bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

The 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

The 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

Neutral 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

The 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

Fat 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

Deposit 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

This 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

Three 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

The 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

Five 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

The 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

A 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

β-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

Four 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

The 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.
A laboratory-scale ultra-high-temperature milk sterilizer for batch operation
Authors: Perkin A. G.
Published: June 2009

The design and operation of a laboratory-scale ultra-high-temperature sterilizer capable of treating 0·5-l quantities of milk are described. Temperature control, sporicidal efficiency and change of composition of the milk during processing are discussed.
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

Concentration 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

Arterio-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

Raw 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

Buffalo 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.
A study of the properties of dissociated bovine casein micelles
Authors: Creamer L. K. , Berry Gillian P.
Published: June 2009

Although casein micelles are disrupted by removal of Ca, individual caseins remain aggregated in sub-micellar casein aggregates or sub-units. These sub-units have been studied by: (1) the use of gel filtration on Sepharose 4B at 6, 20 and 37°C at pH 6·7 and 0·1 ionic strength, (2) ultracentrifugation and (3) electron microscopy. At 37°C the protein composition of the sub-units varied across the gel-filtration peak, with κ-casein being eluted towards the leading edge and the ratio of αs1- to β-casein being almost constant across the peak. Re-chromatography of the protein from the leading edge of this peak gave a new wide peak with the κ-casein again being eluted towards the leading edge. However, αs1-casein was eluted before β-casein in the leading edge of the new peak. Prior treatment of the casein micelles by dispersion with 6 m-urea solution, precipitation with acid or reduction with 2-mercaptoethanol did not alter the gel-filtration pattern. An examination of the purified casein components and their mixtures showed that a 1:1 ratio mixture of αs1- and β-casein had the same peak maximum elution volume as casein micelle sub-units. κ-Casein by itself eluted at the void volume of the gel-filtration column, but after admixture with a sample of small micelles it eluted at the leading edge of the sub-unit peak and was indistinguishable from the κ-casein normally present. These results suggest that the sub-units are in equilibrium with their component caseins and that their size distribution is determined by only those factors (such as protein concentration, pH, temperature and ionic strength) which determine the strength of association between the casein components. The results from electron microscopy and ultracentrifugation support these conclusions.
Autoxidation in milk rich in linoleic acid I. An objective method for measuring autoxidation and evaluating antioxidants
Authors: Sidhu G. S. , Brown M. A. , Johnson A. R.
Published: June 2009

Autoxidation was studied in milk obtained from cows fed on formaldehyde-treated casein-safflower oil supplement. The fat of this milk contained high levels of linoleic acid. A rapid disappearance of dissolved oxygen (DO), measured by using an oxygen electrode, from milk samples stored at 0°C in tubes without headspace, coincided with the development of oxidized flavours detected organoleptically. A correlation coefficient of 0·9 with 69 degrees of freedom (P < 0·001) was obtained between the amount of DO disappearing and the taste panel scores for oxidized flavours.

Butylated hydroxyanisole, sesamol, nordihydroguaiaretic acid, ethoxyquin, or butylated hydroxyanisole with propylgallate or tocopherols, when added in emulsified form to the milk at the rate of 10–15 mg/l milk, checked the development of oxidized flavours and the rapid disappearance of DO. Other antioxidants tested were either ineffective or imparted off-flavours to milk.

Samples of mare's milk neither developed oxidized flavours nor showed rapid disappearance of DO over a test period of 8 d.

