bluuebunny/crossref_metadata_2025 huggingface dataset:
The differentiation of curd made from heated and raw milk
Authors: Guha K. C. , Roy B. R.
Published: June 2009

Since Indian law requires curds to be made from heat-treated milk, a means for distinguishing between curds made from raw and from heat-treated milks was sought. Curds contain whey proteins that are partly or completely denatured by heat treatment; the kinetics of the reaction are first order. The concentrations of native whey proteins in raw and heat-treated milks and in curds made from those milks were measured. No difference was found between the concentrations in heattreated milk and in the curds made from it, so that identical values were obtained for the half-life on heating and for the activation energy of denaturation. The acidity and microbial growth occurring during the production of curd did not affect the whey proteins. On electrophoresis, curd from raw milk gave a few whey protein bands, but curd from milk boiled for 10 min gave none, showing complete denaturation of the whey proteins.
Metabolite levels and enzyme activities in the bovine mammary gland at different stages of lactation: I. Metabolite levels related to energy production
Authors: Waldschmidt Marianne
Published: June 2009

Samples of the mammary gland were obtained from heifers, lactating and dry cows by a freeze-clamping technique. Amounts of lactate, pyruvate, malate, ATP, ADP and AMP were determined in the sample extracts and calculated per g fresh weight and per mg DNA. Pyruvate, lactate and AMP amounts showed only minor changes at different stages of lactation, whereas quantities of malate, ATP and ADP were significantly higher in cows giving high milk yields. Pyruvate levels showed seasonal variations parallel to changes in milk composition. NAD: NADH ratios in mammary cytoplasm showed no significant differences between different groups of cattle, whereas ATP: AMP ratios in mammary gland samples were highest in lactating animals.
Examination of the structure of the bovine milk-fat-globule membrane and of cheese by X-ray crystallography
Authors: Evans E. W. , Pillinger Susan L.
Published: June 2009

Low-angle X-ray diffraction techniques have been applied to the study of the structure of the fat-globule membrane of milk and of Cheddar cheese. Membrane was prepared by freeze-thawing, churning and ether extraction, the endproduct of each method being a pellet produced by centrifuging. High-angle and low-angle reflexions from membrane could be related to triglyceride spacings, and low-angle reflexions due to spacings at about 5·5 nm to phospholipid bilayers. Spacings due to triglycerides were observed in mature Cheddar together with spacings that agreed well with values for some of the amino acids.
Analytical variation in metabolic profile testing
Authors: Manston R. , Rowlands G. J.
Published: June 2009

Results are presented demonstrating quality control of the analytical procedures used during the application of metabolic profile tests to dairy herds over a period of 3 years. The significance of analytical variance is discussed in relation to the average population variance in dairy herds.

It is concluded that analytical variance can be restricted to reasonable proportions providing that careful quality control is continuously employed.
An experimental continuous-culture unit for the production of frozen concentrated cheese starters
Authors: Lloyd G. T. , Pont E. G.
Published: June 2009

Equipment and methods are described for the production, on the laboratory scale, of frozen concentrated cheese starters. A single-stage Porton-type fermenter with a working volume of 3–5 l was used for the continuous culture of theStreptococcus lactisandStr. cremorisstarter strains. The cells grown in a trypsin-digested cheese-whey or trypsin-digested skim-milk, both containing autolysed yeast, were harvested with a Sharples laboratory super-centrifuge, resuspended in skim-milk and layer-frozen in liquid N2. The frozen culture was crushed to a granular free-flowing form facilitating direct addition to and ready dispersion in cheese milk. The cultures were stored at −196°C.
The effect of dissolved O2 on the changes occurring in the flavour of ultra-high-temperature milk during storage
Authors: Zadow J. G. , Birtwistle R.
Published: June 2009

Ultra-high-temperature (UHT)-treated milks containing a range of dissolved O2 levels were prepared using both direct and indirect UHT processes. The O2 content of directly processed UHT milk had a significant influence on the changes in the level of cooked flavour in the product during storage over a 12-week period. At storage temperatures of 2 and 20°C, a noticeable improvement in flavour could be achieved by O2 control. In general, samples with a head-space sufficient to yield an initial of 60–100 mm were most preferred. The effect of O2 control on samples stored at 38°C was only minor when compared with the marked decrease in acceptability of flavour occurring due to the high storage temperature.

