Identification of Odor-Active Trace Compounds in Blooming Flower of Damask Rose ( Rosa damascena).

The flower scent of the damask rose ( Rosa damascena) was studied. Two ultratrace components exhibiting high flavor dilution factors were detected as odor-active compounds via aroma extract dilution analysis (AEDA). One of these had a woody note and was identified as rotundone using multidimensional gas chromatography-mass spectrometry-olfactometry (MD-GC-MS-O), while the other had a citrus note and was identified as 4-(4-methylpent-3-en-1-yl)-2(5 H)-furanone (MPF) by fractionation of a commercial rose absolute from R. damascena. To the best of our knowledge, this is the first study addressing the organoleptic importance of these two compounds in the rose scent. Sensory analysis was conducted to evaluate the effects of rotundone and MPF. Adding 50 µg/kg rotundone and 5 µg/kg MPF to the aroma reconstitute of R. damascena provided it with blooming and natural characteristics. Additionally, the existence of rotundone and MPF in five types of fragrant roses was investigated.

Identification of Odor-Active Compounds Released from a Damaged Plant of the Asian Skunk Cabbage Symplocarpus renifolius.

Symplocarpus renifolius (Asian skunk cabbage) is a perennial herb of the Araceae family. As its common name implies, this plant produces a strong garliclike irritant odor with a rotten note when the plant parts are crushed. To elucidate the odor characteristics, the volatile compounds released from crushed plant parts (rhizome, petioles, and leaf blades) of S. renifolius were identified by a dynamic headspace method. Fifteen sulfur compounds were identified as odor-active compounds by gas chromatography-mass spectrometry-olfactometry (GC-MS-O). The sulfur compounds may be responsible for the strong odor emitted by crushed skunk cabbage. Many of the compounds lack a carbon-carbon bond, and all of the carbon atoms are connected to sulfur. This is regarded as the characteristic structure of the sulfur compounds released from the damaged plant parts of the skunk cabbage. Nine of the sulfur compounds were detected in all three of the plant parts analyzed in this study: hydrogen sulfide, methanethiol, 1-hexanethiol, methyl dithioformate, 2,4-dithiapentane, dimethyl trisulfide, methional, 2,3,5-trithiahexane, and tris(methylthio)methane. Methyl dithioformate and methylthiomethyl dithioformate were identified for the first time as natural products.

Quantitation of Rotundone in Grapefruit (Citrus paradisi) Peel and Juice by Stable Isotope Dilution Assay.

Aroma extract dilution analyses of the aromas of peels and juices of white and pink grapefruits revealed that rotundone, responsible for peppery, spicy, and woody odors, was detected for the first time at high flavor dilution factors of 256-1024. In both juices, rotundone was detected at the highest flavor dilution factor of 1024. Rotundone in grapefruits was quantitated by a stable isotope dilution assay with a newly synthesized deuterium-labeled internal standard, rotundone-d2,3: its levels were 2180 and 1920 ng/kg in white and pink grapefruit peels and 29.6 and 49.8 ng/kg in white and pink grapefruit juices, respectively. On the basis of these results, sensory analysis was performed to assess the effects of rotundone on a white grapefruit juice aroma reconstitute. This sensory analysis revealed that rotundone does not impart a woody odor or affect any of the existing attributes, but increases various attributes, thus confirming that rotundone is indispensable for the aroma of grapefruit juice.

Identification and Characterization of 3-epi-Rotundone, a Novel Stereoisomer of Rotundone, in Several Kinds of Fruits.

A novel stereoisomer of rotundone, 3-epi-rotundone, was identified in the aroma of grapefruit, orange, apple, and mango. 3-epi-Rotundone was prepared by the isomerization of rotundone, and its structural elucidation was confirmed by comparing the 1D and 2D nuclear magnetic resonance and nuclear Overhauser effect spectroscopy spectra with those of rotundone. The odor thresholds of rotundone and 3-epi-rotundone in water were determined by a triangle test as 5 and 19100 ng/kg, respectively. The odor of 3-epi-rotundone was evaluated as woody, spicy, peppery, citrus, grapefruit-like, powdery, and celery-like, which was a greater range of odor characteristics than that for rotundone. Results of odor evaluation of 3-epi-rotundone revealed that its unique organoleptic properties, which were odor description (woody, spicy, and peppery), anosmic properties in neat form, and strong adaptation, were similar to those of rotundone. 3-epi-Rotundone might be a valuable substance to apply new types of woody, peppery, and spicy notes.

