"A2 milk" authentication using isoelectric focusing and different PCR techniques

Imaged capillary isoelectric focusing and online mass spectrometry for milk whey protein characterization in dairy products

Characterizing major bovine milk proteins, including whey and casein, is of significant interest in the dairy industry. The diverse array of protein proteoforms can be different in terms of genetic variation, breed ways, lactation stage, and animal nutritional status. Current routine methods for bovine milk protein profiling are typically based on immunological techniques, infrared spectroscopy, slab gel isoelectric focusing, capillary electrophoresis, and high-performance liquid chromatography. However, there are obvious disadvantages of existing approaches including low throughput, tedious operation, unsatisfactory repeatability, and lack of robust quantitation capability. In this study, we present a novel approach that, for the first time, combines imaged capillary isoelectric focusing with mass spectrometry to separate and characterize whey proteins in milk products. The established method provided a rapid, repeatable, accurate, and simultaneous analysis of α-lactalbumin, β-lactoglobulin A, and β-lactoglobulin B within 10 min for diverse bovine milk samples. The methodology was systematically validated regarding repeatability of pI and peak area, sensitivity, linearity and recovery. The integration of high-resolution mass spectrometry with nano-electrospray ionization and icIEF has been pivotal in accurately identifying intact whey proteins in milk products. This approach has significantly enhanced the precise characterization of protein proteoforms in milk.

Determination of A1 and A2 β-CN in cow milk by HPLC-MS/MS

A2 β-CN milk has gained widespread acceptance due to its nutritional benefits. To verify the authenticity and detect adulteration and contamination in A2 milk, we developed an HPLC-MS/MS method for determining the characteristic peptides of A1 and A2 β-CN in cow milk. The method demonstrated good specificity, sensitivity, and linearity for both A1 and A2 characteristic peptides, with limit of detection of 0.01 mg/L and 0.03 mg/L, limit of quantitation of 0.03 mg/L and 0.1 mg/L, and determination coefficients of 0.9994 and 0.9992, respectively. Whereas accuracy and precision were reasonable, the recoveries varied (69.4%-151%) across concentration levels (0.04, 0.2, 1.0 g/kg), with higher recoveries for both peptides at low concentrations and lower recoveries for A2 peptide at medium and high concentrations, influenced by factors such as adsorption and ionization efficiency. We optimized the tryptic hydrolysis conditions, selecting a trypsin-to-casein ratio of 1:25 and a hydrolysis time of 6 h at 37°C. However, the hydrolysis of A1 and A2 β-CN was incomplete and asynchronous, exhibiting parabolic relationships with their respective concentrations, with hydrolysis degrees of 12.3% for A1 β-CN and 9.6% for A2 β-CN in pure powders. We finally established a regression model to calculate the actual proportion of A1 and A2 β-CN, with the detection limits of 5% for both β-CN. In the quantitation range of this model, A1 β-CN accounting for 10% to 80% or A2 β-CN accounting for 20% to 90%, the measured value of A1/A2 or A2/A1 was a power function relationship with the theoretical value. This method effectively verifies the authenticity of A1 and A2 milk, providing a reliable tool for detecting adulteration and contamination.

Distribution of β-Casein Variants and Effects on Milk Composition in Podolian Cows Reared in Gargano Promontory (Southern Italy)

The aim of the study was to evaluate β-CN variants and their effects on milk nutritional composition and protein profile in Podolian cattle breeds reared in Gargano Promontory (Southern Italy). Individual milk samples of Podolian and Holstein Friesian (HF) cattle were analyzed for β-CN allele and genotype frequencies, chemical composition and protein fractions of milk. In both populations the most common allelic variant was A2, followed by A1, whereas alleles B and I had frequencies lower than 10% in both populations. A total of 6 genotypes in Podolian population (A1A2, A1B, A2B, A1I, A2I, A2A2), and 7 genotypes (A1A1, A1A2, A1B, A2B, A1I, A2I, A2A2) in HF were detected. Milk protein, lactose and casein percentages were affected by β-CN allele in both breeds. In particular, alleles A1 and A2 resulted in higher levels of both protein and casein in HF, whereas in Podolian allele I showed the highest, alleles A1 and A2 intermediate and B the lowest levels of the mentioned parameters. Protein fractions were influenced by β-casein alleles and the most abundant protein fractions were β- and αs1- CNs in both breeds, although with different percentage distribution. In Podolian milk, regardless of the detected allele, it was observed a similar behavior for β- and κ-CNs and opposite to that observed for αs2-CN. The study of the genetic variability of milk proteins offers the opportunity to valorise the nutritional, technological, and functional features of Podolian cattle dairy productions as a strategy to sustain the economic value of this ancient breed which is well adapted to the farming systems in marginal areas.

