bluuebunny/crossref_metadata_2025 huggingface dataset:
Calorimetric identification of several strains of lactic acid bacteria
Authors: Fujita Teruyuki , Monk Paul R. , Wadsö Ingemar
Published: June 2009

A microcalorimetric method has been developed for the identification of 9 representative strains of lactic acid bacteria used in the dairy industry. A chemically defined medium containing several carbohydrates gave reproducible and characteristic growth patterns. The technique is proposed as a rapid alternative method for the identification of bacteria selected for commercial use.
Dynamic responses of the dairy cow's teat to step changes in pressure
Authors: Reitsma Sybren Y. , Scott Norman R.
Published: June 2009

Dynamic responses of the teat end, measured as changes in external diameter and milk flow-rate, due to step changes in pressure, uniformly applied to the whole teat, are presented. The experiment involved a front and a rear teat of each of 6 Holstein–Friesian cows. The measured variables were: (1) step change in pressure, (2) milk flow-rate, (3) step change in external teat end diameter, (4) rise times of pressure and teat end diameter changes, (5) fall times of pressure and teat end diameter changes, and (6) delay times between pressure and teat end diameter changes both at start of rise and of fall times. A statistical analysis showed that front teats expanded more than rear teats (P < 0·05). Several other findings of importance to any system of milk removal through the streak canal of the teat are discussed.
Changes in the activity of lactose synthetase in the goat udder during pregnancy
Authors: Jones Edward A.
Published: June 2009

The lactose synthetase activity of homogenates and particulate fractions prepared from the udders of goats killed at various stages of pregnancy were determined. Both components of the enzyme, galactosyltransferase and α-lactalbumin, became detectable about half way through the gestation period, at the time when rapid proliferation of mammary epithelial tissue commences. Throughout the second half of pregnancy the udder possessed a high level of lactose synthetase activity though the lactose content of the tissue did not increase. These findings are discussed in relation to the endocrine control of lactogenesis in the goat and possible mechanisms for the induction of milk production at parturition.
Effects of restriction of amino acid supply to the isolated perfused guinea-pig mammary gland
Authors: Mepham T. Ben , Peters Andrew R. , Alexandrov Stephen
Published: June 2009

When individual essential amino acids were omitted for periods of 40–100 min from the infusate substrate solution in isolated perfused guinea-pig mammary gland experiments, uptake of methionine, tyrosine, phenylalanine, histidine and tryptophan (group 1) was significantly depressed by a mean of 49·8%, whereas the remaining essential amino acids (group 2) showed no significant decrease in uptake. During depletion periods oxidation of [14C\amino acids was increased. The possible significance of the differences in absorption between the 2 groups of amino acids is discussed.
Biosynthesis and secretion of milk proteins: a review
Authors: Larson Bruce L.
Published: June 2009

Recent years have seen a great increase in the knowledge and understanding of milk proteins. Arising from several origins including the blood stream and various cellular sources, many of the proteins found in milk are products of the secretory cells directly involved in the synthesis and secretion processes of various milk components. The lactation-specific proteins present in major amounts are synthesized in the rough endoplasmic reticulum (RER) under genetic control and undergo further post-translational modifications in their secretory route from the RER through the Golgi apparatus and secretory vesicles before ejection into the lumen with other milk components. Various molecular aspects of these mechanisms and their control are now understood, but many remain to be described.
A phosphate-induced sub-micelle-micelle equilibrium in reconstituted casein micelle systems
Authors: Slattery Charles W.
Published: June 2009

In reconstituted casein systems, complete sub-micelles were previously observed only under extreme conditions of ionic strength, namely a NaCl concentration of 2 M or greater. However, studies with the analytical ultracentrifuge on phosphate-containing casein systems revealed that under certain conditions, a stable sub-micelle-micelle equilibrium was established. Conditions which were standard throughout were 7.5 mg/ml protein, 0.04 M-NaCl, pH 6.6 and 37 °C. The concentrations of added CaCl2 (Ca2+) and inorganic phosphate (P1) were variable. With no P1 present, Ca-sensitive caseins precipitated or formed micelles when k-casein was present, between 6 and 7 mM-Ca2+. With 10–20 mM-P1 precipitation or micelle formation began at about 4 mM-Ca2+ and was complete at about 5 mM-Ca2+. Over this interval, during micelle formation, a sub-micelle peak with s20, w of about 13 S was observed in equilibrium with the broad micelle peak. In a system containing a 2:2:1 weight ratio of ±sI-:²-:k-casein, this sub-micelle was isolated at 4 mM-Ca2+ and 2.5 mM-P1. The mol. wt was 760000 and it thus contained approximately 33 monomer caseins. The reconstituted micelle system formed in the absence of P1 was quite temperature sensitive, forming at 37 °C but disappearing upon cooling. In the presence of P1 the micelles formed at 37 °C but were stable to cooling as are natural micelles. Evidently, a combination of hydrophobic and electrostatic interactions are involved in natural micelle formation, probably with the production of salt bridges of Ca and phosphate ions between sub-micelles.
CPG-chromatography studies on the stability of casein micelles
Authors: Larsson-Raźnikiewicz Märtha , Almlöf Elisabeth , Ekstrand Bo
Published: June 2009

