Quality determination of Chinese rice wine based on Fourier transform near infrared spectroscopy

To evaluate the applicability of near infrared (NIR) spectroscopy for the determination of five enological parameters (alcoholic degree, pH value, total acid, amino acid nitrogen and degrees Brix) in Chinese rice wine, transmission spectra were collected in the spectral range from 800nm to 2500nm in a 1mm path length rectangular quartz cuvette with air as the reference at room temperature. Five calibration equations for the enological parameters were established between the reference data and NIR spectra by partial least squares (PLS) regression, separately. The best calibration results were achieved for the determination of alcoholic degree and degrees Brix. The coefficients of determination in calibration (R-cal(2)) for alcoholic degree and degrees Brix were 0.93 and 0.96, respectively. The predictive deviation ratio (RPD) value of the calibration for alcoholic degree was higher than 3 (3.95), which demonstrated the robustness of the calibration model. The RPD value for degrees Brix was 2.34. The performance of the calibration models for pH, total acid and amino acid nitrogen were not as good as that of alcoholic degree and degrees Brix. The RPD values for the three parameters were 1.41, 1.38 and 1.27, respectively and R-cal(2) values were 0.97, 0.83 and 0.90, respectively. In the validation step, r(val)(2) values for alcoholic degree and degrees Brix were all higher than 0.9. The performance of pH and total acid were acceptable [the coefficients of determination in validation (r(val)(2)) for pH and total acid were 0.82 and 0.77, respectively]. The performance of amino acid nitrogen model was the worst, with an r(val)(2) value of 0.62. The results demonstrated that the NIR spectroscopic technique could be used to predict the concentrations of these five enological parameters in Chinese rice wine.