Genetic polymorphism of ovine milk proteins: its influence on technological properties of milk — a review

Evaluation of Chicken Egg Yolk Plasma and Low-Density Lipoprotein Alone or Enriched with Ewe or Cow Skim Milk in Tris-Citric Acid-Based Diluent for Cryostorage of Ram Semen

The main purpose of the current study was to find suitable and optimum levels of protectants among chicken egg yolk plasma (CEYP) and low-density lipoproteins (LDLs), alone or supplemented with ewe or cow skim milk, for cryopreservation of ram semen. In Experiments 1 and 2, the CEYP (28%) freezing extender was enriched with ewe or cow milk (2.5%, 5%, 10%, or 20%; v/v), respectively. In Experiments 3 and 4, the semen extender was prepared by varying the amounts of fresh or lyophilized LDL (lyo-LDL), respectively. Finally, ewe or cow skim milk was added to the freshly extracted LDL extender and the quality of frozen-thawed semen was examined (Experiments 5 and 6). Kinematics of spermatozoa (assessed using a computer-assisted sperm analysis system), viability, functionality of the plasma membrane, and levels of malondialdehyde (MDA) and total antioxidant capacity (TAC) were evaluated. Results revealed that addition of ewe or cow skim milk (5%, 10%, or 20%; v/v) to the CEYP diluent enhanced kinematics, viability, and membrane integrity of spermatozoa compared with the control (p < 0.05). Moreover, fresh LDL diluent was more effective than lyo-LDL in the cryosurvival of ram spermatozoa. In addition, enrichment of fresh LDL diluent with ewe or cow skim milk improved different variables of spermatozoa compared with the control (p < 0.05). Levels of MDA and TAC were not affected by adding ewe or cow milk to the diluents (p > 0.05). In conclusion, enrichment of fresh LDL extenders with ewe or cow milk also is proposed as an approach to preserve ram semen quality against cold shock and cryodamage injuries.

Separation of α-Lactalbumin-Enriched Fractions from Caprine and Ovine Native Whey Concentrate by Combining Membrane and High-Pressure Processing

Whey from goat and sheep have been gaining attention in the last few years for their nutritional properties. Unfortunately, β-Lg, not found in human milk, may trigger infant allergies if used in infant food formulations, so there is a growing interest in developing ingredients derived from whey with higher α-La/β-Lg ratios. The objective of this work was to study the effect of high-pressure processing (HPP) on caprine and ovine native whey concentrates (NWC) in order to obtain α-Lactalbumin (α-La)-enriched fractions. NWCs were treated at 600 MPa (23 °C) for 2, 4, and 15 min and two pH conditions were studied (physiological pH and pH 4.60). The concentration of β-Lg in supernatant fraction after HPP significantly decreased after 2 min of treatment, while the concentration of α-La was unchanged in both goat and sheep samples. Longer HPP processing times (up to 15 min) progressively increased α-La purification degree but also decreased the α-La yield. Caprine and ovine NWCs treated at physiological pH provided better α-La yield, α-La purification degree, and higher β-Lg precipitation degrees than the corresponding acidified samples, while the corresponding NWC supernatant (NWC_sup) showed lower values for both surface hydrophobicity and total free thiol indices, suggesting a higher extent of protein aggregation. Effects of sample acidification and the HPP treatment were opposite to those previously reported on bovine NWC, so further characterization of caprine and ovine β-Lg should be carried out to understand their different behavior.

pH-dependent sedimentation and protein interactions in ultra-high-temperature-treated sheep skim milk

