Determination of Nitrogen/Protein in Whey and Powdered Dairy Products (FP928)

Significance of the topic

Whey and powdered dairy products are key components in nutrition and food manufacturing. Accurate protein determination guides product labeling, quality control, and regulatory compliance. The Dumas combustion method offers a rapid and precise approach to measure nitrogen content, which is translated into protein levels using established conversion factors.

Objectives and study overview

This application note demonstrates the performance of the LECO FP928 macro combustion nitrogen/protein determinator for quantifying nitrogen and calculating protein content in whey powder, instant breakfast powder, powdered milk, and infant formula. The study evaluates the impact of carrier gas (helium vs. argon) and aliquot loop size (10 cm3 vs. 3 cm3) on analytical precision, sensitivity, and cost per analysis.

Used Instrumentation

• LECO FP928 macro combustion nitrogen/protein determinator
• 528-203 ceramic combustion boats and 611-844 spatula/flat spoon
• Carrier gases: high-purity helium or argon
• Thermal conductivity detector and copper reduction tube

Methodology and Instrumentation

Samples (~0.5 g) were weighed into ceramic boats and introduced into a horizontal ceramic combustion furnace at 1100 °C under pure oxygen. Combustion gases passed through a thermoelectric moisture trap, mixed in a ballast, and an aliquot (3 cm3 or 10 cm3) was taken into a helium or argon carrier stream. A copper reduction tube converted NOx to N2, which was detected by thermal conductivity. The instrument was calibrated using certified EDTA and verified with nicotinic acid standards according to a modified ISO 14891 protocol. Key parameters included a 12 °C/min ramp rate, three purge cycles, and a ballast equilibration time of 10 s.

Main results and discussion

Analysis of four dairy matrices demonstrated consistent nitrogen measurements and protein calculations across all gas and loop configurations. Average nitrogen contents (± standard deviation) for whey powder ranged from 12.41 ± 0.02% to 12.45 ± 0.01%, corresponding to protein values of 79.2 ± 0.1% to 79.4 ± 0.1%. Instant breakfast powder, powdered milk, and infant formula showed similarly tight precision (s ≤ 0.02% for nitrogen and ≤ 0.2% for protein). Helium yielded the highest sensitivity at low nitrogen levels, while argon offered cost advantages with minimal loss in accuracy.

Benefits and practical applications

• High throughput and reproducibility for routine dairy analysis
• Low detection limits and excellent precision with helium, or reduced operating cost with argon
• Flexibility to select loop size for optimal reagent consumption and precision
• Compliance with international standards for regulatory and commercial testing

Future trends and applications

Advancements may include enhanced automation, integration with laboratory information management systems, miniaturized sample handling, and alternative carrier gases to improve sustainability. Expanding the method to broader food matrices and coupling with complementary detectors could further enhance analytical capabilities.

Conclusion

The LECO FP928 delivers accurate, precise, and cost-effective nitrogen/protein analysis in whey and powdered dairy products. Its robust design, flexible gas and loop options, and compliance with ISO 14891 make it an excellent tool for food laboratories, quality assurance, and research applications.

Reference

• ISO 14891: Milk and Milk Products–Determination of Nitrogen Content (Routine method using combustion according to the Dumas principle)