1. RAPID DETERMINATION OF PROTEIN CONTENT IN PROTEIN POWDER FINISHED PRODUCT USING NEARINFRARED (NIR)
Roney Christiana, Yanjun Zhangb, Kan Heb, Piyush Purohita, Prashant Ingleb, Quanyin Gaoa*, Peter Changb, Gary Swansonb and Keith Freel (Metrohm)  aHerbalife Manufacturing, LLC, Crescent Bay Drive, Lake Forest, CA 92630, USA bHerbalife International of America, 950 West 190th Street, Torrance, CA 90502, USA
Abstract
Results and Discussion
Results and Discussion (continued)
Results and Discussion (continued)
A rapid NIR test method for protein determination in protein mix powder product was developed and compared against traditional Dumas method. Twenty protein mix powder samples were tested by rapid NIR and Dumas test method. The comparison of results between both methods shows rapid NIR test method can measure protein with comparable accuracy as Dumas method and at the same time offer advantages: quick results, cost effective and green (no chemicals/reagents are required)
Data generated from prepared 17 samples (by mixing silicon dioxide, soy protein, whey protein and flavor natural vanilla cream) was processed by Partial Least Square(PLS) method. The R2 value obtained was The Standard Error for Prediction (SEP) was 0.10% for the protein powder. The standard error of calibration (SEC) was 0.16 g protein/serving
Twenty protein mix powder samples were tested and protein values are measured by calibration curve. Same set of samples were tested for protein by Dumas method. Bias was calculated between NIR protein result and Dumas protein result. Refer table 2 for results.
Sample
NIR results g/serving (ProteinPLS)
Protein results by Dumas method (in-house lab)
Bias/difference, absolute (NIR vs. Dumas in-house lab1) 1
5.08
5.11
0.03 2
5.07
5.12
0.05 3
5.14
5.10
0.04 4
5.17
0.06 5
5.19
5.21
0.02 6
5.18
5.09
0.09 7
5.13
0.00 8 9 10
4.98
0.11 11
5.40
0.23 12
5.06 13
0.31 14 15
5.16
5.20 16
5.15
0.08 17 18
5.25
0.17 19 20
Introduction
Sample
% protein
Protein powder, g
Silicon dioxide + Flavor g
g protein/serving (6 g), calculated theoretical value
g protein/serving (6 g), Experimental value
(by Dumas method) 1
8.7
0.5
5.5
0.52
0.55 2
17.2 5
1.03
0.98 3
21.5
1.3
4.7
1.29
1.14 4
25.8
1.6
4.5
1.55
1.63
34.3
2.1
3.9
2.06
2.21 6 43
2.6
3.4
2.58
2.69 7
51.7
3.1
2.9
3.12 8
60.2
3.6
2.4
3.61
3.62 9
64.5
3.87
3.82 10
66.2
3.97
4.06 11
68.8
4.1
1.9
4.13 12
73.2
4.4
4.39
4.38 13
74.8
1.5
4.49
4.51 14
77.3
4.6
1.4
4.64
4.55 15
81.7
4.9
1.1
4.92 16
83.5
5.01
5.02 17 86
5.2
0.8
5.16
Protein content is one of the important quality parameter for protein powder products sold in market. Rapid analysis of protein content in protein powder products is needed to replace traditional Kjeldahl and Dumas methods. As traditional methods are longer and involves variety of chemicals it is not feasible to get protein results in time for production quality control. The time required for a determination using near infrared instrumentation is approximately two minutes as compared to about 10 to 30 minutes by traditional methods. A rapid protein test method by NIR technique was studied to explore its optimal method parameters: most suitable regression method, characteristic wavelengths, coefficients, and constants.
Fig. 2 Typical NIR Spectrum of Protein
Material, Equipment and Method
Material:
Silicon dioxide
Soy protein
Whey protein
Flavor natural vanilla cream
Protein drink mix powder
Equipment: NIR SmartProbe Analyzer, XDS (Metrohm)
Method:
Seventeen samples were prepared by mixing silicon dioxide, soy protein, whey protein and flavor natural vanilla cream. These samples range from 9% to 90% protein content. Refer table 1. These prepared powder samples were tested in their original plastic container by reflectance measurements of product using the NIR SmartProbe in the NIR wavelength range of nm and nm. Partial Least Square(PLS) method was used to derive optimal correlation between calculated theoretical % protein vs. lab data (% protein values from Dumas method). Refer table 1 and figure 1.
The prepared calibration curve and mathematical model was studied for bias in protein results between NIR and traditional Dumas method. Twenty protein drink mix powder samples were tested by NIR and Dumas and bias was calculated. Refer table 2.
Fig. 3 NIR Spectrum with SNV and 2nd derivative
Conclusions
Table 1 Calibration set of Calculated data vs. Lab data, R2 = 0.986
Table 2 NIR vs. Dumas method protein results
The calibration model for rapid determination of protein in protein mix powder product was successfully developed. The Standard Error for Prediction (SEP) was 0.10%. The resulting F-value and R2 value was 493 and respectively. The standard error of calibration (SEC) was 0.16 g protein/serving.
Maximum bias between rapid NIR test method and Dumas method was 5.2%. This shows rapid NIR test method is comparable to Dumas method for protein determination in protein mix powder.
Based on results for calibration and samples tested a quantitative model for determination of protein using NIR was developed and successfully demonstrated for the determination of protein.
Absolute bias between both methods (NIR vs. Dumas) protein measurements:
Maximum:0.31 g/ 6 g serving (5.2%)
Minimum: 0.09 g/6 g serving (1.5%)
Average: 0.04 g/6 g serving (0.7%)
Acknowledgments
Fig. 1 Calibration set of Calculated data vs. Lab data, R2 = 0.986
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