bluuebunny/crossref_metadata_2025 huggingface dataset:
Serological and fluorescence studies of the heat stability of bovine lactoferrin
Authors: Baer Augustin , Oroz Marko , Blanc Bernard
Published: June 2009

The heat denaturation of Fe-saturated lactoferrin (If) and Fe-free lactoferrin (apo-lf) was studied using the methods of micro-complement fixation and fluorescence. It was established that the change in conformation of apo-lf, induced by iron binding, conferred a higher heat stability to the molecule: the changes were observed at temperatures above 40 °C for apo-lf and above 60 °C for If. The Fe-binding ability of the protein was partially independent of the degree of denaturation. Fluorescence analyses indicated that tryptophan residues were probably not directly involved in the metal binding. There was no evidence of antibodies interfering with the binding sites.
The formation of γ-caseins during cooling of raw milk
Authors: Reimerdes Ernst H. , Herlitz Erika
Published: June 2009

It has been shown that there is a time-dependent transfer of β-casein and the milk serine proteinase system from micelles to milk serum with change of temperature from 38 to 4 °C. It has been established that the γ-caseins can be formed by proteolytic degradation of β-casein. By a simple extraction technique, the very hydrophobic γ-casein fraction was separated from stored milks (26 and 4 °C) and estimated quantitatively. The results showed that the proteolytic degradation of β-casein is faster at 4 °C than at room temperature and this can be explained by the immobilization of enzyme and substrate at the micelle surface at higher temperatures (26 °C).

The results indicate that irreversible changes during cooling for short periods do not cause problems in milk processing, but the formation of γ-caseins and phosphopeptides may influence the technological properties of raw milk stored for more than 48 h.
Human β-casein
Authors: Greenberg Rae , Groves Merton L.
Published: June 2009

Human β-casein occurs in multiphosphorylated forms having the same amino acid composition but with 0–5 phosphate groups/molecule. Sequence analysis was used to determine whether each of the phosphorylated forms is a mixture of species having a certain number of phosphate groups randomly distributed or whether each form contains phosphate groups on specific seryl or threonyl residues. It was found that forms containing 2, 4 and 5 phosphate groups/molecule are homogeneous with respect to their phosphorylation sites. The monophosphorylated form, however, is a mixture of equal amounts of species phosphorylated at residues 9 or 10.
The determination of the zeta potential of casein micelles
Authors: Darling Donald F. , Dickson John
Published: June 2009

The principle of moving boundary electrophoresis has been employed for the measurement of the electrophoretic mobility and subsequent calculation of zeta potential of bovine casein micelles. The zeta potential of casein micelles was observed to increase with increase in temperature (from 10 to 50 °C) and to decrease with decrease in pH. Heat treatment of milk between 90 °C/30 min and 135 °C/50 min had no significant effect on zeta potential. The zeta potential of casein micelles during rennet action decreases until all the κ-casein has been cleaved by the enzyme.

The results of this study indicate that electrostatic interactions alone are not sufficient for an understanding of the absolute stability of casein micelles.
Covalent bonds formed in proteins during milk sterilization: studies on caseins and casein peptides
Authors: Lorient Denis
Published: June 2009

Formation of covalent bonds at milk sterilization temperatures was studied using caseins and casein peptides. At 120°C lysinoalanyl residues produced even at pH 7·0 were derived from intra-molecular interactions between phospho-serine and lysine; the conditions of formation were determined. It was also found that the formation of isopeptidic cross-links was significant with conditions more severe than those used for milk sterilization.
Effect of free fatty acids on the amount of deposit formed from milk on heated surfaces
Authors: Al-Roubaie Sami M. , Burton Harold
Published: June 2009

Individual fatty acids were added to liquid skim-milk and to reconstituted dried skim-milk in concentrations similar to those produced by natural lipolysis, and their effects on deposit formation from the milk on a heated surface were determined. The use of reconstituted dried skim-milk considerably improved the reproducibility of the results. Butyric, caproic and caprylic acids did not influence the amount of deposit formation. Capric acid had a marked effect in reducing deposit at low concentrations: the effect of ageing of milk in reducing deposit formation is thought to be due to capric acid development. Laurie, myristic and palmitic acids had a slight effect, increasing deposit formation, while stearic acid caused a considerable increase. Capric acid was found to adsorb to the casein micelles in milk, and it may therefore act by interfering with casein aggregation during the build-up of deposit.
259. A note on a simple and accurate viscosimetric form of rennet test
Authors: King C. W. , Melville E. M.
Published: June 2009

Since publication (1) the apparatus previously described by the authors has been altered and improved. The alterations have been concerned mainly with excluding draughts and securing a better form of support. In using the apparatus we have found that the absence of vibration is important for the agreement of duplicates. It would seem that vibration tends to break the cohesion between the curd and the surface of cylinder A. For this reason a part of the laboratory as free as possible from vibrational disturbances was chosen and the support fixed to the wall.
A comparison between ryegrass and cocksfoot hay for milk production
Authors: Castle M. E. , Drysdale A. D. , Watson J. N.
Published: June 2009

Four hays were compared in a 20-week winter feeding trial using eight Ayrshire cows. The hays consisted of either ryegrass (variety S 24) or cocksfoot (S 37), and each grass was cut either on 23–25 May (cut 1) or 3 weeks later on 13–15 June (cut 2). The ryegrass cut 1 hay (R1) had the highest content of digestible dry matter, the cocksfoot cut 2 hay (C2) had the lowest content. The ryegrass cut 2 hay (R2) and cocksfoot cut 1 hay (Cl) had intermediate values. On all the treatments the cows were offered 19 lb of hay daily plus concentrates at the rate of 3½ lb/10 lb of milk.

