Fast Determinations of Lactose and Lactulose in Milk Products Using HPAE-PAD

Significance of the Topic

Milk-based products contain lactose as the main disaccharide and lactulose as a heat-induced isomer. Accurate, rapid analysis of these sugars is vital for labeling, quality control, and consumer safety, particularly for lactose-intolerant individuals.

Objectives and Overview of the Study

This work presents a fast, reliable method for simultaneous determination of lactose and lactulose in milk and dairy products. The approach employs high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) on a Thermo Scientific Dionex ICS-5000+ HPIC system.

Methodology

Sample preparation consists of Carrez I and II precipitation, centrifugation, filtration, and cleanup using a Dionex OnGuard IIA cartridge. Chromatographic separation is performed on Dionex CarboPac SA10-4µm guard and analytical columns at 35 °C with a 4 mM KOH isocratic eluent at 1.45 mL/min. Detection uses a four-potential PAD waveform on a disposable gold on PTFE electrode with a pH-Ag/AgCl reference.

Instrumentation Used

• Thermo Scientific Dionex ICS-5000+ HPIC Reagent-Free™ system
• Dionex CarboPac SA10-4µm guard and 4 × 250 mm analytical columns
• Dionex EGC 500 KOH eluent generator cartridge and CR-ATC 500 trap column
• Dionex AS-AP autosampler with temperature control
• ED detector module with Au on PTFE disposable working electrode and pH-Ag/AgCl reference electrode

Main Results and Discussion

The method achieves baseline separation of lactose and lactulose in under eight minutes (resolution Rs ≈ 7). Limits of detection are 0.036 mg/L for lactose and 0.087 mg/L for lactulose. Recoveries ranged from 99 to 113% for lactose and 89 to 96% for lactulose. Peak area precision was better than 4% RSD. The method demonstrated excellent robustness across raw milk, pasteurized milk, and lactose-free yogurt.

Benefits and Practical Applications

This rapid HPAE-PAD assay supports sensitive monitoring of residual lactose in lactose-free products, verification of pasteurization efficacy, regulatory labeling compliance, and general quality control in the dairy industry.

Future Trends and Possibilities of Use

Advances may include coupling HPAE to mass spectrometry for broader carbohydrate profiling, microfluidic implementations for point-of-need testing, and fully automated workflows to enhance throughput and reduce manual handling.

Conclusion

The described high-pressure HPAE-PAD method on the Dionex ICS-5000+ HPIC system provides a fast, accurate, and reproducible approach for quantifying lactose and lactulose in dairy products, meeting industrial demands for efficient quality assurance.

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