Analysis of Food Sugars in Various Matrices Using UPLC with Refractive Index (RI) Detection

Significance of the topic

The presence and quantification of sugars like fructose, glucose, sucrose, maltose, and lactose in food matrices are essential for quality control, detection of adulteration, nutritional labeling, and process monitoring. Rapid, reliable, and robust analytical methods help laboratories and manufacturers maintain product standards and comply with regulations.

Objectives and overview of the study

This work illustrates a UPLC method coupled with refractive index detection to separate and quantify five common food sugars in diverse samples within 3.5 minutes. The goal was to leverage sub-2 μm particle technology and isocratic elution to maximize throughput, minimize solvent consumption, and avoid column re-equilibration.

Methodology and used instrumentation

• Instrument: ACQUITY UPLC H-Class System
• Detector: ACQUITY Refractive Index Detector
• Column: ACQUITY UPLC BEH Amide (2.1×50 mm, 1.7 μm) at 85 °C
• Mobile phase: 77:23 acetonitrile/water with 0.05% triethylamine
• Flow rate: 0.15 mL/min; injection volume: 1.0 μL
• Data rate: 20 points/s; flow cell temperature: 40 °C
• Standard preparation: six-level dilution of a 1 g/100 mL sugar stock in 50:50 acetonitrile/water
• Sample preparation: centrifugation and dilution protocols for fruit juices, corn syrup, and low-fat milk with 50:50 acetonitrile/water

Main results and discussion

• All five sugars eluted in under 3.5 minutes with baseline separation.
• Calibration curves exhibited linearity (R2>0.999) across the working range.
• Fruit juices: distinctive sugar ratios observed—orange and pineapple showed fructose:glucose:sucrose at approximately 1:1:2; white grape contained fructose and glucose with negligible sucrose; retention time and peak area repeatability were below 0.11% and 1.25% RSD, respectively.
• Corn syrup analysis revealed high levels of glucose (154.4 g/L) and maltose (104.4 g/L), reflecting an enzymatic conversion profile distinct from high-fructose variants.
• Low-fat milk showed a clear lactose peak at 47.9 g/L, demonstrating method versatility.

Benefits and practical applications of the method

• Rapid isocratic analysis reduces turnaround time and boosts sample throughput.
• No column re-equilibration between injections simplifies operation and enhances productivity.
• Low flow rate lowers solvent usage and waste disposal costs.
• Robust amide chemistry tolerates basic modifiers and high temperatures for improved peak shape.
• Refractive index detection offers stable baseline, linear response, and minimal maintenance without the need for gas supplies.

Future trends and applications

Advances may include coupling UPLC-RI methods with mass spectrometry for structural confirmation, expanding the platform to monitor additional carbohydrates and sugar alcohols, integrating automated sample preparation, and adapting the workflow for online process analytical technology in food manufacturing.

Conclusion

The described UPLC-RI method delivers fast, precise, and reproducible quantification of five major food sugars across diverse matrices, offering significant operational efficiencies for laboratories focused on nutritional analysis, quality assurance, and product authenticity.

Reference

1. Sanz A, et al. Inositols and Carbohydrates in Different Fresh Fruit Juices. Food Chemistry. 2004;87:326.