Directly processed samples stored at 20°C all gelled at 14 weeks while those stored at 2°C showed no evidence of gelation after 36 weeks. Storage at 38°C gave rapid flavour deterioration, bitterness at 7 weeks and gelation at 10 weeks.

All indirectly processed samples were found to be severely cooked under the conditions employed, and any differences in flavour due to differing O2 contents were masked by the intensity of this flavour.
Physico-chemical properties of casein micelles reformed from urea-treated milk
Authors: McGann T. C. A. , Fox P. F.
Published: June 2009

Micelles reconstituted from urea-treated milk by exhaustive dialysis against bulk milk were similar to native micelles with respect to colloidal phosphate: casein ratio, ethanol stability, heat stability and susceptibility to first-stage rennin action. Reconstituted micelles were considerably smaller than native micelles as indicated by turbidity, sedimentation and viscosity, had shorter second-stage rennet coagulation times, were unstable to [Ca2+] > 20 mM and had reduced base-binding capacity. It is suggested that the induced Ca sensitivity is due to unfavourable alterations in the micellar κ-casein coat arising from the decrease in average micelle size and can be offset by increasing the κ-casein complement of the system or by increasing the degree of aggregation by slowly raising the [Ca2+] level.
Diacetyl, acetoin, 2,3-butyleneglycol, 2-butanone and 2-butanol concentrations in ripening Cheddar cheese
Authors: Keen A. R. , Walker N. J.
Published: June 2009

Diacetyl, acetoin, 2,3-butyleneglycol, 2-butanone and 2-butanol concentrations have been determined in ripened Cheddar cheese made usingStreptococcus diacetilactisDRC1 orStr. cremorisAM2or HP as starter culture. Diacetyl content was found to be initially higher in the DRC 1 cheese than in the other 2 cheeses, presumably because this starter readily ferments citrate. The disappearance of acetoin appears to be related to the formation of 2,3-butyleneglycol in DRCl and AM2cheeses, but not in HP cheese. Only trace amounts of 2-butanone and 2-butanol were observed in the 3 cheeses even though the concentration of a postulated precursor, 2,3-butyleneglycol, was present in considerable concentration in the DRC1 and AM2cheeses. Analysis of a number of mature AM2and HP cheeses selected at random indicated the presence of 2-butanone in only a few of the AM2cheeses. It is suggested that this compound may have arisen from the presence of a micro-organism which entered the cheese vat at the time of cheese-making.
Milk gel Structure: II. Relation between firmness and ultrastructure of heat-induced skim-milk gels containing 40–60% total solids
Authors: Kalab Miloslav , Harwalkar V. R.
Published: June 2009

Milk gels varying widely in firmness were examined by both scanning and transmission electron microscopy, and a close correlation was found between their ultrastructure and firmness. In gels containing 40 and 50% total solids (14 and 17% protein respectively), casein micelles appeared as individual entities linked by some bridging material. At 60% total solids (20% protein), the micelles were fused and offered a considerably higher resistance to a penetrometer probe. Likewise some additives to gels, such as ammonium persulphate and CaCl2, caused the micelles to fuse. These chemicals appreciably increased firmness of such gels. In gels containing hexametaphosphate, a known inhibitor of gelation, most of the casein micelles were disintegrated; these gels were soft.
Separation of the glycopeptides released by the action of rennin on whole milk
Authors: Simpson G. , Sinkinson G. , Wheelock J. V.
Published: June 2009