The oxygen electrode provides a convenient and sensitive method for studying autoxidation and evaluating antioxidants in milk.
Dephosphorylation of bovine casein by milk alkaline phosphatase
Authors: Lorient D. , Linden G.
Published: June 2009

The pH of optimum activity of alkaline phosphatase from cow's milk depended on the substrate, being 10·1 for p-nitrophenylphosphate, 8·6 for phosphoserine, 8·0 for phosvitin and 6·8 for casein. Individual casein components were dephosphorylated more rapidly than mixtures of αs- and β-caseins or of αs-, β- and κ-caseins and micellar casein. Mixtures of 2 components involving κ-casein were more readily dephosphorylated than αs- and β-casein mixtures. At pH 6·8, lactose, whey proteins and phosphate ions had an inhibitory effect. β-Lactoglobulin had an inhibitory effect only when the pH of the reaction was lower than the optimum pH value of the enzyme. Mg2+ and Zn2+ were not inhibitory. The optimum conditions for dephosphorylation of casein are described.
Contribution of rennet and starter proteases to proteolysis in Cheddar cheese
Authors: O'Keeffe R. B. , Fox P. F. , Daly C.
Published: June 2009

Proteolysis in aseptic, chemically acidified (GDL) cheese and in starter cheese made under controlled bacteriological conditions (i.e. free of non-starter micro-organisms) was measured by gel electrophoresis, the formation of pH 4·6- and 12% TCA-soluble N, gel filtration and the liberation of free amino acids. The results show that rennet was mainly responsible for the level of proteolysis detected by gel electrophoresis, pH 4·6-soluble N and gel filtration i.e. large, medium and small peptides. However, rennet alone was capable of producing only a limited range of free amino acids; only methionine, histidine, glycine, serine and glutamic acid were produced at quantifiable levels (> 0·2 μmoles/g) in GDL cheese; it is suggested that free amino acids in Cheddar cheese are mainly the result of microbial peptidase activity. The levels of free amino acids in the starter cheese were considerably lower than values reported for commercial Cheddar.
Effect of feeding fat to dairy cows receiving a fat-deficient basal diet: I. Milk yield and composition
Authors: Banks W. , Clapperton J. L. , Ferrie Morag E. , Wilson Agnes G.
Published: June 2009

The effects of supplementing a basal diet, in which the low level of fatty acids limited milk production, with soya oil, a palm oil/palmitic acid mixture and tallow, on the yield of milk and of its constituents, and on the composition of the milk, are reported. The yields of milk and milk fat were greatly increased by all the oil-supplemented diets; the mean daily yield of solids-not-fat (SNF) was also increased, but supplementation with soya oil caused the yield of crude protein (CP) to decrease, whereas the other fat-rich concentrate mixtures gave the same mean yield of protein as did the low-fat, control diet. All 3 oil-supplemented diets lowered the proportion of CP in the milk, but the SNF content was unchanged by any treatment. Dietary soya oil tended to lower the proportion of fat in the milk, whilst the palm oil/palmitic acid mixture raised it, with the tallow exerting no effect. The results are discussed in relation to previous work in which these dietary oils have been used, but in which the intake of fatty acids from the control diets did not limit milk production to the extent reported here.
Heat stability of forewarmed milks: influence of κ-casein, serum proteins and divalent cations
Authors: Morrissey P. A. , O'Mahony F.
Published: June 2009

Addition of isolated κ-casein to milk reduced the destabilizing influence of forewarming, while the addition of isolated β-lactoglobulin (β-lg) to the κ-casein-enriched systems resulted in a loss in stability on forewarming. This effect was ascribed mainly to a β-lg:κ-casein interaction. Some individual milks were unaffected by forewarming while others were markedly destabilized by the same treatment. Addition of Ca2++ Mg2+and interchanging of milk sera by dialysis influenced stability.

It is concluded that milks which are destabilized by forewarming generally give a type A response (minimum in the pH–heat stability curves) and that preheat-stable milks generally give a type B curve (no minimum).
The influence of dietary protein intake on milk production and blood composition of high-yielding dairy cows
Authors: Treacher R. J. , Little W. , Collis K. A. , Stark A. J.
Published: June 2009

Cows were fed either 75 or 100% of the recommended intake levels for protein and 100% of recommended energy levels (Agricultural Research Council, 1965) from 8 weeks pre-calving until 14 weeks post calving. From 14 weeks post calving and to the end of lactation all the cows received 100% of the recommended protein and energy intakes.