Casein micelles fractionated on controlled pore glass (CPG-10/3000) were shown to be stable by recycling experiments. Only minor effects on the size distribution of the casein micelles were found after heating skim-milk to 100 °C for 10 min, or freeze-drying skim-milk at – 70 °C followed by resuspension in the synthetic milk serum of Jenness & Koops (1962). The heating caused some whey proteins (β-lactoglobulin) to enter the micelle fractions while the freeze-drying caused some of the largest micelles to disrupt. In colloidal calcium phosphate-free skim-milk prepared according to Pyne & McGann (1960) all the micelles appeared to dissociate into monomeric caseins.
The equilibria of calcium and phosphate ions with the micellar calcium phosphate in cow's milk
Authors: Lyster Richard L. J.
Published: June 2009

Calorimetric measurements of the heat of solution of micellar Ca phosphate suggest that this material more closely resembles OH-apatite than amorphous Ca phosphate or any other crystalline form. Preliminary computer calculations of the ionic equilibria of milk salt solutions indicate that, over a wide range of pH and temperature, such solutions are supersaturated with respect to OH-apatite and to various other Ca salts under certain conditions.
Heat stability in concentrated and non-concentrated milks - the effect of urea and β-lactoglobulin levels and the influence of preheating
Authors: Pearce R. John
Published: June 2009

Heat stability as a function of pH has been studied in concentrated and non-concentrated milk systems. The influence of preheating has also been examined. The concentration of β-lactoglobulin has been shown to affect markedly the heat stability behaviour in both systems but with different characteristics. Increasing the level of urea resulted in increased heat stability in non-concentrated milks, but corresponding concentrated milks showed a small decrease in maximum heat stability. It has not been possible to extrapolate heat stability data from nonconcentrated to concentrated milks.
Electrophoretic mobility of casein micelles
Authors: Darling Donald F. , Dickson John
Published: June 2009

A simplified moving boundary electrophoresis technique has been developed for the measurement of the electrophoretic mobility of casein micelles. The zeta potentials of casein micelles from different skim-milk samples were calculated using Henry's equation and shown to decrease with decrease in pH between pH 6.9 and 5.3 and to increase with increase in temperature between 10 and 45 °C. Neither severe heat treatment (up to 135 °C for 51 min) nor centrifugal fractionation of micelles into different micelle size ranges had any significant effect on zeta potential. The ionic composition of the serum phase has been shown to be extremely important in determining the electrophoretic mobility. Casein micelles electrophoresed through milk ultrafiltrate consistently gave a lower mobilities than the same micelles centrifuged through milk centrifugate. The results are discussed in relation to present theories of casein micelle structure; these theories do not accommodate all of the observations.
Thermograms ofStreptococcus thermophilusandLactobacillus bulgaricusin single and mixed culture in milk medium
Authors: Monk Paul R.
Published: June 2009

Microbial thermograms have been used to investigate the growth ofStreptococcus thermophilusandLactobacillus bulgaricusin single and mixed culture in milk medium. Growth has been observed with different ratios of the strains in the inoculum and, at one ratio, the effect of the amount of inoculum. The effect of serial sub-culture both with and without pH control has been observed, and stimulation ofStr. thermophilusby cell-free fitrates ofL. bulgaricushas been examined. The development of the technique is discussed in terms of the application of microbial thermograms in selecting cultures for incorporation into mixtures and evaluating their performance.
255. A study of persistency in a herd of Ayrshire cows
Authors: Pontecorvo G.
Published: June 2009

Connecting the trend of the different parts of the lactation curve with what is believed to be the underlying hormonal mechanism, it has been pointed out that any analysis of the curve must deal separately with three parts. The central portion, lying between the peak of daily production and the rapid decline (drying off) has been the object of investigations in an inbred Ayrshire herd. Coefficients of persistency were obtained by fitting exponential curves to this central portion. When first lactations were excluded and correction for month of calving applied, the coefficients (P) were found to be reasonably consistent for different lactations of the same cow. Month of calving accounted in this herd for about one-third of the variance of P. Of the remaining variance approximately one-half is attributed to differences among cows. A possible physiological explanation of the cause of the well-known negative correlation between maximum yield and persistency has been suggested. No conclusions can be drawn from this material on the relative importance of heredity and environment in determining persistency.
257. The influence of various factors on the fermentation end-products of the heterofermentative lactobacilli
Authors: Thiel C. C.
Published: June 2009

1. The influence of temperature, oxygen tension, yeast autolysate and chalk on the production of by-products and the ratios of by-products formed to sugar utilized and lactic acid produced in milk by the lactobacilli has been investigated.

2. The total production of lactic acid is increased by the presence of chalk and “growth factors” but is not affected by temperature or oxygen tension. The ratio of lactic acid produced to sugar utilized is decreased at lower temperatures and increased by chalk but yeast autolysate and variation in oxygen tension give variable results.

3. The total production of acetic acid is increased by the presence of chalk, and “growth factors” and by anaerobic conditions. The ratios of acetic acid produced to sugar utilized and lactic acid formed are decreased by chalk and anaerobic conditions and there is a tendency for the ratios to be decreased by the presence of yeast and increased at lower temperatures.

4. The total production of alcohol is increased by anaerobiosis and also by the presence of chalk and yeast in the medium. The ratios of alcohol formed to sugar utilized and lactic acid produced is increased by anaerobic conditions, and chalk also tends to increase the relative amount of alcohol. Temperature and yeast autolysate have little effect.

