Application of NMR spectroscopy for the quality control of beer

摘要

This work describes the use of Nuclear Magnetic Resonance (NMR) spectroscopy for the characterisation of beer. Presenting advantages of rapidity, non-invasiveness and the ability to measure several different families of compounds in one single experiment (that is in a few minutes), NMR is shown to enable the detection of about 30 compounds including organic acids, amino acids, nucleotide bases and alcohols. Further assignments in particularly overlapped and low sensitivity spectral regions, e.g. the sugar and the aromatic regions, were tackled by LC-NMR/MS and applications of this method to the assignment of dextrins and of new aromatic compounds are presented. The tandem use of NMR spectroscopy and chemometric methods (such as Principal Component Analysis, PCA) enables large numbers of samples to be handled in order to rapidly detect compositional differences and correlate them to known external variables. Application of NMR/PCA is described for sets of beer samples differing in 1) type (lagers, ales and alcohol-free) and 2) production sites and lots. The results show that beers from different types and origins may be distinguished in terms of their contents in specific organic acids and in the properties of dextrins (e.g. degree of branching), thus enabling successful tracking of beer samples. These results present NMR/PCA as a potential valuable tool for process understanding and control in the brewing industry.