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

Current knowledge of the genetic polymorphism in ovine milk proteins including heterogeneity detected and their relationships with the technological properties of milk is reviewed. In the casein fraction a great heterogeneity has been determined either by the presence of genetic variants or other factors such as a discrete phosphorylation level and the coexistence of protein forms of different chain length. In the whey fractions, three genetic variants (A, B, and C) are described for β-lactoglobulin (β-LG), and two for α-lactalbumin (α-LA). The topics discussed include the rennetability of ovine milk, cheese yield and susceptibility of β-LG genetic variants to heat denaturation as well as the findings concerning the relationships between ovine milk protein polymorphism and milk production and composition. However, further investigation is needed in order to better outline the relevant features of polymorphism and technological properties of ovine milk.     

Characteristics of a calcium–milk coagulum

The texture, microstructure and composition of a milk coagulum obtained by coagulating milk with calcium chloride and heat were evaluated. A direct relationship was established between the microstructure and texture of the calcium–milk coagulum. The microstructure was comprised of casein micelles that were interlinked by appendages or fused with each other depending on the nature of the pre-heat treatment employed. The casein micellar network also entrapped fat globules. The pre-heat treatment of milk and the pH of milk during coagulation affected the hardness, adhesiveness, protein content and microstructure of the calcium–milk coagulum significantly. This study characterises a calcium–milk coagulum as a novel dairy product which differs from an acid coagulum in texture, microstructure and composition.     

Effects of the circadian rhythm on milk composition in dairy cows: Does day milk differ from night milk?

Metabolism in most organisms can show variations between the day and night. These variations may also affect the composition of products derived from livestock. The aim of the present study was to investigate the difference in composition between the day milk and night milk of dairy cows. Ten multiparous Holstein cows (milk yield = 25.2 ± 5.00 kg/d) were randomly selected during mid lactation. Milk samples were collected at 0500 h (“night milk”) and 1500 h (“day milk”) and analyzed to determine their composition. Mid-infrared spectroscopy was used to analyze macronutrient content of milk. Metabolomics and lipidomics were used to detect and analyze small molecules and fatty acids, respectively. An automatic biochemical analyzer and ELISA kits were used to determine biochemical indicators, as well as antioxidant and immune parameters in the milk. Though milk fat, protein, lactose, and total milk solids were not different between day milk and night milk, small molecules, metabolites and lipids, and hormones and cytokines differed between day milk and night milk. Regarding biochemical and immune-related indicators, the concentrations of malondialdehyde, HSP70, and HSP90 in night milk were lower than that in day milk. However, interferon-γ levels were higher in night milk. Additionally, night milk was naturally rich in melatonin. Lipidomics analyses showed that the levels of some lipids in night milk were higher than those in day milk. Metabolomics analyses identified 36 different metabolites between day milk and night milk. Higher concentrations of N-acetyl-d-glucosamine, cis-aconitate, and d-sorbitol were observed in day milk. However, the other 33 metabolites analyzed, including carbohydrates, lipids, AA, and aromatic compounds, showed lower concentrations in day milk than in night milk. The present findings show that the composition of night milk differs considerably from that of day milk. Notable changes in the circadian rhythm also altered milk composition. These results provide evidence to support the strategic use and classification of day milk and night milk.     

Drivers of choice for fluid milk versus plant-based alternatives: What are consumer perceptions of fluid milk?

