bluuebunny/crossref_metadata_2025_split huggingface dataset:
Association of lipases with micellar and soluble casein complexes
Authors: Downey W. K. , Murphy R. F. 
Published: June 2009

SummaryThe association of lipase with casein micelles and soluble casein complexes was investigated by gel-filtration on Sephadex G-200 and Sepharose 2B columns which were equilibrated with synthetic milk serum. Gel-filtration indicated that the molecular weight of casein micelles in milk is > 108whereas the casein in colloidal phosphate-free milk is present as soluble complexes of molecular weightca.2×106containing αs-, β- and κ-casein. The soluble complexes appear to be stabilized in the micelle by colloidal calcium phosphate linkages. On addition of pancreatic lipase to milk, activity was impaired due to binding of the enzyme both to micellar and to soluble casein complexes. The enzyme dissociated from the latter during gel-filtration on Sepharose 2B columns. The binding of lipase to casein was not dependent on the presence of colloidal phosphate and consequently complete micellar structure is not essential for association of lipase with casein. Binding of the lipase to phosvitin did not result in a loss of enzyme activity. Lipases in milk appear to be involved in the equilibrium between micellar and soluble casein. The activity of lipases in milk is apparently influenced by this equilibrium. Some problems encountered in the use of gel-filtration to study the interactions of lipases with caseins are described.
The effect of the modification of arginine side chains in casein on the coagulation of rennin-altered casein
Authors: Hill R. D. 
Published: June 2009

SummaryThe modification of arginine residues in casein by treatment with glyoxal at pH 8·6 resulted in an inhibition of the coagulation of rennin-treated casein. The effective residues are on the κ-casein fraction and inhibition of coagulation was complete when about 1·5 residues of arginine/mole of κ-casein had been altered. It is suggested that the arginine forms part of a positively charged region that also includes lysine and histidine residues, and that this region is important in the coagulation of the casein.
The primary phase of rennin action in heat-sterilized milk
Authors: Hindle E. J. , Wheelock J. V. 
Published: June 2009

SummaryThe action of rennin in milk subjected to the ultra-high-temperature heat sterilization process has been studied. The primary phase of rennin action, as determined by the release of peptides soluble in trichloroacetic acid, was partially inhibited as a result of the heat treatment. This was largely due to a reduction in the release of non-carbohydrate-containing peptides from κ-casein. It is suggested that when whole milk is heated the formation of a complex between β-lactoglobulin and κ-casein proceeds more readily with the species of κ-casein which lacks carbohydrate. Evidence is presented which shows that there may be more than one type of carbohydrate moiety attached to κ-casein.
The release of peptides and glycopeptides by the action of heat on cow's milk
Authors: Hindle E. J. , Wheelock J. V. 
Published: June 2009

SummaryThe release, as a result of heat treatment on cow's milk, of peptides and glycopeptides which are soluble in the 12% trichloroacetic acid (TCA) filtrate of the milk has been studied. The results showed that the amount of peptides released increased with temperature and duration of the heat treatment. There were differences between milks in their response to a given heat treatment. Glycopeptides were released at temperatures as low as 50 °C but not at 37 °C. A comparison was made of the glycopeptides released by heat treatment and of those released from κ-casein by the action of rennin on the milk. This showed that N-acetyl neuraminic acid,D-galactose and 2-acetamido-2-deoxy-D-galactose were invariably present in both groups of glycopeptides.D-Mannose was also present in the glycopeptides released by heat but was detected on the glycopeptides released by rennin in only one of 6 experiments. It is suggested that glycopeptides released by heat may be derived from κ-casein but that a definite conclusion cannot be reached at present because of lack of information on the carbohydrates attached to other milk proteins.
Composition of the bound lipids in caseins and in ripening cheeses
Authors: Bolcato V. , Spettoli P. , Cagliari A. 
Published: June 2009

