bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrophobic interactions in human casein micelle formation: β-casein aggregation
Authors: Slattery Charles W. , Sood Satish M. , Chang Pat 
Published: June 2009

SummaryThe association of non-phosphorylated (0-P) and fully phosphorylated (5-P) human β-caseins was studied by fluorescence spectroscopy and laser light scattering. The tryptophan fluorescence intensity (FI) level increased between 20 and 35 °C, indicating a change in the environment of that residue. A similar transition occurred when ANS was used as a probe. Transition temperatures were slightly lower in 10 mM-CaCl2 but were not affected by an equivalent increase in ionic strength caused by NaCl. The magnitude of the FI change was less for the 5-P than the 0-P protein but was increased for both by CaCl2 addition. These FI data were characteristic of a conformational change and this was supported by fluorescence polarization which indicated that with CaCl2, tryptophan and ANS mobility increased at the transition temperature even though the extent of protein association also increased. Light scattering suggested that protein association proeeeded with the primary formation of submicellar aggregates containing 20–30 monomers which then associated further to form particles of minimum micelle size (12–15 submicelles), and eventually larger. The temperature of precipitation of the 5-P form in the presence of CaCl2 was lower than the conformational transition and suggested that both hydrophobic interactions and Ca bridges between phosphate esters on adjacent molecules are important in micelle formation.
Surface active properties at the air–water interface of β-casein and its fragments derived by plasmin proteolysis
Authors: Wilson Michael , Mulvihill Daniel M. , Donnelly William J. , Gill Brian P. 
Published: June 2009

Summaryβ-Casein, was enzymically modified by incubation with plasmin to yield γ-caseins and proteose peptones. Whole γ-, γ1-, γ2/γ3-caseins and whole proteose peptone (pp) were isolated from the hydrolysate mixture. The time dependence of surface tension at the air-water interface of solutions of β-casein and its plasmin derived fragments, at concentrations of 10−1 to 10−4% (w/v) protein, pH 7.0, was determined, at 25 °C, using a drop volume apparatus. The ranking of the proteins with respect to rate of reduction of surface tension, during the first rate determining step, at 10-2% (w/v) protein, was γ2/γ3 ≫ pp > whole γ- > γ1- > β-casein. The ranking of the proteins with respect to surface pressures attained after 40 min (π40) was concentration dependent. γ2/γ3-Caseins were found to be very surface active, decreasing surface tension rapidly and giving a high π40. γ1 Casein decreased surface activity somewhat faster than β-casein, but generally reached a lower π40. Whole γ-casein reflected the properties of both γ1 and γ2/γ3-caseins. Proteose peptone was found to decrease surface tension rapidly during the initial rate determining step; it gave a relatively high π40 at a bulk phase concentration of 10−3% (w/v) protein, but, it was the least surface active protein at 10−1 and 10−2% (w/v) protein.
Rheological properties of casein gels
Authors: van Vilet T. , Roefs S. P. F. M. , Zoon P. , Walstra P. 
Published: June 2009

SummaryThe rheological properties of rennet-induced skim milk gels at 30 °C are compared with casein gels formed by acidification to pH 4·6 at 2 °C and subsequent heating to 30 °C. Both types of gels are viscoelastic. However, the gels formed by rennet action are relatively more viscous over time scales longer than 1 s. This implies that on average the protein-protein bonds in these gels are relatively more mobile than in the acid casein gels. It is thought that this is primarily due to differences in the structure of the casein particles and in the type of the main interaction forces in and between the casein molecules and particles.
Incorporation of individual casein constituents into casein aggregates cross-linked by colloidal calcium phosphate in artificial casein micelles
Authors: Aoki Takayoshi 
Published: June 2009

SummaryArtificial casein micelles were prepared at a casein concentration of 2·5% with 10–40 mM-Ca, 12–27 mM-phosphate and 10 mM-citrate and cross-linking of casein by colloidal Ca phosphate (CCP) was examined. No casein aggregates cross-linked by CCP were formed at 10 mM-Ca, 12 mM-phosphate and 10 mM-citrate, which are the approximate concentrations found in the soluble phase of bovine milk. Although the amounts of casein aggregates cross-linked by CCP and of colloidal inorganic phosphate increased with increasing Ca and phosphate concentrations, the effect was not uniform. The incorporation rates of individual casein constituents into casein aggregates cross-linked by CCP were in the order > > β-casein. This was the reverse of the order of dissociation rates during dialysis of casein aggregates cross-linked by CCP reported previously.
Determination of chymosin and bovine pepsin A activity in combined rennets on the basis of immunochemical inhibition
Authors: Beránková Eva , Rauch Pavel , Káš Jan 
Published: June 2009

