bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the precursors of ovine lactoproteins: primary structures of the ‘signals’ and enzymic processing of prelactoproteins by mammary microsomal membranes
Authors: Gaye Pierre 
Published: June 2009

SUMMARYThe radiolabelled primary translation products of ovine mammary mRNAs synthesized in a wheat germ cell-free system were isolated by immuno-precipitation and analysed by automated Edman degradation. The 3 ‘Ca-sensitive’ caseins (α, α andβ ), k-casein, β-lactoglobulin and α-lactalbumin were found to be synthesized as precursors with amino terminal extensions of 15, 21, 18 and 19 amino acid residues respectively. The extra pieces of these various lactoproteins are similar to ‘signal’ peptides of other secretory proteins in their length and hydro-phobicity. The occurrence of an alanyl residue at the C-termini of the extra pieces of the 6 ovine prelactoproteins suggests that the mammary proteinase responsible for the cleavage of the signal peptides may have an elastase-like specificity.When mammary mRNAs were translated in a wheat germ cell-free system in the presence of mammary microsomal membranes, pre-β-casein was converted into authentic β-casein as demonstrated by amino terminal sequence analyses. Additionally, pre-β-casein was post-translationally converted into authentic β-casein by a specific proteinase(s) extracted from rough microsomes with Na deoxycholate.
Post-secretory aggregation of caseins
Authors: Brooker Brian E. , Holt Carl 
Published: June 2009

SUMMARYParticles as large as several µm diam. have been observed occasionally in normal milk and commonly in prepartum and postpartum colostrum. These particles can be dissociated by EDTA and their appearance closely resembles that of normal casein micelles. However, they are often too large to have been completely formed within the Golgi vesicles of mammary epithelium and hence some degree of post-secretory aggregation of caseins is thought to occur. Two possible mechanisms of post-secretory aggregation of caseins are: (1) a continuation of the normal processes of micelle assembly in the alveolus and (2) aggregation as a result of limited proteolysis of the caseins during the time the milk is in the mammary gland. Incubation of milk with fibrinolysin, however, failed to produce aggregation of normal micelles.
Association of proteins
Authors: Bloomfield Victor A. 
Published: June 2009

SUMMARYA review is presented of the various inter molecular forces important in stabilizing protein structure and association. Emphasis is put on entropic as well as enthalpic contributions to the free energy. The factors affecting size and size distribution in protein aggregates are discussed. A theory is presented for the size distribution of casein micelles, taking into account the spherical nature of the micelles and the importance of surface repulsive forces in limiting size.
The kinetics of the precipitation of chemically modified αs1-casein by calcium
Authors: Horne David S. 
Published: June 2009

SUMMARYThe aggregation of αs1-casein by Ca is viewed as resulting from a reduction in the net negative charge by the binding of positively charged Ca2+. This reduction in charge leads to the equivalent of isoelectric precipitation. A quantitative relationship between the rate of aggregation of the casein and the monomer net charge is predicted in this isoelectric precipitation model. Precipitation results are presented for αs1-casein labelled with dansyl chloride. Providing the changes in charge brought about by the modification are taken into account, the precipitation behaviour of these caseins can be reconciled with that of native αs1-casein. This emphasises the role of electrostatic repulsion in this process and lends further support to the isoelectric precipitation model.
Hydration of casein micelles: kinetics and isotherms of water sorption of micellar casein isolated from fresh and heat-treated milk
Authors: Rüegg Max , Blanc Bernard , Lüscher Madeleine 
Published: June 2009

SUMMARYWater vapour sorption isotherms of casein micelles prepared from raw milk and various heat-treated milks were determined. The equilibrium water contents of the heated preparations were markedly lower than that of the raw-milk casein over the whole range of vapour pressures studied. An analysis of the sorption isotherms in the relative vapour pressure range 0·1–0.45, according to the Brunauer, Emmett & Teller (1938) equation, showed that there were significant differences between preparations in the computed monolayer contents. Differences in the rates of water sorption were also observed between the different preparations.As judged from the amount of absorbed water, the influence of the heating methods could be ranked in the order: HTST (92 °C) ≃ UHT (direct) <UHT (indirect) < HTST (72 °C).
The role of calcium, phosphate and citrate ions in the stabilization of casein micelles
Authors: Visser Johannes , Schaier Roland W. , Gorkom Maarten Van 
Published: June 2009