SummaryNeutral lipids and phospholipids, firmly bound to rennet- or acidprecipitated casein and also to α-, β- and κ-casein, have been detected by histochemical means. On sections of the caseins they appeared as areas of variable shape and size, uniformly distributed. In cheeses they partially disappeared, probably owing to the action of the milk and bacterial lipases. This led to new patterns of distribution of the lipids in the sections.Lecithin, cephalin, sphingomyelin, cerebrosides (2 spots), ceramides (1 spot), phosphatidylserine and phosphatidylinositol were identified in the phospholipid fraction of the casein by 2-dimensional thin-layer chromatography. In the bound phospholipid fraction of 3 cheeses the same phospholipids were found together with 1 new unidentified spot.
The specificity for κ-casein as the stabilizer of αs-casein and β-casein. I. Replacement of κ-casein by other proteins
Authors: Green Margaret L. 
Published: June 2009

SummaryThe specificity of the interaction betweenκ-casein,αs-casein andβ-casein which forms the basis of micelle stabilization was studied by investigating the extent to whichκ-casein could be replaced by other proteins. Of those tested, only gelatin replacedκ-casein and even it was only 2·5% (w/v) as effective and required a long pre-incubation period. The micelles formed by each ofκ-casein and gelatin withαs-casein and Ca2+were of a similar size to the casein—Ca complexes which compose natural micelles. Gelatin also formed complexes withαs- and withβ-casein at 30°C in the absence of CaCl2. Evidence was obtained that the interactions between gelatin and the caseins had a much stronger ionic component than had those betweenκ-casein and the other caseins. It was concluded that the interactions betweenκ-casein andαs- andβ-caseins which lead to micelle formation are highly specific and probably involve definite sites in each molecule.
Changes in the composition of bovine milk fat during milking
Authors: Kernohan Elizabeth A. , Wadsworth J. C. , Lascelles A. K. 
Published: June 2009

SummaryFat analyses were carried out on fore-milk and residual milk samples to elucidate the significance of the changes in fatty-acid composition of milk fat during milking previously reported by other workers. The levels of phospholipid in fore-milk samples per unit weight of fat were considerably higher than those of residual milk samples. The fatty acid composition of the triglyceride in fore-milk and residual milk samples was similar. These results suggest that the differences in fatty acid composition of milk fat collected during milking can be attributed to decreases in the relative amount of phospholipid-rich globule membrane associated with increasing globule diameter.
Changes throughout lactation in the amount of deposit formation from milk of individual cows
Authors: Burton H. 
Published: June 2009

SummaryDeposit formation from the milk of 2 individual cows was measured throughout lactation, using the hot-wire laboratory apparatus previously described. The amount of deposit fell slightly to a minimum at about the tenth week of lactation, and then rose to a maximum towards the end of lactation. The ratio of the maximum to the minimum was about 2:1. No correlation was found between amount of deposit and the fat, solids-not-fat, ash and calcium contents of the milks. The presence of mastitis in 1 cow and the administration to it of antibiotics did not affect the amount of deposit formed from its milk.
Formaldehyde-treated casein–safflower oil supplement for dairy cows: II. Effect on the fatty-acid composition of plasma and milk lipids
Authors: Cook L. J. , Scott T. W. , Pan Y. S. 
Published: June 2009

SummaryThis study reports the effect of feeding formaldehyde-treated or untreated spray-dried casein–safflower oil (1:1, w/w) particles on the fatty-acid composition of milk and plasma lipids of cows.When the formaldehyde-treated particles were given to Jersey, Sahiwal and Jersey × Sahiwal crossbred cows (1 kg per cow per day) the linoleic acid (18:2) present in the safflower oil was not hydrogenated by the rumen micro-organisms and was incorporated into milk fat.When the untreated supplement was fed, however, the 18:2 fatty acid was hydrogenated in the rumen and there was an increased proportion of octadecenoic acid (18:1) in the milk fat.The increased proportions of 18:2 (treated supplement) and 18:1 (untreated supplement) were associated with decreased proportions of palmitic (16:0) and myristic (14:0) acids in the milk fat. All 3 breeds showed similar responses.The fatty-acid composition of plasma triglycerides, which are an important source of long-chain fatty acids for mammary-gland lipogenesis, was similarly affected. Furthermore, there were significant changes in the fatty-acid composition of other plasma lipids (e.g. phospholipids and cholesteryl esters). The interrelationships between dietary, plasma and milk fatty-acid compositions are discussed.
Assessment of swine, bovine and chicken pepsins as rennet substitutes for Cheddar cheese-making
Authors: Green Margaret L. 
Published: June 2009

