P-23
Identification of characteristic flavor compounds in malt whisky. The production of malt whisky mainly consists of alcoholic fermentation,
distillation, and maturation in an oak cask. Many volatiles are generated during
these processes. However, only the major constituents, such as fusel alcohols,
ethyl esters, carbonyl compounds, and lactones etc, have been studied
extensively. Few reports have been published on the relationship between
organoleptic estimation and the corresponding compounds, and there have been
only a small number of reports on minor compounds. Therefore, the major
compounds alone could not fully explain the quality of malt whisky. Because
these major compounds affect the assignation of mass spectra and the character
of flavor in GC/mass-spectrometry (GC/MS) and/or GC/olfactometry (GC/O)
analysis, minor compounds would not be adequately recognized in those tests. In
this study, we investigated the characteristic flavor compounds, which consisted
of small amounts that affected the final quality, in malt whisky using the
combination of GC/MS and olfactometry detection. The flavor constituents
gamma-decalactone and gamma-dodecalactone were identified as sweet and fatty compared
to the authentic compounds using GC/O and GC/MS. It was found that these
compounds contributed to the character due to the relationship between the
contents and the organoleptic estimation and, moreover, were generated from
hydroxy and/or keto fatty acid, which formed from unsaturated fatty acid by
lactic acid bacteria. Next, a multidimensional GC/MS-olfactometry (MDGC/MS-O)
measure was used for smaller amounts of compounds that imparted the character to
final quality. Using MDGC/MS-O, E,Z-2,6-nonadienal, E-2-nonenal, and nonan-2-ol
contributed to a green note, yielding to a character of freshness and vividness.
Also using similar equipment, we attempted to identify the other characteristic
flavor compounds, such as fatty note and feint flavor, respectively. In
conclusion, MDGC/MS-O was effective in examining small amounts of compounds in
malt whisky, containing many volatiles, since this method enables the volatiles
in a complicated matrix to be highly resolved without being influenced by large
amounts of those volatiles. Therefore this method could be useful and helpful to
elucidate the characteristic flavor compounds in fermented food such as wine and
beer.
Akira Wanikawa received a B.A. in Agriculture Chemistry from Hokkaido
University in Hokkaido. He began employment with The Nikka Whisky Distilling in
Hirosaki plant in 1987. In July 1992, he transfered the Institute for R&D. Since
April 2001, he moved to Asahi Breweries. In 2002, he earned PhD in Hokkaido
University.
AKIRA WANIKAWA (1), Kenji Hosoi (2), Nobuaki Yamamoto (1), and Kei-ichi Nakagawa
(2). (1) Asahi Breweries, Ltd., Moriya, Ibaraki, Japan, and (2) The Nikka Whisky
Distilling Co. Ltd.