Processing Characteristics Of Milk Research Articles

Review: Genetic and protein variants of milk caseins in goats.

The milk casein genes in goats, are highly polymorphic genes with numerous synonymous and non-synonymous mutations. So far, 20 protein variants have been reported in goats for alpha-S1-casein, eight for beta-casein, 14 for alpha-S2-casein, and 24 for kappa-casein. This review provides a comprehensive overview on identified milk casein protein variants in goat and non-coding DNA sequence variants with some affecting the expression of the casein genes. The high frequency of some casein protein variants in different goat breeds and geographical regions might reflect specific breeding goals with respect to milk processing characteristics, properties for human nutrition and health, or adaptation to the environment. Because protein names, alongside the discovery of protein variants, go through a historical process, we linked old protein names with new ones that reveal more genetic variability. The haplotypes across the cluster of the four genetically linked casein genes are recommended as a valuable genetic tool for discrimination between breeds, managing genetic diversity within and between goat populations, and breeding strategies. The enormous variation in the casein proteins and genes is crucial for producing milk and dairy products with different properties for human health and nutrition, and for genetic improvement depending on local breeding goals.

Short communication: Diets supplemented with starch and corn oil, marine algae, or hydrogenated palm oil differently affect selected metabolite concentrations in cow and goat milk

The objective was to investigate the effects of species (cow vs. goat) and of various dietary lipid supplements, known to modulate milk fat content, on selected metabolites and enzymes in milk and to explore their correlations with performance traits. Twelve Holstein cows and 12 Alpine goats, all multiparous and nonpregnant, and at 86 ± 24.9 and 61 ± 1.8 DIM, respectively, were fed a basal diet (45% forage + 55% concentrate) not supplemented (CTL) or supplemented with corn oil plus wheat starch [COS, 5% of diet dry matter (DM)], marine algae powder (MAP, 1.5% of diet DM), or hydrogenated palm oil (HPO, 3% of diet DM) in a replicated 4 × 4 Latin square design with 28-d experimental periods. Intake, milk production and composition, milk fatty acid profile, and plasma metabolite concentrations were previously reported. Concentrations of 9 milk metabolites [β-hydroxybutyrate (BHB), glucose, glucose-6-phosphate, isocitrate, choline, glutamate, urea, cholesterol, and free amino groups] and 2 milk enzyme activities (alkaline phosphatase and lactate dehydrogenase) were measured on d 24 of each experimental period. Dairy performance data showed marked species and diet effects on milk fat content. Irrespective of diet, cow milk was richer in alkaline phosphatase and glucose compared with goat milk (16 and 3 times more, respectively), whereas goat milk had greater urea and glucose-6-phosphate concentrations compared with cow milk (1.9 and 5.3 times more, respectively). In cows, COS decreased milk BHB and choline (-25 and -43%, respectively) compared with CTL, whereas no effects were observed in goats. The COS and MAP diets increased milk isocitrate compared with CTL in cows, but COS decreased isocitrate concentrations in goat milk. Milk choline was correlated with milk fat content in cows (Spearman r, rS = +0.73) and goats (rs = +0.58), and lactate dehydrogenase activity was correlated with milk somatic cell count (rs = +0.66) in cows but not in goats. We provide evidence of different milk metabolite responses according to species and diets. Metabolites and enzymes secreted in milk may be indicators of specificities of lipid metabolism among ruminant species and may contribute to a better understanding of mechanisms regulating milk fat secretion. Changes in the concentrations of some metabolites considered minor components of milk may be valuable diagnostic tools of mammary gland and animal metabolism as well as of milk processing characteristics.

