Simple partial least squares–attenuated total reflectance Fourier transform infrared spectrometric method for the determination of sugars in fruit juices and soft drinks using aqueous standards

Abstract

A simple analytical procedure was developed for the direct determination of sugars in fruit juices (apple, orange, grape) and soft drinks. The method is based on the partial least squares treatment of attenuated total reflectance Fourier transform infrared spectrometric data obtained in the wavenumber range 4000–700 cm^–1 and does not require any sample pre-treatment. Absorbance and first-derivative spectra were employed for measurements, using a reduced set of eight aqueous standard mixtures of glucose, fructose and sucrose at two concentration levels for calibration. The limits of detection found for absorbance measurements were 0.2 g per 100 ml for total sugar and 0.1, 0.1 and 0.03 g per 100 ml for glucose, fructose and sucrose, respectively. Relative standard deviations varied from 1.7 to 2.0% for six independent measurements of individual and total sugar concentration. In the analysis of real and synthetic samples, precise and accurate results were obtained, providing accuracy errors lower than 2% in all cases. Average recoveries of 96 ± 4% for total sugar and between 93 ± 7 and 99 ± 7% for single sugars demonstrate the applicability of the methodology developed to the direct analysis of fruit juice and soft drink samples.