The consumption of concentrate dry matter was almost identical on the four treatments and averaged 10·1 lb per cow per day but the intake of C2 was slightly, but significantly, below that of the other three hays. On average the hays contributed 62% of the total daily intake of dry matter. The total weight of starch equivalent (S.E.) eaten per day increased from 13·6 lb on the C2 treatment to 15·2 lb on the R1 treatment.

The mean daily milk yields on the four hay treatments were: Rl, 32·1 lb; R2, 29·9 lb; C1, 30·5 lb and C2, 26·9 lb. On average the milk yields from cut 1 hays were significantly higher than the yields from cut 2 hays, and the yields from the ryegrass were significantly higher than the corresponding yields from the cocksfoot. The differences in milk composition between treatments were small. The fat percentage of the milk on C2 was higher than that with the other three hays, and with the higher yielding cows the solids-not-fat (S.N.F.) and crude protein percentages were significantly higher on R1 than on the other hays.

It is concluded that the nutritional value of ryegrass hay is superior to that of cocksfoot hay for milk production.
The manufacture of ‘normal’ and ‘starter-free’ Cheddar cheese under controlled bacteriological conditions
Authors: Perry K. D. , McGillivray W. A.
Published: June 2009

A relatively simple method is described for the manufacture of Cheddar cheese under controlled bacteriological conditions. This method is shown to give the required degree of asepsis and to permit the manufacture of cheeses of uniform and normal composition.

The composition, bacteriology and flavour of 28 ‘aseptic’ cheeses and of 18 ‘nonaseptic’ control cheeses made by this method are discussed. Thirty-nine of these cheeses were made using singly 3 strains of Streptococcus cremoris and 2 strains of Str. lactis as starter and 7 were made using gluconic acid lactone in place of starter. The effect of inoculating the milk with a strain (25·2) of ‘Lactobacillus plantarumcasei’ and a strain (L1) of micrococcus was also investigated.
A thermoduric strain ofStreptomyces albus, isolated from Cheddar cheese
Authors: Fryer T. F. , Sharpe M. Elisabeth
Published: June 2009

A strain ofStreptomyces albus, presumed to have originated in raw milk, was found in large numbers in a pair of experimental cheeses. The numbers of streptomyces in both cheeses remained constant over the 4-month period of sampling and a comparison of the numbers obtained from cheese dissolved in citrate with and without mechanical aid revealed no differences, suggesting that the streptomyces was present in the conidial state. The heat resistance of mycelium and of conidia was determined at 62·7 °C (145 °F) and 71·7 °C (161 °F). The mycelial cells showed no resistance to either temperature, there being 100% kill after 15 min at 62·7 °C and 17 sec at 71·7 °C. The conidia, however, were very much less affected after 2 h at 62·7 °C, and 3% remained viable even after 30 min at 71·7 °C. Although the strain was found to be proteolytic, lipolytic and saccharolytic, it appeared to be inactive in the cheese, being present in the conidial state.
The recovery of small numbers of Staphylococcus aureus infused into the bovine teat cistern
Authors: Newbould F. H. S. , Neave F. K.
Published: June 2009

Small volumes of milk each containing an average of less than 10 colonyforming units of Staphylococcus aureus were injected into the teat cisterns of 39 quarters of 10 cows.

Typical staphylococci were recovered from only 14 quarters following overnight incubation of milk stripped manually from each quarter 10 min after injection. There was an inverse relationship between the total leucocyte count of the milk taken from the quarter before infusion and recovery of staphylococci.

From 4 of 8 quarters from which Staph. aureus could not be recovered by enrichment it was possible to recover the organism by centrifuging the milk and culturing the deposit of leucocytes and bacteria.

It is suggested that release of ingested staphylococci from defunct phagocytes may be important in initiation of infection, failure of antibiotic therapy and recurrence of infection.
The response of the bovine mammary gland to an infusion of staphylococci
Authors: Newbould F. H. S. , Neave F. K.
Published: June 2009

Small numbers of bovine staphylococci, usually less than 30, were infused into the teat cistern of 17 cows secreting less than 100 000 leucocytes/ml milk. Infection was assumed to have occurred if the organisms multiplied sufficiently to be recovered in the foremilk and inflammation was regarded as demonstrated if there was an increase in leucocytes. If the staphylococci were recovered at the 1st post-infusion milking they were consistently recovered thereafter and inflammation always followed but was never evident at the 1st post-infusion milking. Inflammation was usually evident by the 3rd but in one instance was delayed to the 11th post-infusion milking. There was never inflammation in the absence of infection. When there was a high probability that the infusion contained one organism or more, infection occurred in 2 of 10 quarters infused with coagulase-negative staphylococci and 23 of 25 quarters infused with coagulase-positive staphylococci.

