Observations on the influence of high cell count on lipolysis in bovine milk

Ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry MSE-based untargeted milk metabolomics in dairy cows with subclinical or clinical mastitis

In this study, a novel metabolomics technique based on ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry in the MS^E mode was used to investigate the milk metabolomics of healthy, subclinical, and clinical mastitis cows, which were classified based on somatic cell count and presentation of clinical symptoms. Meanwhile, univariate and multivariate statistical analyses were performed to identify the significant differences across the 3 groups. Compared with healthy milk samples, less glucose, d-glycerol-1-phosphate, 4-hydroxyphenyllactate, l-carnitine, sn-glycero-3-phosphocholine, citrate, and hippurate were detected in the clinical mastitic milk samples, whereas less d-glycerol-1-phosphate, benzoic acid, l-carnitine, and cis-aconitate were found in the subclinical mastitic milk samples. Meanwhile, the milk concentration of arginine and Leu-Leu increased in both the clinical and subclinical mastitis groups. Besides, less 4-hydroxyphenyllactate, cis-aconitate, lactose, and oxoglutarate were detected in the clinical than the subclinical mastitic milk samples, whereas the abundance of some oligopeptides (Leu-Ala, Phe-Pro-Ile, Asn-Arg-Ala-Ile, and Val-Phe-Val-Tyr) increased by over 7.95-fold. Our results suggest that significant variations exist across healthy and mastitis cows. The current metabolomics approach will help in better understanding the pathobiology of mastitis, although clinical validation will be required before field application.

Analysis of raw milk quality at reception and during cold storage: combined effects of somatic cell counts and psychrotrophic bacteria on lipolysis

The objective of the article was to analyze the influence of psychrotrophic bacteria counts (PBCs) and somatic cell counts (SCCs) on the extent of lipolysis in bulk samples of cow's milk at reception and during cold storage. Samples of milk were analyzed on the day of sampling and subsequently during cold storage. The acidity, fat, density, chloride content, electrical conductivity (EC), bulk milk SCCs (BMSCC), and PBC values were analyzed on the day of sampling and the levels of acidity, EC, SCC, and PBC were analyzed during cold storage at 4 °C for 72 h. The SCC value 869 × 10(3) mL(-1) was higher than the recommended threshold. Lipolysis level at sampling day was related more closely with SCC than with PBC. There was no significant correlation between milk acidity and PBC among others parameters, while the milk mean density was only significant (P < 0.01) correlated with the fat content. The EC and chloride content were consistently correlated (P < 0.001) with BMSCC that allowed them to be used as indicators of mammary gland infection. The milk acidity, EC, PBC, and lipolysis levels increased in relation to the storage time at 4 °C. The lipolysis level during storage was in closer relation to the SCC, but not relation to the PBC. Effects of SCC and PBC on lipolysis decreased throughout the chilling period. It was concluded that initial lipolysis level and intrinsic milk lipoprotein lipase appear more effective than SCC and PBC on the development of lipolysis during storage.

Effects of somatic cells on the protein profile of hard ovine cheese produced from different breeds

Bulk tank ewe's milks with low (<500,000 ml−1), medium (1,000,000–1,500,000 ml−1) and high (>2,500,000 ml−1) somatic cell counts (SCC) from three breeds were used to manufacture hard ewes’-milk cheese. Physico-chemical analysis and capillary electrophoresis of fresh cheeses and cheeses that had been ripened for 1, 2, 3 and 6 months were carried out. The results showed that high SCC levels in milk affected the moisture content of only freshly made cheeses and the pH, fat content and fat acidity of ripened cheeses. Regarding proteolysis, the levels of all β-CNs in freshly made cheeses were significantly lower as the SCC values increased and the Castellana breed was the most affected by SCC levels because a significant decrease in all α-CNs was also observed as SCC levels rose. Analysis of the casein profile by principal component analysis (PCA) revealed that there were no clear differences according the SCC up to the third month. However in the third and sixth months cheeses with low levels of SC were closely grouped and characterised by the highest levels of intact caseins. Regarding the effect of breed, the results point to a more intense proteolytic activity in the Assaf breed, whose more matured cheeses showed the highest content of casein proteolytic fragments.

Influence of somatic cell count on the whipping properties of cream

Cows were infused with Escherichia coli endotoxin to provide a pool of milks with high somatic cell counts (SCC). This was mixed with bulk tank milk obtained from either of two Institute herds, producing a range of milks containing 0, 10, 20, 30 and 100% high SCC (HCC) milk. Creams containing 38% fat were produced from these milks on nine separate occasions; five times from winter milks and four times from summer milks. The SCC of the milks, the free fatty acid concentration of the unwhipped creams and the whipping time, stiffness and overrun of the whipped cream were measured. Whipping time and stiffness increased and overrun (volume increase) decreased as the proportion of HCC milk in the mixture increased. However, these changes were statistically significant only when comparing the 100% HCC milk with the other treatments containing lower levels of HCC milk. Creams produced in the summer took less time to whip and were less stiff than winter creams but there was no change in overrun. The source of bulk milk supply affected the stiffness and overrun of the whipped creams. Free fatty acid concentration appeared to have no direct effect on whipping characteristics.

