Lactose intolerance and reliance on accurate food labels

Importance of the Topic

This study addresses the critical need for accurate measurement of trace lactose levels in dairy products to support lactose‐free labeling and to protect the health of millions of lactose‐intolerant consumers worldwide. With nearly 70% of the global population experiencing lactose malabsorption and no universally accepted cutoff for lactose‐free claims, highly sensitive analytical methods are essential for regulatory compliance and consumer safety.

Objectives and Overview

The primary goal of this work was to develop and validate a fast, robust ion chromatography method with pulsed amperometric detection (IC‐PAD) for quantifying low‐level lactose in diverse dairy matrices. The method was benchmarked against AOAC single‐laboratory validation criteria and compared sample preparation by traditional Carrez precipitation and automated inline dialysis.

Methodology and Sample Preparation

Samples included infant formula, certified reference milk, yogurts, butter, cream, chocolate, and nutritional supplements. Solids were chopped and liquids/powders homogenized. Aqueous extracts were prepared by weighing 0.1–5 g of sample into 50 mL tubes, adding ultrapure water, vortex mixing, and, when needed, heating to 70 °C. Protein removal used Carrez reagents followed by centrifugation. Alternatively, inline dialysis (5 mL sample volume) eliminated the precipitation step, streamlining preparation and reducing reagent use.

Used Instrumentation

• 940 Professional IC Vario ONE/Prep 1 with inline ultrafiltration or dialysis
• 930 Compact IC Flex Oven/Deg with built-in degasser
• Metrosep Carb 2-250/4.0 high-capacity anion-exchange column
• IC Wall-Jet amperometric cell (Au working, Pd reference electrode)
• IC Amperometric Detector with PAD, flexIPAD modes
• Low-volume inline dialysis accessory
• Inline ultrafiltration 2 pull-mode accessory

Main Results and Discussion

Calibration showed excellent linearity from 0.05 to 80 mg/L (liquid standards) and enabled quantification of 0.2 to 21 000 mg/100 g in real samples. Critical structural isomers (epilactose, lactulose, allolactose, galactosyllactose) were baseline resolved from lactose, ensuring high selectivity. Validation data across reference milk, prebiotic supplements, lactose-free yogurt, and butter demonstrated repeatability and day-to-day RSDs below 7%, spike recoveries between 90% and 110%, and resolution >1.5. Inline dialysis yielded comparable performance to Carrez precipitation with RSDs averaging 3.2%.

Benefits and Practical Applications

IC-PAD offers:

• High sensitivity for trace lactose detection
• Robust separation of lactose from derivates and matrix interferences
• Flexible sample preparation with optional automation
• Compatibility with routine high-throughput workflows
• Potential for inline calibration and dilution integration

Future Trends and Opportunities

Emerging developments include deeper automation of sample handling, integration of inline calibration and intelligent dilution, expansion to non-dairy matrices, and alignment with evolving regulatory thresholds for lactose-free labeling. Advances in detector design and data processing may further reduce detection limits and analysis time.

Conclusion

The validated IC-PAD method reliably quantifies low lactose levels in diverse dairy products, meeting AOAC acceptance criteria. Automated inline dialysis presents a time-efficient alternative to Carrez precipitation. The adaptable Metrohm IC platform supports further automation and offers a powerful solution for routine lactose analysis in quality assurance laboratories.

References

• Muehlhoff E.; Bennett A.; McMahon D. Milk and Dairy Products in Human Nutrition; FAO: Rome, 2013.
• Monti L.; Negri S.; Meucci A.; Stroppa A.; Galli A.; Contarini G. Lactose, Galactose and Glucose Determination in Naturally “Lactose Free” Hard Cheese: HPAEC-PAD Method Validation. Food Chem. 2017, 220, 18–24.
• Bayless T.M.; Brown E.; Paige D.M. Lactase Non-Persistence and Lactose Intolerance. Curr Gastroenterol Rep. 2017, 19(5), 23.
• Facioni M.S.; Raspini B.; Pivari F.; Dogliotti E.; Cena H. Nutritional Management of Lactose Intolerance: The Importance of Diet and Food Labelling. J Transl Med. 2020, 18(1), 260.