SUMMARYTo obtain greater insight into the interaction of Ca, citrate and phosphate ions with casein, 31P NMR measurements were performed on combinations of these ions with αs- and κ-caseins. It was found that addition of αs-casein to a Ca phosphate solution in D2O at 27 °C and pD 6·4 resulted in a downfield shift of the 31P singlet. An almost identical shift was observed with κ-casein, but no shift was found when only phosphate ions were present or when Ca2+ were added to phosphate ions in the absence of casein. Separate experiments with poly-l-lysine, mol. wt approx. 35000, resulted in similar downfield 31P chemical shifts of Ca phosphate as with both caseins, whereas no shift was observed when poly-glycine was added. From these results it can be concluded that Ca and phosphate ions associate with casein in a co-operative manner, probably in the way described by ter Horst (1963) as a complex with the NH3+-groups of lysine or arginine in a structure such as:
(casein—NH3+)—P043-—Ca2+.
The formation of this complex may be enhanced by citrate ions, since preliminary results have shown that addition of Na citrate to a solution of αs-casein with added Ca phosphate produces a broadening of the 31P signal as well as a chemical shift.
Stability of buffalo casein micelles
Authors: Ganguli Nripendra C. 
Published: June 2009

SUMMARYBuffalo skim-milk is less heat stable than cow skim-milk. Interchanging ultracentrifugal whey (UCW) and milk diffusate with micellar casein caused significant changes in the heat stability of buffalo casein micelles (BCM) and cow casein micelles (CCM). Buffalo UCW dramatically destabilized COM, whereas buffalo diffu-sate with CCM exhibited the highest heat stability.Cow κ-casein stabilizes αs-casein against precipitation by Ca better than buffalo º-casein. About 90% of αs-casein could be stabilized by κ: αs ratios of 0·20 and 0·231 for cow and buffalo, respectively.Sialic acid release from micellar κ-casein by rennet was higher than from acid κ-casein in both buffalo and cow caseins, the release being slower in buffalo. The released macropeptide from buffalo κ-casein was smaller than that from cow κ-casein as revealed by Sephadex gel filtration.Sub-units of BCM have less sialic acid (1·57mg/g) than whole micelles (2·70mg/g). On rennet action, 47% of bound sialic acid was released from sub-units as against 85% from whole micelles. The sub-micelles are less heat stable than whole micelles. Among ions tested, added Ca reduced heat stability more dramatically in whole micelles, whereas added phosphate improved the stability of micelles and, more strikingly, of sub-micelles. Citrate also improved the heat stability of sub-micelles but not of whole micelles.
Lipid and protein composition of a membrane-rich fraction of butter oil
Authors: McCarthy Mary , Headon Denis R. 
Published: June 2009

SummaryLipid and aqueous extracts of bovine milk and 5 fractions prepared from bovine milk, including a membrane-rich fraction (MRF) isolated during butter oil production, were analysed for neutral lipid, phospholipid, protein and glycoprotein. The MRF showed an 8·5-fold enrichment in the phospholipid: protein ratio compared to whole milk. The percentage distribution of the 3 major phospholipid classes, phosphatidyl ethanolamine, phosphatidyl choline and sphingomyelin was 30, 36, 31 % respectively, the values of which differ slightly from those of whole milk. Fatty acid analysis of the major neutral and phospholipid classes indicated a predominance of palmitate, stearate and oleate. SDS polyacrylamide-gel electrophoresis in polyacrylamide gradients indicated that the percentage protein having a mol. wt in excess of 75000 increased by a factor of 2 in the MRF when compared to milk. Glycoprotein profiles of the MRF and its precursor cream differ significantly from the patterns evident in whole milk and skim-milk.
Chemical production of essential Cheddar flavour compounds
Authors: Manning Donald J. 
Published: June 2009

SummaryPossible mechanisms for the production of volatile sulphur compounds during the ripening of Cheddar cheese have been studied. Slurries of cheese made with and without starter organisms were treated with dithiothreitol (DTT) and the chemical composition of the headspace examined. Cheeses were also pressed from curd treated with DTT and glutathione (GSH). Reactions occurring between methionine, cystine and Na caseinate and reducing agents cysteine, DTT and GSH were also studied. In addition, the reactions of H2S with methionine and Na casein. ate were investigated.Treatment of cheeses with DTT and GSH resulted in the production of H2S and methanethiol (CH3SH) together with the development of Cheddar flavour. Similar treatment of methionine and Na caseinate also yielded H2S and CH3SH whereas Cystine produced only H2S. H2S reacted with both Na caseinate and methionine to yield CH3SH.These results are consistent with the occurrence of some of the chemical reactions studied during the ripening of Cheddar cheese.
Skin structure and milk production of British dairy cattle
Authors: Nay T. , Jenkinson D. McEwan 
Published: June 2009

