Identification of key odorants in fresh-cut watermelon aroma and structure-odor relationships of cis,cis-3,6-nonadienal and ester analogs with cis,cis-3,6-nonadiene, cis-3-nonene and cis-6-nonene backbone structures

The scope of this study involved the identification of key odorants in fresh cut-watermelon, and the synthesis and evaluation of esters with potential watermelon-like aroma attributes. Aroma formation in fresh-cut watermelon is a dynamic enzymatic process, with the characteristic aroma components being formed immediately after cutting. The characteristic fresh-cut aroma is not long lasting due to further enzyme action that modifies the fresh-cut aroma components. The key to identifying the key components responsible for fresh-cut watermelon aroma was the application of a suitable volatile isolation strategy based on static headspace analysis (SHA). In this study, SHA was used to collect the headspace volatiles one minute after initial cutting of the fruit. This enabled a chemical ???snap shot??? of fresh-cut aroma to be taken. The most potent odorants in the headspace were determined by gas chromatography-olfactometry of decreasing headspace volumes (GCO-H) with confirmation achieved by application of a complimentary method based on GCO and aroma extract dilution analysis (AEDA) of fresh-cut watermelon aroma extracts prepared by solvent-assisted flavor evaporation (SAFE). Eight unsaturated nine-carbon aliphatic aldehydes and one six carbon unsaturated aldehyde were detected by GCO-H. These included cis-3-hexenal, cis,cis-3,6-nonadienal, cis-3-nonenal, cis-6-nonenal, trans-2-nonenal, cis-2-nonenal, trans,cis-2,6-nonadienal, trans,trans-2,4-nonadienal, and trans,trans,cis-2,4,6-nonatrienal. This finding is contrary to previous beliefs that alcohols are the main contributors to fresh-cut watermelon aroma. Most importantly, it was found that cis,cis-3,6-nonadienal was not only a potent odorant, but this compound alone possessed an aroma reminiscent of fresh-cut watermelon. Use of sensory evaluation, including ranking test, revealed that the aroma attributes of purified synthetic cis,cis-3,6-nonadienal closely matched those of fresh-cut watermelon. This ???watermelon aldehyde??? can be considered a potent odorants since its estimated odor detection threshold (in water) is very low (0.2 ppb). Unfortunately, cis,cis-3,6-nonadienal is a labile compound and is prone to both trans isomerization and oxidation of its aldehyde end group. For this reason, an attempt was made to create an ester with watermelon-like aroma attributes. Esters have been widely used in the food and beverage industries as flavoring agents because they are both stable and possess relatively low thresholds. To develop a watermelon-like ester, alcohol (formate, acetate, propionate, and butyrate) and carboxylic acid (methyl, ethyl, propyl, and butyl) esters with cis,cis-3,6-nonadiene backbones were synthesized. To achieve a more thorough understanding of the structure-odor relationship of these esters, the same types of alcohol and carboxylic acid esters were created with cis-3-nonene and cis-6-nonene backbones. The general structure/threshold trend was that threshold increased with increasing carbon number. In addition, threshold was also dependent on the number and position of the cis double bond. Descriptive sensory analysis was used to evaluate the effect of structure on the odor properties of the selected (low threshold) esters; however, no clear trend was found. Finally, further sensory analysis by ranking test was employed to determine, which, if any of these esters might be a suitable replacement for cis,cis-3,6-nonadienal for use as a watermelon flavoring. Although all esters had a ???fruity??? element to their aroma descriptions, none were significantly close in terms of their aroma attributes to cis,cis-3,6-nonadienal

Identification of rotundone as an important contributor to the flavor of oak aged spirits

The practice of barrel aging of spirits has been used for centuries. It began as an alternative storage and transportation method, but aging in an oak cask is now exclusively used as a means to impart flavor to the spirits. Oak wood is the wood of choice for barrel making, not only for its physical characteristics that lend itself to manufacturing a barrel, but also for its unique chemical properties that impart key flavors to aged spirits. Oak aging of spirits develops flavor in a number of different ways, all which contribute to a wide range of odor descriptions, creating the complex flavor with which we are familiar. Extensive research has been performed on oak wood and oak aged spirits; however, the identity of the component(s) responsible for the “woody/incense” flavor attribute of age spirits was, prior to this investigation, unknown. Experiments were conducted in order to unambiguously identify a compound responsible for a “woody/incense” odor note in oak aged spirits. The target compound was isolated from oak wood chips followed by several purification steps, as well as the use of a custom built GC-MS/olfactometry system equipped with a heart-cutting system/internal CryoTrap which enabled the acquisition of an interpretable electron-impact mass spectrum (EI-MS) for the compound. The EI-MS revealed that the unknown target compound possessed a molecular weight of 218. A thorough investigation of naturally occurring organic compounds having a molecular weight of 218, along with deducing the nature of the functional groups on the molecule, indicated numerous compounds as possible candidates. Most of these compounds were found to occur naturally in a number of roots, spices, oils, and herbs, which were subsequently analyzed. Results of the analyses revealed that the compound was most likely the sesquiterpene ketone 5-isopropenyl-3,8-dimethyl-3,4,5,6,7,8-hexahydro-1(2H)-azulenone, or rotundone. This identification was confirmed by comparison of the compound’s EI-MS and GC retention indices against those of authentic rotundone obtained by chemical synthesis. The next question addressed was whether this compound is present in oak aged spirits. Accurate quantification of this trace level target compound was done by stable isotope dilution analysis (SIDA). The presence of rotundone in different aged spirits including bourbons, rye, scotch, whiskey, rum, and tequila was demonstrated. Trends in aging were established, showing that rotundone increases with aging time; however, its quantity may also be influenced by other factors as there was a clear brand to brand variation. Interestingly, rotundone was also found in un-aged (silver) tequila, which suggests that the compound may also be present in the agave plant. Results of quantification of all potent odorant in bourbons, aged 4, 8, and 12 years and calculation of their odor activity values (OAVs) demonstrated rotundone’s importance to the overall flavor of bourbon. From the quantification data some interesting trends were established that demonstrate some effects of barrel aging. OAVs are used as a gauge for potency and, generally, any compound with an OAV above 1, provides evidence of whether a compound is important. With an OAV of 42.8 to 56.6, rotundone lies well above this requirement and is among the top 10 odorants quantified in these samples. Thus, it is concluded that rotundone is an important contributor to the flavor of these aged spirits

Alternate H2 Sinks for reducing rumen methanogenesis

Greenhouse gas (GHG) emissions from livestock is about 7,516 million metric tons CO2-eq.year-1and has multiple components that include enteric methane emissions, methane and nitrous oxide emissions from manure and carbon dioxide emissions associated with feed production and grazing. An uninterruptedly increasing concentration (155 % more than preindustrial level), a comparatively high global warming potential and a short half-life of methane make it a bit more important than any other GHG in the control of global warming and climate change. Enteric methane mitigation is not only important from a global warming point but also for saving animal dietary energy which is otherwise lost in the form of methane. Due to the central regulatory role of H2, it is generally referred as the currency of fermentation and most of the mitigation strategies revolve around its production or disposal in such a way as to ensure the conservation of energy into desirable end products. In the chapter, an attempt is made to address the prospects of some emerging approaches to redirect metabolic H2away from methanogenesis and serve as potential alternate sink for H2in the rumen for conserving energy. The prospects of alternate sinks, for instance, sulphate and nitrate reduction and reductive acetogenesis and propionogenesis, are debated in the chapter along with the anticipated benefits that can be achieved from the practically feasible 20 % enteric methane reduction