Milk Somatic Cells and Lactation in Small Ruminants

The milk somatic cell count (MSCC) is the basis for abnormal milk control programs. The current legal MSCC limit for bulk tank milk for goats and sheep in the United States is 1000 and 750 × 10³/ml, respectively. Milk somatic cell counts for goats are higher than MSCC for cows and sheep. The MSCC for goats free from intramammary infection (IMI) range from 270 to 2,000 × 10³/ml. Cell counts for sheep are similar to cows and range from 10 to 200 × 10³/ml. Neutro-phils comprise the major cell type in milk from uninfected goats and constitute 45 to 74% of the MSCC, compared with 2 to 28% for sheep and cows. The macrophage is the major cell type in milk from cows and sheep. Milk secretion in goats and sheep is largely apocrine in nature and cytoplasmic particles, similar in size to milk somatic cells, are normal constituents of their milk. Concentrations of cytoplasmic particles in sheep milk average 15 × 10³/ml, while goat milk averages 150 × 10³/ml. Therefore, to obtain accurate MSCC for goats, only cell counting procedures specific for DNA should be used. While IMI significantly increases MSCC for goats and sheep, noninfectious factors such as parity, stage of lactation, season and milk yield have been related to increased MSCC. An increase in MSCC for goats has been shown to decrease milk and fat yields. Intramammary infusion of antibiotics at dry-off and postmilking teat dipping in goats decreased the rate of new IMI and MSCC. Thus, mastitis control practices shown to be efficacious in cows are also effective in goats.     

Compositional profile of ovine milk with a high somatic cell count: A metabolomics approach

Ovine milk (Sarda breed) with high somatic cell count (SCC) (>1 × 10⁶ cell mL⁻¹) was compared with similar milk of low SCC (<150 × 10³ cell mL⁻¹) using a metabolomics approach, whereby the metabolite profile of milk was studied by gas chromatography coupled to mass spectrometry. Discriminant analysis indicated that high SCC milk samples have metabolite profiles from those of low SCC samples. Malic acid, ribitol, glucose and medium-short chain fatty acids were up-regulated in milk with high SCC, while stearic acid, oleic acid, scyllo-inositol, glutamine, threonine, and glycine were down-regulated. These differences may be related to metabolite release by somatic cells, inflammation status, altered permeability of the udder tight junctions, and changes in milk osmotic equilibrium. Moreover, high SCC milk samples showed higher levels of proteins, casein and fat, lower concentrations of lactose and urea, and a different fatty acid profile from that of low SCC milk.     

Somatic cell recovery by microfiltration technologies: A novel strategy to study the actual impact of somatic cells on cheese matrix

The actual impact of the somatic cells in the dairy technology is still ill-defined, because the increase in milk somatic cell count, usually correlated with mastitis factors, impairs the raw milk composition, through mainly unwanted proteolysis and lipolysis. This study used microfiltration technologies for recovering high quantity of somatic cells and for clarifying their role in cheese quality. Three series of Swiss-type cheeses were manufactured by adding 0 (control), 4 × 10⁵ and 9 × 10⁵ somatic cells mL⁻¹. These cells were traced for the first time during the cheese making process by using adapted flow cytometry and real-time quantitative PCR. Proteolysis and lipolysis indices were measured throughout ripening time. Only a weak increase in lipolysis (+28%) and proteolysis (+8%) was observed in the highest somatic cell count cheese, despite 73% of the cells trapped within the cheeses. Our approach gives a new view of somatic cell role in cheese milk alteration.     

Development of an immunomagnetic separation–propidium monoazide–polymerase chain reaction assay with internal amplification control for rapid and sensitive detection of viable Escherichia coli O157:H7 in milk

A rapid, reproducible, sensitive and specific combination assay was developed for Escherichia coli O157:H7 comprising sequential immunomagnetic separation (IMS), followed by propidium monoazide (PMA), exclusion by viable cells, internal amplification control (IAC) and polymerase chain reaction (PCR). IMS was used to improve sensitivity, reduce detection time and eliminate false positives. PMA was used to detect viable cells, and IAC was incorporated into the system to eliminate the inhibitors of PCR from the food matrix. In the presence of inhibitors, IAC produced no signal, thereby eliminating false negative results. The results indicated that the IMS cell capture efficiency was about 90% at a concentration of 1 × 10⁶ cfu mL⁻¹ with a detection limit of 2.1 × 10² cfu mL⁻¹ for pure culture. In an unoptimised system, IMS–PMA–PCR with IAC showed a detection limit of 5 × 10³ cfu mL⁻¹ in spiked milk over a 240 min assay, faster than conventional methods of detection.     

