Determination of sugars in dairy products using HPAE-PAD

Significance of the Topic

Accurate quantification of milk carbohydrates is critical for regulatory nutrition labeling, quality control, and product development in the dairy industry. High-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) offers direct, nonderivatized analysis of common mono- and disaccharides with high sensitivity and resolution.

Objectives and Study Overview

This study evaluated the ISO/DIS 22184 method for determining six sugars (galactose, glucose, fructose, sucrose, lactose, maltose) in various dairy matrices. A Thermo Scientific Dionex CarboPac PA1-2 mm column and ICS-5000+ HPIC system were used to assess separation performance, calibration linearity, and precision, analyzing fourteen samples from an international collaborative study.

Methodology and Instrumentation

The HPAE-PAD approach employed gradient elution using sodium acetate and sodium hydroxide eluents with water and post-column NaOH addition. Samples underwent Carrez protein precipitation and filtration. An arabinose internal standard enabled quantification. Instrumentation included a Dionex ICS-5000+ HPIC system, CarboPac PA1 guard and analytical columns, electrochemical detector, AS-AP autosampler, Chromeleon CDS software, and standard reagents (ethanol buffer, Carrez reagents).

Main Results and Discussion

Sugar peaks were baseline resolved with resolution >2. Calibration curves using eight concentration levels fit quadratic models yielding coefficients of determination (r2) >0.999 for most analytes; sucrose and maltose ranges were adjusted for optimal linearity. Method precision was under 2% RSD for peak areas and <0.22% for retention times. Sample analysis revealed lactose dominance in whey powder and infant formula, sucrose in condensed milk and low-lactose formulas, and detectable maltose in infant formula. Duplicate sample analyses confirmed reproducibility. Chromeleon CDS variable internal standard functions facilitated data processing.

Benefits and Practical Applications

• Direct, derivatization-free analysis of dairy sugars
• Compliance with ISO/DIS 22184 standard
• High sensitivity and resolution for QA/QC and nutritional labeling
• Versatile for diverse dairy products

Future Trends and Potential Uses

• Optimization of gradient profiles to improve maltose resolution
• Integration with mass spectrometry for enhanced specificity
• Automation of sample preparation and high-throughput analysis
• Application to emerging dairy-based matrices and lactose-free products

Conclusion

The Thermo Scientific HPAE-PAD method on the CarboPac PA1-2 mm column provides a robust, sensitive, and reproducible protocol for simultaneous determination of six sugars in dairy products, meeting ISO requirements and supporting quality assurance efforts.

References

1. ISO 11292:1995 Instant Coffee–Determination of free and total carbohydrate contents by high-performance anion-exchange chromatography.
2. CEN/TS 15754:2008 Animal feeding stuffs–Determination of sugar content by HPAEC-PAD.
3. Hu J., Rohrer J. Fast lactose determination in lactose-free dairy products by HPAE-PAD. Thermo Fisher Scientific Application Note AN-248.
4. Thermo Fisher Scientific Application Note AN-72632: Fast and sensitive lactose analysis in lactose-free products by HPAE-PAD.
5. Thermo Fisher Scientific Application Note AN-72780: Lactose determination in lactose-free dairy products using HPAE-PAD/MS dual detection.
6. ISO/DIS 22184 & IDF/WD 244, Milk and milk products–Determination of sugar contents by HPAE-PAD, 2017.
7. Sanders P. et al. Development of a new standard method for sugar determination in dairy products. J AOAC Int. 2017, 100(5), 1577–1581.