PLS-NIR determination of total sugar, glucose, fructose and sucrose in aqueous solutions of fruit juices

An analytical procedure has been developed for the direct determination of sugars in fruit juice samples. The method is based on the partial least-squares (PLS) treatment of first derivative near infrared (NIR) spectroscopic data obtained between 1200 and 2450 nm, using 1 mm pathlength cell and a multicomponent calibration set, including seven binary mixtures and 10 ternary mixtures of glucose, fructose and sucrose. The limit of detection values found are of the order of 0.2 g/100 mi for total sugar and 0.2, 0.4 and 0.5 g/100 mi for glucose, fructose and sucrose, respectively. Relative standard deviation Values obtained vary from 0.4% to 2.3% for six independent measurements of individual sugar concentrations from 15.4 to 2.4 g/100 mi and 0.03% for total sugar of the order of 20 g/100 mi. Average recovery percentages of 99+/-2 for total sugar and between 98+/-4 and 100+/-4 for single sugar determinations evidence the applicability of the methodology developed for the analysis of juice samples.