Immunomodulatory activities of Lactobacillus rhamnosus ZDY114 and donkey milk in BALB/c mice

The immunomodulatory activity of Lactobacillus rhamnosus ZDY114 and donkey milk in BALB/c mice was evaluated by assessing the splenic lymphocyte transformation, haemolytic complement activity, carbon clearance ability and natural killer cell activity. Results showed donkey milk (5 g kg⁻¹) in combination with L. rhamnosus ZDY114 (5 × 10⁷ cfu mL⁻¹) exhibited a significant increase in splenic lymphocyte proliferation, carbon granule engulfing ability and natural killer cell activity when compared with donkey milk or L. rhamnosus ZDY114 alone (p < 0.05). An elevated response in serum haemolytic activity was only observed when compared with L. rhamnosus ZDY114. In conclusion, donkey milk (5 g kg⁻¹) in combination with L. rhamnosus ZDY114 (5 × 10⁷ cfu mL⁻¹) was able to enhance specific immune functions.     

HPLC of proteose peptones for evaluating ageing of packaged pasteurized milk

The proteolysis of casein (CN) occurring in packaged pasteurized milk (PM) during refrigerated storage was studied with relation to hygienic and microbiological characteristics of starting raw milk. Six batches of raw milk having standard plate count (SPC) from 1.5×10⁴ to 2.5×10⁵ cfu mL⁻¹ and somatic cell count (SCC) from 1.6×10⁵ to 4.4×10⁵ units mL⁻¹ were pasteurized (73 °C for 15 s), packaged and stored at 4 °C for 12 days. Capillary zone electrophoresis of CN showed breakdown of β-CN in all PM samples during storage. An HPLC method for monitoring proteose peptones (PP) formation was developed. Level of PP in PM samples increased, with keeping time from 667–789 to 947–1383 mg L⁻¹ and PP formation was significantly (P<0.05) related to SCC of starting raw milk. Electrospray ionization–mass spectrometry showed that PP were mainly represented by PP-5 from either A¹ or A² variants of β-CN. Five commercial samples of PM were analysed for PP formation during 14-day storage at 4 °C. Commercial samples prepared by microfiltration process or bactofugation combined with pasteurization showed the slowest formation of PP. The effect of storage temperature on PP formation was evaluated by keeping a conventional PM sample at either 8 or 12 °C for 12 days. Proteolysis of all major CNs upon action of plasmin and bacterial proteinases was observed under these conditions. PP level thus proves to be a reliable analytical index for evaluating the ageing of packaged PM during refrigerated storage.     

Evaluation of pulsed electric field and minimal heat treatments for inactivation of pseudomonads and enhancement of milk shelf-life

