Quality control of beer using high-resolution nuclear magnetic resonance spectroscopy and multivariate analysis

Abstract

High-resolution nuclear magnetic resonance (NMR) spectroscopy is introduced for the quality control and authenticity assessment of beer in official food control. Measurements were performed using a 400-MHz NMR spectrometer using flow injection technology for automatic sample changing. Only degassing and addition of buffer (pH 5.6 in D2O for locking and 0.1% TSP for referencing) is required to prepare the beer samples. Differences in the spectral profiles of beers varying in type and origin were studied by principal component analysis (PCA), considering the spectrum to be a characteristic fingerprint. For the first time, the high throughput of a Flow-Injection NMR system allowed a comprehensive database of beer spectra for PCA classification to be established efficiently. Beers made with barley malt could be distinguished from those made with wheat malt. Clustering of beers from the same brewing sites was observed, as well as significant discrimination of beers with deteriorated quality. Using the partial least squares (PLS) method to correlate NMR spectra with results from reference methods, models for calculating the original gravity, ethanol and lactic acid were established. The results obtained suggest that NMR is a useful tool in the quality control of beer samples, since quantitative determination of essential compounds as well as chemometric classification are simultaneously possible. Compared to conventional methods, 1H NMR spectroscopy is faster and requires simpler sample preparation.