Quantitative analysis of alcohol, real extract, original gravity, nitrogen and polyphenols in beers using NIR spectroscopy

This study was to develop a rapid and accurate NIR analysis method for determinations of alcohol, real extract, original gravity, total nitrogen and total polyphenols. Commercial European beers (110 samples) were used to create calibration models between EBC (European Brewing Committee) and NIR spectral data. The optimal correlation coefficients (r) were 0.94 to 0.98 and the corresponding CV% (coefficients of validation variation) were 4.29, 6.53, 4.50, 6.06 and 4.74 for NIR predictions of alcohol, real extract, original gravity, nitrogen and polyphenols, respectively. The stepwise MLR calibration proved to be a good choice for measurements of alcohol and original gravity, while PLS regression models seem to be better for the predictions of the real extract, nitrogen and polyphenols. Comparisons of results from MLR and PLS, demonstrate that MLR methods (log 1/R) are better than those of PLS (log 1/R) in calibration and prediction sets. The reflection mode is better than those of transmission in all above ...