Pulsed Electric Field (PEF) treatment of milk provides the opportunity to increase the shelf-life of fresh milk for distribution to distant markets. PEF treatments were evaluated in sterile (UHT) milk to determine the inactivation of added spoilage Pseudomonas isolates and the subsequent gains in microbial shelf-life (time taken to reach 10⁷ CFU mL^− 1). Little inactivation of Pseudomonas was achieved at 15 or 40 °C compared with 50 or 55 °C. The greatest inactivation (> 5 logs) was achieved by processing at 55 °C with 31 kV cm^− 1 (139.4 kJ L^− 1). Heat treatment at the application temperature without PEF treatment caused minimal inactivation of Pseudomonas (only 0.2 logs), demonstrating that the inactivation of the Pseudomonas was due to the PEF treatment rather than the heat applied to the milk. At added Pseudomonas levels of 10³ and 10⁵ CFU mL^− 1, the microbial shelf-life of PEF-treated milk was extended by at least 8 days at 4 °C compared with untreated milk. The total microbial shelf-life of the PEF-treated milk was 13 and 11 days for inoculation levels of 10³ and 10⁵ CFU mL^− 1 respectively. The results indicate that PEF treatment is useful for the reduction of pseudomonads, the major spoilage bacteria of milk.Industrial relevancePseudomonads are the major psychrotrophic spoilage microflora of refrigerated, stored HTST pasteurised milk. Long-life (UHT) products are an important component of milk sales in South-East Asia, but in recent years there has been an increasing demand for less processed milk products with extended shelf-life. The recent practice of shipping fresh bulk milk from Australia to South-East Asian countries has necessitated additional heat treatment prior to export and on arrival, to achieve the required shelf-life. Pulsed electric field treatment of HTST milk, applied alone or in combination with mild heat under optimised conditions, offers the opportunity of shelf-life extension, while limiting the reduction in quality attributes of milk associated with more severe additional heat treatments.     

Quantification of major camel milk proteins by capillary electrophoresis

Proteins from dromedary camel milk (CM) produced in Europe were separated and quantified by capillary electrophoresis (CE). CE analysis showed that camel milk lacks β-lactoglobulin and consists of high concentration of α-lactalbumin (2.01 ± 0.02 mg mL⁻¹), lactoferrin (1.74 ± 0.06 mg mL⁻¹) and serum albumin (0.46 ± 0.01 mg mL⁻¹). Among caseins, the concentration of β-casein (12.78 ± 0.92 mg mL⁻¹) was found the highest followed by α-casein (2.89 ± 0.29 mg mL⁻¹) while κ-casein represented only minor amount (1.67 ± 0.01 mg mL⁻¹). These results were in agreement with sodium dodecyl sulphate-polyacrylamide gel electrophoresis patterns. Overall, CE offers a quick and reliable method for the determination of major CM proteins, which may be responsible for the many nutritional and health properties of CM.     

Effectiveness of mid-infrared spectroscopy for prediction of the contents of calcium and phosphorus,and titratable acidity of milk and their relationship with milk quality and coagulation properties

Individual milk samples from Holstein Friesian cows were collected and analysed by inductively coupled plasma optical emission spectrometry (ICP-OES) and titration for the determination of calcium (Ca), phosphorus (P) and titratable acidity (TA) contents, respectively. Prediction models were obtained using partial least squares (PLS) regression analyses using two statistical packages. The average Ca, P and TA were 1156 mg kg⁻¹, 934 mg kg⁻¹ and 3.42 °SH 50 mL⁻¹, respectively. Pearson's correlations between Ca and P and other milk traits were significant (P < 0.05) and ranged from 0.16 to 0.53 for chemical composition traits and from 0.17 to −0.35 for milk coagulation properties (MCP). Results from the two statistical packages were comparable. Prediction models using MIR spectroscopy were satisfactory for Ca, P and TA, with coefficients of correlation of cross-validation greater than 0.73. Moreover, the study highlighted favourable relationships of these traits with milk coagulation properties.     

Tailpipe greenhouse gas emissions from tank trucks transporting raw milk from farms to processing plants

An analysis of greenhouse gas emissions (carbon dioxide equivalents, CO₂e) was conducted from 2007 databases for 211,216 round trips of tank trucks that delivered raw milk from farms to processing plants in the United States of America. The total amount of milk was 4.81 × 10⁹ kg, or about 17.4% of the 2007 total USA production for use as fluid milk products. Average round trip distance was 850 km resulting in tailpipe emissions of 0.050 kg CO₂e kg⁻¹ milk delivered or 0.071 kg CO₂e kg⁻¹ milk consumed representing 3.5% of the total greenhouse gas emissions for fluid milk consumed. Based on this we estimate the total emissions for fluid milk delivery from farm to processor in the US at 1.3 × 10⁹ kg CO₂e y⁻¹. Some overall reduction in total delivery distance could be realized by realigning farm-to-processor relationships, especially in regions where farms are equally distant from multiple processors.     