A comparison has been made of a number of different elution conditions for the separation by ion-exchange chromatography of the glycopeptides released by the action of rennin on whole milk. It was found that the most satisfactory separation was achieved using an NaCl gradient (0·10–0·18m) in 0·049 m-KH2PO4+0·001 m-Na2HPO4at a constant pH of 5·1.
The nature of the stimulation of the growth ofStreptococcus lactisby yeast extract
Authors: Smith J. Selby , Hillier A. J. , Lees G. J. , Jago G. R.
Published: June 2009

Yeast extract was fractionated on Sephadex G-25 into 7 fractions. The fraction most stimulatory to the growth ofStreptococcus lactisC10 contained over 70% of the amino N present in yeast extract and consisted of a wide variety of free amino acids and a small amount of peptide material. Examination of possible replacement factors for this fraction revealed that the amino-acid material present was largely responsible for the stimulation ofStr. lactisC10. Purine and pyrimidine bases and inorganic constituents also contributed to the stimulation. In addition, yeast extract contained a component which decomposed H2O2, a metabolite which accumulates in the growth medium under aerobic conditions and inhibits growth. The nature of the stimulation was studied by isolating slow and fast acid-producing colonies ofStr. lactisC10. It appeared that yeast extract and other amino-acid supplements prevented an observed inhibition of the growth of the slow variants below pH 6·0, apparently by satisfying a nutritional deficiency caused by a drop in pH.
Tributyrate as a substrate for the determination of lipase activity in milk
Authors: Castberg Helge B. , Solberg P. , Egelrud T.
Published: June 2009

A procedure is described for the determination of the lipolytic activity in milk using tributyrate as substrate. The method is based on the titration of liberated butyric acid in a diethyl ether: light petroleum (2·75:1, v/v) extract of the incubation mixture. Some of the fundamental factors involved in the procedure are discussed.
Proteolysis detection in milk: IV. Starch-gel electrophoresis and formol titration
Authors: Juffs H. S.
Published: June 2009

Starch-gel electrophoresis (SGE) and formol titration methods for detecting proteolysis in cold-stored raw milk have been studied to establish their value as quality indices. When examined by SGE, the first evidence of proteolysis in raw milks stored at 5°C was the formation of para-κ-casein. However, this fraction could not be detected on the starch gels until the total bacterial count (TBC) exceeded 107/ml. The SGE method appeared more reliable than the previously discussed tyrosine value method. Formol titration did not appear to have any application in the screening of cold-stored raw milks with TBC < 107/ml, but would detect some milks of poorer bacteriological quality.
Urea and phosphate supplemented molassed sugar-beet pulp nuts used as a major component of milk production concentrates for dairy cows
Authors: Parkins J. J. , Fishwick G. , Ritchie N. S. , Hemingway R. G. , Henderson R.
Published: June 2009

A cubed molassed sugar-beet pulp product containing about 3% urea and with added minerals and vitamins was evaluated in 2 continuous feeding trials over 8–10 weeks with cows in early lactation and which had previously been accustomed to receiving dietary urea. In one experiment 50% substitution of a cereal/vegetable protein mixture resulted in a depression in mean daily milk yield of about 0·8kg. In the second experiment, the concentrate contained about 30% dried distillers grains and in this case replacement of one-half with the supplemented molassed sugar-beet pulp product did not decrease milk yields. There were no significant effects on milk composition.
Association of bovine αs1- and β-casein using the fluorescent properties of 1,8-anilinonaphthalene sulphonate
Authors: Creamer L. K. , Wheelock J. V.
Published: June 2009

The effects of NaCl, CaCl2and temperature on the emitted fluorescence of anilinonaphthalene sulphonate (ANS) in solutions of αs1- and β-casein indicated that the ANS was associated with the protein. Increased aggregation of the protein was responsible for further enhancement of the fluorescence. Addition of CaCl2to a mixture of αs1- and β-casein at 37 °C caused a greater increase in fluorescence than when αs1- or β-casein was used alone, supporting the suggestion that these 2 proteins form co-polymers with different properties from the homopolymers and indicating that hydrophobic bonding between αs1- and β-casein may be important in the presence of Ca.
Membrane material in bovine skim-milk from udder quarters infused with endotoxin and pathogenic organisms
Authors: Anderson M. , Brooker B. E. , Andrews A. T. , Alichanidis E.
Published: June 2009