SummaryThree enzymes were assessed as rennet substitutes for cheese-making. The bovine and chicken pepsins used were relatively crude extracts of bovine stomach mucosa and chicken proventriculae respectively; the swine pepsin was a partially purified commercial product. The ratios of milk-clotting activity to general proteolytic activity were high for rennet and bovine pepsin and low for swine and chicken pepsins. Both bovine mucosa and chicken stomach gave low milk-clotting activities compared with calf stomach. For all the enzymes the chemical reactions causing milk clotting appeared to be the same. The milk-clotting activity showed a decrease with increase in substrate pH for all the enzymes, although they were all still active at pH 6·81.Duplicate cheeses were made from each of the swine, bovine and chicken pepsins, with rennet as a standard in each trial. The cheese-making process was similar with each enzyme, but differences appeared during ripening. The chicken-pepsin cheeses had poor body and weak Cheddar-cheese flavour, with many and intense off-flavours. The cheeses made with bovine and swine pepsins were only slightly inferior in quality and intensity of Cheddar-cheese flavour to the rennet cheeses. From a simulated cheese-making experiment it was concluded that 30–40 % of the added rennet, bovine pepsin and chicken pepsin was probably inactivated during the cheese-making process and that most or all of the swine pepsin was lost. These results provide an explanation for the variations observed in cheese ripening.It was concluded that chicken pepsin would not prove a suitable rennet substitute for making Cheddar cheese because of the quality of the cheese produced, and that bovine pepsin would not prove suitable because of the cost of preparing a suitable extract. Swine pepsin would appear to be suitable if the ripening time were to be lengthened or if another enzyme were to be added to assist ripening; it is cheaper than rennet and other rennet substitutes.
Cheese-making with a vegetable rennet from Cardo (Cynara cardunculus)
Authors: de Sá F. Vieira , Barbosa Manuela 
Published: June 2009

SummaryThe milk-clotting enzyme found in the flowers of Cardo (Cynara cardunculus) was investigated as to its suitability as a substitute for traditional animal rennet used in cheese-making. The influence of milk pH, temperature and quantity on the clotting activity of this enzyme was studied. Rheological behaviour of cow's-milk and sheep-milk curds, from renneting to cutting, was determined with the Plint cheese curd torsiometer for various Ca contents and pH values. Edam, Serra and Roquefort cheeses were made and the protein breakdown which occurred in the cheese during the ripening period was determined. Animal rennet was used as a control in all the experiments. The enzyme from Cardo was a satisfactory substitute for animal rennet with cow's milk and was even more suitable for sheep's milk. It was found to be a very good clotting enzyme for soft-bodied cheese like Serra, but because of its high proteolytic activity it presented some problems in Edam cheese-making. In Roquefort cheese it gave satisfactory results, but with some loss in yield.
Effect of polymorphic composition of calcium caseinate sols on their stability to rennin
Authors: El-Negoumy A. M. 
Published: June 2009

SummaryFive hundred and seven samples of iso-electric caseins were typed by starch-gel electrophoresis and their polymorphic compositions were determined in terms of αs1-, β- and κ-casein variants. Clotting times in minutes were determined on 50 ml of 3% casein solution in milk dialysate containing 0·02 M-Ca as CaCl2 and 2 mg commercial rennin powder at pH 6·60–6·80. The clotting times ranged from 4·06 to 7·41 min. The data indicated that the polymorphic composition of casein significantly influenced its stability to rennin. The polymorphic combinations αs1B+βA+κB and αs1B+βAC+κAB, were the most resistant to rennin action (clotting times of 7·41, 7·39 min respectively). The combinations αs1B+βB+κAB and αs1BC+βB+κB were the least resistant to rennin action (clotting times of 4·25 and 4·06 min respectively). In most cases, caseins with lower stability to rennin contained κB or βB or both in their composition.
Factors affecting the action of rennin in heated milk
Authors: Wilson G. A. , Wheelock J. V. 
Published: June 2009

