Generic combustion method for determination of crude protein in feeds: collaborative study

Area of Science:

• Analytical Chemistry
• Animal Nutrition
• Agricultural Science

Background:

• Accurate crude protein determination is crucial for animal feed formulation and quality control.
• The AOAC mercury catalyst Kjeldahl method has been the standard for protein analysis.
• A need exists for alternative, potentially more efficient, methods for protein determination.

Purpose of the Study:

• To collaboratively study and validate a generically described combustion method for crude protein determination in animal feeds.
• To compare the performance of the combustion method against the official AOAC mercury catalyst Kjeldahl method (7.015).
• To assess the repeatability and reproducibility of the combustion method across multiple laboratories.

Main Methods:

• Nine laboratories participated in a blind collaborative study.
• Samples included feed ingredients and mixed products with protein content ranging from 10-90%, ground to 0.5 mm and 1.0 mm.
• Analysis was performed using both the AOAC mercury catalyst Kjeldahl method and a generic combustion method (primarily LECO analyzers).

Main Results:

• The combustion method showed comparable results to the Kjeldahl method, with grand means for 0.5 mm ground samples at 47.65% (combustion) and 47.41% (Kjeldahl).
• Repeatability (RSDr) for the combustion method was 0.59%, and reproducibility (RSDg) was 1.10%, indicating good precision.
• Only one laboratory failed to meet performance limits, suggesting high reliability of the tested methods.

Conclusions:

• The generic combustion method is a reliable alternative for determining crude protein in animal feeds.
• The combustion method demonstrated comparable accuracy and precision to the AOAC mercury catalyst Kjeldahl method.
• The generic combustion method has been approved interim official first action, paving the way for wider adoption.