The mean of the 305-d milk yields of the 2 groups was not significantly different and although cows on the lower protein intake produced less lactose during the first 14 weeks of lactation there was no significant difference in total lactose, fat, protein or total solids production between the groups. In both groups blood packed-cell volume, red cell count and haemoglobin decreased during the first 10 weeks of lactation and then began to increase in the high-protein group. The cows receiving the low-protein diet showed a similar increase only when they received the high-protein ration from 14 weeks post calving. The mean interval from calving to conception was 27·5 weeks in the high-protein group and 20 weeks in the low-protein group.

It is concluded that feeding 75% of protein requirements to dairy cows during the first 14 weeks of lactation does not reduce milk yield or quality significantly and probably has no adverse effect on fertility.
The heat stability of milk and concentrated milk containing added aldehydes and sugars
Authors: Holt C. , Muir D. D. , Sweetsur A. W. M.
Published: June 2009

The addition of simple aldehydes brought about large increases in the heat stability of both skim-milk and concentrated skim-milk over a comparatively wide milk–pH range. The coagulation time–pH minima of type A milks were completely removed by aldehyde treatment. Some sugars, which react readily as aldehydes on heating, were also shown to stabilize concentrated milk to prolonged heat treatment at 120 °C.
The effect of supplementation of the diet of lactating Jersey cows with varying levels of acetic acid
Authors: Johnson C. Lewis , Kitchen David I.
Published: June 2009

TwO Latin-square experiments using lactating Jersey cows have been made to determine the response to 4 levels of acetic acid given as a supplement to diets fed at Woodman's Standards. The response in milk yield and composition to daily supplementary infusions of acetic acid is curvilinear, the point of inflexion occurring between the levels of 450 and 600 ml acetic acid/d. The direction of responses to the 150-ml level of infusion varied between the experiments. At the 600-ml level of addition the non-significant increases in milk fat, protein and lactose yield led to a significant increase in solids corrected milk yield. The effects of acetic acid infusion on the composition of the milk fat were determined.
Natural variations in the average size of bovine casein micelles: III. Studies on colostrum by electron by microscopy and light scattering
Authors: Brooker Brian E. , Holt Carl
Published: June 2009

Bovine casein micelles in pre- and post-partum colostrum have been characterized by both electron microscopy and light scattering. Attempts have been made to relate the changes in average micelle size to the partitioning of Ca and inorganic orthophosphate betwen the colloidal and aqueous phases. Pre-partum colostrum, and to a decreasing extent post-partum colostrum, contain casein micelles several microns in diameter. These giant micelles often contain closed cavities suggesting that they are formed by aggregation of particles comparable in size to normal casein micelles. Electron microscopy of mammary gland alveoli from nearterm pregnant heifers shows clear differences in average size between micelles immediately before and after secretion from Golgi vesicles. It appears that micelles aggregate in the alveolar lumen, possibly as a result of continuing co-precipitation of casein with Ca phosphate.
Intermicellar relationships in rennet-treated separated milk: II. Process of gel assembly
Authors: Green Margaret L. , Hobbs David G. , Morant Steven V. , Hill Valerie A.
Published: June 2009

The aggregation of casein micelles in milk by the action of rennet, examined by electron microscopy and viscometry, was correlated with visually-observed coagulation. The spatial relationships between micelles were quantified from measurements made on micrographs. Aggregation did not start until about 60% of the rennet-clotting time, when the enzymic action was almost complete. The micelles tended to form chains which then linked into a loose network. This became more extensive with time as the average size of the aggregates increased. By the clotting time, most micelles were in contact with another and a network was beginning to form. Initially, micelles probably linked by bridges. These then appeared to contract, bringing the particles into contact and eventually causing partial fusion.
Peptide hydrolases ofLactobacillus casei: isolation and general properties of various peptidase activities
Authors: Soda Morsi El , Desmazeaud Michel J. , Bergère J.-L.
Published: June 2009

Discovery of an endopeptidase by gel chromatography and separation of 3 exopeptidases (a dipeptidase, an aminopeptidase and a specific carboxypeptidase) fromLactobacillus caseiNCDO 151 by affinity chromatography is described. The 3 exopeptidases were strongly inhibited by the metal chelators EDTA and 1,10-phenanthroline but were reactivated with Co2+and Mn2+. The pH optima for aminopeptidase, dipeptidase and carboxypeptidase activities were 6·5, 7·6 and 7·2, respectively. Maximum activity was obtained at 45 °C for the aminopeptidase, at 30 °C for the dipeptidase and at 40 °C for the carboxypeptidase.