Recent advances in the bovine β-casein gene mutants on functional characteristics and nutritional health of dairy products: Status, challenges, and prospects

β-casein is the second most abundant form of casein in milk. Changes in amino acid sequence at specific positions in the primary structure of β-casein in milk will produce gene mutations that affect the physicochemical properties of dairy products and the hydrolysis site of digestive enzymes. The screening method of β-casein allele frequency detection in dairy products also has attracted the extensive attention of scientists and farmers. The A1 and A2 β-casein is the two usual mutation types, distinguished by histidine and proline at position 67 in the peptide chain. This paper summarizes the effects of A1 and A2 β-casein on the physicochemical properties of dairy products and evaluates the effects on human health, and the genotyping methods were also concluded. Impressively, this review presents possible future opportunities and challenges for the promising field of A2 β-casein, providing a valuable reference for the development of the functional dairy market.

A discussion on A1-free milk: Nuances and comments beyond implications to the health

This chapter provides an overarching view of the multifaceted aspects of milk β-casein, focusing on its genetic variants A1 and A2. The work examines the current landscape of A1-free milk versus regular milk, delving into health considerations, protein detection methods, technological impacts on dairy production, non-bovine protein, and potential avenues for future research. Firstly, it discussed ongoing debates surrounding categorizing milk based on A1 and A2 β-casein variants, highlighting challenges in establishing clear regulatory standards and quality control methods. The chapter also addressed the molecular distinction between A1 and A2 variants at position 67 of the amino acid chain. This trait affects protein conformation, casein micelle properties, and enzymatic susceptibility. Variations in β-casein across animal species are acknowledged, casting doubt on non-bovine claims of "A2-like" milk due to terminology and genetic differences. Lastly, this work explores the burgeoning field of biotechnology in milk production.

New Perspective on the Interaction Behavior Between Riboflavin and β Lactoglobulin-β Casein Complex by Biophysical Techniques

Riboflavin (RF) is a vitamin that only exists in plants and microorganisms and must be procured externally by humans. On the other hand, there are two major allergic factors in cow's milk, including β-lactoglobulin (βLG) and β-casein (βCN), while their allergic properties can be eliminated by binding to micronutrients. In this regard, we examined the binding process of RF to βLG and βCN in the binary and ternary systems by different spectroscopies such as zeta potential, electric conductivity, and molecular modeling. According to the result of the fluorescence spectrum regarding the interaction of RF with βLG and βCN in binary and ternary systems, an increase in RF concentration declined the fluorescence intensity of three systems and also caused the quenching of proteins. Static quenching plays a pivotal role in the formation of stable interactions. The obtained thermodynamic parameters by Van't Hoff equation ascertained the predominance of hydrogen bonds and van der Waals interaction in all the systems. Considering how the negative value of ΔH0 resulted in the negative value of ΔG0, the systems were assumed to be enthalpy driven. The outcomes of circular dichroism (CD) disclosed that the attachment of RF to the targets of systems increased their a-helix content, which particularly included the binding of RF to βLG that led to the conversion of β-sheet to α-helix content. As indicated by the results of zeta potential, the low concentration of RF contained the dominance of hydrophobic forces in the interactions, whereas the enlargement of this concentration prevailed electrostatic forces. Moreover, conductometry measurements showed an extension in the rate of ionizable groups due to the addition of RF to the systems, which may increase the probability of an interaction between RF, βCN, and βLG in binary and ternary systems. In consistency with the outcomes of molecular dynamics simulation, the data of molecular docking approved the capability of RF in forming strong and stable interactions with βCN and βLG.