Sheep milk is considered unstable to UHT processing, but the instability mechanism has not been investigated. This study assessed the effect of UHT treatment (140°C/5 s) and milk pH values from 6.6 to 7.0 on the physical properties of sheep skim milk (SSM), including heat coagulation time, particle size, sedimentation, ionic calcium level, and changes in protein composition. Significant amounts of sediment were found in UHT-treated SSM at the natural pH (∼6.6) and pH 7.0, whereas lower amounts of sediment were observed at pH values of 6.7 to 6.9. The proteins in the sediment were mainly κ-casein (CN)-depleted casein micelles with low levels of whey proteins regardless of the pH. Both the pH and the ionic calcium level of the SSM at all pH values decreased after UHT treatment. The dissociation levels of κ-, β-, and α_S2-CN increased with increasing pH of the SSM before and after heating. The protein content, ionic calcium level, and dissociation level of κ-CN were higher in the SSM than values reported previously in cow skim milk. These differences may contribute to the high amounts of sediment in the UHT-treated SSM at natural pH (∼6.6). Significantly higher levels of κ-, β-, and α_S2-CN were detected in the serum phase after heating the SSM at pH 7.0, suggesting that less κ-CN was attached to the casein micelles and that more internal structures of the casein micelles may have been exposed during heating. This could, in turn, have destabilized the casein micelles, resulting in the formation of protein aggregates and high amounts of sediment after UHT treatment of the SSM at pH 7.0.

Molecular Characterization and Phylogenetic Analysis of Casein Gene Family in Camelus ferus

Camel milk is known for its exceptional medical uses. It has been used since ancient times to treat infant diarrhea, hepatitis, insulin-dependent diabetes (IDDM), lactose intolerance, alcohol-induced liver damage, allergies, and autism. It has the power to treat several diseases, with cancer being the most significant. This study investigated the evolutionary relationship, physiochemical characteristics, and comparative genomic analysis of the casein gene family (CSN1S1, CSN2, CSN1S2, and CSN3) in Camelus ferus. Molecular phylogenetics showing the camelid species clustered casein nucleotide sequences into four groups: CSN1S1, CSN2, CSN1S2, and CSN3. The casein proteins from camels were evaluated and found to be unstable, thermostable, and hydrophilic. CSN1S2, CSN2, and CSN3 were acidic, but CSN1S1 was basic. CSN1S1 showed positive selection for one amino acid (Q), CSN1S2 and CSN2 for three (T, K, Q), and CSN3 showed no positive selection. We also compared high-milk-output species such as cattle (Bos Tarus) and low-milk-yield species such as sheep (Ovies Aries) with camels (Camel ferus) and discovered that YY1 sites are more frequent in sheep than in camels and very low in cattle. We concluded that the ratio of YY1 sites in these species may affect milk production.

Comparative Analysis of the Polymorphism of the Casein Genes in Camels Bred in Kazakhstan

Caseins play an important role in determining the technological properties and quantitative characteristics of camel milk. To date, only a few studies on the genetic polymorphism of casein genes have been reported in the camel populations of Kazakhstan. Therefore, this work aimed to identify the genetic polymorphism level of casein genes among camel populations of the Almaty region of Kazakhstan. The PCR-RFLP method was used for this purpose and the following genotypes were revealed as a result: CSN3 gene—CC, CT, TT, where the T allele predominated in all populations, with a frequency of 0.60; CSN2 gene—AA, AG, GG, with the predomination of A allele (0.64); and CSN1S1 gene—GG and GT, with the predomination of G allele (0.94). Statistical analysis was carried out using the POPGENE and GenAlEx software. The χ2 values were equal to 12.1 (CSN3), 8.6 (CSN2), and 14.5 (CSN1S1). As a result, three out of 53 animals were designated as the “core” of the population—animals with the desired genotypes: CC genotype for the CSN3 gene and AA genotype for the CSN2 gene. Such animals can be selected for further use with an increase in the number of livestock with high productivity rates.

Challenging Sustainable and Innovative Technologies in Cheese Production: A Review

It is well known that cheese yield and quality are affected by animal genetics, milk quality (chemical, physical, and microbiological), production technology, and the type of rennet and dairy cultures used in production. Major differences in the same type of cheese (i.e., hard cheese) are caused by the rennet and dairy cultures, which affect the ripening process. This review aims to explore current technological advancements in animal genetics, methods for the isolation and production of rennet and dairy cultures, along with possible applications of microencapsulation in rennet and dairy culture production, as well as the challenge posed to current dairy technologies by the preservation of biodiversity. Based on the reviewed scientific literature, it can be concluded that innovative approaches and the described techniques can significantly improve cheese production.

