Rapid analysis of sugars in fruit juices by FT-NIR spectroscopy

A simple analytical procedure using FT-NIR and multivariate techniques for the rapid determination of individual sugars in fruit juices was evaluated. Different NIR detection devices and sample preparation methods were tested by using model solutions to determine their analytical performance. Aqueou s solutions of sugar mixtures (glucose, fructose, and sucrose; 0-8% w/v) we re used to develop a calibration model. Direct measurements were made by tr ansflection using a reflectance accessory, by transmittance using a 0.5-mm cell, and by reflectance using a fiberglass paper filter. FT-NIR spectral d ata were transformed to the second derivative. Partial least-squares regres sion (PLSR) was used to create calibration models that were cross-validated (leave-one-out approach). The prediction ability of the models was evaluat ed on fruit juices and compared with HPLC and standard enzymatic techniques . The PLSR loading spectra showed characteristic absorption bands for the d ifferent sugars. Models generated from transmittance spectra gave the best performance with standard error of prediction (SEP) < 0.10% and R-2 of 99.9 % that accurately and precisely predicted the sugar levels in juices, where as lower precision was obtained with models generated from reflectance spec tra. FT-NIR spectroscopy allowed for the rapid ( similar to 3 min analysis time), accurate and non-destructive analysis of sugars in juices and could be applied in quality control of beverages or to monitor for adulteration o r contamination. (C) 2001 Elsevier Science Ltd. All rights reserved.