SummaryThe effect of temperature and time of heating whole milk on the renninclotting time, the primary phase of rennin action and the protein (mainly β-lactoglobulin) soluble in 2% trichloroacetic acid (TCA), have been studied. Considerable changes in these parameters occurred above 60°C. The primary phase was inhibited (the degree of inhibition being both temperature and time-dependent), the clotting time was increased, and the protein soluble in 2% TCA decreased considerably.It is suggested that the inhibition of the primary phase was due to complex formation between κ-casein and β-lactoglobulin, the increase in clotting time to a combination of complex formation and a change in the distribution of Ca, and the decrease in β-lactoglobulin to both its interaction with κ-casein and its heat denaturation. The relevance of such changes to the heat stability of milk is discussed.
The analysis of volatile substances associated with Cheddar-cheese aroma
Authors: Manning D. J. , Robinson Heather M. 
Published: June 2009

SummaryA method for obtaining distillates from whole Cheddar cheese is described. The distillate has an aroma at −80°C closely resembling that of the cheese before distillation. Gas chromatograms of the distillate were obtained by sampling the vapour over the distillate at −80°C, using both a 15-m Apiezon surface-coated open tubular column and a 1·5-m glass column packed with Porapak Q. The aroma of the effluent was evaluated and the chromatograms simultaneously recorded by passing the vapour through a splitting device before the flame-ionization detector of the gas chromatograph. The compounds responsible for the aromas detected in the effluent were identified using a gas chromatograph directly linked to a mass spectrometer. Of the compounds identified in the distillate, H2S, methanethiol, dimethyl sulphide and diacetyl had the most intense aromas, and these compounds are discussed in relation to their importance to Cheddar-cheese aroma.
Proteolysis of β-casein in Cheddar Cheese
Authors: Phelan J. A. , Guiney J. , Fox P. F. 
Published: June 2009

Summaryβ-Casein is highly resistant to proteolysis in Cheddar cheese. A decrease in NaCl concentration reduced its resistance, but even in the absence of salt the amount of proteolysis of β-casein was slight. Proteolysis in Cheddar cheese increased when the moisture levels were raised by adding water. The relative susceptibility of β-casein to proteolysis by rennin was reduced considerably when the concentration of a sodium caseinate solution was raised from 10 to 20%. Sequestering the Ca2+by means of EDTA had no significant effect on proteolysis of β-casein. It would appear that the resistance of β-casein to proteolysis is due to the substrate rather than the enzyme and it is suggested that the reduced relative susceptibility to proteolysis is due to some concentration-dependent physical change in the casein molecule which renders the β-casein inaccessible. The salt concentration would also appear to influence this change.Cheddar-cheese flavour is largely independent of rennet concentration and it is possible to manufacture cheese of satisfactory quality using half-normal rennet levels.
Friction between the teat and teatcup liner during milking
Authors: Mein G. A. , Thiel C. C. , Westgarth D. R. , Fulford Rosemary J. 
Published: June 2009

SummaryFour studies are described of the role of friction in maintaining the teatcup stable on the teat. Measurements of the coefficient of friction between teats and pieces of liners, in which most values for the coefficient fell between 0·5 and 1·0, indicated that friction between skin and rubber-like materials was consistent with the general frictional behaviour of elastic solids. Studies during milking showed that the sudden restriction of milk flow that normally occurs near the end of milking is accompanied by a marked fall in the frictional force between the teat and barrel of the open liner. During the period of peak milk flow-rate, the major source of friction maintaining the teatcup stable on the teat is the large area of contact between the teat and liner barrel. The frictional force is derived from the pressure difference across the teat wall which presses the teat against the comparatively rigid liner. Frictional force between the teat and barrel increases after the start of milking because the coefficient of friction rises as one surface gradually moulds to the other. In addition, the total frictional force increases because of the increasing area of contact whenever the teat moves deeper into the liner, until the end of the peak flow-rate period. When this period ends, friction between the teat and open barrel is reduced suddenly because the teat sinus pressure falls. After this stage, the main source of friction appears to be derived from the force between the teat and mouthpiece lip.
The effects of pregnancy, lactation and involution on the metabolism of glucose by rat parametrial adipose tissue
Authors: Smith R. W. 
Published: June 2009