Impact of β-glucan on debittering,bioaccessibility and storage stability of skim milk fortified with shrimp oil nanoliposomes

Shrimp oil was encapsulated in nanoliposomes and fortified into skim milk. Shrimp oil nanoliposomes (SONL) were thermodynamically stable when added into skim milk at 10 mL 100 mL⁻¹. Mild bitterness in fortified skim milk caused by the SONL was masked by adding β-glucan at various levels (0.05–0.2 g 100 mL⁻¹). With the addition of SONL, fortified skim milk appeared more reddish in colour due to the presence of astaxanthin. Addition of β-glucan resulted in the increase in viscosity of the fortified milk by forming network of junction zones. During the storage of skim milk fortified with SONL and 0.1 g 100 mL⁻¹ β-glucan at 4 °C for 15 days, no major quality changes took place. Simulated in vitro digestion studies revealed that 45.41 g 100 g⁻¹ eicosapentaenoic acid (EPA) and 48.86 g 100 g⁻¹ docosahexaenoic acid (DHA) from shrimp oil were bioaccessible for absorption in the gut after digestion.     

Supercritical fluid extrusion: Die design and physicochemical properties of milk protein extrudates

Extrusion processing has been used to modify the functional properties of proteins. The protein-protein interactions, surface hydrophobicity, and rheological properties of milk protein concentrate extruded using dies of different geometries (circular, annular and slit) were quantified. With the same extrusion treatment history prior to the die, extrudates generated using dies with higher wall shear (slit 1.4 × 10⁴ s⁻¹ > annular 1.1 × 10⁴ s⁻¹ > circular 2.9 × 10³ s⁻¹) showed greater protein extractability, higher index of surface hydrophobicity, and enhanced water solubility index indicating significant breakdown of protein aggregates. Higher viscoelastic moduli (G' and G") and apparent viscosity were observed for slit die extrudate dispersions. However, low flow behavior indices (0.04–0.23(−)) and a high viscous activation energy (43 kJ/mol) of slit die extrudate dispersions implied their shear and temperature sensitivity, respectively. Thus, extrudate functionality can be optimized by selection of the appropriate die design.     

Alkaline phosphatase and microbial inactivation by pulsed electric field in bovine milk

The effects of pulsed electric field (PEF) treatments at field intensities of 25–37 kV cm^− 1 and final PEF treatment temperatures of 15 °C and 60 °C on the inactivation of alkaline phosphatase (ALP), Total Plate Count (TPC), Pseudomonas and Enterobacteriaceae counts were determined in raw skim milk. At 15 °C, PEF treatments of 28 to 37 kV cm^− 1 resulted in 24–42% inactivation in ALP activity and < 1 log reduction in TPC and Pseudomonas count, while the Enterobacteriaceae count was reduced by at least 2.1 log units to below the detection limit of 1 CFU mL^− 1. PEF treatments of 25 to 35 kV cm^− 1 at 60 °C resulted in 29–67% inactivation in ALP activity and up to 2.4 log reduction in TPC, while the Pseudomonas and Enterobacteriaceae counts were reduced by at least 5.9 and 2.1 logs, respectively, to below the detection limit of 1 CFU mL^− 1. Kinetic studies suggested that the effect of field intensity on ALP inactivation at the final PEF treatment temperature of 60 °C was more than twice that at 15 °C. A combined effect was observed between the field intensity and temperature in the inactivation of both ALP enzyme and the natural microbial flora in raw skim milk.Industrial relevanceMilk has been pasteurised to ensure its safety and extend its shelf life. However, the need for retaining heat-sensitive nutrient and sensory properties of milk has resulted in interest in the application of alternative technologies. The results of the current study suggest that PEF as a non-thermal process can be employed for the treatment of raw milk in mild temperature to achieve adequate safety and shelf life while preserving the heat-sensitive enzymes, nutrients and bioactive compounds.     

