Quantification of Whey Protein Content in Milk-Based Infant Formula Powders by Sodium Dodecyl Sulfate-Capillary Gel
Ping Feng1, Christophe Fuerer2, Adrienne McMahon3
1Wyeth Nutrition, 30F, CITIC Square, 1168 Nanjing Rd (W), Shanghai 200041, People's Republic of China.
Insights
This study validates a method for quantifying whey protein in infant formula using capillary electrophoresis. The Sodium Dodecyl Sulfate-Capillary Gel Electrophoresis (SDS-CGE) method proved reliable for milk-based formulas.
Area of Science:
- Analytical Chemistry
- Food Science
- Biochemistry
Background:
- Accurate quantification of whey protein in infant formula is crucial for nutritional assessment and regulatory compliance.
- Existing methods may lack the precision or scope required for diverse infant formula matrices.
Purpose of the Study:
- To evaluate the performance of AOAC First Action Official Method SM 2016.15 for quantifying whey protein in infant formula powders.
- To assess the method's precision, accuracy, and robustness across multiple laboratories and instrument types.
Main Methods:
- A multilaboratory study involving 19 laboratories analyzed 15 infant formula powder samples using Sodium Dodecyl Sulfate-Capillary Gel Electrophoresis (SDS-CGE).
- Samples were analyzed in duplicate, with electrophoregrams recorded at UV220 nm and integrated to determine normalized peak areas of whey and casein proteins.
Main Results:
- The SDS-CGE method demonstrated high precision, with relative standard deviations of repeatability (RSDr) and reproducibility (RSDR) generally within acceptable limits (0.83–2.11% and 2.18–4.22%, respectively).
- Measured whey protein content ranged from 98–108% of declared values for most samples, indicating good accuracy.
- The method showed robustness, performing well across different instrument models and capillary sources, though atypical results were observed for one NIST Standard Reference Material (SRM) sample.
Conclusions:
- The AOAC 2016.15 method using SDS-CGE is fit-for-purpose for quantifying whey protein in milk-based infant formula powders.
- The method's reliability is confirmed by its performance across multiple laboratories and diverse equipment.
- The method is not suitable for hydrolyzed or plant protein-based infant formulas.
Abstract:
A multilaboratory testing study was conducted on AOAC First Action Official Method SM 2016.15: Quantification of Whey Protein Content in Infant Formula Powders by Sodium Dodecyl Sulfate-Capillary Gel Electrophoresis (SDS-CGE). Nineteen laboratories participated in the analysis of duplicate blind-coded samples of 15 formula powder products for infants and young children. Electrophoregrams were recorded at UV220 nm and integrated. The normalized peak areas of whey and casein proteins were summed separately to calculate total whey protein content. Apart from one sample [NIST Standard Reference Material (SRM) 1849a], relative standard deviation of repeatability (RSDr) and reproducibility (RSDR) ranged from 0.83 to 2.11% and from 2.18 to 4.22%, respectively, and Horwitz ratios ranged from 1.02 to 1.85, meeting the precision limits specified in the whey protein Standard Method Performance Requirements and in the guidelines recommended for the Horwitz ratio. In these samples, the measured whey protein content was between 98 and 108% of the declared value. NIST SRM 1849a showed atypical results, with elevated RSDr (3.51%), RSDR (5.94%), Horwitz ratio (2.62), and recovery (134%). There is no clear reason for this. The percent whey protein value for NIST is calculated from the formulation and is not a reference or certified value. Multiple instrument models and makes, as well as capillary sources, were used in this collaborative study, demonstrating the robustness of the method. The method is fit-for-purpose for the quantification of whey protein content in milk-based formula powder products for infants and young children. It is not applicable to the analysis of hydrolyzed or plant protein-based infant formulas.
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