[Testing] A2 β-casein milk introduction and testing method sharing

Protein composition of Milk

To understand what A2 milk is, we first need to understand the proteins in milk. Cow's milk contains approximately 33g of protein, primarily divided into two categories: casein and whey protein. Casein accounts for 80% of milk protein and includes α-casein, α-casein, β-casein, and κ-casein. Whey protein accounts for 20% of milk protein and includes β-lactoglobulin and α-lactalbumin.

β-casein has a molecular weight of approximately 2400 and comprises 30%-35% of casein. Its isoelectric point is pH 5.3. β-casein is highly hydrophobic, but its N-terminus contains a number of hydrophilic groups, making it an amphiphilic agent. When heated at neutral pH, β-casein forms clumps of β-casein.

β-casein comes in two different types: A1 and A2. This is where A2 milk comes from.

Advantages of A2 Beta-Casein

1. Research from Northeast Agricultural University shows that A2 β-casein has a higher digestibility and better ability to regulate intestinal flora.

2. The "A2 β-Casein Milk" group standard requires that the protein content of A2 β-casein milk must be ≥ 3.2g/100g, which is higher than the national standard for general pure milk.

3. Compared with A1 β-casein in milk, A2 β-casein is more stable, more compatible with the human digestive system, and more conducive to the body's absorption and utilization of high-quality protein.

4. Research shows that compared to A1 β-casein, A2 β-casein produces less or no β-casomorphin-7, which can cause gastrointestinal discomfort, making it more suitable for the general public.

What is A2 Beta-Casein Milk?

Milk produced exclusively from A2 cows is called A2 β-casein milk.

Milk contains approximately 3% protein, primarily casein and whey protein, with casein accounting for 80%. Casein is further divided into α, β, and γ types, with β-casein comprising 30%-35%. β-casein is further subdivided into 13 subtypes, including A1, A2, A3, B, and C, with A1 and A2 being the most common.

What is the difference between A1 beta-casein and A2 beta-casein?

The difference lies in the fact that the 67th amino acid residue in A1 β-casein is a histidine (His) residue. The He66-His67 chemical bond is more susceptible to enzymatic hydrolysis, producing a 7-amino acid peptide (BCM-7). In contrast, the 67th amino acid residue in A2 β-casein is proline (Pro)Ile66-Pro67, which has a stronger chemical bond and hydrolyzes into a 9-amino acid peptide (BCM-9). This is the main difference between A1 and A2 β-casein.

The β-casein in regular milk is primarily A1 casein, and may be pure A1 or contain both A1 and A2. If a certain type of milk contains only A2 β-casein without A1, it is called "A2 β-casein milk."

Why is the price of A2 beta-casein milk relatively high?

In fact, naturally occurring milk, including goat milk, yak milk, wild animal milk, and human breast milk, originally contained only A2 casein. This was also true of early domesticated cows. Around 2,000 years ago, a genetic mutation occurred in some dairy cows in Northern Europe, causing them to produce A1 casein. Perhaps because these A1 genotype cows produced more milk, they were prioritized for breeding. As a result, pure A2 genotype cows are now a minority, accounting for approximately 30%. Naturally, these cows produce relatively less milk. Dairy farming companies must use genetic testing to identify and exclusively raise purebred A2 genotype cows, which increases costs.

Physical and chemical indicators of A2 β-casein milk

Detection Method of A2 β-Casein in Dairy Products

01
T/CITS 0012-2022 Determination of A1 and A2 β-caseins in bovine milk-based infant formula and bovine milk by liquid chromatography-tandem mass spectrometry
Experimental principle: The bovine β-casein in the sample is extracted with urea, reduced with dithiothreitol, alkylated with iodoacetamide, and hydrolyzed into peptides by trypsin. The peptides are then determined by liquid chromatography-triple quadrupole mass spectrometry and quantified by the isotope internal standard method.
02
T/CNHFA 003-2022 Qualitative Determination of Bovine Casein in Milk and Dairy Products by Capillary Gel Electrophoresis

Principle of the method: The detection principle based on capillary gel electrophoresis is to denature and add charges to the protein components in the sample with SDS, separate the protein components using a capillary electrophoresis instrument, and determine whether the sample contains bovine milk casein components based on the signal of the bovine milk casein-specific protein peak.