5. Chalk is effective in maintaining thepH at a higher level during growth, but the influence of chalk on the ratios of by-products formed to sugar utilized is probably not entirely a pS. effect since the addition of talc to the medium has an equally strong influence in altering the relative production of lactic acid and alcohol.

6. It was previously shown for the heterofermentative streptococci that the Pasteur effect (suppression of alcoholic fermentation by respiration) is slight; similar results have been obtained with the heterofermentative lactobacilli.
Nutritive properties of freshly prepared and stored evaporated milks manufactured by a normal commercial procedure or by reduced thermal processes in the presence of nisin
Authors: Gregory Margaret E. , Henry Kathleen M. , Kon S. K.
Published: June 2009

From a batch of raw milk, evaporated milk was prepared commercially by 3 procedures:A, a normal commercial procedure involving holding the filled cans at a maximum temperature of 113 °C for 15 min;B, with nisin added and holding at a maximum temperature of 105 °C for 15 min;C, with nisin added and holding at a maximum temperature of 113 °C for 3 min. The content ofBvitamins in the raw and evaporated milks was measured microbiologically; the nutritive value of the proteins was determined in rat tests.

In milkA, 83% of the vitamin B12, 38% of the vitamin B6and 20% of the thiamine were destroyed during processing. In milkB, the losses were 67, 30 and 19%, respectively, only the loss of vitamin B12being significantly lower than in milkA. In milkC, the losses were 67, 23 and 14%, respectively, each of them being significantly lower than in milkA. There was no further loss of thiamine on storage of the milks for 12 months at 4 °C, but at room temperature and at 37 °C further losses occurred in all the milks. Similarly, the vitamin B6activity of the milks decreased on storage, the loss being greatest at 37 °C, but also detectable at 4 °C. No change in the vitamin B12content occurred on storage, and no losses of biotin, nicotinic acid, pantothenic acid or riboflavin were detected during manufacture or storage of the evaporated milks.

The biological value and true digestibility of the proteins of the evaporated milks were slightly lower than for the raw milk. Neither nisin treatment nor storage at room temperature for a year affected these characteristics.
An electron microscope study of the internal structure of casein micelles
Authors: Shimmin P. D. , Hill R. D.
Published: June 2009

A study of casein micelles was made with the electron microscope, using very thin sections cut from micelles embedded in Araldite. The micelles appear to be built up of units that are approximately spherical, about 100 Å in diameter and of about 300000 molecular weight.
Some factors influencing stickiness of butter
Authors: Thomasos F. I. , Wood F. W.
Published: June 2009

The term stickiness, as used in the butter industry, refers to that property of butter which permits it to remain attached to solid surfaces. It is a phenomenon in which the components of force caused by adhesion and cohesion are inseparably involved and have been described by the term ‘hesion’. Hesion measurements of commercial samples of conventionally-made butter were much higher than those of continuously-made butter. The results of experiments on conventional and laboratory continuously-made butter from the same butterfat source indicated that the characteristic crystal structure influenced the hesion values. Homogenization of Gold'n Flow and conventional commercial butters markedly increased hesion readings. When nitrogen gas was added to pre-crystallized continuously-made butter the hesion values decreased with increasing gas content. However, there was an increase in the amount of butter which remained on the adherend when it became detached from the butter surface. Limited experiments on the effect of gas content in conventional butter also indicated that an increase in gas content resulted in a decrease in hesion values with more butter remaining on the adherend. The results of this investigation indicated that the crystal structure was responsible for the adhesive property of butter and the gas content influenced the cohesive property. It would appear, then, that both the crystal structure and the gas content play an important part in causing stickiness of butter.
A method for studying the factors in milk which influence the deposition of milk solids on a heated surface
Authors: Burton H.
Published: June 2009

A laboratory method is described which it is hoped will be of value in the search for some of the chemical factors in milk which control the formation of deposits on heated surfaces during commercial processing. The method uses an electrically heated platinum wire as the surface on which deposits are formed under controlled heat transfer conditions. Preliminary results are given on the effect of milk pH on deposit formation, differences in the sensitivity to deposit formation of different bulk milk supplies, and the effect of forewarming on the reduction of deposition.
The influence of liveweight at calving on milk production in Friesian heifers
Authors: Ridler B. , Broster W. H. , Westgarth D. R.
Published: June 2009

Records of 81 heifers, daughters of 6 bulls, were examined to determine the regressions of milk yield, corrected for lactation length, on initial liveweight and age at calving.

Age was found to have no significant effect and was discarded in the final analysis.

The regression equations were similar for the different groups of half-sibs, except for one group whose members had not been fed according to milk yield. After removal of this group, a highly significant positive relationship between lactation yield and liveweight at calving was found ‘within bull groups’. The mean values of groups of halfsibs did not show this relationship, and significant differences in milk yield still persisted between groups after adjustment for liveweight differences.

