Analysis of volatile thiols in beer with on-fiber derivatization and GC/MS determination

Analytical Session
Minoru Kobayashi, Research & Development Laboratories for Brewing, Asahi Breweries, LTD. 1-21, Midori 1-Chome, Moriya-Shi, Ibaraki 302-0106
Co-author(s): Nana Yako, Susumu Masuda, and Masayuki Aizawa, R&D Laboratories for Brewing, Asahi Breweries, Ltd., Moriya-Shi, Japan

ABSTRACT: Volatile thiols in beer are known to cause off-flavors, even at low concentrations. However, the determination of volatile thiols at low levels in beer is particularly complicated and difficult. A fast and automated method for analysis of volatile thiols, such as 3-methyl-2-butene-1-thiol (MBT), to the nanogram per liter level was developed in this study. We adapted the method used for wine to the analysis of beer. Briefly, a sample is poured into a 20-mL vial, and the headspace gas is extracted with a solid-phase microextraction (SPME) fiber pretreated by exposure to vapors of pentafluorobenzyl bromide. The derivatized compounds are subsequently desorbed in GC-MS. As a result, good analytical precision and linearity can be achieved for MBT, benzenemethanethiol, and 2-mercapto-3-methyl-1-butanol. These volatile thiols can be repetitively detected in beer at concentrations <0.1 ng/L. The proposed procedure is much simpler than the present methods from the viewpoints of processing and time requirements. Therefore, the new method can be used as an alternative to the existing methods, and it is an effective method for brewers to use when evaluating off-flavors in beer. Through the introduction of this analytical method, it has become possible to reduce variation in the amount of thiol formation in the brewing process and improve stabilization of beer flavor quality. In this presentation, we will show some examples of the control of off-flavors in our brewery.

Minoru Kobayashi is a scientist at brewing research and development laboratory, Asahi Breweries Ltd. He received his M.S. degree in applied biological chemistry from Tokyo University in Japan, where he majored in analytical chemistry. He has been engaged in the analytical technology laboratory since 1998, especially in the analytical chemistry section. Since 2003 he has worked in the brewing science section, especially in beer flavors.