Genetic Variants Of Milk Proteins Research Articles

Effect of Protein Genotypes on Physicochemical Properties and Protein Functionality of Bovine Milk: A Review.

Milk protein comprises caseins (CNs) and whey proteins, each of which has different genetic variants. Several studies have reported the frequencies of these genetic variants and the effects of variants on milk physicochemical properties and functionality. For example, the C variant and the BC haplotype of αS1-casein (αS1-CN), β-casein (β-CN) B and A1 variants, and κ-casein (κ-CN) B variant, are favourable for rennet coagulation, as well as the B variant of β-lactoglobulin (β-lg). κ-CN is reported to be the only protein influencing acid gel formation, with the AA variant contributing to a firmer acid curd. For heat stability, κ-CN B variant improves the heat resistance of milk at natural pH, and the order of heat stability between phenotypes is BB > AB > AA. The A2 variant of β-CN is more efficient in emulsion formation, but the emulsion stability is lower than the A1 and B variants. Foaming properties of milk with β-lg variant B are better than A, but the differences between β-CN A1 and A2 variants are controversial. Genetic variants of milk proteins also influence milk yield, composition, quality and processability; thus, study of such relationships offers guidance for the selection of targeted genetic variants.

“A2 milk” authentication using isoelectric focusing and different PCR techniques

Genetic variants of milk proteins have attracted great interest for decades as they are related to important issues such as the composition and technological properties of milk. More recently, an “A1/A2 hypothesis” was developed saying that β-casein variant A1 may be a dietary risk factor for cardiovascular diseases, type 1 diabetes, sudden infant death syndrome and neurological disorders due to the release of β-casomorphin-7, whereas no evidence for such adverse effects was assumed for β-casein A2. Thus, the aim of this study was to adapt and establish analytical methods for the identification of genetic variants of β-casein using isoelectric focusing of milk proteins as well as appropriate PCR techniques. Allele-specific polymerase chain reaction (AS-PCR) proved to be a reliable method for differentiating most common β-casein variants (A1, A2, B, C), amplification-created restriction site (ACRS)-PCR using three different restriction enzymes allowed also the detection of variant A3, and the restriction fragment length polymorphism (RFLP)-PCR method enabled the reliable discrimination between A2 (homozygote/heterozygote) and non-A2 animals. Since traces of β-casein A1 were also found in commercial “A2 milk” in Austria, the authentication of such expensive dairy products is urgently recommended, both by genotyping of all dairy cows at farm level (to confirm that all cows are homozygous β-casein A2A2) and by screening commercial products on the market (to confirm the absence of β-casein variants A1, B, and C in dairy products labelled “A2 milk”) to protect consumers from this unexpected fraud.

Genetic and nongenetic factors contributing to differences in αS-casein phosphorylation isoforms and other major milk proteins

Relative concentrations of αS-casein (αS-CN) phosphorylation isoforms vary considerably among milk of individual cows. We aimed to explore to what extent genetic and other factors contribute to the variation in relative concentrations of αS-CN phosphorylation isoforms and the phosphorylation degree of αS-CN defined as the proportion of isoforms with higher degrees of phosphorylation. We also investigated the associations of genetic variants of milk proteins and casein haplotypes with relative concentrations of αS-CN phosphorylation isoforms and with the phosphorylation degree of αS-CN in French Montbéliarde cattle from the cheese production area of Franche-Comté. Detailed milk protein composition was determined by liquid chromatography coupled with electrospray ionization mass spectrometry from 531 test-day morning milk samples. Parity, lactation stage, and genetic variation of cows contributed to the phenotypic variation in relative concentrations of individual αS-CN phosphorylation isoforms and in the phosphorylation degree of αS-CN. As lactation progressed, we observed a significant increase for relative concentrations of αS-CN isoforms with higher degrees of phosphorylation (αS1-CN-9P, αS2-CN-13P, and αS2-CN-14P) as well as for the phosphorylation degree of both αS1-CN and αS2-CN. Furthermore, the β-CN I variant was associated with a greater proportion of isoforms with lower degrees of phosphorylation (αS1-CN-8P, αS2-CN-10P, and αS2-CN-11P); the β-CN B variant was associated with a greater proportion of isoforms with higher degrees of phosphorylation (αS1-CN-9P, αS2-CN-12P to αS2-CN-14P). The heritability estimates were low to moderate for relative concentrations of αS2-CN phosphorylation isoforms (0.07 to 0.32), high for relative concentrations of αS1-CN-8P (0.84) and αS1-CN-9P (0.56), and moderate for phosphorylation degrees of αS1-CN (0.37) and αS2-CN (0.23). Future studies investigating relations between the phosphorylation degree of αS-CN and technological properties of milk will be beneficial for the dairy industry.

