bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

SummaryLow-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

SummaryResults 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

SummaryEquipment 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

SummaryUltra-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

SummaryMicelles 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

SummaryDiacetyl, 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

SummaryMilk 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

SummaryA 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

SummaryYeast 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

SummaryA 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

SummaryStarch-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

SummaryA 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

SummaryThe 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

SummaryThe 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

SummaryThe 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

SummarySlow, 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

SummaryAcetate 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

SummaryThe 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

SummaryAssay 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

SummaryMilk-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

SummaryPellets 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

SummaryThe 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

SummaryCheddar 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

SummaryChanges 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

SUMMARYFrom 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.