Abstract
The legal method (polarimetric measurement) for the determination of sucrose content since 1964 uses lead acetate. Because heavy metals are polluting, a law could forbid their use in the near future. Near infrared (NIR) spectroscopy is a suitable alternative method to replace it. For two years, 2412 samples of beet brei were analysed by NIR spectroscopy. In this article, spectral pre-processing and regression methods were compared in order to obtain an accurate prediction of sugar content. Analyse of variance and Fisher's tests were calculated to compare models (bias and Standard Error of Prediction corrected for bias) in terms of statistical significance. The model developed with spectra pre-treated by standard normal variate and second derivative gave the best results. The standard error of prediction of the ratio sucrose content/fresh beet weight was low (0.11 g / 100 g). The second part of this study shows that updating of the spectral database was possible. This makes it possible to take into account new variabilities of beet. For an industrial application, calibration transfer has to be studied. Sugar beet spectra or generic standard spectra were used on two NIR instruments. A simple linear regression wavelength by wavelength gives good results for the standardisation, demonstrating a possible use of the model on different instruments. In conclusion, the replacement of the polarimetric method by NIR spectroscopy was feasible.
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