The substrate specificities of the 3 enzymes were also studied. The properties of these 3 enzymes are compared with those of other bacteria.
Proteolysis in Cheddar cheese: role of coagulant and starter bacteria
Authors: O'Keeffe Arthur M. , Fox Patrick F. , Daly Charles
Published: June 2009

Cheddar cheese was produced free of non-starter bacteria, acidified with starter or glucono-δ-lactone and containing active coagulant (chymosin or pepsin) or inactivated coagulant (pepsin). The level and type of proteolysis in the experimental cheeses was monitored by protein solubility at pH 4·6 and in 12 % TCA, polyacrylamide gel and high voltage paper electrophoresis, gel filtration and paper chromatography. The results show that the coagulant was primarily responsible for the formation of large peptides while small peptides and free amino acids were produced principally by the starter, possibly from coagulant-produced peptides.
Whey protein denaturation in heated milk and cheese whey
Authors: Hillier Robyn M. , Lyster Richard L. J.
Published: June 2009

Quantitative polyacrylamide gel electrophoresis has been used to measure residual native whey proteins remaining after heat treatment of skim-milk and cheese whey in a kinetic study. The denaturation of α-lactalbumin (α-la) appeared to be first order, but was probably a second-order reaction displaying pseudo first-order kinetics. The denaturation of both β-lactoglobulin A and B (β-lgA and β-lgB) followed second-order kinetics while that of serum albumin was more complex, and could equally well be described as first or second order. Equations are given relating logk1(in s-1) to temperature for α-la denaturation in skim-milk between 70 and 95 °C and between 100 and 150 °C. Similarly, equations relating logk2(in lg-1s-1) to temperature are given for ²-lgA in skim-milk between 100 and 150 °C, and for ²-lgB between 95 and 150 °C. The relative heat stability of ²-lgA and ²-lgB was found to vary.

Below 95 °C ²-lgA appeared slightly more thermostable than ²-lgB in skim-milk, and the same was observed in cheese whey below 100 °C. Above these temperatures ²-lgB appeared more stable than ²-lgA.

Denaturation of ²-lgB was only slightly more rapid in skim-milk than in whey at temperatures below 95 °C, but was significantly slower at higher temperatures.
Strains ofStreptococcus lactiswhich contain β-galactosidase
Authors: Farrow John A. E. , Garvie Ellen I.
Published: June 2009

In the past the classification of ATCC 7962 as a strain ofStreptococcus lactishas been questioned because it contains β-galactosidase and not β-phosphogalactosidase, and because all extracts do not react with group N antiserum. A comparison was made between ATCC 7962 and known strains ofStr. lactisusing physiological properties, some of the properties of the lactate dehydrogenases and percent guanine plus cytosine in the DNA. ATCC 7962 was distinguished only by its ability to ferment pentoses. The degree of hydribization between the DNA of ATCC 7962 and that of a typical strain ofStr. lactiswas 67 %. ATCC 7962 is an atypical strain ofStr. lactis. The properties of a wild strain ofStr. lactisisolated from radishes in Brunei which contains β-galactosidase and β-phosphogalactosidase, are given also. This strain ferments pentoses.
A genetic and biochemical analysis of a polymorphism of bovine αs2-casein
Authors: Grosclaude François , Joudrier Philippe , Mahé Marie-Françoise
Published: June 2009

Using gel electrophoresis a genetic polymorphism of αs2-casein (Cn) was discovered in individual milk samples from 2 bovine breeds of the eastern part of France (Vosgienne and Montbéliarde). The 3 observed phenotypes (Plate 1) are determined by 2 co-dominant alleles at an autosomal locus. The αs2-Cn A variant was the only one known up to now in European breeds (reference variant) and ±s2-Cn D is a new variant, whose bands overlap the β-casein A band at pH 8.6, and migrate faster than αs2-Cn A at pH 3.0.