我国生牛乳菌落总数和体细胞数调查及其影响因素分析

目的调查我国生牛乳菌落总数和体细胞数情况,分析养殖模式与区域等因素对我国生牛乳菌落总数和体细胞数的影响。方法对17个省(市、自治区)2014—2015年连续12个月共17 527份生牛乳样品菌落总数的数据和6 633份体细胞数的数据进行研究,采用SPSS 19.0的Kruskal-Wallis秩和检验分析养殖模式和养殖区域对生牛乳菌落总数和体细胞数的影响。结果我国生牛乳中的菌落总数、体细胞数的平均值分别为3.27×10~5CFU/ml、46.0万个/ml。来自牧场、养殖小区、散户的生牛乳样品菌落总数的中位数分别为1.00×10~5、1.85×10~5、2.37×10~5CFU/ml,体细胞数的中位数分别为35.0万、73.0万、59.1万个/ml;东北内蒙古产区、华北产区、南方产区、大城市周边产区、西部产区生牛乳菌落总数的中位数分别为2.40×10~5、1.43×10~5、1.50×10~5、1.60×10~5、2.14×10~5CFU/ml,体细胞数的中位数分别为57.2万、33.0万、38.2万、56.0万、40.0万个/ml。结论生牛乳的菌落总数99%以上均可达到我国现行标准的要求,标准对菌落总数的要求有进一步提升的空间。来自大规模牧场的生牛乳菌落总数和体细胞数均较低。     

Contribution of proteolytic activity associated with somatic cells in milk to cheese ripening

The effect of proteolytic enzymes from somatic cells on cheese quality was studied. In preliminary experiments, milk and two sodium caseinate systems (pH 6.5 and pH 5.2, the latter in the presence of 5% NaCl) were used as substrates to investigate the proteolytic activity of somatic cells recovered from mastitic milk. Urea-polyacrylamide gel electrophoretograms of hydrolysates suggested that somatic cell extracts contributed directly to proteolysis both in buffer and in milk, but that such activity was reduced by batch pasteurisation (63 °C for 30 min). Sodium caseinate was readily hydrolysed by somatic cell extracts; hydrolysis of α_s1-casein was greater at pH 5.2 and increased with level of somatic cells, suggesting that somatic cells contain proteolytic enzymes which are more active at acidic pH values. Subsequently, miniature Cheddar-type cheeses were made from batches of milk to which somatic cells were added (at levels of levels of 3×10⁵ or 6×10⁵ cells mL⁻¹), either before or after pasteurisation. Proteolysis during ripening of cheese (as measured by levels of pH 4.6-soluble nitrogen) increased with somatic cell addition, although this effect was reduced by pasteurisation after cell addition. Somatic cells may also have directly influenced cheese moisture content, which has been established as a principal indicator of quality of Cheddar-type cheese. Proteolytic enzymes of somatic cells from milk were shown to contribute directly to proteolysis in milk and cheese.     

Modelling Bacillus cereus adhesion on stainless steel surface as affected by temperature,pH and time

The adhesion of Bacillus cereus to stainless steel was modelled as a function of pH (4.0–8.0), time (2–24 h) and temperature (4.0–36.0 °C) using response surface methodology. Based on the initial inoculum (3 or 6 log cfu mL⁻¹), two equations describing B. cereus adhesion to stainless steel were obtained. The results indicated that B. cereus was able to reach up to 5.5 cfu cm⁻² and 6.4 cfu cm⁻² when the initial inocula were 3 log cfu mL⁻¹ and 6 log cfu mL⁻¹, respectively. The significance of the factors varied with the model; i.e., inoculum of 3 or 6 log cfu mL⁻¹. Bias and accuracy factors showed that the models are adequate to predict B. cereus adhesion to stainless steel surface under conditions assessed and to assess the adhesion of B. cereus under a range of conditions to which this microorganism can be exposed during either milk processing or cleaning procedures.     

Effects of somatic cell counts in milk on physical and chemical characteristics of yoghurt

The quality of plain stirred yoghurt produced from whole milk with somatic cell counts (SCC) at low (147,000 cells mL⁻¹), intermediate (434,000 cells mL⁻¹) and high (1,943,000 cells mL⁻¹) levels was examined. Each milk treatment was obtained from selected cows, according to its SCC status and milk composition. Yoghurt samples were analysed on days 1, 10, 20 and 30 after production. Analyses included pH, acidity, fat, lipolysis (expressed as free fatty acids, FFA), proteolysis and apparent viscosity. Viscosity of high SCC yoghurt was higher (P<0.05) than the low SCC yoghurt on days 10, 20 and 30 of storage. High SCC yoghurt also had higher FFA content (P<0.05). SCC did not affect pH, acidity, fat content and proteolysis of the yoghurt (P>0.05). Results indicate that SCC in milk increases the lipolysis in the resulting yoghurt during storage for 30 d.     

