bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activation of milk lipase by serum proteins: possible role in the occurrence of lipolysis in raw bovine milk
Authors: Clegg Roger A. 
Published: June 2009

SummaryThe increase in unesterified fatty acid content of unpasteurized bulk milk in storage at 4 °C in the presence of known effectors of bovine milk lipoprotein lipase originating from bovine serum was studied. Bovine serum and high density lipoprotein (HDL) caused an increase in developed unesterified fatty acid levels whilst lipoprotein-free serum, apo-HDL, all individual apo-HDL tested, and the unfractionated C-peptide fraction were without lipolytic effect. In the presence of HDL-lipids, 2 C-peptides stimulated considerable lipolysis, as did the combination of HDL-lipid with unfractionated C-peptides. These characteristics of unesterified fatty acid development could be duplicated in milk whose endogenous lipolytic activity had been destroyed by heat treatment (75 °C for 5 min) and then restored by addition of purified bovine milk lipoprotein lipase. Radioactively labelled glycerol trioleate in milk was not hydrolysed in the same way as milk fat on the addition of serum liproproteins.
The content and composition of protein in creamery milks in south-west Scotland
Authors: Davies D. Thomas , Law Andrew J. R. 
Published: June 2009

SUMMAARYThe content and composition of protein in milk samples from creameries in south-west Scotland were determined over a period of 12 months. The composition of the whole casein was expressed in terms of αsl-, β-, κ-, αs2- and γ-caseins, and that of the total milk serum protein in terms of β-lactoglobulins (β-lg), α-lactalbumins, bovine serum albumin, and a mixture of immunoglobulins, proteose-peptone component 3 and lactoferrin (IPL). Concentrations of the individual caseins varied appreciably and for most, concentration was closely correlated with and showed the same seasonal pattern as total casein concentration. Concentrations of the milk serum proteins also varied but only those of β-lg and the IPL fraction were closely correlated with that of total milk serum protein and seasonal trends were not marked. Relative amounts of the individual proteins, on the other hand, showed smaller variations and so throughout the experimental period the milks contained a protein complex of comparatively constant composition. Because of this comparative constancy it would appear that seasonal variations in milk properties in south-west Scotland are unlikely to be determined to a major extent by milk protein composition, but could be more affected by protein concentration.
Formation of lysinoalanine from individual bovine caseins
Authors: Manson William , Carolan Thomas 
Published: June 2009

SummaryThe formation of lysinoalanine, N-є-(2-amino-2-carboxyethyl)-L-lysine, by treatment of αs0-, αsl- and β-casein with alkali, has been studied. In all 3 proteins lysinoalanine was formed by reaction of lysyl residues with dehydroalanyl residues produced by alkaline degradation of those phosphoseryl residues which occupy isolated positions in the proteins' structures. The contribution to lysinoalanine production made by phosphoseryl residues which were arranged in clusters, as occurs in the sequence -Ser(P)-Ser(P)-Ser(P)-, was not significant.
Effect of milk concentration on the rennet coagulation time
Authors: Dalgleish Douglas G. 
Published: June 2009

SummaryMeasurements have been made of the coagulation times (CT) of concentrated and diluted milks when treated with chymosin. After dilution, milks showed a large increase in CT: conversely, concentrated milks showed a similar CT to unconcentrated milk. The results are discussed in terms of a mechanism which reduces to a form similar to that proposed by Holter (1932).
Characterization and response to mitogens of mammary lymphocytes from the bovine dry-period secretion
Authors: Concha Carlos , Holmberg Olof , Morein Bror 
Published: June 2009

SUMMARYFrom bovine mammary secretion during the dry period, the total number of cells was between 1·2 and 5·9 Ǻ 106/ml. A mean of 35% of these cells were classified as lymphocytes and ∼ 85% of them could be isolated by the Ficoll-isopac method. Centrifugation separated 6% of the cells into the fat; 5% of them were lymphocytes. About 47% of the lymphocytes boundHelix pomatiaagglutinin, a T-cells marker, while the proportion of Ig-bearing cells was ∼ 28%. The mammary lymphocytes were stimulated by the lectins phytohaemagglutinin, pokeweed mitogen, concanavalin A and by lipopolysaccharide fromSalmonella typhimurium. The stimulation indices of mammary lymphocytes were generally lower than those for peripheral blood lymphocytes from the same animals. The background values, i.e. counts/min of lymphocytes incubated without mitogen, were often higher for lymphocytes isolated from mammary secretion than from blood.
Heat-induced association of β-lactoglobulin and casein micelles
Authors: Smits Petrus , Brouwershaven Johan H. Van 
Published: June 2009