Serum lipoprotein stimulation of lipolysis and its relevance to free fatty acid development in bovine milk

The role of blood serum lipoproteins in stimulating milk lipolysis was investigated by adding blood serum and heparin to the milk of normal cows and cows in which elevated somatic cell counts were induced by intramammary infusion of Escherichia coli endotoxin and Staphylococcus aureus. There was considerable variation between individual milks in the extent to which lipolysis was stimulated. In some milks there was almost no response. For values obtained from 29 cows during the first 6 months of lactation a relationship was observed between free fatty acid (FFA) levels in the untreated and serum-stimulated samples (r = 0·776). FFA values were higher after 18 h at 4 °C in milks from infused quarters than in those from control quarters, but this difference was not entirely due to higher values from the infused quarters at 0 h. Both blood serum and heparin stimulated lipolysis in high cell count milks and control milks. The response to heparin was greater than that to blood serum, but the response to both was highly correlated with FFA levels in the untreated milks. There were no differences in the ability of skim-milks prepared from infused and control quarters to promote lipolysis in recombined milks containing sterilized homogenized milk fat globules as a source of substrate. Incubation of blood serum with 2 μg/ml trypsin for 1 h at 37 °C reduced the ability of the serum to promote lipolysis. The importance of lipase activation by blood serum lipoproteins in relation to milk lipolysis is discussed.

Effects of somatic cell count and stage of lactation on raw milk composition and the yield and quality of Cheddar cheese

The effects of somatic cell count and stage of lactation on the yield and quality of Cheddar cheese were investigated. Cheese was manufactured in a pilot scale factory using milk of low bulk milk cell count (BMCC) from herds in early (LE) and late (LL) lactation, and milk of high BMCC from herds in early (HE) and late (HL) lactation. The deleterious effect of an elevated BMCC on product yield and quality in late lactation was clear. Cheese made from LL milk was significantly superior to that made from HL milk for most yield and quality characteristics measured. Stage of lactation also affected cheese yield and quality, as evidenced by the lower recovery of fat and poorer flavour score for cheese from LL milk compared with that manufactured from LE milk. The observed differences could be explained largely by differences in raw milk composition. We conclude that the effect of stage of lactation was magnified by an elevated BMCC, and that many of the problems encountered when processing late season milk could be overcome by containing mastitis at this time.

Acceptability and keeping quality of soymilk in Tanzania

Acceptability and keeping quality of two soymilk samples produced by hot water grinding and by presoaking in NaHCO3 was determined in Morogoro town. In terms of flavour and taste the two samples were significantly different from cow's milk (p < 0.05) but when vanilla was added (0.5 ml/l) the two samples were not significantly different from cow's milk. As estimated by using pH, titratable acidity and standard Plate Count, the milk samples could be kept at room temperature (25 +/- 2 degrees C) for up to 12 hours. The destroy 99% of the trypsin inhibitors in the soymilk samples, 45 minutes at 98 degrees C were needed for the alkaline presoaked milk while 75 minutes were needed for the plain water presoaked soymilk.

Influence of bovine mastitis on lipolysis ond proteolysis in milk

Lipolysis and proteolysis in milk were determined before, during, and after experimentally induced mastitis. Streptococcus agalactiae was infused into one quarter of five cows to elicit an infection. Milk protease activity was higher during infection, but milk lipase activity was unchanged. Lipolytic damage to milk fat and proteolytic damage to milk casein occurred in the udder prior to milking during an infection. Lipolysis increased due to increased susceptibility of the milk fat to lipase action during infection. The mechanism of the increased susceptibility of the fat to lipolysis was not determined. After infections were eliminated, SCC, initial and stored FFA concentrations, and initial tryosine values returned to preinfection levels. However, after infections were eliminated, milk protease activity as determined by an increase in tryosine values remained elevated as milk SCC returned to preinfection levels. Protease activity returned to preinfection levels within 10 d after SCC returned to preinfection levels.

Effect of pregnancy, milk yield, and somatic cell count on bovine milk fat hydrolysis

During 12 mo, 1818 milk samples were collected from Holsteins and Jerseys (n = 261) to evaluate effects of advancing lactation and pregnancy on milk fat hydrolysis. Aliquots, cooled immediately and stored 48 h at 4 degrees C, were analyzed for free fatty acid content. Holsteins had higher acid degree values than Jerseys (.90 vs. .62). No difference in values was detected between alternate a.m. (.74) and p.m. (.76) sampling times. Repeatability of acid degree values from lactation to lactation was low (.22). Days in milk, days pregnant, and milk yield had curvilinear effects on acid degree values, whereas SCC effects were linear. Estimated acid degree value at 335 d in milk (average dry-off) was lowered from .80 to .63 when adjusted for days pregnant and to .48 when adjusted also for milk yield. These responses agree with the increased acid degree values associated with two late lactation events: increasing day pregnant and decreasing milk yield. Estrogen secreted by the developing fetal-placental unit could mediate changes in milk composition that promote milk fat hydrolysis.