The effects of infusing endotoxin and a pathogen into different quarters of the udder of the same cow on the appearance and composition of milk membrane material were studied. Milk membrane was prepared by high-speed centrifugation of skim-milk. In samples from the control quarters only, a very thin layer covering the casein pellet was observed, whereas after the infusions it appeared as an opaque diffuse fluffy layer. The fluffy layer persisted for a maximum of 3 d after endotoxin infusion. A similar layer appeared 14 d after infusion of the pathogen and persisted, in spite of antibiotic treatment, throughout the experiment. From comparisons of (a) milk acid phosphatase activities between infused and control quarters, (b) the protein composition of milk membrane, and (c) morphological observations on the distribution of membrane material in milk, it was concluded that milk membrane originates from leucocytes, cell debris from the mammary gland, and the surface of the milk-fat globule membrane. The relative contribution made by these sources to milk membrane from healthy and infected udders is discussed.
Moving boundary electrophoresis of native and rennet-treated casein micelles
Authors: Pearce K. N.
Published: June 2009

The electrokinetic potential of bovine casein micelles was determined under a variety of conditions using moving boundary electrophoresis. The technique used allowed sharp stable boundaries to be formed without addition of density gradient-forming materials. Casein micelles are negatively charged and in any one milk sample all micelles had similar electrophoretic mobilities. The electrokinetic potential of micelles was markedly reduced by the action of rennet and to a lesser extent by a decrease in temperature from 30 to 6°C. Addition of sucrose to milk caused a small increase in the electrokinetic potential. Addition of anionic detergent to milk increased both the electrokinetic potential and the rennet coagulation time. Addition of cationic detergent caused a reduction in both these quantities, promoted syneresis of the rennet coagulum and caused coagulation in the absence of rennet if present in concentrations exceeding about 10 mM. Alteration of cation activities by addition of salts to milk caused complex changes, either increasing or decreasing the electrokinetic potential. The data obtained are most readily explained by a model for the casein micelle in which some, but not necessarily all, of the κ-casein is located at the micelle surface.
Aggregation of whey proteins during storage of acidified milk
Authors: Argyle P. J. , Jones N. , Chandan R. C. , Gordon J. F.
Published: June 2009

Slow, irreversible aggregation of whey proteins in acidified milk or whey at pH 3·4–4·6 held for up to 10 d at 35–45°C was revealed by the reduction of discrete bands in disc electrophoresis. The aggregation was confirmed by precipitation of protein observed in stored, acid whey. The rate of aggregation of all protein fractions increased with the acidity and the storage temperature. It was enhanced by the presence of casein, but was unaffected by the presence of milk fat or by pasteurization of the fresh, unacidified milk at 70°C. The effect may contribute to the physical properties of certain fresh cheeses and other cultured dairy products.
Acetate utilization by the isolated perfused guinea-pig mammary gland
Authors: Mepham T. B. , Davis S. R. , Humphreys J. R.
Published: June 2009

Acetate uptake by isolated perfused guinea-pig mammary glands was approximately l·0 mg g−1 h−1 when perfusate acetate concentrations were in the physiological range (5–11 mg/100 ml plasma). At perfusate concentrations below this range (mean 3·62 mg/100 ml plasma) the uptake was not significantly different, but in one experiment in which the mean acetate concentration was 14·5 mg/100 ml plasma the uptake was markedly elevated. Radioactivity from Na [1-14C]acetate was incorporated into CO2 and milk and tissue fat, being largely present in C16 and C18 fatty acids. The guinea-pig is atypical of non-ruminants and similar to ruminants in respect of the blood concentration and mammary utilization of acetate.
Carotene and immunoglobulin concentrations in the colostrum and milk of pasture-fed cows
Authors: Newstead D. F.
Published: June 2009

