Nitrogen/Protein Determination In Milk
Proteins By Dumas Combustion Method
Muhammad Ali,1 Bilal Khan,1 Liliana Krotz 2 and Guido Giazzi2
1
Vitalus Nutrition Inc., Abbotsford, BC, V2T 5W5 Canada, 2Thermo Fisher Scientific, Rodano, Milan, Italy
Overview
Purpose: Nitrogen/Protein determination by Dumas Combustion Method
Method: Milk protein concentrate samples are analyzed through an elemental analyzer
with automatic autosampler.
Results: Nitrogen/Protein data of different milk protein concentrates and isolates
demonstrates the validity of the method.
Introduction
Milk proteins concentrates and isolates are used as ingredients in a wide variety of
food applications. They are commonly found in infant formulas, enteral nutrition, bakery
products, desserts, meat products, dairy based dry mixes (coffee whitener), dairy
based drinks (UHT applications, coffee), sports nutrition and weight-loss beverages,
protein bars, sauces, toppings, as well as processed cheese products.
Methods
The Elemental Analyzer o
The sample is weighed in
the Thermo Scientific™ M
ensuring a complete comb
After the combustion, the
reactor filled with Copper,
finally detected by the The
A complete N/Protein rep
Eager Xperience dedicate
FIGURE 2. N/Protein Lay
The composition and protein level is a determining factor in choosing the best MPC
(Milk Protein Concentrate). One of the most important analysis in food ingredients is
the determination of Nitrogen and Protein content applied for quality control and R&D
purposes.
So, for this, the use of accurate and automatic analytical techniques which allows the
fast analysis with an excellent reproducibility is required.
The Thermo Scientific™ FLASH™ 2000 Elemental Analyzer (Figure 1), based on the
dynamic flash combustion of the sample, copes effortlessly with the wide array of
laboratory requirements such as accuracy, day to day reproducibility and high sample
throughput. This alternative to the classical Kjeldahl method, based on Dumas
(combustion) method, has been developed and approved by different associations.
FIGURE 1. Thermo Scientific FLASH 2000 Elemental Analyzer.
Results
Calibration method being
Thermo Scientific. For po
standard and 200 - 300
reference to check the cali
For liquid dairy samples,
concentration and then 8
Thermo Scientific™ AS 1
used as a calibration meth
The protein content was
conversion factor may vary
Different types of milk prot
reproducibility of the sys
instrument without any pre
depends of the nature: 80
mg Liquid cream sample
memory effect on the resul
Table 1 shows the protei
when 80 — 100 mg of sam
2 Nitrogen/Protein Determination In Milk Proteins By Dumas Combustion Method
Methods
ustion Method
hrough an elemental analyzer
n concentrates and isolates
TABLE 1. N/Protein data of Mi
The Elemental Analyzer operates with the dynamic flash combustion of the sample.
The sample is weighed in a Tin capsule and introduced into the combustion reactor via
the Thermo Scientific™ MAS 200R™ Autosampler with a proper amount of Oxygen,
ensuring a complete combustion of the sample.
After the combustion, the produced gases are carried by a Helium flow to a second
reactor filled with Copper, then swept through CO2 and H2O traps, a GC column and
finally detected by the Thermal Conductivity Detector. Total run is 5 minutes (Figure 2).
redients in a wide variety of
ulas, enteral nutrition, bakery
xes (coffee whitener), dairy
and weight-loss beverages,
se products.
A complete N/Protein report is automatically generated by the Thermo Scientific™
Eager Xperience dedicated software and displayed at the end of the analysis.
FIGURE 2. N/Protein Layout.
r in choosing the best MPC
nalysis in food ingredients is
d for quality control and R&D
techniques which allows the
er (Figure 1), based on the
essly with the wide array of
producibility and high sample
method, based on Dumas
by different associations.
Table 2 shows the N/Protein re
run on the instrument using
Chromosorb was used to abso
were analyzed in duplicate.
nalyzer.
TABLE 2. N/Protein data of Liq
Results
Calibration method being used is the standard calibrating method developed by
Thermo Scientific. For powder samples, 80-100 mg of aspartic acid is used as a
standard and 200 - 300 mg of Pasta Reference Material is used as a secondary
reference to check the calibration.
