Application of ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (Orbitrap™) for the determination of beta-casein phenotypes in cow 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.

Detection of intact bovine milk proteins after simulated gastrointestinal infant digestion using UHPLC - HRMS

This study demonstrates the development and application of an ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS) method for the rapid and sensitive identification of intact bovine milk proteins following simulated gastrointestinal infant digestion. The new method enables the differentiation between partially hydrolysed/modified and fully intact proteins. In the raw milk, intact α-lactalbumin was visible on SDS - PAGE until the end of the gastrointestinal digestion, while it was not detected with UHPLC-HRMS. Analysis of both raw and heated milk samples revealed that the method is applicable to various milk types. Interestingly, heated milk showed additional signals in the mass spectrum, indicating non-enzymatic post-translational modifications. The relative abundance of these proteoforms could be followed along digestion. These findings highlight the versatility and sensitivity of UHPLC-HRMS in elucidating protein structures and modifications, providing valuable insights into how simulated digestion affects milk protein composition.

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.

Detection of the β-lactoglobulin genotype in zebu cattle (Gangatiri) milk using high-resolution accurate mass spectroscopy

We studied the genetic polymorphism of beta-lactoglobulin (β-Lg) whey protein in Gangatiri zebu cows for this Research Communication. The polymorphic nature of milk protein fractions and their association with milk production traits, composition and quality has attracted several efforts in evaluating the allelic distribution of protein locus as a potential dairy trait marker. Genetic variants of β-Lg have highly significant effects on casein number (B > A) and protein recovery (B > A) and also determine the yield of cheese dry matter (B > A). Molecular techniques of polyacrylamide gel electrophoresis and high-resolution accurate mass-spectroscopy were applied to characterize the β-Lg protein obtained from the Gangatiri breed milk. Sequence analysis of β-Lg showed the presence of variant B having UniProt database accession number P02754, coded on the PAEP gene. Our study can provide reference and guidance for the selection of superior milk (having β-LgB) from this indigenous breed that could potentially give a good yield of β-Lg for industrial applications.

Determination of A1 and A2 β-Casein in Milk Using Characteristic Thermolytic Peptides via Liquid Chromatography-Mass Spectrometry

β-casein, a protein in milk and dairy products, has two main variant forms termed as A1 and A2. A1 β-casein may have adverse effects on humans. The fact that there is only one amino acid variation at the 67th position between A1 and A2 β-casein makes it difficult to distinguish between them. In this study, a novel method using characteristic thermolytic peptides is developed for the determination of A1 and A2 β-casein in milk. Firstly, caseins extracted from milk samples are thermolytic digested at 60 °C without any denaturing reagents required for unfolding proteins, which simplifies the sample pretreatment procedure. The characteristic thermolytic peptides (i.e., fragments 66-76 and 59-76 for A1 and A2 β-casein, respectively) selected to specifically distinguish A1 and A2 β-casein only have eleven or eighteen amino acid moieties. Compared with tryptic characteristic peptides with a length of 49 amino acid moieties, these shorter thermolytic characteristic peptides are more suitable for LC-MS analysis. This novel method, with the advantages of high specificity, high sensitivity, and high efficiency, was successfully applied for the analysis of six milk samples collected from a local supermarket. After further investigation, it is found that this method would contribute to the development of A2 dairy products for a company and the quality inspection of A2 dairy products for a government.

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.

Probing of alpha, beta and kappa-caseins polymorphic variants in Gangatiri cow milk with the use of polyacrylamide gel electrophoresis and HRAMS

This research communication aimed to probe the genetic polymorphisms of alpha, beta, and kappa caseins in Gangatiri cows (an indigenous Indian cattle). Detection of variants has received considerable research interest in the dairy industry and animal breeding in recent years as a source of good quality protein, but also of bioactive peptides that may be linked to health implications. The polymorphic nature of casein fractions and their association with milk production traits, composition, and quality also attracted several efforts in evaluating the allelic distribution of different casein locus as a potential dairy trait marker. Molecular techniques of polyacrylamide gel electrophoresis and high-resolution accurate mass-spectrometry have been applied to this probe. Sequence analysis of different casein types in the cows showed the presence of four specific variants.