The sequence of the polypeptide chain αs2-Cn D differs from that of αs2-Cn A by the deletion of a very acidic nonapeptide, which includes a cluster of 3 phosphoseryl residues. Due to the characteristics of the reference sequence, this deletion cannot be exactly located but it involves residues 50–58, or 51–59, or 52–60.

A genetic analysis shows that locus αs2-Cn is closely linked to the cluster αsl-Cn–β-Cn-K-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.
The formation and structure of some proteose-peptone components
Authors: Andrews Anthony T.
Published: June 2009

Two constituents of the proteose-peptone fraction of bovine milk have been isolated and characterized. Component 5 (PP5) has been shown to represent residues 1–105 and 1–107 of the β-casein amino acid sequence, while component 8-fast (PP8F) corresponds to residues 1–28 of β-casein. Thus, these proteose-peptones represent the N-terminal portions of the β-casein molecule, produced by proteolytic cleavages which form the γ1-, γ2- and γ3-caseins from the C-terminal part. The continuing formation of the total proteose-peptone fraction, PP5, PP8F and the γ-caseins during storage of raw milk at 18 or 37 °C has also been demonstrated
Casein micelles: the colloid-chemical approach
Authors: Payens Theodoor A. J
Published: June 2009

The colloidal properties of micellar casein are reviewed. It is shown that the behaviour of intact micelles is much at variance with the predictions from the Schulze–Hardy rule, and that therefore their stability cannot be explained by the principles of the DLVO theory. Towards electrolyte, micelles behave as a protein rather than a lyophobic colloid.

Casein is a strong protective colloid. In the micelle, however, it does not completely cover the inorganic constituent which remains sensitive to changes in the ionic environment.

The rate theory of the enzyme-induced clotting of casein micelles is summarized. It is shown that the lag phase in the clotting is due to the second order of the coagulation reaction. Flocculation rate constants of micelles have been deduced from clotting times. Their relatively low values can be attributed to an orientational constraint. Practical consequences of the theory with respect to clot structure, gelation of sterilized products and cheese manufacture are discussed.
Properties of artificial casein micelles
Authors: Schmidt Daniël G.
Published: June 2009

A survey is given of the relationships between various properties of artificial casein micelle systems and their composition with respect to αs1-, β and κ-casein, colloidal phosphate and citrate. Properties investigated were: the amount of colloidal phosphate, the micellar size, and the stability of the micelle towards dialysis, pressure, ethanol and heat.
Utilization of milk proteins as starting materials for other foodstuffs
Authors: Morr Charles V.
Published: June 2009

The modern food-processing industry is placing more and more emphasis upon the utilization of protein ingredients to provide specific functional properties to a wide range of formulated foods. Isolated milk protein products represent an important and valuable source of protein ingredients due to their recognized superior nutritional, organoleptic and functional properties. This paper provides up-to-date information on the quantities, production processes, composition, general properties, and specific functional properties of the major milk protein products, e.g. caseinates, co-precipitates, lactalbumin, whey protein concentrates and milk blends. The subject of chemical and enzymic modification to improve certain functional properties of milk proteins is considered briefly.
Observations on the influence of high cell count on lipolysis in bovine milk
Authors: Salih Amer M. A. , Anderson Malcolm
Published: June 2009

The effect that changes in composition which occur in milks possessing high cell counts have on milk lipolysis has been investigated. High cell counts were produced either by intramammary infusion ofEscherichia coliendotoxin orStreptococcus agalactiaeor by addition of washed cells which were isolated from milk obtained from quarters infused with endotoxin. Free fatty acid levels in milk were measured in terms of acid degree value (ADV) either as initial ADV measured immediately after milking or ADV developed after a prescribed incubation period.

