odorants was identified via gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and heart-cut two-dimensional gas chromatography-mass spectrometry/olfactometry (2D-GC-MS/O). The majority of these odorants comprised a series of terpenes, mainly mono- and sesquiterpenes, aldehydes, acids, and lactones, as well as a number of odorants containing a phenolic core moiety. Several odorants are reported here for the first time as volatile organic compounds in oak wood. Identification of the molecular composition of oak wood odor helps to establish a better understanding of the distinctive smell of oak wood, and offers the basis for unveiling its potential effects on humans when being exposed to oak wood smell in daily life. Graphical abstract ᅟ.

Odorants in Fish Feeds: A Potential Source of Malodors in Aquaculture.

Although the microbiota is considered to be the primary source of off-flavors in farmed fish, there is a lack of information about the possible contribution of feeds to fish malodor. For this reason, the current study was designed to perform comprehensive sensory and chemo-analytical characterization of fish feed constituents that can impact the quality of farmed fish, and to determine whether feeds cause malodor accumulation in fish. To this aim, odorants in four commercial fish feeds were extracted using solvent assisted flavor evaporation (SAFE) and characterized by comparative aroma extract dilution analysis (cAEDA) and multi-dimensional gas chromatography-mass spectrometry/olfactometry (MD-GC-MS/O). The odorants in the fish feed samples were correlated with their respective sensory and fatty acid profiles. The cAEDA studies revealed the presence of 81 odorants of which 55 compounds were common to all the samples. Most of these odorants are identified here for the first time in fish feeds, and include skatole, indole, (E,Z,Z)-2,4,7-tridecatrienal, 4-ethyloctanoic acid, and cresols. Additionally, geosmin and 3-isopropyl-2-methoxypyrazine, known for their contribution to fish taint, and other cyanobacterial by-products, dimethyldisulfide and dimethyltrisulfide, were identified in feed samples. The results suggest that fish feed may contribute to fish malodor. Most of these off-flavors were linked to lipid source (fish oil or plant/lard alternatives), unsaturated fatty acids contents, and protein type (plant-based or fishmeal-based sources) in the feed.

Influence of the Chemical Structure on Odor Qualities and Odor Thresholds of Halogenated Guaiacol-Derived Odorants.

Chlorinated guaiacol derivatives are found in waste water of pulp mills using chlorine in the bleaching process of wood pulp. They can also be detected in fish tissue, possibly causing off-odors. To date, there is no systematic investigation on the odor properties of halogenated guaiacol derivatives. To close this gap, odor thresholds in air and odor qualities of 14 compounds were determined by gas chromatography-olfactometry. Overall, the investigated compounds elicited smells that are characteristic for guaiacol, namely smoky, sweet, vanilla-like, but also medicinal and plaster-like. Their odor thresholds in air were, however, very low, ranging from 0.00072 to 23 ng/Lair. The lowest thresholds were found for 5-chloro- and 5-bromoguaiacol, followed by 4,5-dichloro- and 6-chloroguaiacol. Moreover, some inter-individual differences in odor threshold values could be observed, with the highest variations having been recorded for the individual values of 5-iodo- and 4-bromoguaiacol.

Quantitative determination of common urinary odorants and their glucuronide conjugates in human urine.

Our previous study on the identification of common odorants and their conjugates in human urine demonstrated that this substance fraction is a little-understood but nonetheless a promising medium for analysis and diagnostics in this easily accessible physiological medium. Smell as an indicator for diseases, or volatile excretion in the course of dietary processes bares high potential for a series of physiological insights. Still, little is known today about the quantitative composition of odorous or volatile targets, as well as their non-volatile conjugates, both with regard to their common occurrence in urine of healthy subjects, as well as in that of individuals suffering from diseases or other physiological misbalancing. Accordingly, the aim of our study was to develop a highly sensitive and selective approach to determine the common quantitative composition of selected odorant markers in healthy human subjects, as well as their corresponding glucuronide conjugates. We used one- and two-dimensional high resolution gas chromatography-mass spectrometry in combination with stable isotope dilution assays to quantify commonly occurring and potent odorants in human urine. The studies were carried out on both native urine and on urine that had been treated by glucuronidase assays, with analysis of the liberated odor-active compounds using the same techniques. Analytical data are discussed with regard to their potential translation as future diagnostic tool.