Direct spectroscopic sucrose determination of raw sugar cane juices

A more accurate, less time-consuming, and nonpolluting spectroscopic method than the currently used HPLC or polarimetric methods is proposed for the routine quantitative determination of sucrose in complex biological samples. Opaque raw sugar cane juices representative of a sugar cane harvest are analyzed by Fourier transformed mid-infrared attenuated total reflectance, and the spectral data are processed by principal component analysis (PCA) and principal component regression (PCR). The most suitable region for the measurement of sucrose was found to be the 1250-800 cm(-1) region. The spectroscopic representation of the first axis as assessed by PCA in this spectral region featured characteristic absorption bands of sucrose. By PCR on the spectral data from a calibration set, a prediction equation was established to predict sucrose content in unknown samples. Good overall predictions were obtained. The values of the predicted sucrose concentration were more accurate (bias = 0.041 g/100 mL) than those obtained by direct polarimetry (bias = -0.163 g/100 mL). The method is validated on a panel of 1267 samples representative of a sugar cane harvest.