What is the impact of amino acid mutations in the primary structure of caseins on the composition and functionality of milk and dairy products?

The impact of amino acid mutations within the peptide structure of bovine milk protein is important to understand as it can effect processability and subsequently effect its physiological properties. Genetic polymorphisms of bovine caseins can influence the chemical, structural, and technological properties, including casein micelle morphology, calcium distribution, network creation upon gelation, and surface activity. The A1 and A2 genetic variants of β-casein have recently acquired growing attention from both academia and industry, prompting new developments in the area. The difference between these two genetic variants is the inclusion of either proline in β-casein A2 or histidine in β-casein A1 at position 67 in the peptide chain. The aim of this review was to examine the extent to which milk and ingredient functionality is influenced by β-casein phenotype. One of the main findings of this review was although β-casein A1 was found to be the dominant variant in milks with superior acid gelation and rennet coagulation properties, milks comprised of β-casein A2 possessed greater emulsion and foam formation capabilities. The difference in the casein micelle assembly, hydrophobicity, and chaperone activity of caseins may explain the contrast in the functionality of milks containing β-casein from either A1 or A2 families. This review provides new insights into the subtle variations in the physicochemical properties of bovine milks, which could potentially support dairy producers in the development of new dairy products with different functional properties.

•

Impact of β- and other caseins on the casein micelle structure and functionality.

•

Proline and histidine in β-caseins play a key role in casein micelle conformation.

•

Chaperone activity of β-casein A2 towards heat-induced aggregation of whey protein.

•

Gels prepared of milks with β-casein A1 possess a denser and firmer structure.

•

Ordered structure of β-casein A2 led to improved emulsion and foam formation.

Future perspectives on aptamer for application in food authentication

Food fraudulence and food contamination are major concerns, particularly among consumers with specific dietary, cultural, lifestyle, and religious requirements. Current food authentication methods have several drawbacks and limitations, necessitating the development of a simpler, more sensitive, and rapid detection approach for food screening analysis, such as an aptamer-based biosensor system. Although the use of aptamer is growing in various fields, aptamer applications for food authentication are still lacking. In this review, we discuss the limitations of existing food authentication technologies and describe the applications of aptamer in food analyses. We also project several potential targets or marker molecules to be targeted in the SELEX process. Finally, this review highlights the drawbacks of current aptamer technologies and outlines the potential route of aptamer selection and applications for successful food authentication. This review provides an overview of the use of aptamer in food research and its potential application as a molecular reporter for rapid detection in food authentication process. Developing databases to store all biochemical profiles of food and applying machine learning algorithms against the biochemical profiles are urged to accelerate the identification of more reliable biomarker molecules as aptamer targets for food authentication.

Online trypsin digestion coupled with LC-MS/MS for detecting of A1 and A2 types of β-casein proteins in pasteurized milk using biomarker peptides

Bovine A1-or A2-type β-caseins have attracted a growing interest due to their variation in beta-casomorphin-7 (BCM-7) formation, which may affect health. In the present work, identification and quantification of A1 and A2 types of β-casein proteins at the peptide level was achieved for the first time. An automated and online immobilized trypsin digestion system was employed for high throughput digesting of proteins into peptides. Tryptic peptides were separated and analyzed subsequently by liquid chromatography coupled to mass spectrometry platform. Two specific peptides ranging from the position of 49 to 97 in the peptide chain were selected for the identification and quantification of A1 and A2 β-casein, which covered the different amino acids between them. Synthetic isotopically labeled winged peptides were used for absolute quantification. Compared with traditional in-solution digestion, online digestion shortens digestion times from 2 to 24 h to 4 min. The limits of quantification (LOQ) of A1 and A2 β-casein in pasteurized milk are 0.8 and 2.4 µg/g, respectively. To further demonstrate the applicability of the proposed method, commercial pasteurized milk tests were performed with satisfactory results.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13197-022-05376-6.

Determination of Total and A1-Type β-Casein in Milk and Milk-Derived Ingredients by Liquid Chromatography-Mass Spectrometry Using Characteristic Tryptic Peptides

BACKGROUND

Gastrointestinal digestion of A1-type β-casein is conducive to β-casomorphin-7 with potential adverse digestive health effects. Monitoring of A1-type β-casein concentration in milk and milk-derived ingredients used in the formulation of A2-type nutritional products with associated health claims is important from a quality standpoint.