SummaryThe milk clotting activity of chymosin in combined rennets was determined as the difference between the total and residual activity after specific inhibition of chymosin with the purified immunoglobulin fraction of chymosin antiserum. The milk clotting activity of bovine pepsin A was assessed in a similar manner. In bovine rennets milk clotting activity of chymosin was measured directly after immunochemical inactivation of bovine pepsin A. Any method may be used for the determination of milk clotting activity. High correlation was found between the proposed method, which is simple and rapid to perform, and Chromatographic assay.
Effect of udder preparation on transmission of Staphylococcus aureus while milking with a multi-valved cluster
Authors: Grindal Robert J. , Bramley A. John 
Published: June 2009

SummaryWith two groups of 12 cows, a procedure involving foremilking, teat washing and drying before milking was compared with no premilking preparation for its effects on mastitis and teat contamination. Half the cows in each group were deliberately infected in a single udder quarter with Staphylococcus aureus and milked alternately with uninfected cows for 9 weeks. To minimize transfer during milking all cows were milked with the use of a multi-valved claw.Five new staphylococcal infections developed in the 12 animals in the teat preparation group compared to one in the control group. A significantly higher incidence of teat orifice colonization developed in the prepared cows compared to the control cows (17 v. 7). Foremilking and teat preparation led to transfer of staphylococci between quarters (within cow) but this was effectively prevented by the multi-valve claw in the absence of teat preparation.
pH-Induced dissociation of bovine casein micelles. II. Mineral solubilization and its relation to casein release
Authors: Dalgleish Douglas G. , Law Andrew J. R. 
Published: June 2009

SummaryMeasurements of the release of Ca, Mg and inorganic phosphate(Pi) from the casein micelles of bovine milk have been made, as functions of the pH, in the range 4·9–6·7, and at temperatures of 4, 20 and 30 °C. The results are in general agreement with earlier published studies in giving a value of 1·75–1·84 for the micellar Ca:Pi ratio. Mg appeared to behave similarly to Ca, although the amounts of micellar material were much smaller. The results on the acid-solvation of calcium phosphate are considered in relation to published quantitative studies of the pH-induced dissociation of the different types of caseins from the micelle, and of the micellar dissociation caused when micellar calcium phosphate is dissolved at neutral pH. It is evident from this that at present it is not possible to derive a universal relation between the dissociation of minerals and of caseins from the micelles at different temperatures and under different conditions.
Measurement of machine-induced changes in thickness of the bovine teat
Authors: Hamann Jörn , Mein Graeme A. 
Published: June 2009

SummaryMachine milking induced repeatable, short-term changes in thickness of the teat apex. These changes were measured with a spring-loaded caliper instrument under milking conditions that imposed differing forces on the teat apex. The mean percentage changes in teat end thickness (relative to the premilking values for individual teats) varied from 10% decrease up to 20% or more increase depending on the particular milking system used. The overall decrease in teat end thickness associated with cannula milking, milking at very low vacuum levels or milking with positive pressure pulsation may result from: (i) decrease in the intramammary pressure; and/or (ii) small changes in tone of teat musculature; and/or (iii) changes in the distribution of interstitial fluids in the teat apex. The overall increase in teat thickness caused by conventional or PKME milking systems results mainly from oedema (the extravascular accumulation of fluid). It is likely that milking equipment can, and should, be designed to minimize circulatory impairment resulting in oedema of the teat.
Enhancement of proteolysis in bovine skim milk by heat and chemical treatments
Authors: Igarashi Yasuo 
Published: June 2009