SummaryThe possibility of using a skin measurement as an index of potential milkproducing capacity in cattle was re-examined. Skin specimens were obtained by biopsy from 7 dairy herds, and each of 5 anatomical measurements was correlated with (1) milk yield and (2) butterfat percentage.Only one of the pooled within-herd relationships was statistically significant. This relationship indicated that within the breeds studied, cows with the least hair follicle depth would be expected to give the highest milk yield. It is suggested that a more extensive investigation of this relationship might yield results of practical value in assessing milk-producing capacity and in progeny testing.
The effect of adrenocorticotrophic hormone on the yield, composition and butterfat properties of cow's milk
Authors: Campbell I. L. , Davey A. W. F. , McDowall F. H. , Wilson G. F. , Munford R. E. 
Published: June 2009

SummaryA single injection of 100 i.u. ACTH given to milking cows had no statistically significant effect on the yield or composition of the milk. A long-acting preparation of ACTH, when given to cows in single doses of 200 and 400 i.u., depressed milk yield and raised the butterfat content of the milk. There was no significant change in the SNF content of the milk but the SNF content of the milk serum was increased. Three injections of 300 i.u. of long-acting ACTH given at 24-h intervals reduced yields of milk, fat and SNF and increased the fat and SNF contents of the milk.Small but generally consistent changes occurred in the butterfat characteristics of the milk of all groups treated with ACTH. There was a decrease in the iodine number and refractive index and a rise in the softening point of the fat in all the experiments. The Reichert value of the butterfat was lowered by single or multiple injections of the long-acting preparation. The carotene content of the butterfat was lowered by injections of the long-acting ACTH preparation but the vitamin A content was unaffected.
The effect of fatty acids on the metabolism of lactic acid streptococci: II. Resistance of a variant of Streptococcus cremoris strain C 13
Authors: Anders R. F. , Jago G. R. 
Published: June 2009

SummaryIt was previously found that low concentrations of oleic acid in the growth medium inhibited the growth of Streptococcus cremoris strain C 13. However, a variant of this strain has now been isolated which is capable of growth in relatively high concentrations of oleic acid. This was achieved by the extended incubation of inocula of strain C 13 in milk containing various concentrations of oleic acid.
Storage of chilled milk in relation to butter quality
Authors: McDowell A. K. R. 
Published: June 2009

SummaryButter made from cream separated from milk accumulated in a refrigerated tank from morning and evening milkings for 3 days was compared with butter from similar milk unchilled and separated and pasteurized for churning daily.When the milk was of good quality there was no difference in the butters either when fresh or after storage for 4 and 8 months.When the milk was of poor quality the butter from the chilled milk was superior in flavour, both when fresh and after storage, to the butter from the unchilled milk. The defects in the butter from the unchilled milk were probably due to bacterial growth in the milk during the short period of holding of the unchilled milk.
The effect of milking throughout the whole of pregnancy on the composition of cow's milk
Authors: Wheelock J. V. , Rook J. A. F. , Dodd F. H. 
Published: June 2009

SummaryThe changes in yield and composition of milk when 4 cows were milked throughout the whole of pregnancy have been studied. The yield decreased to a minimum 1–20 days before parturition and then gradually increased. The changes in composition before parturition were similar to those observed in late lactation but more pronounced. The content of proteose-peptone plus globulin increased in late pregnancy with a sharp peak, of about 5 times the value observed in mid-lactation, within the last 10 days before parturition, and then decreased rapidly. After parturition milk yield increased rapidly and the changes in composition were less marked than in animals with the usual ‘dry period’. The results are discussed in relation to current knowledge of colostrum formation.
The role of lysine residues in the coagulation of casein
Authors: Hill R. D. , Craker Barbara A. 
Published: June 2009