The carotene and immunoglobulin concentrations in colostra and milks of 6 Jersey, 4 Friesian and 6 Jersey × Friesian cows were determined during the first 21 d of lactation. Carotene concentrations of between 50 and 300 μg/g milk fat were found at first milking and these declined to normal concentrations, in the range 9–21 μg/g milk fat, by the eighth to tenth day of lactation. Immunoglobulin concentrations at first milking were in the range 4–40 g/l milk and decreased to normal concentrations, in the range 0·3–0·5 g/l, by the fifth to seventh day of lactation. For both substances the data from each cow's milk fitted an exponential decay model. The fractional rates of decrease in concentration of carotene were 0·19–0·57/d and of immunoglobulin were 0·40–0·73/d. Breed-group differences were observed in both carotene and immunoglobulin concentrations in milks after the fourteenth day of lactation. In Jersey milks, the average carotene and immunoglobulin concentrations were respectively 18·5 μg/g milk fat and 0·32 g/l of milk, while in Friesian milks the concentrations were respectively 11·4 μg/g milk fat and 0·46 g/l milk. There was also a difference between breed groups in the daily rates of decrease of the immunoglobulin concentrations. The average rate of decrease for the Friesians was about 1·5 times the rate for the Jerseys.
Enzymic methods for estimation of the somatic cell count in bovine milk: 1. Development of assay techniques and a study of their usefulness in evaluating the somatic cell content of milk
Authors: Kitchen B. J.
Published: June 2009

Assay procedures were developed for a number of enzymes in milk which apparently originate from leucocytes. The enzymes studied were acid phosphatase, N-acetyl-β-D-glucosaminidase, β-glucuronidase, arylsulphatase, α-mannosidase, and catalase. Quarter-milk samples were analysed for enzyme activity and results compared with the electronic cell count and the Wisconsin Mastitis Test. All enzymes measured except acid phosphatase and α-mannosidase showed good correlation with the electronic cell count. Of the other 4 enzymes tested, β-glucuronidase and arylsulphatase were unsuitable as diagnostic aids owing to the lengthy incubation periods required in their assay procedures. The assay of catalase, which involved the measurement of the initial rate of release of O2 using an O2 analyser apparatus, was rapid, sensitive and reasonably reliable, if fresh milk samples were used. The assay procedure for N-acetyl-β-D-glucosaminidase was considered to be the most reliable, simple and rapid enzymic method for estimating the number of somatic cells in milk.
Isolation, preparation and the amino acid composition of 4 milk-fat globule membrane proteins solubilized by treatment with sodium dodecyl sulphate
Authors: Cawston T. E. , Anderson M. , Cheeseman G. C.
Published: June 2009

Milk-fat globule membrane (MFGM) proteins were solubilized by treatment with SDS. Four of the major proteins were isolated as SDS complexes using column chromatography. The purity of each isolate was determined by SDS polyacrylamide gel electrophoresis and sufficient of each protein was obtained for amino acid analysis. The amino acid compositions of the isolated MFGM proteins and a total MFGM protein extract were determined. Differences in amino acid composition were found in particular between the major MFGM glycoprotein and the other 3 membrane proteins. The relationships of the amino acid composition to protein properties and structure are discussed.
Characteristic cell fragments in bovine milk
Authors: Brooker B. E.
Published: June 2009

Pellets produced by the centrifugation of bovine milk and of pre- and post-partum colostrum consistently contained small cell fragments (1–4 μm long) morphologically characterized by their possession of abundant microvilli along one margin. They were more common in strippings than in fore-milk and during the first 4–6 weeks of lactation than at later stages. Their possession of cytoplasmic fat droplets and putative casein micelles suggests that they originate from secretory cells of alveoli or small ducts. The significance of their numerous microvilli is discussed.
The metabolism of [14C]bicarbonate byStreptococcus lactis: the fixation of [14C]bicarbonate by pyruvate carboxylase
Authors: Hillier Alan J. , Jago G. Richard
Published: June 2009