Identification of Rotundone as a Potent Odor-Active Compound of Several Kinds of Fruits.

An investigation of the aromas of grapefruit, orange, apple, and mango revealed the presence of an odor-active compound that gave off a strong woody odor when assessed by gas chromatography-olfactometry. We isolated the compound from a high-boiling fraction of an orange essential oil, and subsequent nuclear magnetic resonance analyses of the isolated compound identified it as rotundone. Mass spectra and retention indices obtained from aroma concentrates of grapefruit, apple, and mango were identical to those of rotundone, which was therefore determined to be the common woody compound in these fruits. Sensory analyses were performed to assess the effects of rotundone on model beverages of the various fruits. It was revealed that rotundone added at even subthreshold levels to model beverages did not confer directly the woody odor, but had significant effects on the overall flavors of the beverages, helping them to better approximate the natural flavors of the fruits.

Identification of the key odorants in Tahitian cured vanilla beans (Vanilla tahitensis) by GC-MS and an aroma extract dilution analysis.

The key odorants of Tahitian vanilla beans (Vanilla tahitensis) were characterized by a sensory evaluation, aroma extract dilution analysis (AEDA), quantification, and aroma reconstitution. Vanillin and anisaldehyde were identified in the same highest flavor dilution (FD) factor as the most characteristic odor-active compounds in Tahitian vanilla beans, followed by anisyl alcohol and anisyl acetate. Vanillin and anisyl alcohol were by far the most abundant odorants present with the highest concentration in the beans, followed by acetic acid, anisaldehyde, and anisyl acetate. A sensory evaluation of Tahitian vanilla beans and its reconstitute aroma concentrate characterized both samples as similar. These results indicated vanillin, anisaldehyde, anisyl alcohol, and anisyl acetate to be the key odorants in Tahitian vanilla beans. 3-Methylnonane-2,4-dione were identified for the first time in vanilla beans. ß-Damascenone and phenylacetic acid were identified for the first time in Tahitian vanilla beans.

Key odorants in cured Madagascar vanilla beans (Vanilla planiforia) of differing bean quality.

The odor-active volatiles in Madagascar vanilla beans (Vanilla planiforia) of two grades, red whole beans as standard quality and cuts beans as substandard quality, were characterized by instrumental and sensory analyses. The higher contents of vanillin and ß-damascenone in red whole beans than in cuts beans respectively contributed to significant differences in the sweet and dried fruit-like notes, while the higher contents of guaiacol and 3-phenylpropanoic acid in cuts beans than in red whole beans respectively contributed to significant differences in the phenolic and metallic notes. A sensory evaluation to compare red whole beans and their reconstituted aroma characterized both samples as being similar, while in respect of the phenolic note, the reconstituted aroma significantly differed from the reconstituted aroma with guaiacol added at the concentration ratio of vanillin and guaiacol in cuts beans. It is suggested from these results that the concentration ratio of vanillin and guaiacol could be used as an index for the quality of Madagascar vanilla beans.

Functional characterization of a carotenoid cleavage dioxygenase 1 and its relation to the carotenoid accumulation and volatile emission during the floral development of Osmanthus fragrans Lour.

Carotenoids are the precursors of important fragrance compounds in flowers of Osmanthus fragrans Lour. var. aurantiacus, which exhibit the highest diversity of carotenoid-derived volatiles among the flowering plants investigated. A cDNA encoding a carotenoid cleavage enzyme, OfCCD1, was identified from transcripts isolated from flowers of O. fragrans Lour. It is shown that the recombinant enzymes cleave carotenes to produce alpha-ionone and beta-ionone in in vitro assays. It was also found that carotenoid content, volatile emissions, and OfCCD1 transcript levels are subjected to photorhythmic changes and principally increased during daylight hours. At the times when OfCCD1 transcript levels reached their maxima, the carotenoid content remained low or slightly decreased. The emission of ionones was also higher during the day; however, emissions decreased at a lower rate than the transcript levels. Moreover, carotenoid content increased from the first to the second day, whereas the volatile release decreased, and the OfCCD1 transcript levels displayed steady-state oscillations, suggesting that the substrate availability in the cellular compartments is changing or other regulatory factors are involved in volatile norisoprenoid formation. Furthermore, the sensory evaluation of the aroma of the model mixtures suggests that the proportionally higher contribution of alpha-ionone and beta-ionone to total volatile emissions in the evening is probably the reason for the increased perception by humans of the scent emission of Osmanthus flowers.