Relationships of beta-casein genetics with production, fertility, and survival of purebred organic Holstein dairy cows

The objective of this study was to compare β-casein genotype of purebred certified-organic Holstein cows, and their effect on production, fertility, and survival. Holstein cows (n = 1,982) from 13 certified-organic dairy herds from the western, midwestern, and northeastern United States were genomically tested with CLARIFIDE Plus (Zoetis) for β-casein genotype. Two hundred fourteen cows were A1A1 (11%), 848 cows were A1A2 (43%), and 920 cows were A2A2 (46%). In total, 2,249 lactation records, 1,025 from the first parity and 1,224 records during second and greater parities were used. Test-day milk, fat, and protein production (305-d) and somatic cell score were obtained from the Dairy Herd Improvement Association. A lower limit of 50 d for days open was applied, and cows with more than 250 d open had days open set to 250 d. Independent variables for statistical analysis were the fixed effects of herd, parity, β-casein genotype (A1A1, A1A2, A2A2), and β-casein genotype by parity interaction. Cow nested within parity was the random effect in the statistical models for fertility and production traits. Herd had a significant effect on all fertility, production, and survival variables. Parity affected the number of times bred per pregnancy and days open, milk, fat, and protein production, and somatic cell score. Beta-casein genotype and herd influenced the percentage of cows surviving to first and second lactation. Results indicate no difference in production and fertility regarding β-casein genotype for organic dairy herds. Survival was biased against the A1 allele, which is indicated by lower survival rates during first lactation. These results may offer organic producers more flexibility in breeding and culling decisions to produce A2A2 milk.

Identification of Characteristic Peptides of Casein in Cow Milk Based on MALDI-TOF MS for Direct Adulteration Detection of Goat Milk

It is widely acknowledged that casein is an important allergenic protein in milk which may cause danger to customers. The identification and confirmation of caseins through mass spectrometry requires the selection of suitable characteristic peptides. In this study, by means of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), the three most representative specific peptides of caseins in cow milk were screened out with mass-to-charge ratios (m/z) of 830, 1195, and 1759, respectively. By comparing 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA) MALDI matrices, it was found that DHB was more suitable for peptide detection with the limits of detection (LODs) of 0.1 mg/L for α, β-casein. Furthermore, on the basis of verifying the characteristic peptides of casein from cow milk, this protocol was applied to goat milk authentication. Cow milk addition in goat milk was investigated by using the screened specific peptides. The results showed that the adulteration could be identified when the proportion of cow milk was 1% or more. When applied to inspect adulteration in five brands of commercial goat milk, specific peptides of bovine casein were detected in four of them. The method has the advantages of strong reliability, high throughput, simple preprocessing, and fast speed, which can provide powerful help for prewarning dairy allergen.

An approach on detection, quantification, technological properties, and trends market of A2 cow milk

The genetic variant A2 β-casein integrates the casein protein group in milk and has been often associated with positive health outcomes. Therefore, this review explores the present understanding of A2 β-casein, including detection methods and the market trends for dairy from A2 milk. Also, the interaction of A2 β-casein with αs₁-casein and κ-casein genotypes was examined in terms of technological impacts on A2 milk. A limited number of preliminary studies has aimed to investigate the sensorial and technological impacts of β-casein variants in milk matrices, for instance, in yogurt and other derivatives. Nevertheless, considering studies carried out so far, it is concluded that the manufacture of dairy products from A2 milk is perfectly feasible, as the products presented slight differences when compared to those derived from traditional milk. In one of the works, sensitive drops in rennet coagulation time and curd firmness values were observed in cheese traits. However, it is relevant to point out that variant A of κ-casein plays a negative role in the coagulation features of milk. Therefore, alterations in the pattern of cheese-making properties are not uniquely related to β-casein variants. Attempts to produce A2 β-casein in laboratory (non-natural source), through biosynthesis, for example, have not been found so far. This knowledge gap offers a promising area for future studies concerning proteins and bioactive peptide production.

Characterization of the genetic polymorphism linked to the β-casein A1/A2 alleles using different molecular and biochemical methods

The 2 major subvariants of β-casein (A1 and A2), coded by CSN2 gene, have received great interest in the last decade both from the scientific community and the dairy sector due to their influence on milk quality. The consumption of the A1 variant, compared with the A2 variant, has a potential negative effect on human health after its digestion but, at the same time, its presence improves the milk technological properties. The aim of the present study was to compare the best method in terms of time required, costs, and technical engagement for the identification of β-casein A1 and A2 variants (homozygous and heterozygous animals) in milk to offer a reliable service for large-scale screening studies. Two allele-specific PCR procedures, namely RFLP-PCR and amplification refractory mutation system (ARMS-PCR), and one biochemical technique (HPLC) were evaluated and validated through sequencing. Manual and automated DNA extraction protocols from milk somatic cells were also compared. Automated DNA extraction provided better yield and purity. Chromatographic analysis was the most informative and the cheapest method but unsuitable for large-scale studies due to lengthy procedures (45 min per sample). Both allele-specific PCR techniques proved to be fast and reliable for differentiating between A1 and A2 variants but more expensive than HPLC analysis. Specifically, RFLP-PCR was the most expensive and labor-demanding among the evaluated techniques, whereas ARMS-PCR was the fastest while also requiring less technical expertise. Overall, automated extraction of DNA from milk matrix combined with ARMS-PCR is the most suitable technique to provide genetic characterization of the CSN2 gene on a large scale.