SUMMARYHeat-induced association of β-lactoglobulin (β-lg) and casein micelles, mainly at 85–90 °C, was studied by means of preparative ultracentrifugation, using [3H]-labelled β-lg. Qualitative aspects were studied by gel electrophoresis and electron microscopy. In this association, the formation of intermolecular S–S bonds between β-lg and κ-casein plays a role, but hydrophobic bonds are also involved.After heating mixtures containing 25 g/kg casein and 4 g/kg β-lg at 90 °C for 20 min, the amount of β-lg sedimented with the casein micelles by ultracentrifugation decreased by approximately 30% when the milk salt buffer system was reduced to 0·25 of its normal concentration; it decreased by about 20% when the pH was increased from 6·8 to 7·3 and increased by 15% when the pH was reduced from 6·8 to 5·8. When the β-lg concentration was decreased from 4 to 2 g/kg, the amount of sedimented β-lg decreased by 25% after heating at 90 °C for 6 min. After heating in milk salt buffer, the amount of sedimented β-lg was 15% higher than after heating in a salt solution which contained neither Ca nor citrate ions.Although α-lactalbumin (α-la) is involved in the heat-association of β-lg and casein micelles, no influence of α-la on the amount of associated β-lg was found. In addition to the heat-association product of β-lg and whole casein micelles, an association product consisting mainly of β-lg and κ-casein was also formed. This product was observed by electron microscopy as noodle-like particles. The size of these particles depended on the β-lg/κ-casein ratio.
Factors influencing casein distribution in cold-stored milk and their effects on cheese-making parameters
Authors: Ali Ali E. , Andrews Anthony T. , Cheeseman Gordon C. 
Published: June 2009

SummaryIn assessing the performance of milk for cheese-making, the influence of a number of factors in addition to cold storage time and temperature of the milk on the equilibria between the soluble and micellar phases and on cheese-making parameters has now been examined. An important factor was pH and although not apparent in fresh unstored milk, after storage at 4 °C there was a minimum in the soluble casein concentration at about pH 6·6, largely due to variations in β-casein concentration. As expected, addition of Ca reduced soluble casein concentrations while treatment with EDTA caused increases, and in most cases the cyclic pattern of casein dissociation from the micellar phase followed by a partial reassociation was again observed during storage at 4 °C over a 3-d period. Addition of low levels of urea (up to 75 mg/100 ml milk) led to some dissociation of all casein components, Ca and phosphate into the soluble phase while treatment of milk with urease caused small decreases. Additions of purified casein components to milk were accompanied by only small alterations to the composition of the soluble phase and added casein was largely incorporated into the micellar phase. In spite of this, most added casein was not recovered in curds, and cheese yields were not greatly enhanced by quite considerable additions of caseins to the milk. The effects of pH adjustment, addition of Ca, EDTA, urea, cyanate, purified αs1-, β- or κ-casein and urease treatment on rennet clotting time, curd strength, curd moisture and cheese yield are presented.
Acid-soluble nucleotides of cow's, goat's and sheep's milks, at different stages of lactation
Authors: Gil Angel , Sanchez-Medina Fermin 
Published: June 2009

