bluuebunny/crossref_metadata_2025 huggingface dataset:
The free and masked sulphydryl groups of heated milk and milk powder and a new method for their determination
Authors: Lyster R. L. J.
Published: June 2009

A new method is described for the determination of the free and masked sulphydryl (-SH) groups in heated milk and milk products. The procedure is based on the use of the specific -SH reagent p-chloromercuribenzoate, and utilizes another specific -SH reagent, 5,5' -dithiobis(2-nitrobenzoate), as an indicator producing yellow colours which are matched with the aid of standard glasses in the Lovibond Comparator.

The method was applied to heated skim-milks and a series of commercially prepared milk powders. Measurements were made in particular of the -SH content of UHT-treated milk. The changes in the -SH content of such milks on storage were studied; these changes could not be explained by a reversal of the denaturation of the whey proteins, although evidence was obtained that small amounts of heatdenatured whey protein can revert to the native state.
Histochemical study on the ripening of Parmesan cheese
Authors: Bolcato V. , Pallavicini C. , De Felice M.
Published: June 2009

The results reported suggest that it is possible to follow the ripening of Parmesan cheese by means of histochemical reactions for proteins, glycoproteins, acid mucopolysaccharides and lipids containing choline.

The blue colour, formed when the proteins of the curd were stained with Bonhag's reagent, slowly turned to violet and then to red as ripening progressed.

Glycoproteins and acid mucopolysaccharides, although present in very small amounts, appeared to be a constant characteristic of the cheese.

Lipids containing choline, which were absent from the curd, were clearly visible in 3 to 7-month-old cheese. They then decreased and were absent in the ripened cheese.
A compound responsible for mushroom flavour in dairy products
Authors: Stark W. , Forss D. A.
Published: June 2009

The ‘mushroom compound’ previously reported as a gas chromatographic fraction of oxidized dairy products has been identified as oct-l-en-3-ol. The alcohol was found to have a flavour threshold value of 1 part in 109 in water, 1 part in 108 in skim-milk, and 1 part in 107 in butterfat. A mechanism for the formation of oct-1- en-3-ol is discussed.
Analysis of milk by infra-red absorption
Authors: Goulden J. D. S.
Published: June 2009

The infra-red, absorption of milk and its main constituents has been recorded and it has been found possible to determine quantitatively the fat, protein and lactose contents from measurements of the intensities of the respective absorption peaks at 5·73, 6·46 and 9·6 μm. Solids-not-fat (SNF) content can be obtained from a single intensity measurement at 7·9 μm where the fat shows no attenuation and where the protein and lactose extinction coefficients are approximately equal. Photometric errors due to natural variations in fat globule size distribution can be eliminated by prior homogenization. Based on these observations, an automatic infra-red milk analyser (IRMA) has been constructed, which can determine the fat, protein, lactose and SNF in a pre-warmed milk sample in under 1 min. Preliminary tests carried out on 50 milk samples from individual cows, representing 3 different breeds, gave standard deviations from the chemical analyses for the percentages of fat, protein, lactose and SNF of 0·10, 0·07, 0·07 and 0·19, respectively. The standard deviations for the percentages of fat and SNF on 60 farm bulk milk samples were found to be 0·08 and 0·12.
Mechanics of machine milking: I. Pressures in the teatcup assembly and liner wall movement
Authors: Thiel C. C. , Clough P. A. , Akam D. N.
Published: June 2009

A method is described of measuring pressures in a teatcup assembly using strain gauge transducers and simultaneously following movement of the liner wall by means of a cine camera. In preliminary experiments with a narrow bore type liner it was found that pressures below the teat could vary during a single pulsation cycle from a few inches of mercury below atmospheric pressure (inHg vacuum) to as high as 25 inHg vacuum in the absence of an airbleed. Bleeding air into the barrel of the liner or into the clawpiece considerably reduced fluctuation in pressure, and the vacuum barely rose above the nominal milking vacuum of 15 inHg. Reducing the rate of change of pressure in the pulsation chamber did not greatly affect the maximum vacuum obtained. Opening and closing of the liner by pressure change in the pulsation chamber was under some conditions considerably delayed by the pressure conditions existing inside the liner.

