Simulation of Pilsner-type beer aroma using 76 odor-active compounds.

Gas chromatography-olfactometry (GC-O) analyses of the aroma components extracted from Pilsner-type beer were performed. The concentrations of all 76 components, that were identified after the GC-O analyses, were accurately quantitated. The aroma compounds were then used in the following aroma simulation experiments, with ethanol and water as matrices. The odorants with higher odor intensity in GC-O analysis and odor activity values (OAVs) were selected first, and the selected 25 odorants were used in an aroma simulation experiment. The results of sensory analysis showed that the simulation model using 25 odorants exhibited unbalanced characteristics and lacked the malty/cereal, estery characteristics, the total amount of aroma, and the similarity compared to the reference Pilsner-type beer. Addition of the 24 odorants, which were identified through the fractionations of whole aroma extract of beer and expected to complement the malty/cereal characteristic, could not improve the aroma quality of the simulation model. The aroma simulation experiments using 76 odorants indicated that the synergistic contributions of the multiple odorants, with no independent contribution to the overall characteristics (including sub-threshold components) and with no reminiscence of beer aroma, were necessary for the construction of beer aroma.

Identification of a precursor of 2-mercapto-3-methyl-1-butanol in beer.

2-Mercapto-3-methyl-1-butanol (2M3MB) imparts an onion-like off-flavor to beer and is believed to result from the hot aeration of brewer's wort. However, little has been reported regarding the mechanism of formation of 2M3MB. This paper investigates the precursors of 2M3MB formed during the brewing process. Our study of a cysteine conjugate as a precursor showed its negligible contribution to the formation of 2M3MB. The 2M3MB precursor was found to be a volatile compound because 2M3MB was formed in the distillate of hop extract. The precursor was purified through distillation, column chromatography, and preparative gas chromatography, and the 2M3MB-producing potential was measured as an index for estimating the concentration of the precursor. The accurate mass of the precursor was measured using gas chromatography coupled to quadrupole-time-of-flight-mass spectrometry (GC/QTOF). The molecular structure was identified from the product ion spectra by GC/QTOF to be 2,3-epoxy-3-methylbutanal.

Search for compounds contributing to onion-like off-flavor in beer and investigation of the cause of the flavor.

Onion-like off-flavor is a highly undesirable property in beer. Although several compounds that impart onion-like odors have been identified, the individual contribution of these compounds to the onion-like off-flavor in beer is not clear. In the present study, we searched for compounds that impart an onion-like odor by gas chromatography (GC)-olfactometry. The analysis of several types of beer revealed that 2-mercapto-3-methyl-1-butanol (2M3MB) and 3-mercapto-3-methyl-1-butanol (3M3MB) were possible causative compounds. Based on the difference threshold values in beer (0.13 ng/mL for 2M3MB and 17.5 ng/mL for 3M3MB) and the quantification values of these compounds in beer samples, only 2M3MB was considered to contribute to the onion-like off-flavor in beer. A further formation factor analysis of 2M3MB revealed that 2M3MB was formed in hopped wort after fermentation, and that the concentration of 2M3MB increased following the hot aeration treatment of wort. These results suggest that preventing the hot aeration of wort is a key factor for reducing 2M3MB levels in beer. In a previous report, 3-methyl-2-buten-1-ol (3MBol) was speculated to be the precursor of 2M3MB and 3M3MB; however, the results of the present quantification analysis and wort addition tests indicate that 3MBol did not contribute to the formation of 2M3MB in the brewing process and that unknown precursors of 2M3MB originated in wort. Identifying the precursor of 2M3MB may facilitate elucidation of the mechanism of 2M3MB formation.

Determination of ochratoxin a in ready-to-drink coffee by immunoaffinity cleanup and liquid chromatography-tandem mass spectrometry.

We developed a simple and accurate method for determining ochratoxin A (OTA) in ready-to-drink coffee, using an immunoaffinity column for cleanup and liquid chromatography-tandem mass spectrometry (LC/MS/MS) for identification and quantification. When uniformly stable isotope-labeled OTA (U-[(13)C(20)]-OTA) was employed as an internal standard, the recovery rate of the method was 97.3% (the spiked OTA level was 0.10 ng/mL), the repeatability (relative standard deviation) was 1.9%, and the intermediate precision (relative standard deviation) was 4.0%. The limit of quantification was 0.0065 ng/mL based on a signal-to-noise ratio in coffee of 10:1. The developed method was used for the determination of OTA in ready-to-drink coffee. A total of 30 ready-to-drink coffee samples commercially available in Japan were analyzed. OTA was detected in all of the samples at concentrations ranging from trace levels (0.0020-0.010 ng/mL) to 0.037 ng/mL. This method was shown to be useful for accurately evaluating the intake of OTA from coffee beverages.

Determination of ochratoxin A in wine by immunoaffinity cleanup and liquid chromatography tandem mass spectrometry.

A simple and accurate method has been developed for determining ochratoxin A (OTA), using an immunoaffinity column for cleanup and liquid chromatography-tandem mass spectrometry for identification and quantification. Wine samples were diluted with a solution containing polyethylene glycol 8000 and sodium hydrogen carbonate, filtered through a glass microfiber filter, and cleaned up on an immunoaffinity column. OTA was then eluted with methanol-acetic acid (98:2) and analyzed by liquid chromatography-tandem mass spectrometry. The average recoveries of OTA from red and white wines were 95 and 96.7% (spiked OTA level was 0.05 ng/ml) and repeatabilities (relative standard deviation) were 3.8 and 2.4%, respectively. The detection limit was 0.0003 ng/ml based on the signal-to-noise ratio in wine of 3:1. Analysis of 74 samples of domestic and imported wines showed OTA levels ranging from < 0.0003 to 0.82 ng/ml, with an incidence of contamination of 92.1% for red wines, and < 0.0003 to 0.51 ng/ml, with an incidence of contamination of 77.8% for white wines. These detection rates were higher than those rates of past reports of OTA contamination in wine, due to the high sensitivity of this method. However, all samples analyzed in this study complied with European Union regulations. It is concluded that this method is a useful tool for the quality assurance of wine.