Effect of reducing daily herbage allowance during early lactation on composition and processing characteristics of milk from spring-calved herds

The study investigated the effects of reducing daily herbage allowance (DHA) from 15.0 to 11.8 kg dry matter per cow (>3.5 cm post grazing sward height) to a spring-calved herd during early lactation on the composition, rennet coagulability and heat stability characteristics of milk during early lactation (EL, 29–70 days in milk, DIM), mid lactation (ML, 78–183 DIM), and late lactation (LL, 205–267 DIM). Samples of milk were taken at approximate 10 d intervals during EL and at 1–3 week intervals during ML and LL. Reducing DHA led to reductions in milk yield, milk solids yield, and concentrations of protein (∼0.22%, w/w) and casein (0.13%, w/w) during EL. Otherwise, it had little effect on milk composition or on the selected processing characteristics in ML, LL or overall lactation. Stage of lactation resulted in comparatively large changes in most compositional parameters, rennet gelation and heat stability.

Effect of heat treatment, evaporation and spray drying during skim milk powder manufacture on the compositional and processing characteristics of reconstituted skim milk and concentrate

The effects of key manufacturing steps (heat treatment, evaporation and spray drying) during the manufacture of low- and high-heat skim milk powders (SMP) on the physico-chemical and processing characteristics of milk, and concentrates of varying total solids (TS) levels prepared by reconstituting the milk powders, were evaluated. Milk heat treatment had the most pronounced effect, with an increase in severity of heat treatment from 72 °C × 15 s to 120 °C × 120 s, prior to evaporation resulting in higher heat coagulation time (HCT) at pH 6.3–6.6 and ethanol stability (ES) at pH 6.2–6.6, and a marked deterioration of rennet-induced coagulability. Increasing TS of the milk on reconstitution from 9.4 to 25% reduced HCT at pH >6.3 and ES at pH 6.6–7.0, increased ES at pH 6.2–6.4, and led to partial recovery of rennet-coagulability. The results highlight how heat treatment may be used to customise the functionality of SMP to different applications.

Processing characteristics of dairy cow milk are moderately heritable.

Milk processing attributes represent a group of milk quality traits that are important to the dairy industry to inform product portfolio. However, because of the resources required to routinely measure such quality traits, precise genetic parameter estimates from a large population of animals are lacking for these traits. Milk processing characteristics considered in the present study-rennet coagulation time, curd-firming time, curd firmness at 30 and 60 min after rennet addition, heat coagulation time, casein micelle size, and milk pH-were all estimated using mid-infrared spectroscopy prediction equations. Variance components for these traits were estimated using 136,807 test-day records from 5 to 305 d in milk (DIM) from 9,824 cows using random regressions to model the additive genetic and within-lactation permanent environmental variances. Heritability estimates ranged from 0.18 ± 0.01 (26 DIM) to 0.38 ± 0.02 (180 DIM) for rennet coagulation time; from 0.26 ± 0.02 (5 DIM) to 0.57 ± 0.02 (174 DIM) for curd-firming time; from 0.16 ± 0.01 (30 DIM) to 0.56 ± 0.02 (271 DIM) for curd firmness at 30 min; from 0.13 ± 0.01 (30 DIM) to 0.48 ± 0.02 (271 DIM) for curd firmness at 60 min; from 0.08 ± 0.01 (17 DIM) to 0.24 ± 0.01 (180 DIM) for heat coagulation time; from 0.23 ± 0.02 (30 DIM) to 0.43 ± 0.02 (261 DIM) for casein micelle size; and from 0.20 ± 0.01 (30 DIM) to 0.36 ± 0.02 (151 DIM) for milk pH. Within-trait genetic correlations across DIM weakened as the number of days between compared intervals increased but were mostly >0.4 except between the peripheries of the lactation. Eigenvalues and associated eigenfunctions of the additive genetic covariance matrix for all traits revealed that at least the 80% of the genetic variation among animals in lactation profiles was associated with the height of the lactation profile. Curd-firming time and curd firmness at 30 min were weakly to moderately genetically correlated with milk yield (from 0.33 ± 0.05 to 0.59 ± 0.05 for curd-firming time, and from -0.62 ± 0.03 to -0.21 ± 0.06 for curd firmness at 30 min). Milk protein concentration was strongly genetically correlated with curd firmness at 30 min (0.84 ± 0.02 to 0.94 ± 0.01) but only weakly genetically correlated with milk heat coagulation time (-0.27 ± 0.07 to 0.19 ± 0.06). Results from the present study indicate the existence of exploitable genetic variation for milk processing characteristics. Because of possible indirect deterioration in milk processing characteristics due to selection for greater milk yield, emphasis on milk processing characteristics is advised.

