Norio Miyazawa

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.

Aroma Character Impact Compounds in Kinokuni Mandarin Orange (Citrus kinokuni) Compared with Satsuma Mandarin Orange (Citrus unshiu)

The odor-active volatiles of Kinokuni mandarin (Citrus kinokuni Hort. ex Tanaka), an original mandarin orange in Japan, were characterized by a combination of instrumental and sensory analyses and compared with those of Satsuma mandarin (Citrus unshiu Marcovitch). An aroma extract dilution analysis (AEDA) of the polar fractions of Kinokuni and Satsuma mandarin peel oils identified five odorants in common as the most odor-active volatiles: (Z)-hex-3-enal, decanal, linalool, yuzuol, and (2E)-trans-4,5-epoxydec-2-enal. In addition, seven odorants were identified solely in Kinokuni mandarin as significant contributors: octanal, dodecanal, (2E,4E)-deca-2,4-dienal, geraniol, yuzunone, (2E,7Z)-trans-4,5-epoxydeca-2,7-dienal, and thymol. The odor-active volatiles in both the non-polar components of the peel oil and an extract of the juice prepared from Kinokuni mandarin were also identified. The (S)-isomer of linalool in Kinokuni mandarin peel oil was dominant in the enantiomeric distribution (92%), whereas the (R)-isomer was dominant in Satsuma mandarin peel oil (90%).

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 β-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.

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. β-Damascenone and phenylacetic acid were identified for the first time in Tahitian vanilla beans.

Novel Key Aroma Components of Galbanum Oil

Galbanum oil is composed of monoterpenes in large amounts and pyrazines in small amounts. Although the monoterpenes are the main components of galbanum oil, they hardly contribute to the distinct galbanum aroma. The scanty amounts of pyrazines, in contrast, contribute significantly to the aroma. Considering the complexity and potency of the odor, the essential oil was assumed to contain so far not identified compounds with high odor contribution. By the gas chromatography-mass spectrometry-olfactometry (GC-MS-O) analysis of galbanum oil, fruity-green-balsamic notes were detected at two different retention times. The mass spectra (MS) of the newly discovered notes were elucidated by conducting multidimensional (MD) GC-MS-O. By analyzing the MS data, six chemical structures were proposed: (6E/Z,8E)-undeca-6,8,10-trien-2-one, (6E/Z,8E)-undeca-6,8,10-trien-3-one, and (6E/Z,8E)-undeca-6,8,10-trien-4-one. The compounds were then synthesized in an attempt to match the MS, retention indices (RI), and odor qualities. The MD-GC-MS-O analyses of the candidate compounds led to the identification of the novel key aroma compounds (6Z,8E)-undeca-6,8,10-trien-3-one and (6Z,8E)-undeca-6,8,10-trien-4-one in galbanum oil.

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.

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.