How do Protein Analyzers work?
Protein content is normally calculated from nitrogen, using a conversion factor such as 6.25 for most foods or 5.7 for wheat flour. Combustion instruments (Dumas) burn the sample at high temperature in oxygen, reduce the nitrogen oxides to molecular nitrogen and measure it with a thermal conductivity detector, which is fast, solvent-free and low in waste. Dye-binding methods for milk rely on the binding of anionic dyes such as amido black to protein, which changes the dye concentration in solution. Near-infrared analysers measure absorption bands from N–H bonds and predict protein with a calibration model. Colorimetric methods such as Bradford or Lowry use dyes or reducing reagents whose absorbance changes with protein concentration. Amino acid analysers hydrolyse the sample and separate individual amino acids by ion-exchange chromatography with ninhydrin or fluorescence detection.
Which Protein Analyzers variants are available?
- Dumas Combustion Protein Analyzer — A Dumas combustion protein analyzer burns food or feed in oxygen and measures the released nitrogen by thermal conductivity.
- Near-Infrared Protein Analyzer for Grain and Feed — A near-infrared protein analyzer predicts protein, moisture and other parameters in grain and feed from reflectance spectra in under a minute.
- Dye-Binding Milk Protein Analyzer — A dye-binding milk protein analyser mixes milk with an anionic dye and measures the amount bound by protein, giving a result in minutes.
- Colorimetric Protein Analyzer for Food — A colorimetric protein analyzer uses dye-binding, Bradford or Lowry chemistry read on a spectrophotometer to quantify protein in food extracts and fractions.
- Automated Amino Acid Analyzer — An automated amino acid analyzer hydrolyses a food sample and separates individual amino acids by ion-exchange chromatography with ninhydrin or fluorescence detection.
How do I choose the right variant?
Choose combustion when you need fast, clean nitrogen determination for cereals, feed, meat or dairy and your authority accepts the Dumas method. Combine it with the correct nitrogen-to-protein factor for each product. Near-infrared analysers suit grain and feed at intake, where many similar samples need answers in under a minute, but require a maintained calibration set. Dye-binding analysers give rapid, low-cost protein results in milk intake laboratories. Colorimetric methods are best for small numbers of samples in research and for assays where only a relative protein value is needed. Amino acid analysers answer nutritional and quality questions that nitrogen determination cannot, such as amino acid profile and available lysine.
Where are Protein Analyzers used?
Protein Analyzers are specified in protein declaration for nutrition labelling, grain and flour protein specification and payment, feed and pet food protein control, milk protein testing and dairy standardisation, meat and fish protein content verification and amino acid profile for nutritional evaluation.
Which standards and certifications apply?
Work with Protein Analyzers is commonly governed by ISO 16634, AOAC 990.03, AOAC 992.15, ISO 8968, ISO 5542, ISO 13903 and ISO/IEC 17025. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Whichever method is used, sampling and sample homogeneity matter because protein varies within a lot. Combustion systems need adequate oxygen supply, leak-free seals, leak and blank checks, and regular replacement of consumables such as the reduction column and combustion catalyst. Dye-binding instruments require fresh reagent, calibrated pipettes and careful tube cleaning to avoid residual dye. Near-infrared models need control samples and periodic bias correction against reference chemistry. Amino acid analysis requires careful hydrolysis, since tryptophan is destroyed by acid hydrolysis and must be determined separately. Keep conversion factors documented for each product and participate in proficiency testing.
