Qin Zhou, Oregon State University, Corvallis, OR 97331
Co-author(s): Yanping Qian and Michael Qian, Oregon State University, Corvallis, OR, USA
ABSTRACT: Acetaldehyde, ethyl acetate, isobutyl alcohol, isoamyl alcohol, and isoamyl acetate are the major volatile compounds in beer fermentation; they are considered important quality indicators for brewing. The determination of these compounds helps to evaluate whether complete and proper fermentation has taken place. Therefore, it is critical for brewers to build a simple and reliable method to analyze these compounds. The ASBC headspace GC-FID protocol was re-evaluated in different beer matrices and alcohol concentrations. Sample size and incubation temperatures were also tested to determine the sensitivity of the compounds. Sample preparation, including acetaldehyde standard preparation, was modified. The result showed that the alcohol content in beer affected the recovery of analytes, as well as the internal standard; however, the alcohol content in typical beer range (less than 7%) did not affect the quantification of these compounds as long as an internal standard calibration method was used. Methyl propionate turned out to be a better option as an internal standard than 1-butanol, since it has much less interaction with the beer matrix. Calibration correlation coefficients for all compounds were better than 0.997, and good repeatability was also obtained. Detection limits were below the normal ranges of concentrations in beer and also below the odor thresholds. Recoveries were nearly 100%. The improved procedure could be a more accurate alternative to the ASBC standard procedure for analyzing these compounds in beer.
Qin Zhou received a B.S. degree in chemistry from Wuhan University in China in 2006, and her M.S. degree in fermentation engineering from China National Research Institute of Food and Fermentation Industries in 2009. In 2010, she began pursuing a Ph.D. degree in Michael Qian’s flavor chemistry lab at Oregon State University in the Food Science and Technology Department. Her work focuses on the flavor chemistry of alcoholic beverages, including beer and wine.