Fluid milk consumption has declined for decades while consumption of nondairy alternatives has increased. A better understanding of why consumers purchase fluid milk or nondairy alternatives is needed to assist increased sales of milk or maintain sales without further decline. The objective of this study was to determine the extrinsic attributes that drive purchase within each product category. The second objective was to determine the personal values behind the purchase of each beverage type to give further understanding why particular attributes are important. An online conjoint survey was launched with 702 dairy consumers, 172 nondairy consumers, and 125 consumers of both beverages. Individual means-end chain interviews were conducted with fluid milk consumers (n = 75), plant-based alternative consumers (n = 68), and consumers of both beverages (n = 78). Fat content was the most important attribute for dairy milk followed by package size and label claims. Consumers of fluid milk preferred 1 or 2% fat content, gallon, or half-gallon packaging, conventionally pasteurized store-brand milk. Sugar level was the most important attribute for plant-based beverages, followed by plant source and package size. Almond milk was the most desirable plant source, and half-gallon packaging was the most preferred packaging. Means-end chain interviews results suggested that maintaining a balanced diet and healthy lifestyle was important to all consumer groups. Lactose free was an important attribute for plant-based alternative consumers and consumers of both dairy and nondairy. A distinguishing characteristic of those who only drank nondairy plant-based alternatives was that plant-based beverages contributed to a goal to consume less animal products, beliefs about animal mistreatment, and perceived lesser effect on the environment than fluid milk. Unique to fluid milk consumers was that fluid milk was perceived as a staple food item. These results suggest that the dairy industry should focus on the nutrition value of milk and educating consumers about misconceptions regarding dairy milk. Future beverage innovation should include the development of lactose-free milk that is also appealing to consumers in flavor.     

Addition of gelatin enhanced gelation of corn–milk yogurt

Corn–milk yogurt set by a combination of sodium caseinate plus gelatin at concentrations of 0, 0.2, 0.4 and 0.6% (w/v) were studied. The quality of the gels was determined by measurement of acidity, syneresis, texture profile analysis, viscoelasticity, structure scanning electron microscope and microbiology. Texture profile analysis (TPA) showed that increasing levels of gelatin increased hardness, adhesiveness and springiness as well as the acidity of the products. Viscoelastic behaviour displayed similar trends to the TPA characteristics, the storage modulus was less frequency dependent than the loss modulus giving a loss tangent of 0.2 in the high gelatin systems, which might indicate a true gel system. The microstructure was dense and spongy-like with small air cells, in particular, those having a high concentration of gelatin (0.6%, w/v) gave a very firm structure which might impair palatability. The addition of a commercial gelatin at 0.4% (w/v) gave good acceptability for the product (little syneresis of the gels produced). While the gelatin used for this study had a bloom value of 246 g the authors acknowledge that a different commercial gelatin may well result in a different concentration being required.     

Effect of heat treatments on stability of β-lactams in milk

The presence of residues of antimicrobial substances in milk may have serious toxicological and technical consequences. To date, few studies have been done to evaluate the effect of heat treatments on β-lactam residues in milk. However, the few studies that have been conducted estimate losses of antimicrobial activity under different combinations of temperature and time using microbiological methods. The aims of this study were to calculate the kinetic parameters for the degradation of β-lactam antibiotics in milk and to develop prediction models to estimate the concentration losses of these compounds in conventional dairy heat treatments. To do so, we employed a quantitative HPLC method to calculate losses in concentrations of 10 β-lactam antibiotics in milk with different combinations of temperature and time. Increasing the temperature from 60°C to 100°C decreased the half-life of amoxicillin (372 to 50 min), ampicillin (741 to 26 min), cloxacillin (367 to 46 min), and penicillin G (382 to 43 min). These increases in temperature caused further degradation in cephalosporins, which was accompanied by a decrease in half-life times to reach very low values; for instance, 4, 5, and 6 min for cefoperazone, cephurexime, and cephapirin, respectively. Kinetic equations were applied to different heat treatments used in dairy processing. Heat treatments at high temperatures and long times (e.g., 120°C for 20 min) led to a further degradation of β-lactam antibiotics with percentages close to 100% for cefoperazone and cefuroxime. In contrast, when milk was subjected to heat treatments at lower temperatures and times (e.g., 72°C for 15 s), the degradation of β-lactam in milk did not exceed 1% for the 10 antibiotics tested.     