SummaryThe acid-soluble ribonucleotides of cow's, goat's and sheep's milks were measured by enzymic and ion-exchange chromatographic procedures at different stages of lactation. Colostra and milk from ruminant species contained orotic acid and 13 well-identified nucleotides: AMP, CMP, GMP, UMP, UDP, GDP, UDP-glucose, UDP-galactose, UDP-N-acetyl-glucosamine, UDP-N-acetyl-galactosamine, UDP-glucuronate, GDP-mannose and GDP-fucose. Cow's, goat's and sheep's colostrum contained significant amounts of nucleotides, which increased in amount from the moment of parturition, to reach a maximum 24–48 h later. The nucleotide concentration decreased thereafter with advancing lactation. Cow's milk contained substantial amounts of orotic acid, which increased during lactation, whereas in goat's and sheep's milk no increase took place. The cytidine and adenosine derivatives in ruminants' milk did not change significantly during lactation. The UDP-glucose/UDP-galactose ratio was measured in ruminants' milk at different stages of lactation.
Effects of adding potassium iodate to milk before UHT treatment: II. Iodate-induced proteolysis during subsequent aseptic storage
Authors: Skudder Paul J. 
Published: June 2009

SummaryThe addition of potassium iodate to milk at 0·1 mm before UHT treatment resulted in rapid breakdown of αs- and β-casein during subsequent aseptic storage. Maximum rates of proteolysis were observed at storage temperatures of 37–45 °C, but the reaction was strongly inhibited by storage at 55 °C and by increased holding time at 140 °C during the UHT sterilization. Iodate-induced proteolysis of purified αs1-and β-casein was detected only with solutions in the serum phase of raw milk; no proteolysis occurred with solutions in 01·M-phosphate buffer (pH 6·7) or in milk ultrafiltrate, irrespective of whether whey proteins and lactose were also added. Thus, it appears that iodate increased the activity of one or more proteolytic components which were present in milk and were unable to pass through an ultrafiltration membrane. However, it is unlikely that iodate acts by increasing the activity of proteinases produced by contaminant bacteria; the presence of iodate did not affect the activity of a proteolytic enzyme isolated from Pseudomonas fluorescens PM-1. Furthermore, iodate promoted protein breakdown during storage of milk drawn aseptically from the cow and subsequently UHT processed. It is suggested that iodate increased the activity of native milk proteinases, other than plasmin which was inactivated by UHT treatment, possibly by preventing thiol-disulphide exchange reactions during the heating process.
Derivation of a mathematical model for the mechanism of casein micelle coagulation by rennet
Authors: Darling Donald F. , Van Hooydonk Antoon C. M. 
Published: June 2009

SummaryThe action of rennet on the stability of casein micelles has been described theoretically by combining Michaelis–Menten enzyme kinetics with von Smoluchow-ski's theory for slow coagulation. The casein micelle is considered to be stabilized by stcric interactions arising from a highly hydrated surface protein layer. The stability factor, in von Smoluchowski's theory, is then considered as a variable and determined by the concentration of unhydrolysed κ-casein.The theoretical approach describes semi-quantitatively experimental observations on clotting time (CT) as a function of temperature, rennet concentration, and total protein concentration. The model also predicts that, under certain circumstances, the CT is inversely proportional to the enzyme concentration. Furthermore, the model agrees with other workers' experimental observations on the effect of κ-cascin concentration, the presence of a lag phase, and that the lag phase is commonly about 60% of the CT.
Rapid membrane filtration epifluorescent microscopic technique for the direct enumeration of somatic cells in fresh and formalin-preserved milk
Authors: Pettipher Graham L. , Rodrigues Ubaldina M. 
Published: June 2009

SummaryA rapid method for the direct enumeration of somatic cells in fresh and formalin-preserved raw milk is described. Heat treatment at 80°C for 10 mn fixed somatic cells sufficiently to prevent lysis and subsequent dilution allowed the equivalent of at least 0.5 ml milk to be filtered through a 1.0 μm pore size Nuclepore membrane filter. The somatic cells were concentrated on the membrane and, after staining with acridine orange, fluoresced green, yellow or orange under an epifluorescent microscope. Three different types of cell could be distinguished on the basis of nuclear structure and cell size. These were monocytes, polymorphonuclear leucocytes and the larger epithelial and/or secretory cells. For both fresh and preserved milks the count of somatic cells on the membrane correlated well (r≽ 0·93) with the Coulter count. Differences between counts obtained by different operators were not significant. The technique is rapid, taking about 20min, and is suitable for milks containing between 2 × 104and 1 × 107somatic cells/ml.
The relationship between the levels of free fatty acids, lipoprotein lipase, carboxylesterase, N-acetyl-β-D-glucosaminidase, somatic cell count and other mastitis indices in bovine milk
Authors: Fitz-Gerald Carolyn H. , Deeth Hilton C. , Kitchen Barry J. 
Published: June 2009