A significant positive relationship was found between the number of staphylococci found at the 1st post-infusion milking and the number of leucocytes at the 3rd postinfusion milking.
Changes in moisture distribution caused by partial reworking of butter shortly after churning
Authors: Dolby R. M.
Published: June 2009

Samples of butter were reworked at various times after removal from the churn, either in a laboratory mixer or by pressing between a microscope slide and cover glass. Moisture distribution was studied by microscopic examination and by indicator papers.

Reworking within 30 min of completion of the original working caused no change in moisture distribution but delayed reworking caused aggregation of water droplets. The further the setting of the butter had proceeded before reworking, the greater was the extent of aggregation.

Cream-cooling treatments which resulted in a softer butter delayed or decreased the aggregation of droplets caused by reworking.

A theory is suggested relating changes on reworking with the formation of a crystal structure on setting.
Anti-O chaining titre in colostral serum from cows infused prepartum with Salmonella Pullorum-H
Authors: Porter R. M.
Published: June 2009

A high anti-O chaining titre against Salmonella pullorum-H can be obtained in colostral serum when the killed antigen is introduced into the mammary gland during the dry period. A significant titre, several times the normal level, is maintained in the milk serum for 3 weeks postpartum. There was a definite residual titre in the milk serum of non-infused cows against the O and H antigens of Salmonella typhosa and the O antigen of S. pullorum-H.
Iron and vanadium requirements of lactic acid streptococci
Authors: Reiter B. , Oram J. D.
Published: June 2009

Lactic acid streptococci have an absolute requirement for magnesium and potassium and failed to grow in milk deionized with IRC 50 resin (sodium form) (Reiter unpublished; see also Fisons, 1958; Reiter, 1956). These findings were confirmed in preliminary experiments using the defined medium of Reiter & Oram (1962). Requirements for other metal ions have now been investigated. Two strains of Streptococcus lactis (ML3 and C10) and one of Streptococcus cremoris (HP) were used. They were maintained as milk cultures, and before use subcultured twice in the synthetic medium containing Ca, Mg, Fe, Zn, Mn, Co, Cu and Mo (cf. Reiter & Oram, 1962) and then finally in the synthetic medium containing only Mg and K (20 ppm.), and Fe (0·01 ppm.).
A new approach to the measurement of the quantitative effects of inherent and environmental factors on the composition of the milk of individual cows and of herds, with particular reference to lactose content
Authors: Walsh J. P. , Rook J. A. F. , Dodd F. H.
Published: June 2009

(1) A tentative scheme is proposed for the quantitative estimation of the effects of various factors on one major milk constituent, lactose, from analyses of the milk of individual cows within herds. The potential lactose content in the milk of individual cows is predicted from the observed potassium-to-lactose ratio in the milk, and the difference between the predicted potential and the actual lactose content is partitioned into fractions that are attributed to effects due to age, inter-quarter difference and changes with stage of lactation. The scheme was applied to 2 commercial herds, one (herd A) producing milk of low and the other (herd B) milk of normal SNF content.

(2) Lactation mean values for fat, SNF and lactose contents of the milk of individual cows showed a wide range of the same order in each of the 2 herds. Of the mean difference in SNF percentage of 0·30 between the herds, 0·14, or 47%, was due to a difference in lactose content.

(3) The predicted potential milk lactose content of the cows in the 2 herds ranged from 5·04 to 5·66 (g/100 g milk water). Herd mean values were 5·394 for herd A and 5·244 for herd B.

(4) Herd mean values for the effect on the lactose content (g/100 g milk water) of age, of changes with stage of lactation and of inter-quarter difference were −0·127, −0·080, and 0·073 respectively in herd A, and −0·197, −0·058 and −0·078, respectively, in herd B.

(5) The relative importance of the various factors in accounting for differences between the herds in the lactose content of their bulk milk were: predicted potential lactose content 61%, effect of age 28%, effect of changes with stage of lactation 9% and effect of inter-quarter difference 2%.

(6) The errors attached to the estimation of potential milk lactose content and the effects of age, of changes with stage of lactation and of inter-quarter difference are discussed.
The effects of mono-unsaturated and saturated fatty acids in the diet on milk-fat secretion in the cow
Authors: Steele W. , Moore J. H.
Published: June 2009

The effects of the addition of either 5 or 10% ‘oleic acid’ (78% pure) or 10% of a mixture of saturated fatty acids (64% palmitic acid, 31% stearic acid) to the dietary concentrate mixture on the yield and composition of the milk and milk fat and on the pattern of fermentation in the rumen were investigated in a feeding experiment with 8 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 9·1 kg of hay/day.

The addition of 5% ‘oleic acid’ to the concentrate mixture resulted in increased yields of milk and solids-not-fat (SNF); the percentage of fat in the milk was decreased but the yield of milk fat was unaltered. The addition of 10% ‘oleic acid’ to the concentrate mixture decreased both the yield and percentage of fat in the milk. In contrast, the concentrate mixture containing 10% of the mixture of saturated fatty acids increased the yield of milk fat.