Influence of milk pre-heating conditions on casein–whey protein interactions and skim milk concentrate viscosity

The viscosity of concentrates (50–55% total solids) prepared from skim milk heated (5 min at 80 or 90 °C) at pH 6.5 and 6.7 was examined. The extent of heat-induced whey protein denaturation increased with increasing temperature and pH. More denatured whey protein and κ-casein were found in the serum phase of milk heated at higher pH. The viscosity of milk concentrates increased considerably with increasing pH at concentration and increasing heating temperature, whereas the distribution of denatured whey proteins and κ-casein between the serum and micellar phase only marginally influenced concentrate viscosity. Skim milk concentrate viscosity thus appears to be governed primarily by volume fraction and interactions of particles, which are governed primarily by concentration factor, the extent of whey protein denaturation and pH. Control and optimization of these factors can facilitate control over skim milk concentrate viscosity and energy efficiency in spray-drying.     

Effect of κ-carrageenan on milk protein polysaccharide mixtures

The effect of κ-carrageenan (0, 0.025, 0.05%) on phase separation between polysaccharides (0.36% of locust bean gum (LBG), guar gum, or xanthan gum) and milk proteins (from 10.5% skim milk powder) in solution was studied. Xanthan gum was seen to be the most incompatible with milk proteins, followed by guar gum and LBG. Casein micelles were more incompatible with all polysaccharides than whey proteins. Whereas at either concentration κ-carrageenan inhibited visual phase separation, it was seen by transmission electron microscopy that samples with κ-carrageenan showed microscopic phase separation. Samples with 0.05% κ-carrageenan and either LBG or guar gum and all samples with xanthan gum could be described rheologically as weak gels, while those with no or 0.025% κ-carrageenan and either LBG or guar gum could be described as concentrated solutions. Thus, no correlation was seen between the inhibition of macroscopic phase separation by κ-carrageenan and the formation of a weak gel in solution.     

Species identification of ruminant milk by genotyping of the κ-casein gene

The development of molecular genetic and bioinformatic systems for identifying the species of milk and the raw material composition of dairy products is of great scientific and practical importance with the purpose of introducing developments in the system for controlling the turnover of falsified products. The aim of the research is to develop a method of PCR-RFLP analysis for species identification of milk and dairy products from agricultural ruminant animals by the κ-casein gene (CSN3) with the possibility of qualitative and relative quantitative assessment of species-specific DNA of the tested biomaterial. The objects of research were samples of raw milk and milk powder, pasteurized cream, and hard and semi-hard cheeses. The developed method of species identification of milk and dairy products includes sample preparation of the studied samples, nucleic acid extraction, combined PCR-RFLP technique, detection of obtained results by the method of horizontal electrophoresis in agarose gel and their analysis, including using the developed mathematical algorithms and software. The synergistic effect established in combined operation of 2 restriction enzymes ensured their application in a mix with increased performance in an ergonomic way in the context of DNA authentication of cow, goat, and sheep milk and dairy products based on them. The specificity and sensitivity of the proposed method is potentially suitable for implementing the development of a system to control the turnover of falsified and counterfeit goods.     

Detection of the adulteration of water buffalo milk and mozzarella with cow’s milk by liquid chromatography–mass spectrometry analysis of β-lactoglobulin variants

A liquid chromatography–mass spectrometry method for detecting a fraudulent addition of cow’s milk to water buffalo milk and mozzarella is described. The presented approach utilises the whey protein β-lactoglobulin as marker for an adulteration. It offers a rapid determination combined with unequivocal identification of the marker protein in every run. An in-depth discussion of the subsequent data analysis highlights the potential problems of obtaining quantitative information on the level of adulteration. In an examination of 18 commercial buffalo mozzarella samples three products were found to be adulterated with high levels of cow’s milk.     