SummaryEffect of heating and of some chemical treatments on the proteolysis of skim milk caused by its major proteinase system, plasmin, was investigated. Degree of proteolysis was expressed as the increase in γ-casein content of skim milk (mg/ml) after incubation with 0·02% (w/v) NaN3 at 37 °C for 20 h. Apart from reduced proteolysis in skim milk heated at > 70 °C for 10 min or at 75 °C for ∼ 5 min, some enhancement (10–80%) was observed on heating at 55–63 °C for 10 min or at 60–65 °C for 15 s. Heating at pasteurization conditions (63 °C/30 min or 72 °C/15 s) had no apparent effect on the amount of proteolysis. Addition of ascorbic acid (0·2 mg/100 ml) or H2O2 (1/100 ml) to unheated skim milk also increased the amount of proteolysis by 38 and 28%, respectively. However, the extent of this increase diminished with increasing amounts of both chemicals. Furthermore, there was a steady increase (∼ 33%) in proteolysis with time of exposure to light for up to 3 h. These results suggest that oxidative conditions lead skim milk to enhanced proteolysis by inactivating an inhibitor(s) operating in the plasmin system in milk.
The cheesemaking potential of milk concentrated up to four-fold by ultrafiltration and heated in the range 90–97 °C
Authors: Green Margaret L. 
Published: June 2009

SummaryProperties of interest to cheesemaking were investigated with milks concentrated by ultrafiltration and heated at 90 °C or 95–97 °C for 15 s. The effects of light homogenization before concentration and of addition of CaCl2 after heating were assessed. No changes in casein–fat or casein–whey protein interactions were detected by electron microscopy. The heat denaturation of whey protein increased linearly as the milk became more concentrated. Coagulability by rennet after heat treatment increased with concentration to close to the unheated value in 3·5 to 4-fold concentrates. The decrease in curd firming rate by heat treatment was slightly affected by concentration and addition of CaCl2 restored some of the difference. Heat treatment reduced the rate of whey loss and slightly improved the curd structure but did not affect fat losses. Light homogenization slightly reduced heat denaturation of whey protein and whey loss.
Proteinase, peptidase and esterase activities of cell-free extracts from wild strains ofLactobacillus delbrueckiisubsp.bulgaricusandStreptococcus salivariussubsp.thermophilusisolated from traditional Greek yogurt
Authors: Kalantzopoulos Georgios , Tsakalidou Efthimia , Manolopoulou Eugenia 
Published: June 2009

SummaryProteinase, peptidase and esterase activities were detected in cell-free extracts of fourLactobacillus delbrueckiisubsp.bulgaricusand fourStreptococcus salivariussubsp.thermophilusstrains. Post-electrophoretic detection was based on hydrolysis of L-leucine-βnaphthylamide and α-naphthylacetate. The substrates L-leucine-p–nitroanilide,N-acetyl-L-alanine-p–nitroanilide, 2-nitrophenylbutyrate and 4-nitrophenylbutyrate were used for the spectrophotometric detection of the enzymes. Estimation of total proteolytic activity was based on hydrolysis of bovine whole casein. Interesting differences were observed between the two French strains and those isolated from traditional Greek yogurt.
In-vivo magnetic resonance imaging studies of mammogenesis in non-pregnant goats treated with exogenous steroids
Authors: Fowler Paul A. , Knight Christopher H. , Foster Margaret A. 
Published: June 2009

SummaryMammogenesis and lactation were induced in five multiparous, non-pregnant goats by treatment with oestrogen and progesterone for 11 d, followed by dexamethasone for 3 d. Reserpine was administered during the last 5 d. All five goats lactated, although milk yield was less than had been achieved in previous natural lactations. Mammary development was assessed in vivo, using magnetic resonance imaging. Although parenchyma volume increased by more than 6-fold overall, only 25% of this increase occurred during steroid treatment. Most development took place after the cessation of treatment, when milking commenced. Maximum size was not achieved until week 8 of the induced lactation, and was only 70% of normal parenchyma volume. After 18 weeks lactation the activities of three key milk synthetic enzymes were very similar to values previously found in natural lactations, and secretion efficiency (milk production per unit volume of parenchyma) was also similar to that of natural lactations. We conclude that the lower than normal milk yields were associated with incomplete proliferation of mammary tissue, rather than inadequate differentiation of individual secretory cells.
Potential value of photoacoustic spectroscopy for determining iron content of milk protein concentrates
Authors: Dóka Ottó , Kispéter József , Lörincz András 
Published: June 2009

SummaryPhotoacoustic and proton-induced X-ray emission measurements were performed on iron-enriched milk protein concentrates. The possibility of measuring Fe content by photoacoustic measurements in the visible region of the spectrum is discussed.
Effect of heat treatment on the proteolytic/peptidolytic enzyme system of aLactobacillus delbrueckiisubsp.bulgaricusstrain
Authors: López-Fandiño Rosina , Ardö Ylva 
Published: June 2009