MALDI-TOF-MS integrated workflow for food authenticity investigations: An untargeted protein-based approach for rapid detection of PDO feta cheese adulteration

Advances in Matrix-assisted Laser Desorption/Ionization -Time-Of-Flight Mass Spectrometry (MALDI-TOF-MS) have led to its supremacy for complex assessment of food authenticity studies, like dairy products fraud, holding promise for the discovery of potential authenticity (bio)markers. In this study, an integrated untargeted protein-based workflow in combination with advanced chemometrics is presented, to address authenticity challenges in PDO feta cheese which is legally manufactured by the mixture of sheep/goat milk. Potential markers attributed to specific animal origin were found from protein profiles acquired for authentic feta and white cheeses (prepared from cow milk), belonging to 4 kDa-18.5 kDa mass area. Rapid detection of feta cheese adulteration from cow milk was also achieved down to 1% adulteration level. The discriminative models showed high predictive ability for feta cheese authenticity (Q² = 0.920, RMSEE = 0.053) and its adulteration (Q² = 0.835, RMSEE = 0.121), introducing a reliable approach in routine analysis. The methodology was successfully applied in detection of cow milk in sheep yoghurt.

Association of β-casein gene polymorphism with milk composition traits of Egyptian Maghrebi camels (Camelus dromedarius)

The objectives of this study were to detect the polymorphism of 2126A/G SNP in the β-casein (CSN2) gene among Egyptian Maghrebi camels and to investigate the association of 2126A/G SNP genotypes, parity, lactation stage, and temperature–humidity index (THI) with the milk composition traits of Maghrebi camels. Sixty-eight hair samples were collected from three different populations of Maghrebi camels for DNA extraction. Fat, protein, total solids, solids-not-fat, and lactose percentages were determined in Maghrebi camel milk using an automatic milk analyzer device. Three different genotypes – A/A, A/G, and G/G – were identified in the 5′ flanking region of β-casein gene by using PCR-RFLP method with the A/G genotype showing the highest frequency. Association among these three genotypes with milk composition traits suggests a positive effect of A/A genotype on acidity and protein percentage. Higher protein and acidity values were observed in the milk of individuals carrying the A/A genotype. The protein percentage of this study significantly increased from the first till the fourth parity and then decreased. Fat and total solid percentages were significantly higher in the late stage of lactation, while lactose showed a decreasing trend from the early till the late stages of lactation. Fat and protein percentages were highest in the low THI class. Our results encourage the utilization of Maghrebi camel milk for cheese and butter processing at the late lactation stages of the middle parities of their productive life. Moreover, the A/G SNP of the CSN2 gene may be used as a DNA marker in selection programs for the improvement of camel milk composition. Further studies are needed in order to fully explore the variation in the chemical composition of camel milk due to the effect of CSN2 gene, parity, lactation stage, and THI factors.

Comparative milk proteome analysis of Kashmiri and Jersey cattle identifies differential expression of key proteins involved in immune system regulation and milk quality

BACKGROUND

Exploration of the bioactive components of bovine milk has gained global interest due to their potential applications in human nutrition and health promotion. Despite advances in proteomics profiling, limited studies have been carried out to fully characterize the bovine milk proteome. This study explored the milk proteome of Jersey and Kashmiri cattle at day 90 of lactation using high-resolution mass spectrometry based quantitative proteomics nano-scale LC-MS/Q-TOF technique. Data are available via ProteomeXchange with identifier PXD017412.