When the concentrate mixture containing 5% ‘oleic acid’ was given to the cows, the yields and percentages of the fatty acids from 4:0 to 16:0 (except 12:0) in the milk fat were decreased, but the yields and percentages of 18:0 and 18:1 were increased. Similar but more pronounced effects on the yields and percentages of the fatty acids from 4:0 to 16:0 (except 12:0) in the milk fat were observed when the cows were given the concentrate mixture containing 10% ‘oleic acid’, but under these dietary conditions the yield and percentage of only 18:1 in the milk fat were increased. The addition of the mixture of saturated fatty acids to the concentrate mixture decreased the percentages of the fatty acids from 4:0 to 14:0 (except 12:0) in the milk fat but decreased the yields of only 10:0 and 14:0; the yields and percentages of 16:0 and 18:1 were increased.

When the cows were given the concentrate mixture containing 5% ‘oleic acid’ there was a small but significant decrease in the acetic acid:propionic acid ratio in the rumen liquor. A similar but more pronounced change in the acetic acid:propionic acid ratio in the rumen liquor was observed when the cows were given the concentrate mixture containing 10% ‘oleic acid’, but in this instance there was a significant reduction in the concentration of total volatile fatty acids in the rumen liquor. Apart from a small increase in the relative proportion of propionic acid, the addition of the mixture of saturated fatty acids to the concentrate mixture had no effect on the concentrations of volatile fatty acids in the rumen liquor.
The responses in milk solids-not-fat and protein contents to improved feeding of cows receiving winter-stall diets and underfed for varying periods
Authors: Wright J. A. , Rook J. A. F. , Wood P. D. P.
Published: June 2009

The effect of varying periods of energy undernutrition on milk yield and composition was determined in 30 British Friesian cows receiving a typical winterstall diet. An absence of steaming-up, and underfeeding from the beginning of lactation, depressed both milk yield and solids-not-fat (SNF) content, especially in early lactation. Initially the reduction in milk SNF content was accounted for mainly by a loss in lactose content, but as lactation progressed this effect lessened and an effect on milk protein content was established. Protein content was similarly depressed by underfeeding in mid-lactation. The restoration of normal feeding in mid-lactation after varying periods of underfeeding was associated with only small responses in SNF and protein contents.

The effect of the type of basal diet and supplementary concentrates on the extent of the increase in SNF and protein contents in response to improved feeding was examined in 2 further experiments. Responses were in all instances small and it was concluded that with the diets commonly in use in Great Britain the provision during the winter period of supplementary concentrates, whatever their composition, is unlikely to give a marked improvement in milk SNF or protein contents.
Responses in rumen fermentation and milk-fat secretion in cows receiving low-roughage diets supplemented with protected tallow
Authors: Storry J. E. , Brumby P. E. , Hall A. J. , Johnson V. W.
Published: June 2009

The effects on rumen fermentation and milk-fat secretion of a dietary supplement of protected tallow given to 4 Friesian cows established on a low-roughage ration and with depressed milk fat is reported. The ratios of acetate to propionate in the rumen were unaffected by the supplement and remained typical of those associated with low-roughage diets in that the proportion of propionate was increased. The supplement produced almost complete recoveries in yield and content of milk fat without any increase in intramammary fatty-acid synthesis. The recoveries were due to transfer of about 20% of the total fatty acids of the tallow supplement. These results are discussed in relation to the effects of low-roughage diets on milk-fat secretion and it is concluded that in the ‘low-fat syndrome’ the capacity of the mammary gland to absorb preformed fatty acids is not impaired.
Studies on the heat stability of milk protein: I. Interconversion of type A and type B milk heat-stability curves
Authors: Sweetsur A. W. M. , White J. C. D.
Published: June 2009

Coagulation time–pH curves with a coagulation-time minimum around pH 6·8 (type A curve) could progressively become type B (no minimum) as the heating temperature was decreased from 150 to 130°C. The short coagulation time that most milks have when pH is around 6·8 was found to be the result of a ‘premature’ coagulation, probably caused by calcium phosphate deposition on the larger caseinate micelles. This is followed by a second coagulation, not visually detected, that coincides with the coagulation time that would be expected if no coagulation-time minimum existed on the coagulation time-pH curve. The coagulation time of milks giving type A and type B curves may therefore not be comparable.

Forewarming milk for 30 min at 80°C can introduce or accentuate a coagulationtime minimum when the milk is subsequently heated at a higher temperature. The effects of adding β-lactoglobulin, copper and N-ethylmaleimide on the heat stability of milk were examined and explanations proposed for these effects.
Water vapour sorption properties of dried milk baby foods
Authors: Varshney N. N. , Ojha T. P.
Published: June 2009

Water vapour adsorption and desorption properties of spray- and roller-dried milk baby foods were determined by a dynamic method at 25, 35 and 45°C. The equilibrium moisture content increased with increase in relative humidity and decrease in temperature; values for the spray-dried milk baby food were higher than those for the roller-dried product. The desorption and adsorption isotherms exhibited hysteresis. The desorption isotherms were of sigmoid shape: the adsorption isotherms were of similar shape except for a region of discontinuity. The relative humidity at which this discontinuity occurred depended on the temperature at which sorption was determined. Monomolecular moisture contents and latent heat ratios are reported.
Changes during storage in stability and composition of ultra-heat-treated aseptically-packed cream of 18% fat content
Authors: Anderson M. , Brooker B. E. , Cawston T. E. , Cheeseman G. C.
Published: June 2009

