Application of two-dimensional J-resolved nuclear magnetic resonance spectroscopy to differentiation of beer

Abstract

A number of ingredients in beer that directly or indirectly affect its quality require an unbiased wide-spectrum analytical method that allows for the determination of a wide array of compounds for its efficient control. 1H nuclear magnetic resonance (NMR) spectroscopy is a method that clearly meets this description as the broad range of compounds in beer is detectable. However, the resulting congestion of signals added to the low resolution of 1H NMR spectra makes the identification of individual components very difficult. Among two-dimensional (2D) NMR techniques that increase the resolution, J-resolved NMR spectra were successfully applied to the analysis of 2-butanol extracts of beer as overlapping signals in 1H NMR spectra were fully resolved by the additional axis of the coupling constant. Principal component analysis based on the projected J-resolved NMR spectra showed a clear separation between all of the six brands of pilsner beer evaluated in this study. The compounds responsible for the differentiation were identified by 2D NMR spectra including correlated spectroscopy and heteronuclear multiple bond correlation spectra together with J-resolved spectra. They were identified as nucleic acid derivatives (adenine, uridine and xanthine), amino acids (tyrosine and proline), organic acid (succinic and lactic acid), alcohol (tyrosol and isopropanol), cholines and carbohydrates.