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ISO 29981:2009 — Milk and Milk Products — Determination of β-Lactoglobulin Content by RP-HPLC
Quantitative determination of β-lactoglobulin A and B genetic variants in milk by reversed-phase HPLC | IDF 220 | Dairy protein analysis
1. Standard Scope and Analytical Principle
ISO 29981 | IDF 220:2009 specifies a reversed-phase high-performance liquid chromatography (RP-HPLC) method for the quantitative determination of β-lactoglobulin (β-Lg) content in milk and milk products. The method is capable of separately quantifying the two major genetic variants, β-Lg A and β-Lg B, which is significant because their relative proportions affect the processing properties and allergenic potential of dairy products.
Key Advantage: Unlike immunochemical methods that measure total β-Lg, RP-HPLC provides individual quantification of genetic variants, enabling detailed characterization of milk protein composition for breeding programs and quality control.
2. Methodology and Chromatographic Conditions
The method involves whey protein separation by RP-HPLC on a C18 or C8 column with UV detection at 205 nm or 280 nm. Whey is first isolated from the milk sample by precipitation of caseins at pH 4.6, followed by filtration. The chromatographic separation uses a gradient of acetonitrile in water with 0.1 % trifluoroacetic acid as the ion-pairing agent. β-Lactoglobulin elutes as two distinct peaks corresponding to variants A and B, with retention times typically between 12-18 minutes depending on column characteristics.
| Parameter | Specification | Optimization Notes |
|---|---|---|
| Column type | C18 or C8, 5 μm, 250 × 4.6 mm | Wide-pore (300 Å) for better protein recovery |
| Detection wavelength | 205 nm or 280 nm | 205 nm provides higher sensitivity |
| Mobile phase A | Water + 0.1 % TFA | Use HPLC-grade TFA, not reagent grade |
| Mobile phase B | Acetonitrile + 0.1 % TFA | HPLC-grade, UV-cutoff ≤ 190 nm |
| Column temperature | 40 °C | ± 1 °C for retention time stability |
| Flow rate | 1.0 mL/min | Backpressure typically 100-150 bar |
Critical Consideration: β-Lactoglobulin is heat-sensitive. Samples must not be subjected to temperatures above 60 °C during preparation to avoid denaturation, which would cause peak broadening and quantification errors. Raw milk samples should be analyzed within 24 hours of collection or stored at −20 °C.
3. Applications in Dairy Science and Industry
The standard is widely used in dairy research and quality assurance. β-Lg A and B variants differ in their heat stability, rennet coagulation properties, and emulsification capacity. Milk from cows homozygous for β-Lg B has been associated with higher casein content and better cheese yield, making this standard valuable for selective breeding programs. Additionally, β-Lg is a major whey allergen, and its quantification is relevant for hypoallergenic formula development. The method detection limit is approximately 0.5 mg/L, with a quantification limit of 2 mg/L.
4. Frequently Asked Questions
Q1: Can this method be used for processed dairy products?
A: Yes, but heat-treated products may show reduced β-Lg content due to denaturation. Results should be interpreted with this limitation in mind.
A: Yes, but heat-treated products may show reduced β-Lg content due to denaturation. Results should be interpreted with this limitation in mind.
Q2: What is the difference between β-Lg A and B variants?
A: They differ by two amino acid substitutions (A: Asp64, Val118; B: Gly64, Ala118), affecting their chromatographic retention and functional properties.
A: They differ by two amino acid substitutions (A: Asp64, Val118; B: Gly64, Ala118), affecting their chromatographic retention and functional properties.
Q3: How long does a complete analysis take?
A: Sample preparation takes approximately 30 minutes, chromatographic run time is 25-35 minutes, and data analysis adds 10 minutes.
A: Sample preparation takes approximately 30 minutes, chromatographic run time is 25-35 minutes, and data analysis adds 10 minutes.