RESULTS

Proteins from whey were fractionated by precipitation into high and low abundant proteins. A total of 81 high-abundant and 99 low-abundant proteins were significantly differentially expressed between Kashmiri and Jersey cattle, clearly differentiating the two breeds at the proteome level. Among the top differentiating proteins, the Kashmiri cattle milk proteome was characterised by increased concentrations of immune-related proteins (apelin, acid glycoprotein, CD14 antigen), neonatal developmental protein (probetacellulin), xenobiotic metabolising enzyme (flavin monooxygenase 3 (FMO3), GLYCAM1 and HSP90AA1 (chaperone) while the Jersey milk proteome presented higher concentrations of enzyme modulators (SERPINA1, RAC1, serine peptidase inhibitor) and hydrolases (LTF, LPL, CYM, PNLIPRP2). Pathway analysis in Kashmiri cattle revealed enrichment of key pathways involved in the regulation of mammary gland development like Wnt signalling pathway, EGF receptor signalling pathway and FGF signalling pathway while a pathway (T-cell activation pathway) associated with immune system regulation was significantly enriched in Jersey cattle. Most importantly, the high-abundant FMO3 enzyme with an observed 17-fold higher expression in Kashmiri cattle milk seems to be a characteristic feature of the breed. The presence of this (FMO3) bioactive peptide/enzyme in Kashmiri cattle could be economically advantageous for milk products from Kashmiri cattle.

CONCLUSION

In conclusion, this is the first study to provide insights not only into the milk proteome differences between Kashmiri and Jersey cattle but also provides potential directions for application of specific milk proteins from Kashmiri cattle in special milk preparations like infant formula.

Single nucleotide polymorphism of the β-lactoglobulin gene in sheep breeds reared in Bulgaria

In the present study, single nucleotide polymorphism in exon II of the β-lactoglobulin gene was investigated in four Bulgarian sheep breeds: Bulgarian Dairy Synthetic Population sheep (BDSP), Copper-red Shumen sheep (CRSH), Stara Zagora sheep (STZG) and Pleven Blackhead sheep (PLBH). Two genetic variants of β-LG gene (A and B) have been identified through PCR-RFLP assay. A 103 bp fragment of the polymorphic β-LG locus were amplified and digested with endonuclease enzyme RsaI. The obtained restriction fragments revealed three genotypes: AA, AB and BB, observed in 31%, 65.5% and 3.5% of the BDSP population and in 48%, 28% and 24% of CRSH sheep population, respectively, with departure from the Hardy-Weinberg equilibrium (P<0.05) in these groups. The allele frequencies demonstrated a prevalence of the A allele (0.638 and 0.620) over the B allele (0.362 and 0.380) in both populations. On the contrary, the distribution of allele frequencies in STZG and PLBH was 0.240 and 0.100 for allele A, respectively and 0.760 and 0.900 for allele B. Therefore, the homozygous BB genotype in these sheep populations was more frequently encountered (0.520 and 0.800) than the heterozygous AB genotype (0.480 and 0.200), with HWE correspondence (P>0.1). The homozygous genotype AA was absent in STZG and PLBH sheep populations. The greatest Nei’s genetic distance calculated by UPGMA method was found between the populations BDSPand PLBH (0.5334), while the closest relationship (0.0006) was established between CRSH and BDSP. The results obtained from the present investigation confirmed the presence of the SNP polymorphism in exon II of the β-lactoglobulin gene. Therefore, the genetic variability established in this polymorphic locus could be applied in further association studies with milk production traits in sheep.

Variant discovery in the sheep milk transcriptome using RNA sequencing

BACKGROUND

The identification of genetic variation underlying desired phenotypes is one of the main challenges of current livestock genetic research. High-throughput transcriptome sequencing (RNA-Seq) offers new opportunities for the detection of transcriptome variants (SNPs and short indels) in different tissues and species. In this study, we used RNA-Seq on Milk Sheep Somatic Cells (MSCs) with the goal of characterizing the genetic variation within the coding regions of the milk transcriptome in Churra and Assaf sheep, two common dairy sheep breeds farmed in Spain.