It was concluded that herd improvement by choosing heifers solely on the basis of liveweight shortly after calving appears unlikely to be effective unless the sire's potential is known and the feeding during lactation takes into account the greater maintenance requirements of heavier animals.
Steam distillation of taints from cream: X. Vapour liquid equilibrium relationships for benzyl mercaptan
Authors: McDowall F. H.
Published: June 2009

The vapour/liquid equilibrium coefficient for benzyl mercaptan, which is the substance causing ‘landcress’ taint in butter from the milk of cows grazing pastures infested with the cruciferous weed Coronopus didymus, was found by use of a continuous vaporization equilibrium still to be 105 from solution in water and 1·30 from solution in cream of 30% fat content. It was concluded that complete removal of heatdeveloped landcress taint from cream would not be commercially practicable.
The labelling of certain milk proteins with iodine131
Authors: Veringa H. A. , Mogot M. F. Kerkhof
Published: June 2009

Whole casein, β-casein, β-lactoglobulin and euglobulin were labelled with131I. The conditions under which iodination was carried out were chosen so as to avoid any modification of the original characteristics of the proteins. This was checked by starch-gel electrophoresis and determination of sedimentation constants, apparent molecular weights and, for euglobulin, the clustering effect on fat globules.

As was shown by autoradiograms of the starch-gel plates, the radioactivity was incorporated in all zones of the electrophoresis pattern.
β-Lactoglobulin variation in milk from individual cows
Authors: Kiddy C. A. , Townend R. E. , Thatcher W. W. , Timasheff S. N.
Published: June 2009

The β-lactoglobulin types of 812 individual cows of various breeds were determined by paper and polyacrylamide gel electrophoresis. The results support the hypothesis that β-lactoglobulins A and B are controlled genetically by codominant autosomal alleles (LgAand LgB).

Milks from 5 heterozygous cows (LgA/LgB) were examined by free electrophoresis and column chromatography to estimate the relative quantities of β-A and β-B produced by these animals. The results indicate that β-A and β-B are produced in approximately equal amounts, with β-A being slightly in excess of β-B.

Lacteal secretions were obtained from 2 castrated males and typed for β-lactoglobulin by means of paper electrophoresis. These animals were found to produce β-lactoglobulins (B and AB) consistent with their expected genotypes as deduced from pedigree analysis.
The effect of intravenous injections of oxytocin during milking and the removal of residual milk on the composition of cow's milk
Authors: Wheelock J. V. , Rook J. A. F. , Dodd F. H.
Published: June 2009

After an injection of oxytocin and the removal of residual milk, the milk obtained at the next milking had an increased content of sodium, chloride and whey proteins and a decreased content of lactose. The effect persisted for several milkings. It is suggested that this was due to a direct effect of oxytocin on the permeability of the mammary epithelium and that oxytocin should be used with caution in certain types of milk secretion experiment.
The effect of intramammary infection during the dry period on the milk production of the affected quarter at the start of the succeeding lactation
Authors: Smith A. , Dodd F. H. , Neave F. K.
Published: June 2009

Intramammary infection present in quarters of dairy cows, either throughout the dry period or originating in the dry period, reduces the milk yield after calving. Relative to the milk yield of equivalent non-infected quarters of the same udder the reduction was found in this work to be about 35%. The relative milk yield of quarters found infected in late lactation was depressed by 48% but if the infection was eliminated during the dry period, the depression in milk yield was only 11% after parturition.
The effect of regular intravenous injections of oxytocin at milking time on the proportion of the yield obtained as residual milk in the ewe
Authors: Morag M.
Published: June 2009

The changes in the size of the milking and residual fractions following milking intervals of 4, 8, 12, 16, 20 and 24 h were investigated in 18 ewes receiving regular injections of oxytocin at each milking. The observations were carried out using a 6×6 Latin square design in which each treatment interval was repeated 4 times. The milking and the residual fractions were found to increase significantly with the lengthening of the interval. The amount of hand strippings was also related to interval length. When a given interval was repeated there were no changes in the relative sizes of the fractions. A change in the milking interval, however, caused significant changes in the various fractions. It is suggested that in the present experiment the milking fractions consisted in the main of milk that was present in the sinuses prior to milking.
The quantitative partition of the albumin fraction of milk serum proteins by gel chromatography
Authors: Davies D. T.
Published: June 2009

A method for the quantitative partition of the albumin fraction of milk serum proteins is described. The partition, which is carried out by chromatography on a column of Sephadex G-100 (2·5×90cm) at 4°C in the presence of 0·02 m-sodium phosphate buffer (pH 6·7) containing 0·1 m-NaCl, yields 4 fractions. By gel electrophoresis it was shown that the fractions represent, in order of elution from the Sephadex, the following: fraction 1, a mixture of the largest proteins present, probably comprising γ-globulins, proteose-peptones and lactoferrin; fraction 2, bovine serum albumin and bovine serum transferrins; fraction 3, β-lactoglobulins; and fraction 4, α-lactalbumins. The protein contents of the various fractions were determined by nitrogen analysis and the results showed that good agreement was obtained between values from duplicate fractionations, and also that the recovery of material was satisfactory. The partition of the albumin fraction was not complete, but at least 90% of the material was found in fractions which represent essentially single proteins. The influences of some aspects of the pretreatment of samples, buffer composition and column preparation are described.
Electron microscope studies of the development of structure in Cheddar cheese
Authors: Kimber Alwyn M. , Brooker B. E. , Hobbs D. G. , Prentice J. H.
Published: June 2009

