Determinação de açúcares redutores em bebidas alcoólicas e não alcoólicas por ressonância magnética nuclear de baixo campo

Abstract

Time Domain nuclear magnetic resonance (TD-NMR) has been widely applied in different areas due to its versatility, speed, direct analysis or with minimal sample preparation steps and non-destructive nature. The analysis of paramagnetic ions by TD-NMR has a wide range of applications and is a tool that has been gaining prominence in analytical Chemistry. In this study, a novel analytical method based on TD-NMR was developed and validated for the quantification of reducing sugars in alcoholic beverages, such as cachaça, and non-alcoholic beverages, including juices and soft drinks. The method is based on the reaction of reducing sugars with Cu²⁺ ions from Benedict’s reagent, forming Cu₂O and enabling the indirect determination of glucose concentration through variations in transverse relaxation times (T₂), through the standard pulse sequence CPMG. The experimental conditions were optimized for the working ranges of glucose and copper, establishing linearity from 2.0 to 10.0 g·L⁻¹ (with 45 g·L⁻¹ of CuSO₄·5H₂O) and from 0.2 to 1.0 g·L⁻¹ (with 6.0 g·L⁻¹ of CuSO₄·5H₂O). For analytical validation of the proposed method, the limits of detection (LOD), limits of quantification (LOQ), and accuracy were determined by comparing with reference methods (UV-Vis and HPLC-RI). Overall, good statistical agreement was observed among the methods. Compared with UV-Vis, relative errors were below 11% and no statistically significant differences were found. In relation to HPLC-RI, a general statistical agreement was also verified, although some samples presented relative errors higher than 20%. These results demonstrate that TD-NMR is a robust and promising alternative for the determination of reducing sugars in beverages, with potential application in routine analyses and quality control.