RESULTS

A total of 216,637 variants were detected in the MSCs transcriptome of the eight ewes analyzed. Among them, a total of 57,795 variants were detected in the regions harboring Quantitative Trait Loci (QTL) for milk yield, protein percentage and fat percentage, of which 21.44% were novel variants. Among the total variants detected, 561 (2.52%) and 1,649 (7.42%) were predicted to produce high or moderate impact changes in the corresponding transcriptional unit, respectively. In the functional enrichment analysis of the genes positioned within selected QTL regions harboring novel relevant functional variants (high and moderate impact), the KEGG pathway with the highest enrichment was "protein processing in endoplasmic reticulum". Additionally, a total of 504 and 1,063 variants were identified in the genes encoding principal milk proteins and molecules involved in the lipid metabolism, respectively. Of these variants, 20 mutations were found to have putative relevant effects on the encoded proteins.

CONCLUSIONS

We present herein the first transcriptomic approach aimed at identifying genetic variants of the genes expressed in the lactating mammary gland of sheep. Through the transcriptome analysis of variability within regions harboring QTL for milk yield, protein percentage and fat percentage, we have found several pathways and genes that harbor mutations that could affect dairy production traits. Moreover, remarkable variants were also found in candidate genes coding for major milk proteins and proteins related to milk fat metabolism. Several of the SNPs found in this study could be included as suitable markers in genotyping platforms or custom SNP arrays to perform association analyses in commercial populations and apply genomic selection protocols in the dairy production industry.

Lama glama αS1-casein: Identification of new polymorphisms in the CSN1S1 gene

South American camelids have been poorly genetically investigated and little information is available in llamas (Lama glama) regarding the diversity of the caseins at the protein and gene level. Exon skipping and duplication events previously reported in the α_S1-casein gene (CSN1S1) led us to investigate the genetic variability at this locus. Seventy-two positive clones for the α_S1-casein transcripts were analyzed and randomly sequenced. The comparative analysis of the sequences revealed 2 transitions, c.366A>G and c.690T>C, at the 10th nucleotide of exon 12 and 94 bp of exon 19, respectively. These SNP are responsible for 2 amino acid changes, Ile→Val in position 86 and Tyr→His in position 194 of the mature protein. Both polymorphisms clarify the genetic events behind the protein variants A and B. This result was confirmed by isoelectric focusing analysis of llama milk samples. Quick methods based on PCR-RFLP and allele-specific PCR were set up for allelic discrimination in a population of 128 animals. Based on genotyping results, 4 haplotypes were observed and the estimated frequencies indicated B as the most common haplotype (0.629) in the investigated population. These data add knowledge to the genetic variability of a species little investigated, and open opportunity for new investigation in the field of milk protein for South American camelids, including the possibility, in the future, to select alleles with favorable characteristics.

Variability of the caprine whey protein genes and their association with milk yield, composition and renneting properties in the Sarda breed: 2. The BLG gene

The variability of the promoter region and the 3'UTR (exon-7) of the BLG gene, encoding the β-lactoglobulin, was investigated by sequencing in 263 lactating Sarda goats in order to assess its association with milk traits. Milk traits included: milk yield, fat, total protein and lactose content, pH, daily fat and protein yield (DFPY), freezing point, milk energy, somatic cell count, total microbial mesophilic count, rennet coagulation time (RCT), curd firming rate (k20) and curd firmness (a30). A total of 7 polymorphic sites were detected and the sequence analysed was given accession number KM817769. Only three SNPs (c.-381C>T, c.-323C>T and c.*420C>A) had minor allele frequency higher than 0.05. The effects of farm, stage of lactation and the interaction farm × stage of lactation significantly influenced all the milk traits (P T and c.*420C>A (P T (P < 0.001). The c.-381TT homozygous goats showed lower pH, RCT and k20 than c.-381CT (P < 0.05). In conclusion the polymorphism of the goat BLG gene did not affect the total protein content of the Sarda goat milk, and only weakly influenced RCT and k20. On the other hand, an interesting effect on milk yields and DFPY emerged in two SNPs. This information might be useful in dairy goat breeding programs.