The stability of homogenized ultra-heat-treated (UHT) aseptically-packed cream of 18 % fat content when added to hot coffee was indirectly monitored in 10 batches of cream, stored for 10 weeks at different temperatures. A tendency to coagulate under standard conditions (instability) is known as feathering. Stability was determined by a procedure in which acetate buffer instead of coffee solution was used as the test solution. The distribution of components between the fat and aqueous phases of the stored cream was also monitored. Feathering score (stability) decreased during storage but was not accompanied by any increase in non-protein nitrogen levels. The amount of casein and Ca in the fat phase of the cream increased with time and was inversely related to feathering score. Some batches of cream contained 0·1 % Na2CO3and 0·1 %Na citrate as stabilizers and these additions were found to improve feathering scores early in the storage period. Initially, the fat phase of these creams contained less casein and Ca than those without the additives, but after 10 weeks the differences in feathering score and in casein and Ca distribution, between the 2 types of cream diminished. Examination by electron microscopy showed that casein micelles were associated with fat globules, apparently linking several globules together, which was less in the creams containing additives, but after 10 weeks the appearance of all creams was similar. Electrophoretic separation of the fat globule membrane (FGM) proteins by SDS-polyacrylamide-gel electrophoresis showed that casein was the principal protein component, but that β-lactoglobulin and native FGM proteins were aslo present.
Progressive changes in individual milk protein concentrations associated with high somatic cell counts
Authors: Anderson M. , Andrews A. T.
Published: June 2009

Progressive changes in the concentrations of milk protein components were followed after infusions ofStreptococcus agalactiaeor bacterial endotoxin into different quarters of individual cows. Both types of infusion produced similar increases in somatic cell count and resulted in similar changes in milk proteins, although the effects of the endotoxin infusion lasted for a shorter length of time.

The treatments had little effect on α-lactalbumin and β-lactoglobin concentrations, but serum albumin and immunoglobulin (Ig) concentrations increased markedly. The greatest effect on serum albumin was after the endotoxin infusion and on Ig after theStr. agalactiaeinfusion. Changes in the individual globulins indicated that passive transfer of blood proteins to milk could not account for the observed increases in IgM and IgA.

αs1-Casein and β-casein concentrations were reduced and inversely related to somatic cell count during the immediate post-infusion period, and this was accompanied by an increase in para-κ-casein. Para-κ-casein was not detected in pre-infusion or post-recovery milk samples. The decrease in β-casein was greater than that of αs1-casein. Casein concentrations returned to pre-infusion levels 2 d and 5 d after the endotoxin andStr. agalactiaeinfusions respectively.

The possibility that proteolytic enzymes are partly responsible for the changes in casein concentration is discussed.
Dipeptide utilization by starter streptococci
Authors: Law B. A.
Published: June 2009

Of 8 strains ofStreptococcus cremoristested, 5 grew almost as well in defined media in which various essential amino acids were supplied in dipeptides as they did in media containing the equivalent free amino acids. The remainder grew poorly or not at all in the peptide-containing media. Growth of peptide-utilizing strains was inhibited by also including structurally-related dipeptides in the medium, presumably due to competition for uptake by transport system carriers. Both types of starters produced cell-free dipeptidases recoverable from the medium of exponential phase cultures. Addition of the partly-purified extracellular dipeptidases to dipeptidecontaining test media initiated growth in strains unable to use peptides.Str. lactisgrew in defined peptide media, but the further addition of structurally-related dipeptides did not inhibit growth, either bcause each dipeptide was transported by a specific carrier or because peptides were hydrolysed extracellularly. The presence of cell-bound extracellular dipeptidase was indicated by the hydrolysis of dipeptides with washed whole cells in buffer. This was not observed withStr. cremorisstrains.
Detection and quantification of non-milk fat in mixtures of milk and non-milk fats
Authors: Timms Ralph E.
Published: June 2009

The triglyceride compositions of 76 Australian milk fats obtained from 3 factories during a whole year were determined by gas-liquid chromatography. It was shown that all the data fitted the equation

with a S.D. of of 0·7088 where C40, C42 and C44 are the weight percentages of triglycerides with carbon numbers 40, 42 and 44. The triglyceride compositions of 10 samples of milk fat from countries other than Australia were also shown to fit the equation. If the equation is assumed to define pure milk fat, it is shown that as little as 5% of any non-milk fats can be detected with > 99% confidence. The amount of non-milk fat in mixtures of milk and non-milk fats can be quantified to better than ±2% with > 95% confidence. Also, the identity of the non-milk fat can usually be deduced by calculation of its triglyceride composition. Analyses of known mixtures and of chocolate and a table spread comprising butter and vegetable oil showed an agreement between observed and expected results well within the predicted confidence limits.
The effect of the chemical structure of additives on the coagulation of casein micelle suspensions by rennet
Authors: Marshall Richard J. , Green Margaret L.
Published: June 2009