Time-dependent flow properties of starch–milk–sugar pastes

The time-dependent flow properties of starch–milk–sugar (SMS) pastes have been studied. The flow properties were assessed from the measurement of the shear stress versus time of shearing at constant shear rate. Corn and wheat starches were used in this study, while the sugars were glucose, sucrose, and fructose. The Weltman model was used to evaluate the flow properties of SMS pastes prepared under different conditions. SMS pastes heated at 95 and 85 °C exhibited a thixotropic behavior, while pastes heated at 75 °C behaved like a rheopectic fluid. It was noted that the thixotropy occurred at high shear stress (above 50 Pa), and the rheopexy occurred at low shear stress (below 45 Pa). The degree of thixotropy, as assessed by the Weltman model parameters, increased significantly with starch concentration, and with less pronounced effect with sugar concentration. The effect of sugar type on the degree of thixotropy of SMS pastes heated at 95 °C decreased in the following order: fructose>sucrose>glucose. The type of starch played a role in the time-dependent flow properties of the SMS paste, with a general conclusion that wheat starch had a greater degree of thixotropy than corn starch.     

Interaction of milk α- and β-caseins with tea polyphenols

The interaction of α- and β-caseins with tea polyphenols (+)-catechin (C), (−)-epicatechin (EC), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG) was examined at a molecular level, using FTIR, UV–visible, CD and fluorescence spectroscopic methods as well as molecular modelling. The polyphenol binding mode, the binding constant and the effects of polyphenol complexation on casein stability and conformation were determined. Structural analysis showed that polyphenols bind casein via both hydrophilic and hydrophobic interactions with overall binding constants of K_C–α-cas = 1.8 (±0.8) × 10³ M⁻¹, K_EC–α-cas = 1.8 (±0.6) × 10³ M⁻¹, K_EGC–α-cas = 2.4 (±1.1) × 10³ M⁻¹ and K_{EGCG–α-cas} = 7.4 (±0.4) × 10³ M⁻¹, K_C–β-cas = 2.9 (±0.3) × 10³ M⁻¹, K_EC–β-cas = 2.5 (±0.6) × 10³ M⁻¹, K_EGC–β-cas = 3.5 (±0.7) × 10³ M⁻¹ and K_{EGCG–β-cas} = 1.59 (±0.2) × 10⁴ M⁻¹. The number of polyphenol bound per protein molecule (n) was 1.1 (C), 0.9 (EC), 1.1 (EGC), 1.5 (EGCG) for α-casien and 1.0 (C), 1.0 (EC), 1.1 (EGC) and 1.5 (EGCG) for β-casein. Structural modelling showed the participation of several amino acid residues in polyphenol–protein complexation with extended H-bonding network. Casein conformation was altered by polyphenol with a major reduction of α-helix and β-sheet and increase of random coil and turn structure suggesting further protein unfolding. These data can be used to explain the mechanism by which the antioxidant activity of tea compounds is affected by the addition of milk.     

Identification of rare genetic variants of the αS-caseins in milk from native Norwegian dairy breeds and comparison of protein composition with milk from high-yielding Norwegian Red cows

Several factors influence the composition of milk. Among these, genetic variation within and between cattle breeds influences milk protein composition, protein heterogeneity, and their posttranslational modifications. Such variations may further influence technological properties, which are of importance for the utilization of milk into dairy products. Furthermore, these potential variations may also facilitate the production of differentiated products (e.g., related to specific breeds or specific genetic variants). The objective of this study was to investigate the genetic variation and relative protein composition of the major proteins in milk from 6 native Norwegian dairy breeds representing heterogeneity in geographical origin, using the modern Norwegian breed, Norwegian Red, as reference. In total, milk samples from 144 individual cows were collected and subjected to liquid chromatography-electrospray ionization/mass spectrometry–based proteomics for identification of genetic and posttranslational modification isoforms of the 4 caseins (α_S1-CN, α_S2-CN, β-CN, κ-CN) and the 2 most abundant whey proteins (α-lactalbumin and β-lactoglobulin). Relative quantification of these proteins and their major isoforms, including phosphorylations of α_S1-CN and glycosylation of κ-CN, were determined based on UV absorbance. The presence and frequency of genetic variants of the breeds were found to be very diverse and it was possible to identify rare variants of the CN, which, to our knowledge, have not been identified in these breeds before. Thus, α_S1-CN variant D was identified in low frequency in 3 of the 6 native Norwegian breeds. In general, α_S1-CN was found to be quite diverse between the native breeds, and the even less frequent A and C variants were furthermore detected in 1 and 5 of the native breeds, respectively. The α_S1-CN variant C was also identified in samples from the Norwegian Red cattle. The variant E of κ-CN was identified in 2 of the native Norwegian breeds. Another interesting finding was the identification of α_S2-CN variant D, which was found in relatively high frequencies in the native breeds. Diversity in more common protein genetic variants were furthermore observed in the protein profiles of the native breeds compared with milk from the high-yielding Norwegian Reds, probably reflecting the more diverse genetic background between the native breeds.     