The effect of addition of skimmed milk on the characteristics of Myzithra cheeses

Myzithra cheese is a traditional Greek whey cheese. Three types of Myzithra cheese were produced from A: 100% whey; B: 90% whey+10% ovine milk and C: 90% whey+10% skimmed ovine milk and were evaluated. The addition of skimmed milk to whey resulted in a new dietary product, containing 9.24% fat, with good quality, a harder texture and higher levels of ash, Ca, Mg and K than those of experimental cheeses A and B. Electrophoretic patterns and HPLC chromatograms of the proteins of Myzithra cheeses revealed the presence or not of αs-CN to the whey cheeses. In addition, SDS-electrophoresis of proteins under special preparation of samples permitted for first time the separation of whey-cheese protein (WP) components that had been denatured during cooking of the whey.

Investigating the genetic polymorphism of sheep milk proteins: a useful tool for dairy production

Sheep is the second most important dairy species after cow worldwide, and especially in the Mediterranean and Middle East regions. In some countries, the difficult environmental conditions require a peculiar adaptation and, in these contexts, sheep are able to provide higher quality protein than cattle. In the least-developed countries, the amount of dairy sheep and ovine milk production is progressively increasing. In order to improve dairy productions, in particular those with local connotations, it is necessary to obtain in-depth information regarding milk quality and rheological properties. The genetic polymorphisms of milk proteins are often associated with quantitative and qualitative parameters in milk and are potential candidate markers that should be included in breeding strategies similar to those already available for cattle. Due to the current and growing interest in this topic and considering the large amount of new information, the aim of this study was to review the literature on sheep milk protein polymorphisms with a particular emphasis on recent findings in order to give scientists useful support. Moreover, the effects of different protein variants on milk yield and composition are discussed.

The β-casein in camels: molecular characterization of the CSN2 gene, promoter analysis and genetic variability

The β-casein is the most abundant protein in camel milk and its encoding gene (CSN2) is considered in other species a 'major' gene for the presence of alleles associated to different level of expression. In the present paper, we report for the first time the characterization of the nucleotide sequence of the whole β-casein-encoding gene (CSN2) plus 2,141 bp at the 5'-flanking region in Camelus dromedarius. The promoter region and the complete cDNA are also provided for the first time in Camelus bactrianus. The gene is spread over 7.8 kb and consists of 9 exons varying in length from 24 bp (exon 5) to 519 bp (exon 7), and 8 introns from 95 bp (intron 5) to 1,950 bp (intron 1). The composite response element (CoRE) region was identified in the promoter, whereas the presence of mature microRNA sequences improves the knowledge on the factors putatively involved in the gene regulation. A total of 46 polymorphic sites have been detected. The transition g.2126A>G falls within the TATA-box of dromedary CSN2 promoter with a putative influence on the transcription factor binding activity. The frequency of the G allele is 0.35 in a population of 180 she-camels belonging to 4 different ecotypes. In the same population, a conservative SNP (g.4175C>A) was found at the codon 7 of the signal peptide, whereas a comparative analysis with a cDNA sequence available in the database evidenced a missense SNP (g.4180T(Leu)>G(Arg)) at exon 2. Four SNPs were found in the bactrian camel. The SNP c.666G>A is responsible for the amino acid change Met(201)→Ile and it represents the first missense allele at the β-casein in camels. Finally, five interspersed repeated elements were identified at intronic level, whereas the presence of putative bio-functional peptides belonging to ACE-inhibitor and anti-oxidative families confirms the potential protective role of the camel milk for the human nutrition.