Casein micelles in milk-salts solution adsorbed charged detergents and highly-charged polypeptides strongly, neutral detergents less strongly and low molecular-weight amines weakly. A tetra-amine was adsorbed more strongly than a tri-amine. The extent of adsorption of proteins tended to rise as the molecular weight increased. Glycerol and lactate were adsorbed to a limited extent but dextran and α-ketoglutarate were not adsorbed at all. Proline was partly adsorbed, indicating that hydrophobic binding sites were available, and caused some disruption of the casein micelles. Additives were bound to approximately the same extent by casein micelles and rennet coagula. The proportions adsorbed were constant over at least 10-fold ranges of concentration. Additives which increased the rennet clotting time (RCT) acted by binding Ca2+. Most additives decreased the RCT, the extent increasing with the amount adsorbed and the positive charge on the additive. The greatest reduction in RCT was observed with those additives which had positively-charged and hydrophobic moieties and bound most strongly to casein micelles. Of the additives tested, only sodium dodecyl sulphate affected the enzymic action of rennet. The reduction in RCT may have resulted from the neutralization of the negative charge of the micelles or enhancement of their hydrophobicity, favouring hydrophobic interactions between the particles.
Influence of storage of milk on casein distribution between the micellar and soluble phases and its relationship to cheese-making parameters
Authors: Ali Ali E. , Andrews Anthony T. , Cheeseman Gordon C.
Published: June 2009

The influence of storage time and temperature on the distribution of individual milk proteins between the micellar and soluble phases has been examined. Storage at 4 or 7 °C is accompanied by a dissociation of micellar caseins, particularly β-casein, into the soluble phase during the first 48 h, but on further storage there is a partial reversal of this process. At higher storage temperatures (10–20 °C) the contents of all the individual caseins in the soluble phase decrease throughout storage. During cheese–making, losses of fat and curd fines in whey were greater with increased soluble phase casein and clotting times were prolonged. Curd structure was weaker, curds were more moist and slightly lower cheese yields were obtained in stored milks with elevated soluble–phase casein. When milks were stored for up to 3 d at 4 °C cheese gradings were virtually unaffected by storage, but higher temperatures (10–15 °C) led to cheeses being downgraded, largely for body and texture defects but also for flavour after 3 d.

Attempts to reverse the pattern of casein dissociation and to minimize the detrimental effects of milk storage on subsequent cheese-making showed that a heat treatment of 30 min at 60 °C was the most beneficial.
Effect of atropine on plasma amino acid levels and milk secretion of cows
Authors: Roets Eddy , Peeters Georges
Published: June 2009

Subcutaneous injections of 30 mg atropine into lactating cows induced a 20–40% decrease of free amino acid (AA) levels in arterial plasma. Minimum levels were observed after 30–50 min. The decline persisted for more than 6 h. The greatest fall in concentration was noted for tyrosine, methionine, lysine, arginine, phenylalanine and threonine. Arterial glucose levels remained unaffected. The effect of atropine on milk secretion was studied in 2 cows which were milked every hour with the aid of oxytocin. Maximal effects were observed after 3–4 h. They included reduction in concentration of casein and ±-lactalbumin (±-la) and a decline in production of milk (20%), casein (35%), ±-la (45%) and lactose (18%). Uptake by the lactating udder over a period of about 1 h after injection of atropine was studied in 2 cows. Mammary blood flow and glucose uptake remained unaffected. There was a positive correlation between arteriovenous differences of essential AA and arterial plasma concentrations. The uptake of essential AA decreased by approximately 50 %. There was no evidence that atropine has a direct inhibiting effect on the udder. It is suggested that the decrease of ±-la synthesis might induce an inhibition of lactose synthesis and milk production.
The pyruvate test for monitoring the bacteriological quality of raw silo tank milk
Authors: Cousins Christina M. , Rodrigues Ubaldina M. , Fulford Rosemary J.
Published: June 2009

Samples of milk from silo tanks were stored at refrigeration temperatures and examined at intervals for pyruvate content and total colony count. Significant relationships between pyruvate, μg/ml, and log colony forming units (cfu)/ml were established for samples stored at 2°C for 2, 3 and 4 d (3, 4 and 5 d of age respectively) but at 5 and 7°C the relationships after 2-d storage (3 d of age) were not significant. From an overall relationship it was predicted that 4 μg pyruvate/ml would correspond to a bacterial content of 3·7 x 106cfu/ml with 95% confidence limits of 6·6 x 10 cfu/ml. 2·1 x 107cfu/ml.
Mechanism of aggregation of casein micelles in rennet-treated milk
Authors: Green Margaret L. , Morant Steven V.
Published: June 2009

The frequency distribution of aggregates of casein micelles was determined inelectron micrographs of rennet-treated skim-milk. The average degree of aggregation was constant until after 60% of the coagulation time, then increased linearly to 100% of the coagulation time and subsequently rose more slowly. The observations indicated that the rate of aggregation of casein micelles was determined by the random collision of particles, with no preference for the formation or reaction of aggregates of any particular size. The linking together of micelles was not rate-determining.
Factors affecting the ethanol stability of bovine milk
Authors: Horne David S. , Parker Thomas G.
Published: June 2009

