Evaluation of the quality of solid sugar samples by fluorescence spectroscopy and chemometrics

It has been shown that fluorescence spectroscopy of sugar in aqueous soluti on carries important quality and process information related to beet sugar factories, which is accessible by multivariate analyses, A method for measu ring crystalline sugar directly on-line in the process should be advantageo us. In this paper we compare the solution measurement technique with two me thods of fluorescence measurement on solid sugar. Surprisingly, it was poss ible to measure fluorescence through the sugar crystals by using the same t ransmission techniques with 90 degrees detection as with the sugar solution s. This method was compared with a 45 degrees front-surface reflection meth od. Sugar samples from six different sugar factories were examined. The spe ctral responses were reasonable, but they were influenced by the heterogeno us sample composition and the sample geometry. It was possible with the two methods to separate sugar samples according to factory with the use of pri ncipal component analysis (PCA). Seasonal time trends were found in weekly samples front the same factory. Partial least-squares regression (PLS) was used to predict quality parameters, where color (range: 6-41), ash (range: 0.003-0.018), and alpha-amino-N (range: 0.28-5.07) could be modeled with er rors of 2.3-2.6, 0.0015-0.0016, and 0.40-0.42, respectively. Model errors f or similar solution data have been determined to 2.4, 0.0012, and 0.266, re spectively.