Profiling Selected Volatiles in Whiskey by Fizzy Extraction Time-of-Flight Mass Spectrometry: Correlation with Perceived Quality and Age

Abstract

Fizzy extraction (FE) is an extraction technique that extracts volatile organic compounds (VOCs) from liquid matrices using pressure-induced effervescence. The sudden decompression of a gas-saturated sample solution generates numerous microbubbles, which trap and transfer VOCs with different volatilities from the liquid phase into the headspace of the sample solution. Here, we coupled FE with an atmospheric pressure chemical ionization interface of a quadrupole time-of-flight mass spectrometry system to perform analysis of VOCs present in whiskeys. The hyphenated system has been optimized by using chemical standards. The optimized conditions are the following: saturation time, 40 s; equilibration time, 0 s; extraction time, 20 s; extract transfer tubing I.D., 1.0 mm; extract transfer tubing length, 80 cm. The limits of detection for ethyl acetate, ethyl propionate, ethyl butanoate, ethyl hexanoate, and ethyl octanoate are 7.48 × 10–8, 2.41 × 10–8, 1.63 × 10–9, 9.31 × 10–9, and 5.24 × 10–9 M, respectively. The repeatability relative standard deviations (RSDs) ranged from 6.00 to 12.17% (10 replicates on one day) while the reproducibility RSDs ranged from 4.01 to 11.47% (3 replicates on each of 6 different days). The resulting method was applied in analysis of 40 whiskeys originating from different countries or distilleries. The VOC profiles were used to characterize the whiskeys’ quality and age. Ethyl propionate and ethyl butanoate were found to be potential markers of whiskeys’ quality (using price per mL as the proxy of quality). In some cases, the concentrations of selected volatiles were found to increase when the age of whiskey increased. Additionally, we also determined the losses of selected volatiles in whiskey by analyzing the whiskey recurrently after opening the bottle. Overall, the developed method provides a fast (∼3 min), reliable, and green way to analyze VOCs in whiskey samples.