The composition and content of trace compounds in the aroma of Chinese liquor by Fourier transform infrared (FTIR) difference spectroscopy.

The aroma of liquor is one of the key indicators used to evaluate the liquor. Therefore, accurately determining the composition and its content of a liquor's aroma is crucial for assess its quality. In this study, Fourier transform infrared difference spectroscopy was used to record the aroma composition of Chinese liquor at room temperature. Through measuring the infrared absorption spectra of the volatiles from liquor and an aqueous ethanol solution, the spectra of the trace chemical compounds in the aroma were obtained using the difference spectroscopy. According to the infrared absorption spectra of standard compounds, the vibrational bands in the IR spectra of the aroma in eight different brands of Chinese liquor were regarded as the molecular vibration from ethyl acetate, ethyl lactate, ethyl caproate, caproic acid and isoamyl alcohol. Using the Lambert Beer's law, the contents of these trace compounds were quantitatively determined to be around 1-6 mg/L. This study demonstrates the difference IR spectroscopy is a powerful tool for assess quality of liquor.