Determination of whey proteins in different types of milk

Protein analysis is very important both in terms of milk protein allergy, and of milk and dairy product adulteration (β-lactoglobulin may be an important marker in the detection of milk adulteration). The aim of this study was to detect major whey proteins α-lactalbumin and β-lactoglobulin and their genetic variants by reversed-phase high-performance liquid chromatography. Milk samples from cows (n = 40), goats (n = 40) and sheep (n = 40) were collected at two farms and milk bars in the Czech Republic from April to June 2010. The concentration of α-lactalbumin was higher in goat’s milk (1.27 ± 0.05 g·l-1, P < 0.001) and cow’s milk (1.16 ± 0.02 g·l-1, P = 0.0037) compared to sheep’s milk (0.95 ± 0.06 g·l-1); however, concentration of α-lactalbumin in goat’s milk and cow’s milk did not differ significantly (P < 0.05). Goat’s milk contained less β-lactoglobulin (3.07 ± 0.08 g·l-1) compared to cow’s milk (4.10 ± 0.04 g·l-1, P < 0.001) or sheep’s milk (5.97 ± 0.24 g·l-1, P < 0.001). A highly significant positive correlation (r = 0.8686; P < 0.001) was found between fraction A and B of β-lactoglobulin in sheep’s milk, whereas in cow’s milk there was a negative correlation (r = -0.3010; P = 0.0296). This study summarizes actual information of the whey protein content in different types of milk which may be relevant in assessing their allergenic potential.

Farm animal milk proteomics

Milk is one of the most important nutrients for humans during lifetime. Farm animal milk in all its products like cheese and other fermentation and transformation products is a widespread nutrient for the entire life of humans. Proteins are key molecules of the milk functional component repertoire and their investigation represents a major challenge. Proteins in milk, such as caseins, contribute to the formation of micelles that are different from species to species in dimension and casein-type composition; they are an integral part of the MFGM (Milk Fat Globule Membrane) that has being exhaustively studied in recent years. Milk proteins can act as enzymes or have an antimicrobial activity; they could act as hormones and, last but not least, they have a latent physiological activity encoded in their primary structure that turns active when the protein is cleaved by fermentation or digestion processes. In this review we report the last progress in proteomics, peptidomics and bioinformatics. These new approaches allow us to better characterize the milk proteome of farm animal species, to highlight specific PTMs, the peptidomic profile and even to predict the potential nutraceutical properties of the analyzed proteins.

Molecular genetic characterization of ovine CSN1S2 variants C and D reveal further important variability within CSN1S2

Within this study, the recently identified ovine CSN1S2 variants C and D were characterized at the molecular genetic level. Sequencing of the cDNA and of parts of the DNA identified several sequence differences within CSN1S2*C and D in comparison to CSN1S2*A and B. CSN1S2*C is characterized by two non-synonymous single nucleotide polymorphisms (SNPs) within exon 7 (c.178A>G, c.187G>T) leading to the amino acid substitutions p.Val45Ile and p.Ala48Ser. CSN1S2*D is caused by the SNP c.183G>C, leading to an amino acid replacement at position 46 (p.Arg46Ser). A very common c.527G>A-SNP within exon 15, resulting in the amino acid substitution p.Arg161His and producing the new variant CSN1S2*G, not detectable by isoelectric focusing and previously misidentified as CSN1S2*A, was also identified. On the basis of the identified sequence differences, a new nomenclature is proposed and a possible phylogenetic pathway shown for ovine CSN1S2 variants.

MALDI-MS and multivariate analysis for the detection and quantification of different milk species

The extensive consumption of milk and dairy products makes these foodstuffs targets for potential adulteration with financial gains for unscrupulous producers. Such practices must be detected as these can impact negatively on product quality, labelling and even health. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) is a potentially useful technique, with proven abilities in protein identification and more recently through the use of internal standards for quantification purposes of specific proteins or peptides. In the current work, we therefore aim to explore the accuracy and attributes of MALDI-ToF-MS with chemometrics for the detection and quantification of milk adulteration. Three binary mixtures containing cows' and goats', cows' and sheep's, and goats' and sheep's milk and a fourth tertiary mixture containing all types of milk were prepared and analysed directly using MALDI-ToF-MS. In these mixtures, the milk concentrations of each milk varied from 0% to 100% in 5% steps. Multivariate statistical methods including partial least squares (PLS) regression and non-linear Kernel PLS regression were employed for multivariate calibration and final interpretation of the results. The results for PLS and KPLS were encouraging with between 2% and 13% root mean squared error of prediction on independent data; KPLS slightly outperformed PLS. We believe that these results show that MALDI-ToF-MS has excellent potential for future use in the dairy industry as a rapid method of detection and enumeration in milk adulteration.