Comparative Analysis of the Protein Composition of Goat Milk from French Alpine, Nubian, and Creole Breeds and Holstein Friesian Cow Milk: Implications for Early Infant Nutrition

Simple Summary

Goat’s milk is a food that contains proteins of value for nutrition. The protein profile in the milk of goat breeds is different from that of cow milk, with a lower relative abundance of allergenic proteins. In addition, regardless of the breed, goat milk has beta-casein of type A2 in a more significant proportion than cow milk, which impacts different bioactive peptides hydrolyzed in the milk of the species.

Abstract

Of the diversity of proteins and high digestibility, goat milk will be a food of significant value for infant nutrition. The genetic polymorphisms of milk proteins play an essential role in the different degrees of allergic reactions. This work aimed to identify the proteins and peptides in the composition of goat milk and compare them to those in cow’s milk. The work was performed with goats French Alpine, Nubian, and Creole breeds and Holstein Friesian milking cows at the Universidad Autónoma de Querétaro, Amazcala. We investigated the relative abundance of goat and cow milk protein fractions by SDS-PAGE resolution and the densitometric analysis of gels. The protein alfa-casein was (17.67 ± 0.46) for Creole, (19.18 ± 0.88) French Alpine, (17.35 ± 0.49) Nubian, and (35.92 ± 1.96) Holstein cows. The relative abundance obtained from alfa-casein was statistically different between goats and cows, and this protein was vital because it is a protein related to allergies. On the other hand, the amino acid in position 67 of the beta-casein from three goat breeds is a Proline, so it is assumed that the beta-casein variant of goat milk is an A2-type. The latter has excellent relevance for infant nutrition and differs from cow milk.

A2 Milk: New Perspectives for Food Technology and Human Health

Although milk consumption is increasing worldwide, in some geographical regions, its consumption has persistently declined in recent decades. This fact, together with the increase in milk production prices, has caused both milk producers and the dairy industry to be immersed in a major crisis. Some possible solutions to this problem are to get people who do not currently consume milk to start drinking it again, or to market milk and dairy products with a higher added value. In this context, a type of milk called A2 has recently received attention from the industry. This type of milk, characterized by a difference in an amino acid at position 67 of the β-casein polypeptide chain, releases much smaller amounts of bioactive opioid peptide β-casomorphin 7 upon digestion, which has been linked to harmful effects on human health. Additionally, A2 milk has been attributed worse technological properties in the production of some dairy products. Thus, doubts exist about the convenience for the dairy industry to bet on this product. The aim of this review is to provide an update on the effects on human health of A2 milk, as well as its different technological properties to produce dairy products.

Development of a Microsphere-Based Immunoassay Authenticating A2 Milk and Species Purity in the Milk Production Chain

Processed milk and milk products produced from bovine milk, commonly contain β-casein A1 (βCA1) and β-casein A2 (βCA2). Since the presence of βCA1 is linked to milk intolerance and digestion problems, A2A2 milk, which only contains βCA2, is proposed as a healthier alternative. To support this health claim, the purity of A2A2-milk has to be guaranteed. In the presented study, a multiplex immunoassay, able to distinguish between βCA2 and βCA1, was developed and real-life applicability was shown on raw milk samples from genotyped A1A1, A1A2 and A2A2 cows. Because of its ability to discriminate between βCA2 and βCA1, this newly developed method was able to detect the addition of common bovine A1A2 milk to A2A2 milk, as low as 1%. Besides the detection of A2A2 milk purity, the developed assay can also be implemented as a rapid phenotyping method at dairy farms to replace the more invasive DNA-based screening. Additionally, the developed method was capable of detecting the addition of common bovine milk up to 1% in sheep, goat, buffalo, horse and donkey milk, which conforms to EU recommendations. In conclusion, a newly developed multiplex method capable of reliably detecting the dilution of A2A2 milk of multiple species, with common bovine milk up to 1%, is presented.