Factors associated with milk processing characteristics predicted by mid-infrared spectroscopy in a large database of dairy cows

Despite milk processing characteristics being important quality traits, little is known about the factors underlying their variability, due primarily to the resources required to measure these characteristics in a sufficiently large population. Cow milk coagulation properties (rennet coagulation time, curd-firming time, curd firmness 30 and 60 min after rennet addition), heat coagulation time, casein micelle size, and pH were generated from available mid-infrared spectroscopy prediction models. The prediction models were applied to 136,807 spectra collected from 9,824 Irish dairy cows from research and commercial herds. Sources of variation were investigated using linear mixed models that included the fixed effects of calendar month of test; milking time in the day; linear regressions on the proportion of Friesian, Jersey, Montbéliarde, Norwegian Red, and "other" breeds in the cow; coefficients of heterosis and of recombination loss; parity; stage of lactation; and the 2-way interaction parity × stage of lactation. Within- and across-parity cow effects, contemporary group, and a residual term were also included as random effects in the model. Supplementary analyses considered the inclusion of either test-day milk yield or milk protein concentration as fixed-effects covariates in the multiple regression models. Milk coagulation properties were most favorable (i.e., short rennet coagulation time and strong curd firmness) for cheese manufacturing in early lactation, concurrent with the lowest values of both pH and casein micelle size. Milk coagulation properties and pH deteriorated in mid lactation but improved toward the end of lactation. In direct contrast, heat coagulation time was more favorable in mid lactation and less suitable (i.e., shorter) for high temperature treatments in both early and late lactation. Relative to multiparous cows, primiparous cows, on average, yielded milk with shorter rennet coagulation time and longer heat coagulation time. Milk from the evening milking session had shorter rennet coagulation time and greater curd firmness, as well as lower heat coagulation time and lower pH compared with milk from the morning session. Jersey cows, on average, yielded milk more suitable for cheese production rather than for milk powder production. When protein concentration was included in the model, the improvement of milk coagulation properties toward the end of lactation was no longer apparent. Results from the present study may aid in decision-making for milk manufacturing, especially in countries characterized by a seasonal supply of fresh milk.

Prediction of individual milk proteins including free amino acids in bovine milk using mid-infrared spectroscopy and their correlations with milk processing characteristics

The aim of this study was to evaluate the effectiveness of mid-infrared spectroscopy in predicting milk protein and free amino acid (FAA) composition in bovine milk. Milk samples were collected from 7 Irish research herds and represented cows from a range of breeds, parities, and stages of lactation. Mid-infrared spectral data in the range of 900 to 5,000cm−1 were available for 730milk samples; gold standard methods were used to quantify individual protein fractions and FAA of these samples with a view to predicting these gold standard protein fractions and FAA levels with available mid-infrared spectroscopy data. Separate prediction equations were developed for each trait using partial least squares regression; accuracy of prediction was assessed using both cross validation on a calibration data set (n=400 to 591 samples) and external validation on an independent data set (n=143 to 294 samples). The accuracy of prediction in external validation was the same irrespective of whether undertaken on the entire external validation data set or just within the Holstein-Friesian breed. The strongest coefficient of correlation obtained for protein fractions in external validation was 0.74, 0.69, and 0.67 for total casein, total β-lactoglobulin, and β-casein, respectively. Total proteins (i.e., total casein, total whey, and total lactoglobulin) were predicted with greater accuracy then their respective component traits; prediction accuracy using the infrared spectrum was superior to prediction using just milk protein concentration. Weak to moderate prediction accuracies were observed for FAA. The greatest coefficient of correlation in both cross validation and external validation was for Gly (0.75), indicating a moderate accuracy of prediction. Overall, the FAA prediction models overpredicted the gold standard values. Near-unity correlations existed between total casein and β-casein irrespective of whether the traits were based on the gold standard (0.92) or mid-infrared spectroscopy predictions (0.95). Weaker correlations among FAA were observed than the correlations among the protein fractions. Pearson correlations between gold standard protein fractions and the milk processing characteristics of rennet coagulation time, curd firming time, curd firmness, heat coagulating time, pH, and casein micelle size were weak to moderate and ranged from −0.48 (protein and pH) to 0.50 (total casein and a30). Pearson correlations between gold standard FAA and these milk processing characteristics were also weak to moderate and ranged from −0.60 (Val and pH) to 0.49 (Val and K20). Results from this study indicate that mid-infrared spectroscopy has the potential to predict protein fractions and some FAA in milk at a population level.