Impact of genetic variants of milk proteins on chymosin-induced gelation properties of milk from individual cows of Swedish Red dairy cattle

Chymosin-induced gelation properties of the milk of around 400 Swedish Red dairy cows was investigated with the aim of identifying genetic protein variants that influence chymosin-induced gelation for optimisation of cheese milk through breeding practices. The variation in chymosin-induced gelation properties was shown to be large in the milk of Swedish Red and there was a high frequency of cows producing non-coagulating milk, 18%. The present study showed that the common composite β-κ-casein genotypes A1A2/AE and A2A2/AA were associated with both poor gelation properties and non-coagulation in the milk of Swedish Red. The present study suggests that if the frequencies of composite genotypes A1A2/AE and A2A2/AA were decreased in the Swedish Red population in favour for A1A1/AA and A1A1/AE, this could have a positive effect on the rennetability of the milk.

Milk protein polymorphism in a Holstein–Friesian nucleus exploited in the North-East of Romania

Since the discovering of the first genetic polymorphism at beta-lactoglobulin locus (β-LG) by Aschaffenburg et.al. [2], the researchers worldwide became interested in genetic polymorphisms of major milk proteins. As a fact, until now, numerous studies were carried in order to show the influence of the genetic variants of milk proteins on milk quality and quantity. Nowadays at least 39 genetics variants (alleles) are known for the six major milk proteins . These alleles occur because of the substitutions or deletions of the peptidic chain aminoacids [12]. Because of some certain genetic variants impact on the quantity, quality and processing properties of milk, we can discuss about an economic importance. Knowing the genetics polymorphisms helps in practice, because we can select through genetic tests, those individuals who might have important alleles. This way we can accelerate the improvement process of milk production [3; 11]. Major proteins polymorphisms are related to human nutrition in many ways: hypoallergenic properties of some types of milk; releasing the peptides with biological functions from milk proteins and other. [9]. The information gathered in this study may be used for milk improvement, specialy of the casein content. For example, the cheese production capacity is associated with a higher content of protein, casein and fats [7]. More than that these information can be used in order to produce a healthier milk with no negative effects on human health [5].

Genetic variants of milk proteins and their effects on the yieldand quality of cheese.

Abstract Milk protein genes, which are inherited by simple Mendelian genetics, could be used as marker traits for production and milk compositional traits. Genetic variants of certain milk proteins have been shown to be associated with coagulating properties of milk, cheese yield and cheese composition. In most of the cases, the observed differences in cheesemaking properties between some genetic variants are the result of their associations with the levels of fat and casein in the milk, which significantly influence cheese yield and composition. However, in some instances, differences between genetic variants are the result of the direct effect as a result of substitution of amino acids along the polypeptide chain leading to a change in the conformation and hence altering the physiochemical properties of the protein. Differences in heat stability, protein/protein interactions, and rate of proteolysis of different genetic variants are some examples of the direct effects in some cheese varieties. In bovine species, most studies have demonstrated that the B variant of κ-casein and the B variant of β-lactoglobulin (which are associated with higher levels of fat and casein in the milk) give higher cheese yield and better cheese composition than the A variant of the two proteins. Most research on caprine milk has concentrated on the αas1-casein loci. Variant A, which is associated with higher levels of synthesis of αs1-casein and total casein, is more suitable for cheese production than either variant E or F. In the ovine species, it has been shown that variant D of αs1-casein is not favourable for cheesemaking, while β-lactoglobulin A milk is more suitable than β-lactoglobulin B for the making of cheese.

Capillary electrophoretic analysis of genetic variants of milk proteins from different species

Polymorphism of bovine, ovine and caprine milk proteins was studied by CE. Identification of some rare bovine variants was carried out by isoelectric focussing (IEF) using PhastSystem. Genetic variants A and D of bovine α s2-casein, β-casein variants A 1, A 2, A 3, B and C and α s1-casein variants B and C were determined by CE. In addition, the different casein fractions including some genetic variants of ovine and caprine milk were identified by CE. In order to carry out this identification, collected fractions from a cation-exchange FPLC separation were injected by CE.