There was an increase in initial ADV after the infusion either of endotoxin or ofStr. agalactiaerelative to a control quarter. This increase appeared to be associated with changes in cell count, but in absolute terms the influence of cells on ADV became less as cell count increased. Neither type of infusion had any effect on lipoprotein lipase activity. The addition of washed cells to normal milk resulted in an increase in developed ADV, but the increment was not as large as that produced by the addition of 1% blood serum. When cream and skim-milk from endotoxin-treated quarters and control quarters were mixed in different combinations with and without additional cells, developed ADV was higher in those samples containing endotoxin cream and those with added cells. Milk from a quarter treated with endotoxin was diluted with its own skim-milk to produce different cell counts and ADV was determined after various time intervals at 4 and 37 °C. Lipolysis increased with increasing cell count, but a depression in lipolytic rate was noted after incubation for 6 h at 4 °C and 20 min at 37 °C.

The proportion of skim-milk lipoprotein lipase activity in milk serum was larger both in milks possessing high cell counts and in normal milk adjusted to between 5 and 20 mM-NaCl by addition of solid NaCl. These levels of NaCl inhibited lipolysis.

The possible direct and indirect effects of high cell count on milk lipolysis are discussed.
Effect of proteolytic raw milk psychrotrophs on Cheddar cheese-making with stored milk
Authors: Law Barry A. , Andrews Anthony T. , Cliffe Allan J. , Sharpe M. Elisabeth , Chapman Helen R.
Published: June 2009

The effect of proteolytic, psychrotrophic strains of Pseudomonas fluorescens, Ps. putida and Acinetobacter spp. on cheese-making with stored milk has been investigated. Ps. fluorescens and Ps. putida growing for 72 h in raw milk at 7·5 °C to levels of approx. 107 colony-forming units/ml caused a low degree of β- and к-casein breakdown detectable by gel electrophoresis, but this was insufficient to affect N losses in whey or cheese yields. Variations in cheese-making times with pasteurized milks were not attributable to the counts of psychrotrophs in the corresponding raw milks. The water-soluble and TCA-soluble N fractions of maturing cheeses were unaffected by psychrotroph counts in raw milks, but small differences in levels of casein fractions of cheeses made from milks stored for 72 h were detected by quantitative polyacrylamide gel electrophoresis. The incidence of casein breakdown in raw milk and subsequently in cheese were not necessarily related. None of the cheeses developed off flavour related to excessive protein breakdown but many became lipolytically rancid, despite the selection of strains with low lipolytic activity on a diagnostic medium. It is concluded that the numbers of psychrotrophic bacteria likely to occur in stored raw milk under commercial conditions are unlikely to cause significant changes in the yields or quality of Cheddar cheese through their proteolytic activity.
The conductivity of milk—the effect of the volume and degree of dispersion of the fat
Authors: Prentice J. H.
Published: June 2009

The conductivity of raw and homogenized milks was measured using apparatus capable of high precision. The effect of fat content was examined and found to conform to the established behaviour for a polydisperse suspension of nonconductors in a homogeneous conducting medium. Homogenization of the milk over a range of pressures was found to have no measurable effect on the conductivity.
A modified method for the determination of glyceride glycerol
Authors: Moore J. H.
Published: June 2009

A routine method giving accurate results was required for the determination of the glyceride content of eluate fractions obtained in the silicic acid chromatography of lipid mixtures. The technique of determining glyceride glycerol by saponification, oxidation of the liberated glycerol to formaldehyde, reaction of the formaldehyde with chromotropic acid and measurement of the resulting chromogen at 570 mμ has been investigated. Procedures based on this principle have appeared in the literature but none of these has been found to be entirely satisfactory. Accordingly, a modification of the method has been developed that is capable of giving results of a high degree of accuracy.
A compound responsible for metallic flavour in dairy products: I. Isolation and identification
Authors: Stark W. , Forss D. A.
Published: June 2009

The ‘metallic compound’ previously reported as an important cause of off-flavour in oxidized dairy products has been identified as oct-l-en-3-one. The compound was found to have a flavour threshold value of one part in 109 in butterfat and one part in 1010 in water. This compound was also isolated from oxidized safflower oil.