Lipoprotein lipase activity of milk from cows with prolonged subclinical mastitis

The influence of prolonged subclinical mastitis on bovine milk lipoprotein lipase activity was investigated. Nine cows with at least one quarter with prolonged subclinical mastitis and at least one nonmastitic quarter were selected in various stages of lactation. Milk from subclinical quarters had a mean somatic cell count of 5.7 X 10(6) cells/ml while milk from nonmastitic quarters had an average somatic cell count of 9.4 X 10(4) cells/ml. Quarters with a subclinical infection contained the same pathogenic organisms for a minimum of 6 wk. The average milk lipoprotein lipase activity of 108.7 units/ml milk from subclinical quarters was 27.1% higher than the average enzyme activity of 79.2 units/ml milk from nonmastitic quarters. Conditions present in the mammary gland during prolonged subclinical mastitis could lead to increased milk lipoprotein lipase activity in raw milk.

Lipid composition of milks from cows with experimentally induced mastitis

Changes in milk lipid composition were measured during the course of mastitis infections induced in cows by infusion of either Escherichia coli endotoxin or Streptococcus agalactiae into 2 quarters of the udder; untreated quarters were used as controls. Experiments were divided into 3 distinct phases: a pre infusion period during which several samples were collected before infusion; a post infusion period following infusion and corresponding to the occurrence of elevated cell counts in milk from infused quarters; a recovery period followed after a short pause and represented the return of the cell count in milk from infused quarters to the level in the corresponding controls. Milk total fatty acid composition was unaffected by the infusion. Free fatty acid (FFA) composition did, however, undergo some alteration. There was a significant increase in long-chain saturated acids in milk from infused quarters relative to the corresponding controls during the post infusion period. FFA concentration (mequiv./100 g fat) also increased significantly during this period although the net increase was only slight. Phospholipid and cholesterol concentrations were significantly higher post infusion in milk of infused quarters. The results suggest that changes in concentration and composition of those milk constituents synthesized and secreted by the mammary epithelium occur after secretion in the alveolar lumen and milk ducts.

Effect of exogenous estradiol and progesterone upon lipase activity and spontaneous lipolysis in bovine milk

Three of six lactating Jersey cows received estradiol--17 beta and progesterone (.10 and .25 mg/kg body weight per day subcutaneously for 7 consecutive days. Lipase activity and acid degree were determined for morning milk samples stored 24 h at 4 degrees C. Whole milk lipase activity did not increase over control milk samples; however, lipase activity of cream fraction and percent whole milk lipase activity in cream fraction increased 200 and 100%. Increases in acid degree occurred also and were closely correlated (.8 to .9) with lipase activity of cream fraction and percent whole milk lipase activity in cream fraction. Cooling was not required to effect association of lipase with cream fraction. Two treated cows developed mastitis-like symptoms after elevation in lipase activity of cream fraction and acid degree. Estradiol alone evoked similar responses.

Factors affecting the distribution of lipoprotein lipase activity between serum and casein micelles in bovine milk

The influence of mastitis and early lactation, and the effect of treating milk with heparin, blood serum and trypsin, on the proportion of lipoprotein lipase (LPL) activity in mild serum was investigated. The relative importance of milk serum LPL and LPL bound to micellar casein in promoting lipolysis was also examined. Colostrum contained LPL activity, 45% of which was found in the serum phase in samples obtained from the first milking post partum, but this value fell to 34% in samples taken 24 h later. The proportion of serum LPL was also increased in milks from quarters infected with Staphylococcus aureus, but not after overnight treatment of normal milk at 4 degrees C with 5% (w/v) blood serum or 2 microgram/ml trypsin. The addition of 5 microgram/ml heparin resulted in a consistent increase in serum LPL which varied between 14 and 50% of total milk LPL. Heparin did not release all the enzyme bound to casein micelles even after a second heparin treatment of resuspended micelles. Serum LPL was more effective in promoting lipolysis and was more responsive to blood serum activation than LPL bound to casein micelles. Lipolysis increased after heparin treatment but the increase was not related to serum LPL activity.

The relationship between the levels of free fatty acids, lipoprotein lipase, carboxylesterase, N-acetyl-beta-D-glucosaminidase, somatic cell count and other mastitis indices in bovine milk

A large-scale survey of milks from healthy and mastitic bovine quarters was undertaken to establish the influence of mastitic infection on milk lipase activity and free fatty acid (FFA) level. Mastitic milks tended to have higher FFA levels, but lower lipoprotein lipase activities compared with milk from healthy quarters. These effects became significant at relatively severe levels of infection. The elevated FFA was attributable to higher FFA levels on secretion and to greater lipolysis during storage. Levels of carboxylesterase activity increased with severity of mastitis and showed high positive correlation with mastitis indices. Marked increases in carboxylesterase, N-acetyl-beta-D-glucosaminidase and phospholipase occurred following the induction of mastitis by intramammary infusion of Escherichia coli endotoxin, in parallel with changes in somatic cell count and other mastitis indices. Relativity little change in lipoprotein lipase activity was observed.