Technological properties of milk as influenced by genetic polymorphism of milk proteins — A review

Abstract Current knowledge of the effects of genetic polymorphisms of milk proteins on technological properties of milk is reviewed. The topics discussed include the rennetability of milk, syneresis of curd, cheese yield and quality, susceptibility of β-lactoglobulin genetic variants to heat denaturation, heat stability of milk and concentrated milk, as well as the few findings concerning the relationships between milk protein polymorphs and micellar stability of casein, water sorption of casein, quality of fermented milk and proteolysis of casein. Although genetic variants of milk proteins clearly have been demonstrated to influence technological properties of milk, in particular those of importance for cheesemaking, further research is necessary to elucidate the underlying mechanisms involved and possible relationships between milk protein loci and traits other than those important for milk processing.

The Effects of Milk Protein Polymorphisms on Milk Components and Cheese-Producing Ability

A Total of 2005 first lactation Holstein-Friesian cows with known 305-d lactation yield for milk, fat, and protein were available. For each cow, genotypes for αs1-casein, β-casein, κ-casein, and β-lactoglobulin were known. It appears that the milk protein variants αs1-casein, β-casein, and κ-casein may not be segregating independently. Effects of genetic variants of milk proteins on estimated individual Parmesan cheese yields were investigated. The relationships of the genetic variants of milk proteins to total lactation milk yield, fat yield, protein yield, fat percentage, and protein percentage were also investigated. Least squares analysis of the data indicated that αs1-casein genotype significantly influenced milk yield, fat yield, and protein yield with the highest yields obtained for the genotype BB. Cheese yield on a fixed amount of milk and fat percentage were significantly related to β-lactoglobulin genotype with the highest estimates obtained for BB. Protein percentage was influenced by αs1-casein and κ-casein, with the genotypes BC and BB, respectively, having the highest percentages. Significantly higher lactation cheese yields were estimated with αs1-casein genotype BB. Using the prediction equation to estimate cheese yield (on data from another study), it was found that differences in Parmesan cheese yield from milk of either κ-casein genotype AA or BB were greater than expected based on composition. Differences in salted curd yield from another study using milk of either β-lactoglobulin genotype AA or BB were also greater than expected.

Method to estimate genotype probabilities at individual loci in farm livestock

A Bayesian method to estimate genotype probabilities at a single locus using information on the individual and all its relatives and their mates has been developed. The method uses data over several generations, can deal with large numbers of individuals in large livestock families and allows for missing information. It can be extended to multiple alleles and can be used for autosomal or sex-linked loci. The allele frequencies and the form of expression (dominance, penetrance) must be specified. An algorithm using the method and involving an iterative procedure has been developed to calculate the genotype probabilities for practical use in livestock breeding. The method and algorithm were used to determine the accuracy of estimating genotype probabilities of sires for a female sex-limited trait, such as genetic variants of milk proteins. Data were similated and genotype probabilities estimated for 100 sires (20 replicates) with 3, 6 and 12 female offspring per sire, for different population frequencies, for additive and dominance gene action and for variable genotypic expression. Such simulation is useful in the design of testing systems for the use of information on specific genetic loci in selection.

Relationships Between Milk Protein Polymorphisms and Cheese Yielding Capacity

A total of 31 Holstein cows were selected for their phenotypes for β-casein, κ-casein, and κ-lactoglobulin. Over 14 mo, milk samples were collected individually on a monthly basis from each cow during lactation. Effects of genetic variants of milk proteins on cheese yielding capacity were investigated. To minimize variations due to cheese making practices, cheese was made under laboratory conditions. Least-squares analysis of the data indicated that higher cheese yields were obtained with β-casein A1A1, κ-casein BB, and β-lactoglobulin BB when compared with other phenotypes of the respective proteins under study. Regression analyses indicated that each percentage increase in fat content in milk resulted in an increase of 1.07, 1.34, and 1.33% in actual, adjusted, and theoretical yield. For a similar increase of casein in milk, there was 1.59, 1.26, and 1.81% increase in actual, adjusted, and theoretical yield, respectively. Relative proportions of different caseins and whey proteins also had some influence on the yields. Relationships were negative between initial milk pH and yields.

SUBJECT: MILK PROTEINS:FORM AND FUNCTION OF MILK PROTEINS

Present knowledge of the occurrence of milk proteins, their isolation and composition, is reviewed and reference is made to the relationship of their physico‐chemical properties to their physiological function. The nature of genetic variants of milk proteins and their distribution is summarized and discussed. The importance of understanding milk protein interaction during processing treatments and their effect on the behavioural properties of milk and milk products is stressed.

Section G. Genetics. Genetic variants of milk proteins: their breed distribution

Section G. Genetics. Genetic variants of milk proteins: their breed distribution