It is suggested that inertia effects of milk in the cluster and the natural frequency of the system are largely responsible for the observed pressure changes under the teat.
The effect of antioxidants on the keeping quality of whole milk powder: II. Tocopherols
Authors: Abbot J. , Waite R.
Published: June 2009

Spray-dried whole milk powders were prepared containing 0·01% of γ-tocopherol and of a mixture of α-γ- and δ-tocopherols. Control powders and powders containing 0·01% of dodecyl gallate, an antioxidant of known effectiveness, were also made. The powders were stored at 37°C and examined at intervals for taste, peroxide value and absorbed oxygen. The protection against oxidation afforded by both the tocopherol additions was small, although γ-tocopherol was more effective than the mixture of tocopherols. Dodecyl gallate was again found to be a good antioxidant for whole milk powder.
Survival of strains of lactic streptococci during frozen storage
Authors: Gibson C. A. , Landerkin G. B. , Morse Pamela M.
Published: June 2009

Sixteen single-strain cultures, 10 ofStreptococcus cremoris, 3 ofStr. lactisand 3 ofStr. diacetilactiswere examined for their ability to withstand freezing and storage at –17·8 and –23·3°C. The numbers of surviving bacteria decreased as storage time increased. For the majority of strains, the survival rate was greater at the lower temperature. At both storage temperatures there were differences between the percentages of surviving bacteria for different strains.

The results suggest that the relative proportion of strains in mixed cultures would not remain constant under frozen storage.
The effect of silage made from grass at different stages of maturity on the yield and composition of milk
Authors: Murdoch J. C.
Published: June 2009

In cross-over experiments it has been established that milk yield increased and the fat solids-not-fat (SNF) contents of the milk decreased when cows were given approximately 15 lb dry matter/day of early-cut silage compared with the values obtained by giving the same amount of silage made from herbage cut at a later stage of maturity.

Increasing the proportion of concentrates to silage in the cow's diet so that the milk yield remained unchanged increased the SNF content of the milk but had no effect on the fat content.

Supplementing early-cut silage with 5 lb hay/day increased the fat content of the milk, but had no effect on either milk yield or the SNF content of the milk.

Compared with a silage to which molasses had been added, untreated silage decreased milk yield, and increased the fat content without affecting the SNF content of the milk.
The effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk
Authors: Wheelock J. V. , Rook J. A. F. , Dodd F. H.
Published: June 2009

The effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk has been investigated. At the 1st milking after either treatment, the yield of milk was augmented by a carry-over of milk but at the 2nd milking the yield was invariably depressed and then increased until the original yield, or slightly less, was recovered within 5 days. The concentration of lactose and potassium decreased and of sodium, chloride, whey proteins and casein increased during the period of the treatment, and on the resumption of normal milking the original composition was rapidly recovered. The changes in the composition of fat were less clearly defined because of residual milk effects but over the period of the treatment and the succeeding 6 milkings the effect was invariably to increase fat percentage. The differing effects on composition resulted in a more marked effect on the yields of lactose, potassium and casein than on those of sodium, chloride or the whey proteins throughout the treatment and recovery periods. When milk was removed in portions after an extended milking interval there were decreases in the concentrations of lactose and potassium and increases in those of sodium and chloride throughout normal milking. When the residual milk was obtained after an injection of oxytocin the composition of the portions of milk resembled that of the first portions of milk removed from the udder. The possible effects of the treatments on the secretory cells and the permeability of the udder tissue are discussed.
Studies on the laboratory soiling of milking equipment
Authors: Bačić Branca , Cousins Christina M. , Clegg L. F. L.
Published: June 2009

A laboratory method has been developed for studying the action of chemical disinfectants on milking equipment using a wet film and both metal and rubber surfaces. It was shown that milking machines may be soiled as effectively with fresh milk of low bacterial content as with aged milk of high bacterial content. When a single heat treatment preceded the soiling with milk and subsequent treatment with detergent and chemical disinfectant, a build-up of bacteria began on the third day. However, when the surfaces were heat treated daily 18 h before soiling, followed by cleaning and disinfection, no build-up occurred. These findings support the hypothesis that contamination of milk results from bacteria developing on the milking equipment and not merely from those added to it at each milking. The sites of bacterial contamination were shown to be the under surfaces of lid gaskets and the joints of the short milk tubes and the metal clawpiece nipples.
Some properties of the extracellular proteolytic enzymes of the milk-spoiling organismPseudomonas aeruginosaATCC 10145
Authors: Juffs H. S. , Doelle H. W.
Published: June 2009