Study of milk/κ-carrageenan mixtures by atomic force microscopy

Structural characteristics of milk components and milk/κ-carrageenan mixtures were studied by atomic force microscopy (AFM). Samples were adsorbed on highly ordered pyrolytic graphite (HOPG) and mica substrates. Sample attachment by physisorption and imaging in air by AFM resulted in a very promising technique to investigate structures and interactions between biological macromolecules under “near-native” conditions. Differences in adsorption of casein micelles on HOPG and mica surfaces were observed. Casein micelles were adsorbed satisfactorily on HOPG while poor adsorption was obtained on mica surface. Topographical images of casein micelles adsorbed on HOPG denoted pseudo-spherical structures forming aggregates which were polydisperse in size and shape. In the case of milk/κ-carrageenan mixtures, it was observed that as κ-carrageenan concentration increased, the amount of casein micelles attached on HOPG surface decreased. An opposite behavior was observed when samples were adsorbed on mica. Hydrophobic and hydrophilic interactions between samples and substrates helped in improving the understanding of the interactions between the macromolecules studied. Our findings agreed with previous studies suggesting a surface level interaction between casein micelles and κ-carrageenan, the structures observed being dependent on polysaccharide concentration. It can also be concluded that mica may be a suitable substrate for imaging milk/κ-carrageenan mixtures.     

Development of milk protein fiber/ wool blended yarn北大核心

The blended yarn was produced by 15% milk protein fiber and 85% wool. To ensure the dyeing effect, the milk protein fiber and wool were dyeing with soft water respectively. Before spinning, it should pretreat the milk protein fiber with 1% (owf) antistantic agent and 0. 9% (owf) hair oil, to match the moisture at 13% -14%. Gilling put 6 word needle comb and the antistatic coating rubber roller, which speed was low. Roving compaction should slant small, while roving areas after the distance should be appropriately amplification.     

Stability of antioxidants in an apple polyphenol–milk model system

The stability of antioxidants in an apple polyphenol–milk model system was examined. The model system consisted of skim milk fortified with pH-neutralised apple polyphenols (AP, 0–200 mg per 100 ml milk), with or without ascorbic acid (100 mg per 100 ml milk). Physical and chemical changes were evaluated after thermal treatment (120 °C, 5 min) and oxidative storage (20 °C and 38 °C, up to 12 weeks). Antioxidant capacity was determined using both oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay. Significant antioxidant capacity was detected in the presence of milk. Antioxidant capacity was retained during thermal treatment but decreased slowly during storage.     

Size of native and heated casein micelles,content of protein and minerals in milk from Norwegian Red Cattle—effect of milk protein polymorphism and different feeding regimes

Milk samples of 59 cows of the Norwegian Red Cattle breed receiving three different supplementary concentrates, were analysed for genotypes of caseins and whey proteins, the content of different milk salts (Ca²⁺, Ca, Mg and citrate), the content of total protein, casein and whey protein and the mean micellar size of native and heated casein micelles. The genotype of α_s1-casein had a statistically significant effect on the content of protein and casein, and the content of whey protein and the casein number were significantly influenced by different feeding regimes, and the content of citrate. The mean size of native and heated casein micelles was significantly influenced by the feeding regimes, genotype of α_s1-casein (native mean size only) and κ-casein, pH and the content of casein, whey protein and casein number. The heat-induced changes in mean micellar size were significantly affected by the calcium ion activity which accounted for approximately 40% of the total variation.     