SummaryA 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-β-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. Relatively little change in lipoprotein lipase activity was observed.
Factors affecting the ethanol stability of bovine milk.: I. Effect of serum phase components
Authors: Horne David S. , Parker Thomas G. 
Published: June 2009

SummaryBy resuspending casein micelles in whey and dialysate it is shown that the role of whey proteins in the ethanol (EtOH)-induced coagulation of skim-milk is minimal. Experiments involving the interchange of milk sera indicated that the position of the EtOH stability/pH profile along the pH axis was governed by the diffusible constituents of the milk serum phase. The identities of those serum components governing the shape and position of the EtOH stability/pH profile were investigated. The addition of Ca2+ caused a shift in the entire profile to higher pH. Reduction of the available Ca2+ by addition of EDTA (up to 5 ran) shifted the profile to lower pH. The addition of phosphate (up to 5 mM) or citrate (up to 1 mM) had no effect on the profile, though higher concentrations of citrate (up to 5 mMi) caused slight shifts to lower pH. When equimolar amounts of Ca and phosphate were added, the system showed a shift in profile approximately equivalent to that of the free Ca introduced. Increasing the ionic strength of a milk by the addition of NaCl did not shift the profile, but decreased the maximum EtOH stability of the high pH arm of the sigmoidal profile. The EtOH stability/pH profile retained the same sigmoidal shape in all cases.
Electrofocusing and two-dimensional electrophoresis of bovine caseins
Authors: Trieu-Cuot Patrick , Gripon Jean-Claude 
Published: June 2009

SummaryThe main components of bovine whole casein were characterized by electrofocusing; pi values of αs1-, β-, κ-, γ1-, γ2- and γ3-caseins were determined. A further identification of casein components was achieved by a 2-dimensional electrophoresis study. 2-Dimensional patterns of γ-caseins obtained from a hydrolysate of β-cascin by bovine plasmin are in good agreement with those of γ-caseins naturally present in whole casein.
Mineral and protein equilibria between the colloidal and soluble phases of milk at low temperature
Authors: Pierre Alice , Brule Gerard 
Published: June 2009

SummaryMechanisms controlling exchange and partition of minerals and β-casein between micellar and soluble phases during cooling have been studied using suspensions of milk proteins of varying concentrations in the presence of aqueous phases having varying mineral compositions. In these studies the final equilibrium between Ca and phosphate was found to be regulated by formation of Ca phosphates of varying solubilities. The effect of the total casein level on mineral and protein equilibria was also studied. In milk, part of the β-casein content is bound to micelles by hydrophobic bonds; the proportion present in this form was increased by spontaneous micellar demineralization during cooling as well as by addition of a complexant to milk. At low temperatures, an equilibrium between the micellar and the monomeric states was reached which depends upon the total casein level and on the hydrophobic-bonded β-casein content. Not all of these hydrophobic bonds were broken when milk was cooled.
Effect of nutrition on fertility and blood composition in the milk cow
Authors: Bogin Eitan , Avidar Yaacov , Davidson Menachem , Gordin Salli , Israeli Bit-Ami 
Published: June 2009

SUMMARYThe relationship between nutrition, fertility and blood composition was studied in 400 cows from commercial farms. Fertility evaluated by overall conception rate (OCR) was shown to be significantly related to the relative proportion of concentrate and roughage feeds in the diet, and to its content of dry matter, digestible protein, Ca and P. The ratio of serum total lipids to glucose and a newly introduced parameter, ΔPi(a calculated value, obtained by subtracting whole blood levels of Pifrom those of the blood serum), showed a highly significant relationship to OCR. No significant relationship was found between OCR and serum, total lipids, cholesterol, urea, Ca, Mg, organic and inorganic phosphate. The values and significance of the 2 blood parameters which showed a relationship to fertility are discussed.
Inorganic constituents of milk III. The colloidal calcium phosphate of cow's milk
Authors: Holt Carl 
Published: June 2009