Influence of ammonia and lysine supplementation on yeast growth and fermentation with respect to gluten-free type brewing using unmalted sorghum grain

Because gluten-free type brewing with unmalted sorghum does not provide adequate nitrogen for complete fermentation, wort supplementation with ammonia (as diammonium phosphate, DAP) or lysine on yeast performance was investigated. By Phenotype Microarray, under aerobic conditions, greater yeast growth was indicated with DAP than lysine both as a single source and combined with sorghum wort amino acids. With sorghum fermentation, both DAP and lysine improved maltose and maltotriose uptake. However, DAP supplementation also maintained yeast numbers (24.0–21.3 × 10⁶ cells mL⁻¹), whereas there was a decline with lysine supplementation. Lysine supplementation also resulted in adverse effects on yeast cell morphology. Neither DAP nor lysine supplementation resulted in evident genetic change to the yeast, but the change in substrate from barley malt wort to unmalted sorghum wort slightly altered the yeast genetically. Therefore, ammonia as DAP has potential as a nitrogen supplement for improving yeast fermentation performance in sorghum gluten-free brewing.     

Microbiological quality of bulk tank raw milk in Prince Edward Island dairy herds

The objectives of this study were to evaluate microbiological quality of bulk tank milk in Prince Edward Island, to evaluate correlation among milk quality criteria, and to determine seasonal effects on milk quality parameters. Bulk tank raw milk quality was evaluated on all Prince Edward Island dairy herds (n = 235) over a 2-yr period (March 2005 to March 2007). Biweekly total aerobic (TAC), preliminary incubation (PIC), laboratory pasteurization, and coliform (CC) counts were determined using a Petrifilm culture system. Additionally, bulk tank somatic cell count was determined weekly. The mean and median values were 12.8 × 10³ and 4.9 × 10³ cfu/mL for TAC, 29.6 × 10³ and 13 × 10³ cfu/mL for PIC, 87 and 12 cfu/mL for laboratory pasteurization count, 21 and 5 cfu/mL for CC, and 218 × 10³ and 187 × 10³ cells/mL for somatic cell count. There was moderate correlation (0.57) between TAC and PIC. All other correlation coefficients were low (<0.26). Correlation results suggest that a single quality parameter could not predict others used in this study. Seasonal data indicate that 1) in general, all counts tended to be low in winter, 2) the CC and somatic cell count were always high in summer, and 3) TAC tended to be high during summer.     

Fate of enterotoxigenic Staphylococcus aureus in the presence of nisin-producing Lactococcus lactis strain during manufacture of Jben,a Moroccan traditional fresh cheese

The inhibitory effect of nisin-producing Lactococcus lactis subsp. lactis UL730 on the growth of enterotoxigenic Staphylococcus aureus J10 during manufacture of Jben, a Moroccan traditional fresh cheese prepared from recombined milk, was investigated.With an inoculum level of 10³ cfu mL⁻¹, S. aureus was absent in Jben four days after inoculation when the nisin-producing lactococcus was used as lactic starter. In contrast, it survived after that period, when the starter was non-nisin-producing. No staphylococcal thermonuclease was detected in all Jben samples made from milk inoculated with S. aureus at the level of 10³ cfu mL⁻¹.With a higher inoculum of 10⁵ cfu mL⁻¹, S. aureus was still present in Jben after manufacture and persisted during the storage of the product for 3 days in the laboratory, even when the starter used was nisin-producing. Staphylococcal thermonuclease and type C enterotoxin were detected in all Jben samples made from milk inoculated with 10⁵ cfu mL⁻¹. Thermonuclease and enterotoxin were already produced in the coagulum, at 24 h after milk inoculation with S. aureus.