SummaryLactobacillus delbrueckiisubsp.bulgaricuscells heat treated at 67 or 68 °C for 15·5–16 s had significantly less acidification capacity and much lower endopeptidase activity than untreated cells, while they still retained high aminopeptidase activities against amino acids commonly found in bitter peptides. A stimulatory effect of heat treatment on the leakage of aminopeptidases from cells was observed at pH 5·4. These properties make them suitable as extra sources of important ripening enzymes in cheesemaking.
Detection of propionic acid bacteria in cheese
Authors: Drinan Finbarr D. , Cogan Timothy M. 
Published: June 2009

SummaryMesophilic lactic starters and thermophilic lactobacilli but notStreptococcus salivariussubsp.thermophilusgrew on the sodium lactate agar (SLA) used for estimating the numbers of propionic acid bacteria (PAB) in cheese. The addition of cloxacillin (4 μg/ml) to SLA inhibited the starter bacteria but had no effect on the PAB. It was possible to count low numbers of PAB in the presence of high numbers of starter bacteria. A correlation coefficient of 0·9 was obtained between the level of propionic acid and the counts of PAB in cheese (n= 40). A disadvantage of the medium is that other bacteria found in cheese (mesophilic lactobacilli, enterococci,Clostridium tyrobutyricum) also grow on it; however, these bacteria are easily distinguishable from PAB on the basis of size, colour and absence of catalase.
Milk yield responses to sequential treatments with recombinant bovine somatotrophin and frequent milking in lactating goats
Authors: Knight Christopher H. 
Published: June 2009

SummaryLactating goats routinely milked twice daily were used. Starting at peak lactation, two groups of five goats were milked three times daily unilaterally (right gland) for 6 weeks, then one group received recombinant bovine somatotrophin (BST) by daily injection for 6 weeks, and finally both groups were returned to unilateral thrice-daily milking (left gland) for 6 weeks. Thrice-daily milking increased milk yield significantly by 10·4%. As thrice-daily milking finished and BST treatment began there was a small (2·7%) but significant increase in whole-udder milk yield in the treated goats and a decline in the control goats; throughout the BST treatment period treated goats produced 14·3% more milk than controls. The effect of BST was the same in glands previously milked thrice daily as in those previously milked twice daily. Milk yield declined as BST treatment finished, but this decline was less in the glands that then began thrice-daily milking. The effect of milking frequency was similar in this period to that obtained earlier in the experiment, and was not different between goats that had previously received BST and those that had not. The results are discussed in relation to the proposed modes of action of BST and frequent milking, and possible interactions between the two.
Separate and additive stimulation of bovine milk yield by the local and systemic galactopoietic stimuli of frequent milking and growth hormone
Authors: Knight Christopher H. , Hillerton J. Eric , Kerr Marian A. , Teverson Rachel M. , Turvey Alan , Wilde Colin J. 
Published: June 2009

SummaryLactating heifers were treated for 4 weeks with recombinant bovine growth hormone (bGH, n = 9) or were untreated (n = 9). In addition, two mammary glands of each heifer were milked four times daily rather than the normal twice daily for the same 4 weeks, and for the following 2 weeks. Over the 4 weeks, milk yield was increased 12·8% by bGH, 14·0% by frequent milking and 28·5% by the combined treatment. The effect of bGH as administered here was slower in onset than that of frequency, but eventually produced a higher peak yield. ANOVA revealed significant effects of each stimulus independently and an additive, but not synergic effect of the combined treatment. The effect of the combined treatment tended to persist beyond the end of treatment; most of this response was related to the milking frequency component rather than the bGH. Mammary differentiation was assessed in biopsies of mammary tissue obtained prior to and at the end of treatment. Mammary enzyme activities (expressed on a per cell basis) indicated minimal differentiative response to either treatment, but synthesis rates for lactose and casein determined in vitro were increased by bGH treatment. Histological examination revealed a stimulatory effect of milking frequency on epithelial cell size. The results indicate that these two galactopoietic stimuli operate through independent mechanisms, and neither stimulus alone is sufficient to maximize milk yield in dairy heifers.
Effect of calcium on the stability of mares' milk lysozyme
Authors: Lyster Richard L. J. 
Published: June 2009