SUMMARYExperiments involving the depletion of milk calcium phosphate (MCP) with EDTA have shown that it has a Ca to phosphate ratio of 1·61±0·04, close to that of dental enamel. The calcium phosphate also contains small amounts of citrate (citrate/Pi = 0·097±0·011) and Mg (Mg/Pi = 0·044 ± 0·011). These experiments and model calculations indicate that the Ca binding capacity of casein is not reduced by mineralization with calcium phosphate and hence that ion binding sites and nucleation sites are distinct, or nearly so. Calculations of the ionic equilibria in the aqueous phase of milk show that there is an invariant ion activity product for a molecular formula close to that of dicalcium phosphate. It is suggested that MCP is a mixture of salts, with dicalcium phosphate a precursor of more basic salts such as octacalcium phosphate and hydroxyapatite.
Application of the plastein reaction to caseins and to skim-milk powder: II. Chemical and physical properties of the plasteins and the mechanism of plastein formation
Authors: Sukan Gonca , Andrews Anthony T. 
Published: June 2009

SUMMARYChemical and physical properties of plasteins derived from caseins and skim-milk powder have been investigated. Plasteins were very similar in properties regardless of starting material or of the proteinase used in their production. Plastein formed from Na caseinate hydrolysate at pH 5 was stable over the pH range 1·5–9·0 and had the properties of a thixotropic gel. More extreme pH values caused dissolution as did various chaotropic reagents. 8 M-urea disrupted plastein structure almost entirely, as did various organic acids at concentrations of 50% (v/v) and strongly ionic detergents. Non-ionic or weakly cationic detergents and 6 M-guanidine hydrochloride were less effective. Treatment with strong salt solutions, Ca2+ and EDTA had no effect. Gel filtration experiments demonstrated that plasteins were completely disrupted under dissociating conditions and peptide mapping confirmed that all the peptides originally present in the hydrolysate were also present in plastein. Amino group contents were unchanged on plastein formation. These experiments together with gel electrophoresis studies clearly showed that only hydrophobic and ionic bonding mechanisms were involved in plastein formation and no detectable peptide bond formation or transpeptidation occurred. In accordance with this, amino acid analysis suggested that hydrophobic peptides were preferentially incorporated. Implications for use of plasteins in food products are discussed.
Homogenizing valve design and its influence on milk fat globule dispersion: I. Low rate of flow (100 1 h–1, Re ≤ 3000)
Authors: Phipps Leslie W. 
Published: June 2009

SummaryThe efficiencies of small capacity homogenizing valves of the high pressure type have been studied in relation to their design. The performance of a valve was strongly affected by the magnitude of the effective inlet diameter D0 of the seating for a given exit diameter D when D0/D > 0·5. The indications are that narrow mating faces situated such that D0/D → 1 should maximize performance. Milk fat globule dispersion varied regularly with a valve's face angle; optimum angles for maximum disruptive effect were about +35° and –30°. Perforated metal insets interposed between flat faces of a valve piece and its seat noticeably improved fat dispersion; reductions in mean globule diameter of up to 25% were obtained.Variations in the sensitivity of different milks to homogenization were observed but avoided by appropriate experimental procedures.
An improved method for measurement of the syneresis of curd formed by rennet action on milk
Authors: Marshall Richard J. 
Published: June 2009

SummaryIn this method, the curd, formed in a beaker, was retained after cutting by means of a wire grid placed on top of it. This enabled the whey to be poured off easily at timed intervals for measurement of its volume. The method gave results reproducible within 1·5%. Increasing the amount of rennet added to the milk increased the rate of syneresis of the curd slightly. Adding CaCl2 to the milk, raising the temperature and decreasing the pH, all increased the rate of syneresis. Addition of fat, as cream, to skim-milk decreased the rate of syneresis proportionally. The rate of syneresis was decreased if the milk was concentrated by ultrafiltration and increased if the milk was diluted with permeate. In all instances the early stages of syneresis followed first-order kinetics, the rate depending on the amount of whey remaining within the curd. The later stages of syneresis appeared to depend on hydrophobic forces. Probably, the increasing aggregation of the casein within the curd caused the whey to be squeezed out.