Determination of Nitrogen/Protein in Cheese

Importance of the Topic

The accurate measurement of protein content in cheese is essential for nutritional labeling, quality control, and economic valuation. Rapid and precise determination supports consistent product quality and regulatory compliance in dairy processing.

Study Objectives and Overview

This application note evaluates the LECO FP828 combustion (Dumas) nitrogen/protein determinator for cheese analysis. The goals are to demonstrate method speed, precision, and flexibility using different carrier gases (helium or argon) and aliquot dose loops (3 cm3 or 10 cm3), and to compare results across common cheese varieties.

Methodology

Samples of uniform consistency are weighed into tin foil cups (~0.25 g) and analyzed without chemical digestion. The sequence includes system conditioning, blank determination, calibration/drift correction using reference materials, and sample analysis. Key procedural steps:

• Condition the system with reference or sample replicates.
• Establish blank level from multiple blank runs (target SD ≤ 10 ppm for helium, ≤ 50 ppm for argon).
• Calibrate or drift-correct with certified reference material (e.g., EDTA, ~9.58 % N).
• Analyze cheese samples in replicates, recording nitrogen content.

Used Instrumentation

The LECO FP828 employs a vertical quartz furnace in a pure oxygen environment (950 °C), followed by an afterburner at 850 °C. Moisture is removed by a thermoelectric cooler before gases mix in a ballast. A selectable 3 cm3 or 10 cm3 aliquot dose loop delivers the sample to a thermal conductivity detector. Carrier gas options are helium (highest sensitivity) or argon.

Main Results and Discussion

Typical analyses on Parmesan, Swiss, Pepperjack, and Sharp Cheddar show:

• Consistent nitrogen values with standard deviations ≤ 0.02 % (helium) and ≤ 0.04 % (argon).
• Protein contents (using factor 6.38) closely match expected compositions (e.g., 30.6 % in Parmesan, 19.4 % in Swiss).
• Minimal impact of loop size on precision; helium yields slightly better sensitivity at low nitrogen levels.

Benefits and Practical Applications

The automated Dumas method on the FP828 provides:

• Analysis in under five minutes per sample without hazardous reagents.
• High precision and accuracy across cheese varieties.
• Operational flexibility via choice of carrier gas and aliquot loop size.
• Reduced reagent cost and simplified workflow for routine quality control.

Future Trends and Potential Applications

Advancements may include integration with inline sampling, further miniaturization, alternative inert gases, and enhanced software automation. Expansion of Dumas applications to other dairy products and real-time process monitoring are promising areas.

Conclusion

The LECO FP828 offers a robust, fast, and safe method for nitrogen/protein determination in cheese. Its adaptability and reliability make it well-suited for high-throughput dairy laboratories and quality assurance programs.

Reference

• ISO 14891: Milk and Milk Products — Determination of Nitrogen Content (Routine combustion method by Dumas principle), modified version used for data generation.