The proteolytic enzymes present in the culture supernatant ofPseudomonas aeruginosaATCC 10145 were active in the pH range 5·5–9·0 with a maximum activity at pH 7·3. Heating for 15 sec at 72°C resulted in a 36% loss of proteolytic activity whereas heating for 30 min at 63°C resulted, in a 6% loss. Boiling for 2 min completely inactivated the proteolytic enzymes. At 2°C the proteolytic enzymes were stable for at least a month and casein was readily hydrolysed at this temperature.
Microcalorimetry applied to certain species of bacteria growing in sterilized separated milk
Authors: Berridge N. J. , Cousins Christina M. , Cliffe A. J.
Published: June 2009

The heat produced per colony-forming unit (CFU) of growing bacteria was found to depend on the species and was greater the younger the culture. With the exception of 2 determinations out of 13, with 6 species the results show that it should be possible to detect < 5×105CFU/ml by the heat produced. A seventh species, a micrococcus, could be detected at a lower level of CFU presumably because the unit was a clump of several cells. Gross variations which occurred with fullcream milk await investigation.
A quantitative gel-filtration method for analysis of the proteinaceous fraction of Cheddar cheese
Authors: Foster P. M. D. , Green Margaret L.
Published: June 2009

Methods are described for the solubilization of the nitrogenous portion of cheese in a dissociating solvent system and separation of the solution into fractions on a Sephadex G-100 column under conditions where the proteins and peptides would be expected to be split into monomeric units. TheE280measurement of the fractions, expressed as a percentage of the total material eluted, followed a reproducible pattern, both with duplicate runs on the same sample and comparative runs on non-identical samples of the same type. With cheese curd, a small peak of undissociated material was obtained at the void volume of the column; this was followed by a main peak and a minor third peak, with a small quantity of material being eluted at larger volumes. A qualitatively similar pattern was obtained with 43-day-old cheese as the sample, but the main peak was smaller, the third peak was larger, and a relatively larger amount of material was eluted at greater volumes. There was only partial separation of the proteins on the column; the main peak contained β- and αs-caseins, their larger breakdown products and some para-κ-casein, and the third peak contained smaller breakdown products of the main casein fractions and para-κ-casein. Although the resolution was considerably inferior to that obtained by gel electrophoresis, the method has the advantage over this and other methods in that it gives a quantitative analysis of the sample based on molecular size. Thus, it is suggested that it may find use in analysing protein breakdown in cheese during ripening.
A method of diagnosing intramammary infection in dairy cows for large experiments
Authors: Griffin T. K. , Dodd F. H. , Neave F. K. , Westgarth D. R. , Kingwill R. G. , Wilson C. D.
Published: June 2009

Diagnosis of microbial infections in the udders of cows in commercial dairy farms for large experiments cannot be without error. Limitations of sampling method and routine prevent collection of the necessary information for sure diagnosis. However, with an organized method of repeated bacteriological examinations using consistent and proven methods of aseptic sampling the errors were shown to be very low. A method based on bacteriological tests on aseptic milk samples was used in 32 herds (approximately 2000 cows) for a 3-year period. This is described and examined in terms of other criteria to validate its use in experimental work. With this method it was not difficult to differentiate between those quarters which regularly shed pathogens and those which did not. Other evidence indicated that it was reasonable to assume that this classification accurately distinguished between infected and uninfected quarters. The errors using this method were quite small: when measuring the state of infection of all quarters in the herds the errors did not exceed 1 %. Some small modifications to the method described are suggested to improve further its diagnostic accuracy.
The theory of branching processes applied to milk proteins: I. Heat-induced coagulation of whole milk
Authors: Parker T. G. , Dalgleish D. G.
Published: June 2009

The theory of branching processes is used to present a unified kinetic model for the heat induced coagulation of milk. Nitrogen depletion curves for the overall reaction are fitted to a theoretical curve to demonstrate that the reaction is a single process and that the idea of a lag phase up to the coagulation time, followed by the aggregation reaction proper, is an unnecessary complication. Coagulation times as a function of temperature are then used to determine the activation energy of the reaction; the average value of 126 kJ/mol agrees with that found from analysis of the post-coagulation reaction.
Quantitative analysis of food products by pulsed nuclear magnetic resonance II. Simultaneous analysis of water and fat in milk powder and cottage cheese
Authors: Hester R. E. , Quine D. E. C.
Published: June 2009

