Determination of Nitrogen/Protein in Whey and Powdered Dairy Products

Significance of the Topic

The quantification of protein content in whey and powdered dairy products through Dumas combustion is essential for nutritional labeling, quality assurance, and regulatory compliance in the dairy industry. Accurate nitrogen analysis underpins product specification, consumer safety, and commercial transactions.

Objectives and Study Overview

This application note evaluates the performance of the LECO FP828 nitrogen/protein determinator in measuring nitrogen and calculating protein content in various dairy matrices. Data were generated using a modified ISO 14891 protocol, focusing on sensitivity, precision, and operational efficiency.

Used Instrumentation

• LECO FP828 Nitrogen/Protein Determinator: vertical quartz furnace operating at 950 °C, pure oxygen environment, and an afterburner at 850 °C.
• Thermoelectric cooler for moisture removal.
• Thermal Conductivity detector for nitrogen detection.
• Aliquot dose loops (3 cm³ and 10 cm³) for gas sampling.
• Carrier gases: Helium (for highest sensitivity) and Argon (cost-effective alternative).

Methodology

• Sample Preparation: Dry, homogeneous samples; use of certified reference materials (LCRM, LRM, NIST).
• Calibration and Drift Correction: Linear calibration through origin using ~0.25 g EDTA LCRM (9.59 % N), verification with nicotinic acid (11.37 % N).
• Analysis Parameters: Combustion at 950 °C, afterburner at 850 °C, aliquot fill pressure drop 175 mm Hg, interleaved analysis enabled, no sample drop detection.
• Carrier Gas Settings: Helium and Argon options; ballast equilibration (10 s He, 8 s Ar).
• Burn Profiles: Performance model (5.00 LPM/1.00 LPM steps), Base model (high/medium flow steps).
• Replicate Analyses: Conditioning (3–5 replicates), blank determination (≥5 replicates), sample analysis (multiple replicates per sample).

Main Results and Discussion

The study analyzed whey powder, dietary supplements, instant breakfast powder, powdered milk, and infant formula under four conditions (10 cm³ He, 3 cm³ He, 10 cm³ Ar, 3 cm³ Ar). Key findings:

• Whey powders: Average %N ≈ 12.44–12.47, corresponding to ~79.3–79.6 % protein; standard deviation ≤ 0.2 % protein.
• Instant breakfast powder: %N ≈ 2.39–2.42 (15.2–15.5 % protein); precision < 0.2 % protein.
• Powdered milk: %N ≈ 5.91–5.95 (37.7–38.0 % protein); SD ≤ 0.1 % protein.
• Infant formula: %N ≈ 1.85–1.91 (11.8–12.2 % protein); SD ≤ 0.2 % protein.
• Helium offered enhanced sensitivity at low N levels, while Argon provided robust performance at reduced operational cost.

Benefits and Practical Applications

• Rapid, solvent-free combustion analysis suitable for high-throughput laboratory workflows.
• Automated sampling and interleaved analysis minimize operator intervention and maximize productivity.
• Flexible configuration allows optimization of sensitivity versus reagent longevity and cost per analysis.
• Applicable to a wide range of dairy products for regulatory and commercial quality control.

Future Trends and Potential Applications

• Integration with laboratory information management systems (LIMS) and advanced data analytics for real-time quality assurance.
• Development of microdosing and miniaturized loops for detection of ultra-low nitrogen levels.
• Expansion to plant-based and composite food matrices for broader industry application.
• Standardization of nitrogen-to-protein conversion factors to harmonize international trade.

Conclusion

The LECO FP828 determinator delivers precise, reliable nitrogen and protein analysis in whey and powdered dairy products, meeting modified ISO 14891 requirements. Its operational versatility and automated design support rigorous quality control in dairy manufacturing.

Reference

• ISO 14891: Milk and Milk Products – Determination of Nitrogen Content (Combustion, Dumas Principle).