OBJECTIVE

New analytical methods were developed and validated for total and A1-type β-casein in milk and milk-derived ingredients. Data on total and A1-type β-casein concentrations in milk, nonfat dry milk, and whey protein concentrate was generated.

METHOD

The methods are based on a bottom-up proteomic approach using tryptic marker peptides and stable isotope dilution liquid chromatography-mass spectrometry. The measurement includes all protein sequences (intact, modified, and partial) which are potential sources of β-casomorphin-7.

RESULTS

Total β-casein was quantified using a neat calibration curve. Recovery and between-day precision RSD were 98% and 5.8%, respectively. A1-type β-casein was quantified by the method of standard additions. Between-day precision RSD was 7.2% and limit of quantitation was 0.01% in nonfat dry milk. The mass fraction of A1-type β-casein in the β-casein standard was 0.444. Samples manufactured from A2-type milk contained 0.26-5.0% A1-type β-casein relative to total β-casein.

CONCLUSIONS

The methods described enable the monitoring of the A1-type β-casein concentration in milk and milk-derived ingredients destined for the manufacture of A2-type products with associated health claims.

HIGHLIGHTS

New methods are presented for the analysis of total and A1-type β-casein in milk and milk-derived ingredients. The mass fraction of A1-type β-casein in a commercial β-casein standard was determined to enable its use as a calibrant.

A1 and A2 milk caseins-comparative FTIR and spectroflourimetry analysis

Around 35% of the total caseins are β-caseins, which are further classified as A1 β-caseins and A2 β-caseins, based on differences in the amino acid composition of both. A2 is the wild type genetic variant of β-casein while A1 is the mutant. The present study aimed at the isolation of A1 and A2 casein from different cow milk sources and its characterization by using simple chemical techniques, viz. FTIR and spectrofluorimetry. The commercial milk sample from Bos indicus (Gir) (A2) was obtained from Bombay Panjrapole, Mumbai and two commercially available packaged cow milk samples (pasteurized, skimmed) namely from Gokul and Mother Dairy (A1) were also obtained for comparison analysis from the local market. The isolation of casein was performed by standard method and analyzed using SDS-PAGE, FTIR and spectrofluorimetry. There was evidence that the A2 milk lacked histidine and rich in aromatic amino acids like tryptophan using FTIR and spectrofluorimetry techniques.

Beneficial Effects of Milk Having A2 β-Casein Protein: Myth or Reality?

Diet has been shown to play an important role in maintaining normal homeostasis in the human body. Milk and milk products are a major component of the Western diet, but their consumption may predispose sensitive individuals to adverse health outcomes. Current literature about milk products recognizes various bioactive components including lactate, whey protein, and β-casein protein. Specifically, cow milk has 2 major subvariants of its β-casein protein, A1 and A2, due to a single nucleotide difference that changes the codon at position 67. Whereas the A2 polymorphism is unlikely to undergo enzymatic cleavage during digestion, the A1 polymorphism is more likely to undergo enzymatic cleavage resulting in the product peptide β-casomorphin-7, a known μ-opioid receptor agonist. The objective of this article is to review the current understanding of the 2 major β-casein subvariants and their effects on various organ systems that may have an impact on the health of an individual. Synthesis of the current existing literature on this topic is relevant given the increased association of milk consumption with adverse effects in susceptible individuals resulting in a rising interest in consuming milk alternatives. We discuss the influence of the β-casein protein on the gastrointestinal system, endocrine system, nervous system, and cardiovascular system as well as its role in antioxidants and methylation. A1 milk consumption has been associated with enhanced inflammatory markers. It has also been reported to have an opioid-like response that can lead to manifestations of clinical symptoms of neurological disorders such as autism spectrum disorder. On the other hand, A2 milk consumption has been associated with beneficial effects and is easier to digest in sensitive individuals. Further research is warranted to investigate the short- and long-term effects of consumption of A1 β-casein in comparison with milk with A2 β-casein proteins.