The development of structure in Cheddar cheese was followed using electron microscopy, of both thin sections and freeze-etched preparations. The casein micelles, at first separate, were seen to aggregate into a network, coalesce and finally form a granular mass. The fat globules, also separate at first, were gradually forced into clumps as a result of shrinkage of the casein network and incomplete fusion took place during ripening. Starter bacteria were seen trapped in the casein near the fat–casein interface, which was shown to be the region of highest water content in the mature cheese.
Disinfection properties of some bovine teat dips
Authors: King J. S. , Neave F. K. , Westgarth D. R.
Published: June 2009

The efficacy of 18 disinfectant teat dips was tested on teats artificially contaminated with a milk suspension of Staphylococcus aureus. A solution of Na hypochlorite with 40 g/l available chlorine was significantly more bactericidal than one containing 1 g/l available chlorine and than most other disinfectants tested. The method was not able to distinguish differences in efficacy between solutions containing 40 g/l and 10 g/l available chlorine nor between these and some of the iodophors containing 5 g/l available iodine. The addition of 190–416 g/l (15–33 % v/v) glycerol significantly reduced the bactericidal properties of 3 iodophors (5 g/l available iodine), but soluble lanolin at approximately 20 g/l did not appear to lower the efficiency of NaOCl (45 g/l available chlorine) or of an iodophor (5 g/l available iodine).
Isoelectric focusing of milk-clotting enzymes
Authors: Righetti P. G. , Molinari Bruna M. , Molinari G.
Published: June 2009

Isoelectric focusing in thin-layer polyacrylamide gel has been applied successfully to the characterization and identification of calf rennet and its substitutes. The use of acidic pH gradients (pH range 2·5–6) allows the identification of calf and microbial rennets and bovine and pig pepsins.

A new, very rapid and sensitive zymogram technique has been developed by overlaying the gel with a highly porous, transparent cellulose acetate film impregnated with casein.
Kinetics of the heat-induced aggregation of milk protein
Authors: White J. C. D. , Sweetsur A. W. M.
Published: June 2009

This investigation was a first attempt to characterize the kinetics of the heat aggregation of the caseinate micelles in milk. The aggregation reaction subsequent to the beginning of visible aggregation in milk heated at temperatures in the range 110–140 °C appeared to be second order, with an activation energy of about 30 kcal/mol (124 kJ/mol). The kinetic parameters of the aggregation reaction were not significantly altered by the removal of serum proteins or of colloidal calcium phosphate, or by the inactivation of β-lactoglobulin.
Mammary blood flow during experimental Escherichia coli endotoxin induced mastitis in goats and cows
Authors: Dhondt G. , Burvenich C. , Peeters G.
Published: June 2009

The effect of intramammary infusion of Escherichia coli endotoxin upon mammary blood flow was studied in lactating goats and cows. Blood flow was recorded by means of an electromagnetic flow probe chronically implanted around one mammary artery.

Endotoxin mastitis was always accompanied by a significant increase in mammary blood flow, characterized by 2 conspicuous peaks. The flow returned to control values by the thirteenth hour after infusion. Other symptoms of acute mastitis were: fever, increased heart rate, swelling, heat and pain of the gland, increased chloride and total cell count in milk.
Resistance of 17 mesophilic lacticStreptococcusbacteriophages to pasteurization and spray-drying
Authors: Chopin Marie-Christine
Published: June 2009

For 17 phages active againstStreptococcus cremoris, Str. lactisandStr. lactissubsp.diacetylactis, the killing efficiency of pasteurization (logNo/N) at 72°C for 15 s in skim-milk showed large variations from > 6 to 0; the efficienty of killing during spray-drying ranged from 3.7 to 0.2 and phages survived well storage of milk powder at room temperature. Destruction in a heat exchanger was found to be greater than that calculated from biphasic curves obtained by heating phages in sealed ampoules. No relationship was established between lytic classification of phages and their heat resistance.
Heat stability of milk
Authors: Darling Donald F.
Published: June 2009

The heat stability of a standard reconstituted skim-milk preparation has been investigated as a function of pH, temperature of coagulation, and forewarming treatment. Apparent activation energies have been calculated from the temperature dependence of coagulation time, and a constant value of 144 kJ/mole has been found for milks between pH 6·6 and 6·9. The effect of forewarming resulted in a decrease in stability at the most acid pH values, a slight increase at higher pH but below the pH maximum, and a decrease in the region of the pH minimum. A working hypothesis is proposed for the mechanisms leading to the coagulation of milk at elevated temperatures, based upon Ca induced precipitation of casein, protein polymerization, β-lactoglobulin: κ-casein interaction, and precipitation of insoluble Ca phosphates.
Binding of calcium ions to bovine β-casein
Authors: Parker Thomas G. , Dalgleish Douglas G.
Published: June 2009

The isotherms for Ca2+ binding to bovine β-casein have been measured at 5 temperatures in the range 4–40 °C and at 4 different ionic strengths. The results are interpreted by an interactive-site binding model, and are compared with results previously obtained on αs1-casein. The affinity of β-cesein for the first Ca2+ to bind is similar to the affinity of αsl-casein for the same binding event: however, binding of subsequent Ca2+ to β-casein is weaker than the binding to αs1-casein. The results are discussed in terms of precipitability of the 2 caseins caused by the binding of Ca2+.
Heat stability of milk: interrelationship between assay temperature, pH and agitation
Authors: Hyslop Douglas B. , Fox Patrick F.
Published: June 2009