SummaryThe three aspartic acid residues that form part of the Ca-binding site of mares' milk lysozyme have apparent pK values of 4·9, 4·3 and 4·1. The fluorescence of tryptophan has been used to compare the denaturation of mares' milk lysozyme by guanidinium chloride at various concentrations of Ca with that of hens' egg-white lysozyme (EC 3.2.1.17) and α-lactalbumin. Fluorescence revealed an intermediate stage in the denaturation of mares' milk lysozyme. The Ca-free form of mares' milk lysozyme is slightly more stable than that of α-lactalbumin, but its interaction with Ca is similar to that of α-lactalbumin, since only the native state binds Ca. Three-state models of denaturation can usefully be displayed on a ternary diagram.
Texture and microstructure of chhana and rasogolla made from cows' milk
Authors: Adhikari Amitava K. , Mathur Om N. , Patil Girdhari R. 
Published: June 2009

SummaryThe relationships between the composition, texture and microstructure of chhana (an Indian-style soft cottage cheese analogue) and rasogolla (a sweetened dairy product made from chhana) were analysed. Chhana contained a significantly higher proportion of fat, protein, lactose and minerals than did rasogolla. Cooking of chhana in 60% sucrose solution introduced sucrose and changed the texture and structure to that typical of rasogolla. As chhana was transformed to rasogolla, the Instron textural properties, hardness, gumminess and chewiness, fell significantly, whereas springiness increased dramatically. Market rasogolla had a slightly different composition from the laboratory-made samples, but both had similar Instron textural and sensory textural attributes. Scanning electron microscopy showed that chhana had a structure like cottage cheese or cream cheese, a compact, coalesced casein matrix with fat globules embedded in it. Rasogolla had a conglomerated, ragged and porous casein matrix with uneven surface and numerous large void spaces. The collapsed and ruptured fat globules were found embedded in the agglomerated protein particles of rasogolla. The textural attributes of both chhana and rasogolla could be explained by the microstructure.
Effects on milk yield, somatic cell count and milk conductivity of short-term non-milking of lactating quarters of cows
Authors: Hamann Jörn , Gyodi Peter 
Published: June 2009

SummaryCompensatory changes in daily milk production between quarters within an udder were investigated, together with related changes in cell count and electrical conductivity of fore milk samples. Two quarters per cow were left unmilked for 2 d (Group 1, four cows) or for 4 d (Group 2, four cows), and then all quarters of all cows were milked twice daily for a further period of 16 d. The mean daily yield per cow fell 50% during the period of milking two quarters. Daily yield for cows in Group 1 decreased significantly only during the treatment period and the first post-treatment period of 4 d, whereas the daily yield for Group 2 was significantly reduced during the whole post-treatment period. The cell count for all continuously milked (control) quarters was stable during the experiment, but increased in the treated quarters during the first 4 d of the post-treatment period. Non-milking was accompanied by a significant increase in fore milk conductivity which persisted for an additional 4 d after the resumption of normal milking. Throughout the last 12 d of the post-treatment period milk from both control and treated quarters had significantly decreased conductivity levels compared with the pretreatment values.
High affinity (Na++ Cl-)-dependent taurine transport by lactating mammary tissue
Authors: Shennan David B. , McNeillie Sandra A. 
Published: June 2009

SummaryThe transport of taurine by lactating rat mammary tissue has been examined. Taurine uptake was found to be dependent upon the presence of extracellular Na+and Cl-, which is consistent with (Na++ Cl-+ taurine) cotransport. TheKaandVmaxof taurine influx were respectively 43 μM and 37·5 μmol/kg cell water per 15 min. It is apparent that the mechanism responsible for taurine uptake is highly selective for β-amino acids. Taurine efflux consisted of a fast extracellular component and a slow membrane-limited component. The slow component was relatively insensitive to temperature, suggesting that it may represent simple diffusion. Mammary tissue was found to contain a high level of intracellular taurine: 7·29–7·44 mmol/kg cell water. We suggest that taurine is taken up and concentrated by the mammary gland by a (Na++ Cl-+ taurine) cotransport mechanism situated in the blood-facing aspect of the secretory epithelium and that a low outward permeability to taurine allows a high intra-to-extracellular concentration gradient to be maintained. Milk taurine may be derived from taurine diffusing from the cell cytosol across the apical membrane.