SummaryThe incorporation of14C from [1-14C] and [6-14C]glucose into CO2, fatty acids and glycerol by rat parametrial adipose tissue was measured at intervals during pregnancy, lactation and involution. There were small increases in the incorporation of both the C-1 and C-6 atoms into CO2and glycerol on the seventh and sixteenth days of pregnancy. Fatty acid synthesis from glucose was negligible on the twentieth day of pregnancy and during lactation. Three days after weaning the rate of oxidation of the C-1 atom was doubled and the incorporation of both carbon atoms into fatty acids was increased at least 20-fold. There were no changes in the activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase during pregnancy and lactation, but 3 days after weaning the activities of both enzymes were doubled. These results are discussed in relation to other evidence that the total body fat is increased during pregnancy, and to the idea that the fat depots are mobilized during lactation.
The structure of the deposit formed on the membrane during the concentration of milk by reverse osmosis
Authors: Glover F. A. , Brooker B. E. 
Published: June 2009

SummaryConcentration of milk by reverse osmosis is severely hindered by the formation of deposits on the membrane. Electron micrographs of this deposit show a thin (11nm) continuous electron-dense layer adjacent to the membrane. An electronlucent zone (10–15nm thick) separates this layer from the main bulk of the deposit which is 30 μm thick and consists largely of granules with some vesicles in a diffuse matrix. The density of packing of the granules increases with proximity to the membrane. Their appearance, size and digestion with pronase suggest that these are milk protein granules. The order and nature of these various layers could explain the pattern of flux decline.
Hour-to-hour variation in amino acid arterio-venous concentration differences across the lactating goat mammary gland
Authors: Mepham T. B. , Linzell J. L. 
Published: June 2009

SummaryArterio-venous (AV) blood plasma concentration differences of amino acids across the mammary glands of 2 lactating goats were measured at intervals throughout a day. One gland of each animal had been transplanted to the neck for experimental purposes. The variation throughout the day in arterial concentration of all amino acids was similar. The variation in AV differences was slight for most essential amino acids, greater for glutamic acid and proline and very marked for aspartic acid, alanine, glycine and citrulline. There was no statistical difference between the AV difference of any amino acid measured simultaneously across the 2 glands of either goat. The arterial concentrations of certain pairs of amino acids were significantly correlated. The implications of the results for estimation of rates of amino-acid synthesis in the mammary gland using the intra-arterial infusion technique are discussed.
Proteolysis detection in milk: III. Relationships between bacterial populations, tyrosine value and organoleptic quality during extended cold storage of milk and cream
Authors: Juffs H. S. 
Published: June 2009

SummaryRaw bulk milk samples were stored at 5°C in the laboratory mostly for 7 or 8d and examined at intervals for bacterial content, proteolysis as indicated by tyrosine value, and organoleptic quality. Data are presented for these samples illustrating relationships between bacterial population counts, tyrosine values and organoleptic quality ratings. Bacterial counts (total bacteria, psychrotrophs and proteolytic psychrotrophs) generally exceeded 106/ml before a definite increase in tyrosine value or any deterioration in organoleptic quality could be detected. Tyrosine value was indicated to be useful as a general index of bacteriological and organoleptic quality of commercial raw milk subjected to prolonged cold storage. The tyrosine value procedure was also shown to have application for monitoring the development of proteolysis in cold-stored pasteurized milk and cream.
Preparation and properties of αs-casein from buffalo's milk
Authors: El-Salam M. H. Abd 
Published: June 2009

SummaryBuffalo αs-casein (α-sb) was found to be heterogeneous; on starch gelurea electrophoresis 4 electrophoretic components were detected.The αsb-fraction was isolated by urea and alcohol fractionation. A preparation containing only the 2 main components was obtained by chromatography on DEAE-cellulose. Its amino acid pattern was different from that of cow αs1-casein. The fraction was also free of carbohydrate, cystine and cysteine.Buffalo αsb-casein was less stable than cow αs-casein in solutions containing Ca, and the maximum stability of the αs-/κ-casein complex occurred at a lower Ca concentration.