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.

Bovine milk β-casein: Structure, properties, isolation, and targeted application of isolated products

β-Casein, an important protein found in bovine milk, has significant potential for application in the food, pharmaceutical, and other related industries. This review first introduces the composition, structure, and functional properties of β-casein. It then reviews the techniques for isolating β-casein. Chemical and enzymatic isolation methods result in inactivity of β-casein and other components in the milk, and it is difficult to control the production conditions, limiting the utilization range of products. Physical technology not only achieves high product purity and activity but also effectively preserves the biological activity of the components. The isolated β-casein needs to be utilized effectively and efficiently for various purity products in order to achieve optimal targeted application. Bovine β-casein, which has a purity higher than or close to that of breast β-casein, can be used in infant formulas. This is achieved by modifying its structure through dephosphorylation, resulting in a formula that closely mimics the composition of breast milk. Bovine β-casein, which is lower in purity than breast β-casein, can be maximized for the preparation of functional peptides and for use as natural carriers. The remaining byproducts can be utilized as food ingredients, emulsifiers, and carriers for encapsulating and delivering active substances. Thus, realizing the intensive processing and utilization of bovine β-casein isolation. This review can promote the industrial production process of β-casein, which is beneficial for the sustainable development of β-casein as a food and material. It also provides valuable insights for the development of other active substances in milk.

Kappa and beta-casein alleles in dairy zebu cattle

The kappa (CSN3) and beta-casein (CSN2) genes are intensively genotyped in dairy cattle for selection purposes. This information is also generated and disseminated for Zebu breeds adapted to tropical climates. The objective of this work was to gather information on the genotypes for the CSN3 and CSN2 genes in three breeds (Gyr, Guzerat and Sindhi), and to verify the genotypic frequencies in the populations. The genotype AA and allele A frequencies are high for the CSN3 gene, without changes in values over the years, possibly indicating a small gene participation in traits under selection. In addition, the A2A2 frequencies are high for the CSN2 gene (<∼0.80). It is recommended to verify the association and contribution of CSN3 genotypes in productive traits for these breeds. The potential of A2 milk production by these genetic groups is also confirmed.

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.

Do non-bovine domestic animals produce A2 milk?: an in silico analysis

A2 milk is an easily digestible product since it has only A2 beta-casein. In cattle, the A1 and A2 alleles are found in the population and the A2 milk is produced from A2A2 animals. Little is known about these alleles in other domestic dairy species. The present study aims to analyze sequence of genetic material available on public databases and quantify the animals genotyped. Eight domestic species were analyzed. There is strong evidence that domestic non-bovine species only carry A2 beta-casein. The data reported here for goats already confirm it due to the large number of animals genotyped as well as buffaloes. It means that they naturally produce A2 milk and no selection must be done. Thus, the fact that A2 milk is easier to digest can be used to add value to dairy product of these species. It helps to conquer new markets. It also improves people's health and breeder profitability.

Novel LNA probe-based assay for the A1 and A2 identification of β-casein gene in milk samples

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A novel LNA probe-based qPCR allowed the detection of A1 and A2 alleles from β -casein gene in bovine samples.

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100% of agreement between results obtained by rHamp and LNA qPCR assays.

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The limit of detection of A1 in A2 samples was 1% or 7.5 DNA copies.

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This method is a highly sensitive and specific tool for detecting A1 and A2 alleles directly in milk.

The rising consumption of A2 milk and its derivatives in recent years has garnered attention from both consumers and producers, mainly due its possible health benefits, such as enhanced digestion and easier absorption. Thus, a novel real-time PCR using a combination of locked nucleic acid modified (LNA) conjugated probes was developed to genotype A1 and A2 alleles of β-casein gene (CSN2) and to detect and quantify the A1 presence in A2 samples. The limit of detection for each probe (A1 and A2) was evaluated using decreasing serial dilutions. Besides, the sensitivity of A1 allele detection in the A2 samples was also tested. The limits of detection of A1 and A2 alleles were 6 copies, while for A1 allele detection in A2 samples was 7.5 copies (1%). The LNA-probe based method was found to be rapid, robust, highly sensitive, cost effective, and can be employed as screening test to certificate the A2 dairy products.

Guzerat indicine cattle and A2 milk production

Cow milk might be associated to gastrointestinal disorders and abdominal pain in some people, which are, in part, due to the digestion of A1 beta-casein. Within this context, A2 milk has emerged as an alternative since it only contains A2 beta-casein that does not cause these complications. This milk is produced by cows with the A2A2 genotype. The aim of this study was to investigate the allele and genotype frequencies for the beta-casein gene in Guzerat cattle and to evaluate the feasibility of selection and production of A2 milk. The genotypes of 283 Guzerat cows from 10 herds were analyzed. The frequency of the A2A2 genotype was 0.80 and the frequency of the A2 allele was 0.90. These frequencies are slightly lower than those reported in previous studies involving populations of the same breed, but the number of animals, herein, genotyped was higher. Thus, the estimates are believed to be better and are also equally high. The Guzerat cattle has the potential for A2 milk production since most animals of the herd carry the favorable genotype for A2 milk production. Furthermore, the frequency of the A2A2 genotype can be rapidly increased by marker-assisted selection without compromising genetic variability.

Water buffaloes (Bubalus bubalis) only have A2A2 genotype for beta-casein

Beta-casein is a milk protein that has two variants: A1 and A2. Some individuals have difficulties digesting beta-casein A1, which can cause gastrointestinal disorders. A2 milk has emerged as an alternative. This milk only contains beta-casein A2 and is obtained from females carrying the A2A2 genotype of the gene. In cattle, allele and genotype frequencies vary according to breed and marker-assisted selection is performed to obtain A2A2 animals and the consequent production of A2 milk that is easier to digest. This study aimed to evaluate the alleles of beta-casein in buffaloes. A total of 657 buffaloes of four different breeds were genotyped and all animals carried the A2A2 genotype, i.e., allele A1 does not exist in the buffalo species. Thus, all milk products of buffaloes are naturally A2. This result adds value to products derived from buffalo milk.