Invited review: milk protein polymorphisms in cattle: effect on animal breeding and human nutrition

The 6 main milk proteins in cattle are encoded by highly polymorphic genes characterized by several nonsynonymous and synonymous mutations, with up to 47 protein variants identified. Such an extensive variation was used for linkage analysis with the description of the casein cluster more than 30 yr ago and has been applied to animal breeding for several years. Casein haplotype effects on productive traits have been investigated considering information on the whole casein complex. Moreover, mutations within the noncoding sequences have been shown to affect the specific protein expression and, as a consequence, milk composition and cheesemaking. Milk protein variants are also a useful tool for breed characterization, diversity, and phylogenetic studies. In addition, they are involved in various aspects of human nutrition. First, the occurrence of alleles associated with a reduced content of different caseins might be exploited for the production of milk with particular nutritional qualities; that is, hypoallergenic milk. On the other hand, the frequency of these alleles can be decreased by selection of sires using simple DNA tests, thereby increasing the casein content in milk used for cheesemaking. Furthermore, the biological activity of peptides released from milk protein digestion can be affected by amino acid exchanges or deletions resulting from gene mutations. Finally, the gene-culture coevolution between cattle milk protein genes and human lactase genes, which has been recently highlighted, is impressive proof of the nonrandom occurrence of milk protein genetic variation over the centuries.

Focusing on casein gene cluster and protein profile in Garganica goat milk

A survey was carried out in eight goat dairy farms, a total of 71 individual Garganica goat milk samples were collected for genomic DNA extraction. Casein alleles and haplotype frequencies of Garganica population were estimated. Individual milks were also analysed for chemical composition, rheological properties, and protein profile. The strong A* allele of CSN1S1 was predominant in the population investigated, the weak allele F of CSN1S1 showed a relatively high frequency and the null alleles N and 01 were first observed in this breed. At CSN1S2 locus the strong A* allele was the most frequent, followed by the F allele and the null allele. The strong A* allele was predominant at CSN2 locus, and relatively high incidence of null allele 0 was observed. CSN3 locus was monomorphic for B* allele. The exact test of sample differentiation based on haplotype frequencies discriminate the farms into two groups characterized by the highest frequency of strong (S-CSN1S1) or weak (W-CSN1S1) alleles at CSN1S1. Protein and casein contents were higher in the group characterized by strong allele than in the group with weak allele at CSN1S1. The 2D electrophoresis technique was performed to screen goat casein variability at the protein level and to evaluate global casein genotype (alphas1, alphas2, beta and kappa-CN). Gels displayed the protein profile associated with casein genotype, and demonstrated differences in the protein expression deriving from interactions between loci. The variability of goat casein loci in Garganica goat breed could be exploited to differentiate the population on the basis of milk utilization and could represent a strategy to preserve the genotype of this autochthonous breed.

A critical analysis of production-associated DNA polymorphisms in the genes of cattle, goat, sheep, and pig

Increasing productivity is one of the main objectives in animal production. Traditional breeding methods have led to increased gains in some traits but gains are not easily attainable in traits with low heritabilities. Exploiting the genetic variations underlying desired phenotypes is the goal of today's animal producers. Such positive genetic variants must, however, be known before possible application. Consequently, candidate genes of traits of interest have been searched for possible relationships with such traits or to explain reported quantitative trait loci (QTL) for such traits. DNA variants or polymorphisms have been identified in many such genes and their relationships with production traits determined. However, only a few genes have been evaluated, given the wealth of information on reported QTL for production traits, and in most cases genes are only partially investigated. This review presents available information on DNA variants for production traits and discusses steps that are required for effective utilization of this information for successful marker-assisted selection programs.