Novel character impact compounds in Yuzu (Citrus junos Sieb. ex Tanaka) peel oil.

Yuzu ( Citrus junos Sieb. ex Tanaka), a tree-grown fruit similar to a kind of sour orange, is widely used in Japanese food/cooking for its pleasant flavor. To clarify the odor-active volatiles that differentiate yuzu from other citrus fruits, sensory evaluations were conducted on yuzu peel oil. The results revealed that the polar part of yuzu peel oil was the source of the characteristic aroma of fresh yuzu fruit. By aroma extract dilution analysis (AEDA) of the polar volatile part of yuzu peel oil, seven odorants were newly identified as odor-active volatiles in yuzu peel oil in the highest flavor dilution (FD) factors of 128 and 32: oct-1-en-3-one, (E)-non-4-enal, (E)-dec-4-enal, 4-methyl-4-mercaptopentan-2-one, (E)-non-6-enal, (6Z,8E)-undeca-6,8,10-trien-3-one (Yuzunone), and (6Z,8E)-undeca-6,8,10-trien-4-ol (Yuzuol). Among the most odor-active volatiles in yuzu, (E)-non-6-enal and Yuzunone were identified for the first time solely in yuzu peel oil and not in the peel of other citrus species, and Yuzuol was identified for the first time in nature. Sensory evaluation of yuzu aroma reconstitutions revealed that the newly identified compound, Yuzunone, contributes greatly to the distinct yuzu aroma.

Flavor enhancement of chicken broth from boiled celery constituents.

The flavor-enhancing effects of the volatile constituents in celery were investigated. The test samples were prepared by adding celery fractions to chicken broth at a concentration that distinct odors of them were not detected, and the samples were sensorially evaluated for the perceived intensities of 8 terms such as "thick," "impactful," "mild," "lasting," "satisfied," "complex," "refined," and "clarified," which are considered to be the elements of the complex flavor and for 3 terms such as "sweet," "salty," and "umami" taste. A comparison of effects between the volatile and nonvolatile fractions of celery revealed that the volatile compounds in celery enhanced the complex flavor of chicken broth more than the nonvolatile compounds. Among the characteristic odorants of celery, three phthalides, namely, sedanenolide, 3- n-butylphthalide, and sedanolide, were shown to contribute to the complex flavor of chicken broth, and sedanenolide was most effective. The three phthalides enhanced perceived intensities of "umami" and "sweet" despite their no taste properties in addition to the complex flavor.

Potent odorants characterize the aroma quality of leaves and stalks in raw and boiled celery.

The raw and boiled odors of celery leaves and stalks were investigated. Among 12 compounds identified as potent odorants, 3-n-butylphthalide 1, sedanenolide 2, and trans- and cis-sedanolides 3, 4 were assessed to be most contributive to the overall odor of celery. These three phthalides, (3E,5Z)-1,3,5-undecatriene, myrcene, and (E)-2-nonenal were common to both raw and boiled materials. Two compounds, ((Z)-3-hexenal and (Z)-3-hexenol), were dominant in raw materials and four compounds, (2-methylbutanoic acid, sotolon, beta-damascenone, and beta-ionone), were dominant in boiled materials. Sensory evaluations were performed on natural celery odor and a series of reconstructed model aromas by assigning each intensity ratings for a set of seven odor qualities which aptly describe the odors of raw and boiled celery. According to the evaluation results, six common components contributed to the moderate odor of raw celery, two components dominant in raw materials enhanced the raw celery character, and four components dominant in boiled materials reduced the raw celery character and enhanced the boiled celery character. It was clarified that boiling-induced changes in celery odor were not affected by the amounts of phthalides, but by thermally generated compounds such as sotolon, beta-damascenone, and beta-ionone, which reduce the "green spicy" note.

"Aqua-space", a new headspace method for isolation of natural floral aromas using humidified air as a carrier gas.

A new method called "Aqua-space" was developed for the isolation of the natural fragrances of plants. Living flowers were enclosed in a space under simulated natural conditions, and humidified air was pumped into the space as a fragrance carrier. In a comparison among three isolation methods, i.e., Aqua-space, headspace, and solvent extraction, the Aqua-space method proved to be the most effective in retaining natural fragrances with abundant oxygenated components key to floral fragrances.