The fixation of [14C]bicarbonate into aspartate byStreptococcus lactisC10 was achieved by the combined reactions of pyruvate carboxylase (E.C. 6.4.1.1) and glutamate-oxaloacetate transaminase (E.C. 2.6.1.1). The pyruvate carboxylase fromStr. lactisC10, which was most active at pH 8·0, was activated by the divalent metal ions Mn2+, Mg2+and Co2+, and inhibited by sulphydryl reagents. The enzyme was inhibited non-competitively by aspartic acid and competitively by oxaloacetate.
Cheddar cheese flavour studies: I. Production of volatiles and development of flavour during ripening
Authors: Manning Donald J.
Published: June 2009

Cheddar cheeses were pressed from a batch of curd each month over a period of 1 year to study the production of headspace volatiles and the development of flavour in ripening cheese. At 2-monthly intervals, samples taken from selected sites in the cheese were presented to a trained panel for assessment of quality and intensity of Cheddar flavour. Using a headspace technique samples of vapours from bore holes in different parts of the cheese were analysed for H2S, methanethiol, acetone, butanone, methanol, ethanol and 2-pentanone. Most of the compounds increased in concentration during the ripening period, but ethanol and butanone varied in concentration in an unsystematic way. Possible precursors of the headspace volatiles are discussed.
Microflora of Cabrales cheese: changes during maturation
Authors: Nuñez Manuel
Published: June 2009

Changes in microbial flora during the cheese-making and maturation processes of Spanish mould-ripened Cabrales cheese have been studied. In the interior of the cheese lactic streptococci, mainlyStreptococcus lactis, predominated before and during salting (0–4 d);Str. lactisand lactic acid-utilizing yeasts during dryingroom ripening (5–15 d); moulds, mainlyPenicillium roqueforti, and lactobacilli, mainlyLactobacillus plantarum, predominated during cave-ripening (16–120 d). On the cheese surfaceStr. lactiswas the majority flora before and during salting;Str. lactis, micrococci and leuconostocs were the main microbial groups during drying-room ripening, and micrococci throughout cave-ripening. Coliforms and coagulase-positive staphylococci died off during the first month of maturation.
The health and performance of cows fed large amounts of urea
Authors: Treacher Royce J. , Stark Anthony J. , Collis Keith A.
Published: June 2009

From 6 weeks before calving to the end of lactation 2 groups of 8 cows were fed a ration incorporating a dairy nut containing 29 g/kg urea or an isocaloric isonitrogenous nut containing fish-meal and groundnut. During the 18 weeks after calving, concentrates were fed to appetite. 305-d yields of milk (7023 and 5796 kg) and lactose (345.7 and 273.4 kg) were significantly lower in the urea-fed cows (P< 0·05). Intakes of dry matter, metabolizable energy and digestible crude protein were similar in both groups until 18 weeks after calving when feeding according to yield commenced, but by 6 weeks after calving the urea-fed cows lost only 5% of their immediate post-calving weight compared with 7% in the controls. There was no evidence of ammonia toxicity in the urea-fed cows. Blood glucose concentrations were similar in both groups, but higher serum urea concentrations in the urea-fed cows suggested that there was poor utilization of ingested N. A model proposed by Royet al.(1977) has been used to calculate the requirements of rumen-degradable protein and undegraded protein (UDP) of the 2 groups from their energy intakes and milk yields. Between 4 and 11 weeks post-calving, dietary requirement for UDP closely matched intake of UDP. It is concluded that UDP intake was a major factor in determining the peak milk yield. Mechanisms by which the degradability of the dietary protein might influence milk yield are discussed.
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

The 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

Particles 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

A 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

The 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

Water 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

To 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

Buffalo 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

Lipid 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

Possible 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

The 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

A 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

It 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

Butter 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

The 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

Coagulation 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

Some 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

The 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

The 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

In 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

1. 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

The 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.