Analysis of A1-type and A2-type β-casein in Maiwa Yak and Pien-niu milk by HPLC-high-resolution MS and tandem MS

In this study, a peptide-based method employing ultra high performance liquid chromatography electrostatic field orbitrap high-resolution mass spectrometry and triple quadrupole mass spectrometry was developed for quantification of A1-type and A2-type β-casein in milk from Yak, cows, and their offspring of crosses, Pien-niu. The specific peptides of A1-type and A2-type β-casein were screened and confirmed by protein software after analysis of high-resolution mass spectrometry. The multiple reaction monitoring method was established based on the qualitative results, and isotope-label peptides were used as internal standards. The linear correlation coefficients of this method were >0.99. The relative standard deviations of repeatability test were 0.2-3.6%. The recovery rate ranged from 93.3 to 114.4% with relative standard deviations <6% at three different spiking levels. The method was applied to analyze 45 milk samples from different species. The results showed that β-casein in Yak and Pien-niu milk was about 30% higher than that in cow milk. Furthermore, the β-casein in the Yak milk only contains A2-type β-casein. A1-type and A2-type β-casein coexist in most samples of Pien-niu and cow milk, a few samples contain only one type of β-casein. These results provide further understanding in nutritional value of milk from Yak and Pien-niu.

Quantitative mass spectrometry-based analysis of proteins related to cattle and their products - Focus on cows' milk beta-casein proteoforms

Modern mass spectrometers can accurately measure thousands of compounds in complex mixtures over a given liquid chromatograph method, depending on desired outcome and method duration. This stream of analytical chemistry has wide ranging application across food, pharma, environmental, forensics, clinical and research. With consistent pressure on both the ruminant production and product industries to face new and substantial challenges, liquid chromatography-mass spectrometry (LC-MS) is an ideal tool to identify, detect and quantify markers of breeding, production and adaption to support both research and industry to overcome these challenges. Herein, we provide a description of the theoretical basis and framework for LC-MS as a rapidly developing technique and highlight its application in measuring cattle and cattle product traits through protein quantitation with specific focus on beta-casein proteoforms.

Changes in Metabolites from Bovine Milk with β-Casein Variants Revealed by Metabolomics

Simple Summary

Changes in milk protein content have been associated with β-casein variants. However, the specific changes in the metabolites of β-casein variant milk remain unclear. Thus, a metabolomics approach was employed to determine the abundance of different metabolites in milk samples with β-casein variant A1/A1, A2/A2, and their heterozygote. The metabolites with the highest abundance were methionine, proline, and α-lactose in variant A2/A2 milk, choline, glycine, citric acid, and cyclic adenosine monophosphate (cAMP) in variant A1/A1 milk, and uric acid and cytosine in heterozygote milk. These results may facilitate further explorations of the differences in the biosynthesis of milk components in the mammary gland and help to elucidate the potential influence of β-casein variants on the physiological function of milk.

Abstract

β-casein is a primary protein in milk, and its variants have been associated with changes in the protein content of bovine milk. However, there has been little research focused on the effects of β-casein variants on milk metabolites. In the present study, dairy cows producing milk with β-casein variant A1/A1 (A1), A2/A2 (A2), and their heterozygote A1/A2 (A12) were screened by a high-resolution melting method. Individual milk samples were then collected from each of the cows, and the milk metabolites were separated and analyzed using nuclear magnetic resonance spectroscopy- and liquid-chromatography mass spectrometry-based metabolomics techniques. Differences in metabolites among the variant groups were evaluated by multivariate statistical analysis. The relative abundances of methionine, proline, and α-lactose were the highest in β-casein variant A2 milk, whereas choline, glycine, citric acid, and cyclic adenosine monophosphate (cAMP) showed the highest abundances in variant A1 milk. Metabolic pathways analysis indicated that the differential metabolites between variants A1 and A2 were involved in pantothenate and coenzyme A biosynthesis, butanoate metabolism, and valine, leucine, and isoleucine biosynthesis. Our results reveal the differences in milk metabolites among the β-casein variants A1, A2, and the heterozygote. These findings, thus, provide novel insights into the effects of β-casein variants on milk metabolites, facilitating further research into the mechanism of the biosynthesis of milk components in the mammary gland and the potential physiological function of milk associated with β-casein variants.