As determined by the standard subjective assay procedure, the minimum in the heat stability–pH curve of milk persisted down to at least 116 °C. However when samples were not agitated during heating the minimum became progressively less pronounced as the assay temperature was lowered and it disappeared at approximately 116 °C. Activation energies (Ea) for unagitated samples were approximately 30 Kcal/mole at pH 6·87 (maximum) and at pH 7·18, throughout the temperature range 116–145 °C and for the pH 6·95 (minimum) sample at 116–125 °C; however Eα for the pH 6.95 sample increased to approximately 100 Kcal/mole in the range 127–135 °C suggesting that some highly temperature-dependent reaction had occurred and caused premature coagulation at certain pH values, i.e. to a heat stability minimum. The stability of concentrated milk (20% total solids) was very low at pH values above 6·9, regardless of whether the samples were agitated or not during heating and the maximum/minimum in the heat stability–pH curve persisted down to at least 90 °C in both agitated and quiescent samples.
Leucocytes of sheep colostrum, milk and involution secretion, with particular reference to ultrastructure and lymphocyte sub-populations
Authors: Lee Chee-Seong , Outteridge Peter M.
Published: June 2009

The leucocytes in sheep colostrum, milk and involution secretion were studied using the electron microscope. The predominant cell type in colostrum was the polymorphonuclear leucocyte (PMNL) (41–84%), followed by the macrophage (8–49%), and the lymphocyte (6–11 %). Plasma cells were present in low numbers (1–2%) while no secretory epithelial cells were observed. In mid-lactation the cell components changed so that the macrophage was the predominant cell (83–86%) followed by the lymphocyte (10–17%). In early involution secretion, PMNL reappeared but declined in secretion obtained 21 d after weaning, when the macrophage was again the predominant cell. Associated with the whole cells were membranous extracellular materials and ‘sunburst’ fragments of the secretory epithelial cells. These were phagocytosed by both PMNL and macrophages, which also engulfed fat droplets from the milk. The lymphocytes were examined for plasma membrane markers and the T-cell percentage (E+ rosettes) fluctuated within wide limits, (0–80 %). However, there was no discernible trend associated with stage of lactation. The B-cell markers (C1 and Fcγ) also fluctuated widely and it was evident that contaminating monocytes reduced the accuracy of the count. However, it appeared that more B-cells were present in milk than in blood.
Goat's milk yoghurt made from non-homogenized and homogenized milks, concentrated by different methods
Authors: Abrahamsen Roger K. , Holmen Tove Blytt
Published: June 2009

Quality characteristics of goat's milk yoghurt made from homogenized and non-homogenized concentrates prepared by vacuum evaporation, addition of dried skimmed goat's milk, reverse osmosis or ultrafiltration were observed. Yoghurts made from ultrafiltered milk gave the best flavour and viscosity, whilst homogenization of the concentrates also increased these qualities. Cow's milk yoghurts prepared in the same way were improved to an even greater extent by homogenization. Stirred goat's milk yoghurt had too low a viscosity to be acceptable, unless made from homogenized ultrafiltered milk.
Yoghurt made from single starter organisms using heat- or enzyme-treated milk or milk to which casein hydrolysate or sodium formate is added
Authors: Marshall Valerie M. E. , Cole Wendy M. , Mabbitt Leonard A.
Published: June 2009

Yoghurts were made with single strain starter organismsLactobacillus bulgaricusandStreptococcus thermophilus, L. bulgaricusbeing cultured in milk + 50 ppm Na formate or in autoclaved milk andStr. thermophilusin milk treated with the proteinase Maxazyme(R)or with added casein hydrolysate. They were assessed chemically and organoleptically and compared with conventional mixed starter yoghurt. The single starter yoghurts all had acceptable acidities and acetaldehyde levels and keeping quality was good. The coagulum of each was firm and when stirred no syneresis occurred; the yoghurts remained smooth and all had an excellent appearance.
The effect of preheat temperature and urea addition on the seasonal variation in the heat stability of skim-milk powder
Authors: Kelly Philip M.
Published: June 2009

The manufacture of skim-milk powder with heat stable characteristics was investigated commercially during the course of 8 trials carried out over a 12-month period. Skim-milk was preheated to temperatures ranging from 110 to 130 °C with a 2-min holding time prior to evaporation and drying. The effect of added urea was also examined during each trial run. Heat coagulation times at 120 °C were determined upon reconstitution of the powders to 20% total solids. From February to April the heat stability of the skim-milk powders increased, with the more heat stable samples being obtained at the higher preheating temperatures. Addition of urea increased the heat stability, particularly so in those milks which had been preheated to 130 °C. The presence of added urea during preheating was not found to be necessary as an equal effect on heat stability was observed when urea was introduced at the concentrate stage before drying. Later in the season optimum heat coagulation times were obtained by maintaining preheating temperatures at 118–120 °C.
Use of the Limulus test to determine the hygienic status of milk products as characterized by levels of Gram-negative bacterial lipopolysaccharide present
Authors: Hansen Karlo , Mikkelsen Tom , Møller-Madsen Aage
Published: June 2009

