Fast determination of lactose in dairy products

Importance of the Topic

Lactose intolerance affects a large portion of the adult population worldwide and drives the demand for reliable analysis of residual lactose in so called lactose free and low lactose dairy products. Precise quantification at trace levels is essential for regulatory compliance, consumer safety, and product labeling. The development of a fast, sensitive, and robust method addresses the needs of quality control laboratories facing high sample throughput requirements.

Objectives and Study Overview

This study aimed to develop and validate a high performance anion exchange chromatography method with pulsed amperometric detection (HPAEC-PAD) using a novel Dionex CarboPac PA20 Fast-4 µm column. The goal was to achieve fast separation and accurate quantification of lactose and lactulose in various dairy matrices labeled as lactose free or reduced lactose, with limits of quantification below 0.001 % (w/w).

Methodology and Instrumentation

Sample Preparation

• Carrez precipitation: 1.5 g sample in water, addition of Carrez I and II reagents, volume adjustment, and filtration to remove proteins and particulates.
• Final dilution and filtration through 0.45 µm syringe filters.

Chromatographic Conditions

• System: Thermo Scientific Dionex ICS-3000 IC with pulsed amperometric detector.
• Column: Dionex CarboPac PA20 Fast-4 µm guard (2 × 30 mm) and analytical (2 × 100 mm).
• Eluents: water (A), 0.2 M NaOH (B), 0.1 M NaOAc (C), and 1 M NaOAc in 0.2 M NaOH (D).
• Gradient: isocratic 6 % B for 10 min, step to 10 % B with 2.5 % C until 14 min, return to 6 % B.
• Flow rate: 0.2 mL/min, column temperature: 30 °C.
• Detection waveform: carbohydrate waveform with gold working electrode and Ag/AgCl reference.

Key Results and Discussion

External calibration over 0.1–20 mg/L showed excellent linearity (r2 > 0.999). Retention time precision was better than 0.4 % RSD and quantification precision (lactose at 0.04 % w/w) was 1.5 % RSD on a single column and 4–5 % RSD across column sets. Limits of detection and quantification were estimated at 0.0003 % and 0.0008 % (w/w) based on repeat injections of real samples. Analysis of lactose-free milk and cream cheese yielded recoveries around 98 % and consistent lactulose detection. Application to whole milk demonstrated the method is also suitable for typical lactose concentrations (4.8 % w/w) with 1.7 % RSD.

Benefits and Practical Applications

The fast cycle time (21 min including rinsing), high selectivity, and sensitivity make this method ideal for routine quality control of lactose in fresh and unripened dairy products. The approach eliminates the need for multiple calibration curves and supports trace analysis down to low ppm levels, meeting strict national labeling standards.

Future Trends and Opportunities

Further improvements may include integration of online sample cleanup, use of smaller particle columns to reduce analysis time below 15 min, and expansion to a broader range of dairy matrices. Coupling with mass spectrometric detection could enable simultaneous screening for other oligosaccharides and contaminants.

Conclusion

The developed HPAEC-PAD method using the CarboPac PA20 Fast-4 µm column provides a rapid, robust, and accurate solution for lactose and lactulose determination in lactose-free and conventional dairy products. It meets stringent regulatory requirements and offers high throughput for industrial and research laboratories.

References

1. ISO 22662:2007 Milk and milk products Determination of lactose by HPLC with RI detection
2. Technical Note 71: Eluent Preparation for HPAEC-PAD, Thermo Fisher Scientific 2013
3. Perati P et al Application Note 248 Lactose determination by HPAEC-PAD, Thermo Fisher Scientific 2016
4. van Scheppingen WB et al J Chrom B 2017 395–399
5. EFSA Journal 2010 Lactose thresholds in intolerance