SummaryCoagulation of rennin-treated casein was inhibited by treatment of the casein with dimethylaminonaphthalene sulphonyl chloride. The effect was caused by substitution on lysine side chains of theκ-casein fraction, and inhibition was complete when 2–3 lysine residues/molecule were blocked. This level of substitution did not affect other properties of theκ-casein, such as the release from it of non-protein nitrogen (NPN) by rennin and its ability to stabilizeαs-andβ-caseins in the presence of Ca++. The evidence suggests that lysine side chains onκ-casein take part in the coagulation of rennin-treated casein.
Oxidation of some milk lipid materials in model systems in presence of copper and ascorbic acid
Authors: El-Negoumy A. M. , Ku P. S. 
Published: June 2009

SummarySome milk lipid materials representing the phospholipid protein complex—fat globule membrane from buttermilk (FGMI) and from butter serum (FGMII), intact fat globules (dialysed cream) and triglycerides (butter oil)—were subjected to copper-induced oxidation in systems containing distilled water, phosphate buffer of pH 6·60 or milk dialysate. These model systems usually contained 2% lipid material and were allowed to oxidize for 48 h at 3–5 °C. Oxidation intensity was measured by means of the 2-thiobarbituric acid test.The oxidation intensity was dependent on the composition of the lipid material and of the aqueous phase. Ascorbic acid in absence of added copper catalysed the oxidation of the membrane materials and of globular fat. The oxidation intensity produced by FGMI (from buttermilk) differed significantly from that produced by FGMII (from butter serum) and the difference was well correlated with differences in their composition. Butter-oil preparations gave the lowest oxidation intensities, indicating that they are not the site for development of oxidative defects in aqueous media.
The effects of variations in pH, of the removal of calcium and of the addition of sulphur-bond inhibitors on the rate of setting of renneted milk
Authors: Tuszyński W. , Burnett J. , Blair G. W. Scott 
Published: June 2009

SummaryThe rate of increase of the complex rigidity modulus of renneted skimmilk was measured, both in a modified form of the torsiometer previously described and in the thrombelastograph, an instrument designed for the study of blood coagulation. Milk diluted with water was also tested.The effect of holding the milk is to slow down the process of coagulation without affecting the ‘coagulation time’ (i.e. its starting time). In undiluted milk a fall in pH from 6.66 to 6.18 does not affect maximum firmness but a later softening of the curd is accentuated in diluted and undiluted milk. Again, the coagulation time is not affected but the rate of firming up is reduced. Potassium oxalate, used to reduce the calcium content, shows similar effects.N-Ethyl maleimide, a reagent specific for sulphydryl groups, had no effect on undiluted milk; but with dilute milk, at a pH of about 6·0, there was a decrease in maximum firmness and there were also differences in the later softening of the curd.The significance of these effects on bonds formed during postenzymic coagulation is discussed.
Electronic counting of cells in milk: examination of a chemical treatment for dispersal of milk fat
Authors: Phipps L. W. 
Published: June 2009

SummaryThe chemical method of Tolle, Zeidler & Heeschen, (1966) for dispersing the fat in milk to allow electronic counting of the cells in suspension has been examined. The optimum conditions prescribed for obtaining the best estimates of cell counts were largely confirmed though inaccurate counts occasionally occurred. The reproducibility of counts made on the same milk samples was acceptable. For milk samples from individual quarters, cell counts determined after the chemical treatment and those after centrifugal separation of the fat could be related by a linear regression line of unit slope through the origin. The surface active liquid Lissapol NXP (I.C.I. Ltd.) appeared to be a suitable substitute for the Witopal CO (Chemischen Werken in Witten/Ruhr), an alkylphenol polyglycol ether, used by Tolle et al. (1966).
The passage of staphylococci through the bovine teat canal
Authors: Forbes D. 
Published: June 2009