For liquid dairy samples, water soluble urea is used as a standard at a desired
concentration and then 80 ul is injected as a calibration method, manually or by
Thermo Scientific™ AS 1310 Liquid Autosampler into the instrument. K factor was
used as a calibration method.
The protein content was calculated using the protein factor of 6.38. The protein
conversion factor may vary depending on the type of matrix.
Different types of milk protein concentrates and isolates were analyzed to evaluate the
reproducibility of the system. Samples are directly weighed or injected into the
instrument without any pre-treatment or any digestion and the weight used for analysis
depends of the nature: 80 — 100 mg Milk Protein Concentrate samples, 100 — 150
mg Liquid cream samples and 80 — 100 mg ul Liquid concentrate samples. No
memory effect on the results was observed changing the sample nature.
Table 1 shows the protein results obtained with Milk Protein Concentrate samples
when 80 — 100 mg of samples were analyzed in duplicate.
Thermo Scientific Poster Note • PITTCON • PN42226-EN 0215S 3
TABLE 1. N/Protein data of Milk Protein Concentrate samples.
c flash combustion of the sample.
ced into the combustion reactor via
with a proper amount of Oxygen,
Table 3 shows the N/Pro
the FLASH 2000 Analyz
injected and each sample
TABLE 3. N/Protein data
ied by a Helium flow to a second
and H2O traps, a GC column and
r. Total run is 5 minutes (Figure 2).
rated by the Thermo Scientific™
at the end of the analysis.
Table 2 shows the N/Protein results obtained when Liquid Concentrate samples were
run on the instrument using the solids methodology. In this case, 30 - 50 mg of
Chromosorb was used to absorb approximately 100 - 150 mg of samples. Samples
were analyzed in duplicate.
TABLE 2. N/Protein data of Liquid Concentrate samples.
alibrating method developed by
g of aspartic acid is used as a
Material is used as a secondary
sed as a standard at a desired
ibration method, manually or by
nto the instrument. K factor was
tein factor of 6.38. The protein
matrix.
tes were analyzed to evaluate the
ly weighed or injected into the
n and the weight used for analysis
Concentrate samples, 100 — 150
Liquid concentrate samples. No
the sample nature.
Milk Protein Concentrate samples
licate.
4 Nitrogen/Protein Determination In Milk Proteins By Dumas Combustion Method
amples.
d Concentrate samples were
n this case, 30 - 50 mg of
50 mg of samples. Samples
s.
Table 3 shows the N/Protein results obtained when Dairy Liquid samples were run on
the FLASH 2000 Analyzer using the liquid injection method; 80 ul of sample was
injected and each sample was analyzed in duplicate.
FIGURE 3. Thermo Scientific
TABLE 3. N/Protein data of Dairy Liquid samples.
Conclusion
The Thermo Scientific FLASH
the analysis of Nitrogen/Pro
automation, speed of analysis
The system allows the analysis
and Nitrogen content.
The FLASH 2000 Elemental
extremely robust and practica
Kjeldahl method and there
analyzing several different ma
and the instrument itself. Th
effective way of time and cos
prepared once and then can be
service and requires very few c
All trademarks are the property of Therm
encourage use of these products in an
encourage use of these products in any
Published at the Pittcon Conference and
PO42226
Thermo Scientific Poster Note • PITTCON • PN42226-EN 0215S 5
ry Liquid samples were run on
method; 80 ul of sample was
FIGURE 3. Thermo Scientific FLASH 2000 Analyzer.
Conclusion
The Thermo Scientific FLASH 2000 Nitrogen/Protein Analyzer is a valuable solution for
the analysis of Nitrogen/Protein in terms of accuracy, reproducibility, sensitivity,
automation, speed of analysis and cost per analysis.
The system allows the analysis without matrix effect when changing the sample nature
and Nitrogen content.
The FLASH 2000 Elemental Analyzer also requires very low maintenance and is
extremely robust and practical. Sample preparation is much easier as compared with
Kjeldahl method and there are no hazardous wastes either. The system allows
analyzing several different matrices with minimum or no changes to the methodology
and the instrument itself. The auto-samplers are extremely efficient and is a very
effective way of time and cost saving. Using autosamplers, several samples can be
prepared once and then can be run on the instrument. The system is easy to install and
service and requires very few changes to any laboratory systems and functionality.
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