Effect of probiotic co-cultures on physico-chemical and biochemical properties of small ruminants’ fermented milk

Small ruminants' fermented probiotic milk is an alternative to fermented cows' milk, especially because of the monounsaturated/polyunsaturated fatty acid profiles. The technological and biochemical potential of Bifidobacterium and Lactobacillus co-cultures, with or without inulin, on goats' and ewes' milk was assessed. Microbial stability, lactose consumption, organic acid production, proteolytic parameters and conjugated linoleic acid (CLA) production in situ, were followed in ewes' and goats’ fermented milk (EFM and GFM, respectively) over 21 days at 4 °C; technological feasibility for probiotic fermented milk production was shown. In EFM, all co-cultures presented high viable cell numbers (>7.0 log cfu mL⁻¹) throughout storage, presenting faster acidification capacities and higher CLA isomer levels than in GFM. Inulin had no impact on probiotic growth, yet contributed to storage stability. CLA isomers and proteolysis indices were co-culture dependent traits: for example, co-culture of Bifidobacterium animalis B94 with Lactobacillus acidophilus L10 registered the best CLA-production in GFM.     

Predicting enteric methane emission of dairy cows with milk Fourier-transform infrared spectra and gas chromatography–based milk fatty acid profiles

The objective of the present study was to compare the prediction potential of milk Fourier-transform infrared spectroscopy (FTIR) for CH₄ emissions of dairy cows with that of gas chromatography (GC)–based milk fatty acids (MFA). Data from 9 experiments with lactating Holstein-Friesian cows, with a total of 30 dietary treatments and 218 observations, were used. Methane emissions were measured for 3 consecutive days in climate respiration chambers and expressed as production (g/d), yield (g/kg of dry matter intake; DMI), and intensity (g/kg of fat- and protein-corrected milk; FPCM). Dry matter intake was 16.3 ± 2.18 kg/d (mean ± standard deviation), FPCM yield was 25.9 ± 5.06 kg/d, CH₄ production was 366 ± 53.9 g/d, CH₄ yield was 22.5 ± 2.10 g/kg of DMI, and CH₄ intensity was 14.4 ± 2.58 g/kg of FPCM. Milk was sampled during the same days and analyzed by GC and by FTIR. Multivariate GC-determined MFA–based and FTIR-based CH₄ prediction models were developed, and subsequently, the final CH₄ prediction models were evaluated with root mean squared error of prediction and concordance correlation coefficient analysis. Further, we performed a random 10-fold cross validation to calculate the performance parameters of the models (e.g., the coefficient of determination of cross validation). The final GC-determined MFA–based CH₄ prediction models estimate CH₄ production, yield, and intensity with a root mean squared error of prediction of 35.7 g/d, 1.6 g/kg of DMI, and 1.6 g/kg of FPCM and with a concordance correlation coefficient of 0.72, 0.59, and 0.77, respectively. The final FTIR-based CH₄ prediction models estimate CH₄ production, yield, and intensity with a root mean squared error of prediction of 43.2 g/d, 1.9 g/kg of DMI, and 1.7 g/kg of FPCM and with a concordance correlation coefficient of 0.52, 0.40, and 0.72, respectively. The GC-determined MFA–based prediction models described a greater part of the observed variation in CH₄ emission than did the FTIR-based models. The cross validation results indicate that all CH₄ prediction models (both GC-determined MFA–based and FTIR-based models) are robust; the difference between the coefficient of determination and the coefficient of determination of cross validation ranged from 0.01 to 0.07. The results indicate that GC-determined MFA have a greater potential than FTIR spectra to estimate CH₄ production, yield, and intensity. Both techniques hold potential but may not yet be ready to predict CH₄ emission of dairy cows in practice. Additional CH₄ measurements are needed to improve the accuracy and robustness of GC-determined MFA and FTIR spectra for CH₄ prediction.