Changes in the ethanol (EtOH) stability/pH profile of skim-milk induced by forewarming have been investigated as a function of temperature and duration of forewarming and of milk pH prior to heating. Forewarming increased the EtOH stability of a milk in the mid-pH range, shifting the profile laterally to more acid pH values, with little effect being observed on the maximum and minimum EtOH stabilities. No significant changes in forewarming effects were obtained on adding the sulphydryl-blocking agent, N-ethylmaleimide, indicating the lack of involvement of serum protein interactions in the stabilizing effects of forewarming. It is suggested that the observed effects of forewarming are due to a heat-induced precipitation of colloidal calcium phosphate. This suggestion is supported by measurements of Ca2+ levels in forewarmed and untreated skim-milk as a function of pH and is in agreement with the previously suggested mechanism for the EtOH-induced coagulation of skim-milk. The effects of permitted additives (citrate, phosphate and Ca) on the EtOH stability of forewarmed milk paralleled their effect on untreated milk. A comparison is made of the effects of forewarming on the heat and EtOH stabilities of skim-milk.
Casein compositional studies: II. The effect of secretory disturbance on casein composition in freshly drawn and aged bovine milks
Authors: Barry J. Gerard , Donnelly William J.
Published: June 2009

Whole casein preparations obtained from paired quarters (one healthy and one subclinically infected) of each of 6 individual cows were fractionated quantitatively by column chromatography on hydroxyapatite. Infection was associated with an apparent decrease in the αs- and β-casein fractions and increase in the γ- and κ-casein fractions. The increase in the κ-casein fraction was attributable mainly to enrichment with chymosin-resistant minor components of casein.

The profile produced by column chromatography on DEAE-cellulose of casein isolated from a healthy quarter of a single cow differed significantly from that from a subclinically infected quarter of the same cow. These differences were increased by incubation of the quarter milks at 37 °C for 8 h. Extensive fragmentation of [14C]methylated αs2- and β-casein, and less extensive fragmentation of [14C]methylated αs1-casein, occurred during incubation of these proteins in milk from an infected quarter. Fragmentation was almost entirely inhibited by soybean trypsin inhibitor. From a consideration of the chromatographic behaviour of the radiolabeled fragments on DEAE-cellulose, and other data presented, it was concluded that proteolysis of caseins by a plasmin-like enzyme was sufficient to account, in qualitative terms, for most of the compositional changes exhibited by casein from subclinically infected quarters.
Effect of cheese-making temperatures on the interactions of lactic streptococci and their phages
Authors: Mullan W. Michael A. , Daly Charles , Fox Patrick F.
Published: June 2009

The interactions of 23 bacteriophages on strains of lactic streptococci at 30, 38 and 40 °C were studied in reconstituted skim-milk and broth media. In milk, 3 different temperature mediated responses were observed. Extensive phage replication at 30, 38 and 40 °C with inhibition of acid production by infected cultures was observed for 8 phages; extensive phage replication at 30 and 38 °C, but not at 40 °C, was observed for 4 phages, while 11 phages replicated at 30 °C but not at 38 or 40 °C. Studies in broth media revealed that failure of phage to replicate at 38 and 40 °C was not due to lack of host growth in most cases, but due to a temperature sensitivity on the part of the phage. In one phage–host system, phage replication continued after growth of the host had ceased. The significance of these findings to starter selection for cheese manufacture is discussed.
Effects of dietary supplements of protected lipids on the concentration and transport of β-carotene and cholesterol in bovine blood and milk: unusual chromatographic behaviour of the high-density lipoprotein with high levels of β-carotene
Authors: Ashes John R. , Burley Ralph W. , Davenport James B. , Sidhu Gurcharn S.
Published: June 2009

The effects of feeding lipids protected against microbial degradation in the rumen, on the metabolism of β-carotene and cholesterol in the blood and milk of cows were studied. The diets fed to the cows consisted of a basal mixture of crushed oats and lucerne hay with a protected vitamin supplement containing α-tocopheryl acetate and β-carotene fed in conjunction with either (i) protected sunflower oil-seed rich in linoleic acid (PO), (ii) protected tallow (PT), or (iii) formaldehyde-treated casein (C) as a control. Diets PO and PT raised the concentrations of β-carotene and cholesterol in the blood plasma over that observed for diet C. Milk cholesterol concentrations were not affected by dietary supplements, but the level of β-carotene in milk of cows on diet PO showed a tendency to fall compared with milk from cows fed PT or C. The properties of the high density lipoprotein (HDLP) of the blood plasma which contained the β-carotene were affected by the PO diet. As a result of feeding this diet, the fatty-acid composition of the HDLP was altered and it emerged from a gel-filtration chromatographic column earlier than the control. This change in chromatographic behaviour was used as a measure of the effect of the diet, which, for some cows, was apparent long after the diet was changed. It is suggested that the altered lipid composition resulting from the PO diet affected the distribution of particle sizes of the HDLP and might interfere with the transfer of β-carotene from plasma to milk.
Surface properties of milk fat globules: interfacial tension studies
Authors: Phipps Leslie W. , Temple Dilys M.
Published: June 2009

A method capable of determining the interfacial tension (γ) of individual emulsified liquid drops has been investigated and applied to a study of the surface properties of milk fat globules. Measurements on several organic liquids in bulk against water were made to validate and standardize the technique. With one exception, results agreed well with literature values, but the reproducibility of measurements was not as good as that of other, standard, methods. Measurements performed on small drops were affected by several factors and precision was not high.