The Limulus test was used to investigate the occurrence of Gram-negative bacterial lipopolysaccharide (LPS) in milk and dairy products. This test specifically detects the extremely heat-resistant LPS, and so determines the total accumulated quantity of LPS in a product whether it has been heat-treated or not. A positive correlation between number of psychrotrophic bacteria and amount of LPS in fresh farm milk was found (r = 0·63). Fresh farm milk and freshly produced market milk contained on average < 1 ng LPS/ml. The Limulus test is considered highly suitable for use in the dairy industry, being a method which will characterize quickly and specifically the hygienic level of a product by the extent of the cumulative contamination by Gram-negative bacteria.
Changes in the concentrations of metabolites in milk at the onset and cessation of lactation in the goat
Authors: Faulkner Anne , Blatchford David R. , White Jann M. , Peaker Malcolm
Published: June 2009

Changes in the concentrations of various metabolites in mammary secretions (organic acids, UDP-hexoses and nucleotides) have been observed at the onset and cessation of lactation. All metabolites, with the exception of galactose, increased dramatically in concentration just before and immediately after parturition. Galactose concentrations decreased with the onset of lactation. After regular milking ceased, the concentrations of these metabolites in milk contained within the udder fell, but the rates of decline varied.
Electronically controlled feeding troughs for dairy cows: some nutritional implications
Authors: Broster William H. , Clough Peter A. , Clements A. June , Siviter John W.
Published: June 2009

Over 3 years, 4 groups of heifers and 6 groups of cows calving in the autumn were used in a study of electronically controlled compound feed dispensers. For each group the treatments consisted of access or no access to the dispensers (selector feeders) arranged factorially with 2 levels of compound feed in the milking parlour. These were applied in weeks 3–15 of lactation. A basal diet including high quality silage was fed ad lib. communally to each group. The mean intake of compound from the dispensers was 5·6 kg/d, but there was considerable variation from animal to animal. The dispensers were visited at all times of the day and notably during the night. There was no bullying around the feeders. Milk yield was greater with the higher level of parlour feeding, and with access to the feed dispenser at the lower, but not the higher level of parlour feeding. Liveweight change benefited from additional compound feed supplied by either method.
Alkylglycerols in bovine colostrum and milk in relation to precursor levels
Authors: Ahrné Lennart , Björck Lennart , Claesson Olof
Published: June 2009

The concentrations of dihydroxyacetone phosphate (DHAP), glycerol- 3-phosphate (GP), glucose and alkylglycerols were measured in bovine colostrum and milk. Concentrations of GP were higher in colostrum than in milk, and corresponded to intracellular concentrations at the onset of lactation. This suggests that GP equilibrates over the apical membrane at onset of lactation, which is believed to occur also in full lactation. The ratio of DHAP to GP showed a peak in colostrum that was more than twice that in milk, indicating that concentration changes in colostrum/milk were not caused by dilution. DHAP was positively correlated to metabolical compounds such as glucose and alkylglycerols. As DHAP is a required precursor for alkylglycerol synthesis, the positive correlation suggests that DHAP may be limiting for alkylglycerol synthesis and thus could explain the elevated levels of alkylglycerols found in colostrum.
Effects of thermization and cold storage on some properties of rennet-induced milk gels
Authors: Johnston Donald E. , Murphy Robert J. , Whittaker Norah R.
Published: June 2009

The effects of thermization (a sub-pasteurization heat treatment), followed by cold storage at 7 °C for up to 3 d on the post-gelation behaviour of rennet-induced gels from alternate-day collected milks, pasteurized before testing, were investigated. Observations of the time course of gel rigidity modulus development and of the syneresis of cut curds were fitted to a general exponential relationship to aid interpretation. Milk performance was assessed by measurements of rennet coagulation time at pH 6·5, various gel rigidity and syneresis parameters and losses of protein and Ca to the whey. A small but significant reduction in protein losses to the whey (mean 0·05%) was the only effect resulting from thermization. Cold storage gave rise to significantly weaker gels than those from unstored controls. The gels from cold-stored milks attained 50% of their maximum rigidity modulus in significantly less time and lost significantly more protein (mean 0·11%) to the whey. Samples cold stored for 1, 2 or 3 d were not significantly different from each other and no other parameters were affected. No significant interactions between thermization and cold storage were found.
Pulsation failure as a consequence of milking with short teatcup liners
Authors: Mein Graeme A. , Brown Murray R. , Williams David M.
Published: June 2009

Half-udder comparisons were made using 72 and 59 cows in 2 experiments of 8 months duration to assess the incidence of pulsation failure, and its effects on teat condition and mastitis, as a consequence of milking with shortened teatcup liners. Diagonally opposite quarters of all cows were milked with control liners of 148 mm effective length or with the same liners shortened to an effective length of 110–130 mm by inserting a rigid sleeve in the lower barrel of the liner. Milking with shortened teatcup liners resulted in a high incidence of pulsation failure (defined for this experiment as failure of the liner to collapse fully beneath the teat in each pulsation cycle throughout milking). More than 50% of hind teats and 90% of front teats in the research herd penetrated deeply enough into the teatcup to prevent cyclic collapse of liners shortened to 130 mm. Such failure occurred with all teats in liners shortened to 125 mm for front teats or 110 mm for hind teats. The combined results for the 2 experiments showed that almost twice as many new mastitis infections occurred in quarters milked with the shortened liners (47 υ. 25, P < 0·01). This effect was confined to front quarters for which there was a 3-fold difference in the number of new infections (32 for the short liners υ. 11 for the controls, P < 0·001). In both lactations, significantly more teats had petechial haemorrhages when milked with the shortened liners and the electrical conductivity of milk from uninfected front quarters was higher. These results might reflect an interaction between pulsation failure and differences in the degree of overmilking that usually occur between front and hind quarters.
Nutrient content of liquid milk
Authors: Scott K. John , Bishop Dinah R. , Zechalko Alicja , Edwards-Webb John D. , Jackson Patricia A. , Scuffam David
Published: June 2009