Effect of shortening or omitting the dry period of Holstein-Friesian cows on casein composition of milk

The aim of this study was to evaluate the effect of shortening or omitting the dry period of dairy cows on milk casein composition. For this study, we analyzed milk samples of 90 cows with a dry period of 0, 30, or 60d and either a glucogenic or a lipogenic ration in early lactation. Milk was sampled at 6 and 2wk prepartum and at 2, 6, and 12wk postpartum. Milk was analyzed for casein (CN) composition by capillary zone electrophoresis, and isoforms of κ-CN were measured by reversed phase-HPLC. Shortening the dry period from 60 to 30d reduced the αS1-CN fraction by 3.8% and increased the αS2-CN fraction by 5.5%. In milk from cows with a 0-d dry period, the glycosylated κ-CN fraction in late lactation increased from 8 to 12% between 6 and 2wk prepartum. After calving, the glycosylated κ-CN fraction in milk was higher for cows with a 0-d dry period (6.7%) compared with cows with a 60-d dry period (5.2%). The glycosylated κ-CN fraction at 2wk postpartum was negatively correlated with milk yield, suggesting that glycosylation was related to reduced productivity of mammary epithelial cells. In early lactation, the β-CN fraction was reduced in milk of cows with a 0-d dry period. A lowered β-CN fraction was associated with high somatic cell count and greater parity, indicating that it was the result of proteolytic activity. In conclusion, casein composition changes that result from shortening the dry period from 60 to 30d are not expected to affect processing characteristics of milk. Applying a 0-d dry period may affect processability of milk because of a higher glycosylated κ-CN fraction, and possibly because of higher proteolytic activity compared with a 60-d dry period.

Naturally occurring variations in milk pH and ionic calcium and their effects on some properties and processing characteristics of milk

Considerable variations were found for ionic calcium and pH in milk from individual cows. Milk with lower pH tended to have a higher Ca2+ concentration, although the relationship was weak. Milk samples with a higher Ca2+ concentration and lower pH produced less sediment during in‐container sterilisation, which was contrary to expectations. Rennet coagulation time was lower for milk with a higher Ca2+ concentration, but curd firmness was not related to Ca2+ concentration. There was a poor correlation between the pH reduction caused by acid addition and that resulting from increasing temperature. Sediment formation was related to pH change at high temperature.

The effect of spring shearing on milk yield and milk composition in Tsigai ewes

Milk yield and milk composition responses to shearing were assessed in Tsigai ewes kept indoors. Sheep was offered 700g/head daily concentrate and chopped hay administered ad libitum and was milked twice daily - at 08:00 and at 18:00 h. Average for the two weeks post-shearing, daily milk yield dropped by 7.2 % due to the 8.2 and 2.2 %, respectively, reduction in the morning and in the afternoon milk yields. Fat and protein concentrations in the morning and in the afternoon milk on day 1, day 7 and day 14 after shearing surpassed vastly pre-shearing values whilst milk lactose concentration showed a trend towards postshearing reduction. On the three sampling post-shearing days daily output of different milk constituents exceeded the corresponding mean pre-shearing values by 16.2, 11.6 and 9.1 % in milk fat, 1.6, 3.5 and 6.2 % in milk protein, and 4.1, 7.2 and 2.2 % in total solids. The increase in daily output of milk constituents occurred despite the decline in daily milk yield. Lactose daily output, on the contrary, dropped by 6.9, 7.7 and 9.3 % relative to the mean pre- shearing value. Postshearing adaptive adjustments including changes in nutrient partitioning appear to underlie the alterations in milk yield and milk composition. It may be concluded that post-shearing changes in milk composition makes for the improvement of milk processing characteristics.