The influence of different milk treatments upon the interfacial tension of milk fat globules was studied. Agitation of milk had the effect of increasing γ while the effect was reversed upon allowing agitated milk to stand. Dilution of normal milk with water resulted in an increase in γ while acidification and alkalization produced a decrease. Pasteurization of raw milk caused a slight, non-significant decrease. Values of γ were low, 1–2 mN m-1, irrespective of the nature of the milk treatment and were an order of magnitude smaller than those obtained for interfaces of butter oil and milk protein solutions. The results support the concept of a 2-layer membrane and suggest that changes in γ follow mainly the adsorption/desorption of surface active components in the outer hydrophilic layer of the globule membrane. An inner, firmly bound lipophilic layer, resistant to many different milk treatments, appears to determine the overall low γ value under most conditions.
A viscometric study of the flocculation of the components in stored homogenized ultra-heat-treated cream
Authors: Phipps Leslie W.
Published: June 2009

The apparent relative viscosity (ηr) of stored homogenized ultra-heat-treated ‘coffee’ cream increased with time (t) at a rate which was a function of mean fat globule diameter (d) and fat volume fraction (ø); the rate was also influenced by Na2CO3and Na citrate when present as stabilizing additives. Viscosity increases were attributed to the progressive flocculation of fat globules and to the strengthening of the structure formed by the gradual accretion of casein micelles on to globule surfaces and their points of contact (bridging). The expression

wheretis in days anddin μm, was found to hold over a 12-week storage period for a batch of creams (ø = 0·143) of differentdvalues prepared from the bulk cream containing carbonate and citrate stabilizers; η0is the relative viscosity att= 0 andkis a rate parameter. In the absence of stabilizers the parameterkassumed a smaller value and so appeared to be a function of chemical composition of the cream and of forces of particle interaction; seasonal factors were also suspected of influencingk. The effect of the fat volume fraction on storage behaviour was not fully resolved, but there was some evidence that the proportionality log ηrα1/ø½ was appropriate.
Effect of milking machine factors on the somatic cell count of milk from cows free of intramammary infection: II. Vacuum level and overmilking
Authors: Olney George R. , Mitchell Robert K.
Published: June 2009

The effect of milking vacuum levels and overmilking on the somatic cell count of milk from cows free of intramammary infections was determined. In the first experiment, 4 levels of vacuum ranging from 35 to 70 kPa were compared in a Latin square design with 20 cows being milked at each of the 4 vacuum treatments for periods of 19 d. In the second experiment 40 cows were milked for 16 weeks at either 50 or 70 kPa with or without 5 min overmilking. Neither vacuum level nor overmilking affected somatic cell count and it is concluded that these factors do not cause stress or irritation that will lead to an increase in somatic cell count in the absence of mastitis infections.
Effect of milking machine factors on the somatic cell count of milk from cows free of intramammary infection: III. Pulsator rate
Authors: Olney George R. , Scott George W.
Published: June 2009

The effect of pulsator rates on the somatic cell count of milk from cows free of intramammary infections was determined. Four pulsator rates ranging from 30 to 120 cycles/min were compared in a Latin square design with 20 cows being milked at each of the 4 pulsator rates for periods of 19 d. Somatic cell count was not affected by any of the pulsator rates and it is concluded that varying pulsator rates will not cause stress or irritation that will lead to an increase in somatic cell count in the absence of mastitis infections.
Thermal stability of an extracellular proteinase fromPseudomonas fluorescensAFT 36
Authors: Stepaniak Leszek , Fox Patrick F.
Published: June 2009

A metalloproteinase, isolated from a shaken milk culture ofPseudomonas fluorescensAFT 36 by chromatography in DEAE and CM-cellulose and Sephadex G-150, was very unstable in 0·1 m-phosphate buffer, pH6·6, being completely denatured above 70 °C in 1 min. It was also unstable in a Ca-containing buffer (synthetic milk salts, SMS) between 50 and 60 °C (minimum at 55 °C), but stability was very high above 80 °C in this buffer. D-values were determined at 10 °C intervals in the range 70–150 °C in SMS from which a Z value of 31·9 °C and anEaof 8·82 × 104J mol-1were calculated; the half-life at 150 °C was 9 s.

Instability at 55 °C was due to autolysis as evidenced by gel electrophoresis, gel filtration and increase in 2,4,6-trinitrobenzenesulphonic acid-reactive amino groups. The extent of inactivation experienced at 80 °C was inversely related to the rate of heating to 80 °C,i.e.length of time spent in the neighbourhood of 55 °C. Addition of increasing concentrations of caseinate substrate reduced inactivation of the enzyme at 55 °C, presumably due to substrate binding. Attempts to stabilize the enzyme at 55 °C by addition of EDTA or by adjusting the reaction pH to 4·2, at which the enzyme has little proteolytic activity, were unsuccessful, although autolysis was prevented.

Unlike the proteinase fromPs. fluorescensMC 60, AFT 36 proteinase did not inactivate itself on cooling to 55 °C from 80, 100 or 150 °C, but did regain autolytic activity on cooling to below 50 °C to an extent dependent on the duration of holding at the lower temperature. It is suggested that on heating to ∼ 55 °C, a conformational change occurs which renders the enzyme susceptible to proteolysis by still active enzyme; at higher temperatures the enzyme, although susceptible to autolysis, is inactive; an active conformation is restored on cooling to below 50 °C.