SummaryIn order to determine how bacteria pass through the teat canal into the teat sinus, milk samples were taken by syringe, through the teat wall, from 12 quarters of 7 cows, before and after each milking for up to 16 days. Three of the teat canals were naturally infected before the start of the experiment and the remainder were artificially infected with Staphylococcus aureus by the Hadley–Wisconsin swab technique. In 3 of the quarters the inoculum was introduced into the teat sinus through the teat canal by the inoculation technique although the swabs were inserted only 3–5 mm into the canal. The other 9 of the 12 quarters were milked a total of 149 times during the experiment but only once was a colony-forming unit of the bacterium present in a teat canal infection isolated from the milk taken from the teat sinus after milking. One quarter developed an intramammary infection, the bacterium first being detected in the teat sinus prior to the third milking after inoculation of the teat canal. The invasion of the bacteria into the teat sinus therefore occurred between milkings. Staph. aureus persisted in teat canals between 5 and 32 or more milkings after inoculation. The experiment showed that bacteria in the teat canal are seldom refluxed into the residual milk in the teat sinus during correctly conducted milking with an efficient machine.
Influence of sodium chloride on the proteolysis of casein by rennet and by pepsin
Authors: Fox P. F. , Walley B. F. 
Published: June 2009

Summary1. Proteolysis of β-casein by rennin and by pepsin was completely inhibited in the presence of 10% NaCl and was very significantly reduced by 5% NaCl. The rate of proteolysis of αs-casein was maximal in the presence of 5–10% NaCl. 2. The inhibitory effect of NaCl on the proteolysis of β-casein was independent of pH and incubation temperature. 3. The effectiveness of NaCl in controlling the development of bitter flavour in Cheddar cheese may be due to its inhibitory effect on the proteolysis of β-casein. 4. Rennin hydrolysates of β-casein were bitter in flavour whereas those of αs-casein were not.
Bovine milk esterases
Authors: Kitchen B. J. 
Published: June 2009

SummaryThe type and distribution of esterases in milk has been investigated using selective inhibitors during normal assay procedures and during histochemical staining of polyacrylamide gels. Enzyme solutions were obtained from skim-milk by acid and alkali precipitation, followed by ammonium sulphate fractionation, ultra-filtration and Sephadex G-100 chromatography. The major type of esterase present was an aryl-esterase (E.C. 5.1.1.2) while a smaller amount of a choline-ester hydrolase (E.C. 3.1.1.7; 3.1.1.8) was detected. The significance of these findings is discussed.
Synthesis of milk fat from β-hydroxybutyrate and acetate in lactating goats
Authors: Smith G. H. , McCarthy S. , Rook J. A. F. 
Published: June 2009

SummaryThe relative importance of β-hydroxybutyric acid (BHBA) and acetate as precursors for milk-fat synthesis was studied in lactating goats by infusing separately tracer quantities of [3−14C]DL-BHBA and [1−14C]acetate into the jugular vein, and [1−14C]butyrate into the portal vein. The concentrations and specific radioactivities of blood plasma constituents, the yields and specific radioactivities of individual milk fatty acids and the relative radioactivities of individual carbon atoms of milk fatty acids were determined.The infusion of [1−14C]butyrate resulted in the appearance of labelled BHBA in the blood plasma which behaved almost identically with infused [14C]BHBA as a precursor for milk fatty acids.The relative radioactivity of carbon atoms of the fatty acids of milk fat following the infusions provided direct evidence that BHBA had provided an intact 4-carbon unit at the methyl end of each fatty-acid chain. Acetate provided 2-carbon units both for the elongation of the 4-carbon units and for completede novosynthesis. BHBA also provided 2-carbon units which behaved in a similar fashion to those from acetate.Acetate and BHBA together accounted for all of the C4–C12acids of milk fat, about 75% of the C14, 45% of the C16and 10% of the C18.The total contributions of the various precursors to the fatty acids of milk fat were: acetate 42%, BHBA 9·4% and other plasma precursors (by difference) 48·6%.
Some factors associated with the late-winter decline in the lactose content of herd bulk milks
Authors: Dawson R. R. , Rook J. A. F. , Wood P. D. P. 
Published: June 2009

SummaryA survey of the composition of the milk of individual cows in 6 commercial herds in the North of England was undertaken from October 1968 to July 1969. In all herds there was a decline in solids-not-fat (SNF) content; in 4 of the herds this was mainly the result of a fall in protein content, although in all herds there was a decline in lactose content in association with an increase in udder infection and an advance in average stage of lactation. Between-herd differences in the minimum value for lactose content were related to differences in udder infection, stage of lactation and lactation number.Two of the herds were selected for further study from October 1970 to April 1971. After a preliminary period each herd was divided into 2 matched groups. One group received the usual management, and the other was subjected to remedial changes of supplementary feeding and antibiotic therapy and improved udder hygiene. In both herds, treatment reduced udder infection and improved lactose content and in one of the herds there was also an increase in protein content.