Variation of Milk Citrate with Stage of Lactation and De Novo Fatty Acid Synthesis in Dairy Cows

Citrate is a normal constituent of milk that affects milk-processing characteristics. It is an intermediate in the tricarboxylic acid cycle and plays an indirect role in fat synthesis by providing reducing equivalents in the form of NADPH. The objective of this study was to investigate variation in citrate with stage of lactation and de novo fatty acid synthesis, without confounding dietary effects. Twenty-four cows were fed the same diet, and milk citrate and fatty acids were determined over a 10-d period. Eight cows were in early lactation [13±1.8 d in milk (DIM; mean ±standard error], 8 in midlactation (130 ±4.6 DIM), and 8 in late lactation (283 ±3.4 DIM). For cows in early, mid, and late lactation, milk yield was 34.4, 34.4, and 21.4 L/d [standard error of difference (SED) 1.78]; milk fat was 50.4, 40.3, and 41.4g/L (3.68); milk citrate was 11.3, 9.7, and 10.1 mmol/L (0.64); the ratio of 4–14C:18–20C fatty acids was 0.9, 1.3, and 1.2 (0.07). Activity of the fatty acid synthase enzyme system (EC 2.3.1.85) was calculated as acetate used for chain elongation (ACE); ACE (mol/d) for cows in early, mid, and late lactation, was 7.3, 11.1, and 8.1 (SED 1.05). For individual cows, citrate (mmol/L) = 14.3 − 0.44 ×ACE (r2 = 0.58). We propose that ACE provides a more accurate indication of synthase activity than do fatty acid ratios or yields. This study confirms the hypothesis that variation in milk citrate with stage of lactation is related to de novo synthesis of fatty acids and that the relationship is independent of diet and milk yield.

Dissociation of caseins in high pressure-treated bovine milk

In this study, reversibility of high pressure (HP)-induced solubilisation of alpha(s1)- and beta-casein and HP-induced changes in micellar hydration and levels of ultracentrifugally-sedimentable solids in raw skim milk were examined. HP treatment of milk at 100-600MPa resulted in considerable solubilisation of alpha(s1)- and beta-caseins, with the extent of solubilisation reaching a maximum around 250 MPa. HP-induced solubilisation of caseins was probably a result of solubilisation of colloidal calcium phosphate and disruption of hydrophobic interactions. On storage of HP-treated milk at 5degreesC, dissociation of caseins was largely irreversible but at 20degreesC, considerable reassociation of caseins was observed. Hydration of the casein micelles was increased by HP treatment at 100600 MPa, possibly due to HP-induced interactions between caseins and whey proteins; these changes were more extensive at higher pressures. The level of ultracentrifugally sedimentable solids was reduced by HP treatment, with a minimum occurring at 250 MPa; Changes in micellar hydration and the level of ultracentrifugally sedimentable solids were largely irreversible at 5degreesC, but partially reversible at 20degreesC. These results indicate that HP treatment increases levels of alpha(s1)- and beta-caseins in the soluble phase of milk and produces casein micelles with different properties compared to those in untreated milk; therefore, HP treatment may have a considerable influence on the processing characteristics of milk. (C) 2004 Elsevier Ltd. All rights reserved.

The Hannah Research Institute

The Hannah Research Institute, founded in 1928 to undertake research into milk production and milk utilisation, is situated close to the town of Ayr, Scotland. It is administered through the Department of Agriculture and Fisheries for Scotland, Edinburgh, and the Agricultural Research Council advises on the programme of work. There are currently three main areas of research: (i) the efficient production and utilization of feed nutrients for milk production, (ii) the chemistry and physical chemistry of milk constituents, especially protein, in relation to the nutritive role and processing characteristics of milk, and (iii) the effect of environment on the physiology of cattle.