A survey was undertaken to update and extend available information on the vitamin content of pasteurized milk as produced at processing dairies in mainland UK and to investigate regional, seasonal and breed effects. The concentration of total retinol in milk from non-Channel Island (NCI) breeds averaged 61·9 βg/100g in summer and 41·2 βg/100g in winter. Concentrations of β-carotene were 31·5 and 10·5 βg/100g in summer and winter respectively. Concentrations of retinol in milk from Channel Island (CI) breeds were similar, but concentrations of β-carotene were on average 3 times higher. The concentration of vitamin D3in milk from NCI breeds was 0·033 βg/100g in summer and 0·026 βg/100g in winter. There was no marked seasonal variation in the mean concentration of total vitamin C (14·5 βg/ml). Values for the concentration of B vitamins (βg/ml) were: folic acid 0·060, vitamin B120·0042, riboflavin 1·78, nicotinic acid 0·71, pantothenic acid 3·60, biotin 0·020, thiamin 0·46 and vitamin B60·61. Seasonal variation in the concentration was most marked for folic acid (c.v. 17·4%) and to a lesser extent for vitamin B12(c.v. 10·3%). The only breed differences in the B vitamin content were for riboflavin and folic acid, the mean values obtained for milk from CI breeds being respectively 20 and 10 % higher than those from NCI breeds.
Evaluation of a fluorimetric assay on the lipases from strains of milk psychrotrophic bacteria
Authors: Stead Donald
Published: June 2009

A fluorimetric assay, developed for the assay in milk of the lipase of the raw milk psychrotrophPseudomonas fluorescensAR11 (Stead, 1983), was evaluated in both buffer and in milk using cell-free lipase preparations from 11 strains of lipolytic psychrotrophic bacteria isolated from milk. Lipases of all strains were more active against 4-methylumbelliferyl nonanoate (4-MUN) than against 4-methylumbelliferyl oleate (4-MUO) in the buffer system but most were less active against 4-MUN than against 4-MUO in the milk assay system. In both systems, 4-MUO had a much lower rate of non-enzymic hydrolysis than did 4-MUN. Lipase activities measured by radial diffusion in tributyrin agar and trioctanoin agar reflected activities against 4-MUO and 4-MUN, except that lipase from a strain of coliform was relatively more reactive against the 4-MU esters. When compared with assay in the buffer system the most effectively activated lipase in the milk system was that from AR11; of those from other strains, 6 were 50–69% as effectively activated, 2 were about 17% and 2 were 7–8% activated. This difference in behaviour was related to the direct inhibition of lipases of some of the strains by the mixture of sodium taurocholate (NaTC) and cetyltrimethylammonium bromide (CTAB) needed in the milk assay system to dissociate lipase from milk protein. Increasing the proportion of NaTC to CTAB increased the activities of the more weakly activated lipases but decreased those of others. The assay in milk may therefore underestimate the lipase from certain strains of psychrotrophic bacteria.
Glucose levels in normal and mastitic milk
Authors: Marschke Ronald J. , Kitchen Barry J.
Published: June 2009

Glucose levels in 188 quarter fore milks from different cows were determined by an enzymic procedure. Mean glucose content was 0·22 mM (standard error ±0·009) and results ranged from 0·02–0·57 mM. Abnormal quarters had lower glucose levels (P < 0·01) than normal quarters but variability within each classification was large. Glucose content was negatively correlated with both somatic cell count (r = –0·49) and N-acetyl-²-D-glucosaminidase level (r = –0·61). Milk glucose was considered to be of limited value as a diagnostic test for mastitis.
Chemical composition and coagulating properties of renneted milks from cows during early lactation
Authors: Grandison Alistair S. , Ford Graeme D. , Millard David , Owen A. Jane
Published: June 2009

The detailed composition, pH, and the properties of rennet clotting, coagulum development and syneresis at pH 6·4 were estimated in milks from 4 Friesian cows during the first 9 weeks of lactation. The concentrations of casein, fat, citrate, Ca, Mg, Pi and Na decreased significantly during early lactation whilst the pH and concentration of lactose increased. Levels of whey protein and K and the casein:fat ratio were unaltered. Considerable variation occurred in the relative proportions of α-, β- and κ-casein. These changes in composition were associated with decreasing coagulum strength and an increased rate of whey drainage although rennet clotting time (RCT) did not follow a significant trend. RCT was positively related to levels of Na and whey protein but negatively correlated with Pi, K and lactose. There were significant positive correlations between coagulum strength and casein, fat, non-protein nitrogen, Pi, Ca, Mg and citrate. The correlation with α-casein was stronger than that with β- or κ-casein. Syneresis time was positively related to fat, Ca and coagulum strength, but negatively related to the concentration of lactose.