Beverages Applications Notebook - Milk

Importance of the Topic

Monitoring the composition of milk and dairy‐based products is critical for food safety, nutrition labeling and regulatory compliance. Milk may be contaminated by harmful inorganic ions (iodide, nitrate, nitrite), adulterants (melamine), residual nutrients (choline, lactose, sialic acids) or require measurement of fat content for quality control. Reliable, high‐throughput methods reduce consumer risk and support industry quality assurance.

Objectives and Study Overview

This collection of application notes presents rapid, robust analytical workflows for milk analysis. Key goals include:

• Determining trace iodide, choline, nitrate, nitrite and lactose with ion chromatography (IC) and IC‐based suppression or absorbance detection.
• Identifying melamine adulteration using HPLC–UV on mixed‐mode and reversed‐phase columns.
• Measuring total and fatty acid composition of milk fats using accelerated solvent extraction (ASE) versus classical methods.
• Quantifying sialic acids (Neu5Ac, Neu5Gc, O-acetylated forms) via HPAE‐PAD and UHPLC–fluorescence after derivatization.

Methodology and Instrumentation

Our approaches combine modern sample preparation with Dionex/Thermo Scientific chromatography:

• ASE 150/350/200 systems for automated fat extraction in <10 min, comparing gravimetry and FAME analysis versus Roese‐Gottlieb or Mojonnier.
• Ion chromatography with Reagent‐Free™ IC systems (ICS‐1100/1600/2100/3000/5000) and CS/AS column families for anions (iodide, nitrate, nitrite) and cations (choline).
• HPLC methods on Acclaim 120/300 C18, RSLC 120 C18 and mixed‐mode WCX-1 columns for melamine and other small organics.
• HPAE‐PAD with CarboPac PA20 columns for direct saccharide and sialic acid analysis.
• UHPLC–fluorescence with DMB derivatization on RSLC 120 C18 for detailed sialic acid profiling.
• Chromeleon™ CDS for single‐point instrument control and unified data processing.

Main Results and Discussion

• Trace iodide in infant formula and milk was determined by IC with pulsed amperometric detection on an AS11 column, with <5 µg/L sensitivity, 80–100% recoveries and <3% RSD.
• Choline in dry milk and infant formula was analyzed by cation‐exchange IC with suppressed conductivity, achieving linearity to 200 mg/L and >95% recovery.
• Melamine in raw and powdered milk was quantified in <10 min by HPLC-UV on the mixed-mode WCX-1 and RSLC 120 C18 columns, with MDLs <0.05 µg/mL.
• Total fat in milk powder, cheese and butter was extracted in 8–24 min by ASE with 20–30 mL solvent, matching official methods (±1%), and confirmed by FAME and HPLC–ELSD.
• Lactose in lactose-free milks and cottage cheese was determined by HPAE-PAD with MDLs of 0.12 mg/L and recoveries of 86–100%.
• Sialic acids in enriched infant formulas were profiled by HPAE-PAD and UHPLC–fluorescence, resolving Neu5Ac, Neu5Gc and O-acetylated species in <30 min.
• Nitrate and nitrite in milk were measured by RFIC with in-line protein precipitation and InGuard cartridges, enabling 1000+ samples with MDLs of 0.005 and 0.002 mg/L.

Benefits and Practical Applications

These methods deliver:

• High throughput: ASE extractions in minutes, IC methods with <10 min runs, UHPLC–fluorescence in <20 min.
• Cost efficiency: Automation, minimal solvent use, and long consumable life (InGuard, RFIC eluents).
• Enhanced reproducibility: Reagent-Free™ IC, controlled UHPLC conditions and robust detectors ensure <5% RSD.
• Regulatory compliance: Matches or exceeds performance criteria for AOAC, EPA, and other standard methods.

Future Trends and Potential Uses

• Integration of IC and LC with mass spectrometry for confirmatory analyses and broader analyte coverage.
• Miniaturized and portable IC/PAD systems for on-farm or point-of-use testing.
• Expanded mixed-mode stationary phases for simultaneous multi-class analyte screening.
• Automated workflows combining ASE, IC, and UHPLC for continuous process monitoring in dairy plants.

Conclusion

This suite of chromatographic methods provides dairy analysts with rapid, reliable, and automated protocols for key analytes in milk matrices. By leveraging advanced sample prep, high-capacity columns, and unified data systems, laboratories can enhance throughput, reduce costs, and ensure consistent quality and safety in milk and infant formula products.

References

1. U.S. EPA Method 300.0, Determination of Inorganic Anions in Water by IC.
2. AOAC Method 933.05, Fat in Cheese; Method 938.06, Fat in Dried Milk.
3. ASTM D6867-16, Melamine in Food Products by HPLC.
4. J. HPLC Science 12(4), 487 (2019): DMB Labeling of Sialic Acids.
5. Food Chem. 84, 447–450 (2004): Lactulose Assay Development.