A small process analyser employing the pulsed nuclear magnetic resonance technique has been used to determine both water and fat contents of milk powder and cottage cheese samples. The procedures used for establishing and eliminating cross-interferences in these analyses are described. For milk powders, water and fat contents in the ranges 1–5 and 0·5–25 % respectively were determined with standard deviations of 0·20 % water and 0·64 % fat. Cottage cheese samples with water and fat contents in the ranges 77–81 and 2–7 % respectively were determined with standard deviations of 0·30 % water and 0·16 % fat.
Selective denaturation of milk coagulants in 5 M-urea
Authors: Mulvihill D. M. , Fox P. F.
Published: June 2009

Porcine and bovine pepsins were very stable in 5·0 M-urea at pH 2·0 or 2·5 at 30 °C while chymosin and Mucor miehei and M. pusillus proteases were rapidly denatured under these conditions. These differences may provide the basis of a quantitative assay of the complement of individual milk clotting enzymes in a coagulant and a possible scheme is suggested.
Effect of diet and stage of lactation on bovine milk lipolysis
Authors: Salih Amer M. A. , Anderson Malcolm
Published: June 2009

The effect of lactation and diet on milk lipoprotein lipase activity (LPL), cell count, serum albumin concentration and free fatty acid levels, expressed in terms of acid degree value (ADV), was examined in 2 experiments. In addition, the ability of blood plasma from cows on different diets to activate LPL was also investigated.

Changes in ADV were not consistently associated with changes in LPL, cell count or serum albumin throughout lactation, although results indicated that ADV appeared to be influenced by cell count in early lactation, and by the amount of blood plasma proteins reaching the milk during the remainder of lactation. LPL activity was low in colostrum, but increased rapidly between d 2 and 12 post-partum, reaching a peak at 5 months. Activity was unaffected by diet.

There was no effect on ADV of feeding concentrate: hay ratios of 75:25 and 60:40, but ADV was higher in cows fed a low protein diet (crude protein 9%) between 10 and 60 d post-partum, than in cows fed a high protein diet (crude protein 18 %) during the same period. In addition, the blood plasma for cows on the low protein diet had a greater ability to activate LPL although, on the basis of the millk: blood serum albumin ratio, a smaller proportion of blood constituents had reached the milk. The ability of blood plasma to activate LPL was also found to increase with increasing levels of lipoprotein lipid in the blood.
Proteolytic specificity of chymosin on bovine αs1-casein
Authors: Mulvihill Donald M. , Fox Patrick F.
Published: June 2009

In dilute buffers ⋟ pH 5·8, chymosin hydrolysed bovine αs1-casein to αs1-I, αs1-II and αs1-III/αs1-IV in a sequential manner while at pH 4·6 αs1-casein was hydrolysed to αs1-I which was then hydrolysed to αs1-V. In the presence of 5 % (w/v) NaCl at pH 5·2, αs1-casein was hydrolysed to αs1-I which was then hydrolysed to αs1-VII and αs1-VIII. αs1-I, αs1-II and αs1-III/αs1-IV were isolated by chromatography on cellulose phosphate followed by preparative slab-gel electrophoresis; αs1-V was isolated by repeated preparative slab-gel electrophoresis and αs1-VII by gel filtration on Sephadex G-150 followed by preparative slab-gel electrophoresis. The mol. wts of the peptides, estimated by gel filtration on Sephadex G-100, were 21000, 17600, 15600, 19900 and 14600 for αs1-I, αs1-II, αs1-III/αs1-IV and αs1-V and αs1-VII respectively. Characterization of the peptides by amino acid, phosphorus and terminal residue analysis showed that they probably consisted of segments of the αs1-casein chain as follows: αs1-I: residues 24/25–199; αs1-II: residues 24/25–169; αs1-III/αs1-IV: residues 24/25–149–150; αs1-V: residues 29/33–199; αs1-VII: residues 56–179. Peptide bonds close to phosphate residues on the αs1-casein chain were not hydrolysed by chymosin at high pH values (⋟ 5·8) when the phosphate groups were charged, but became available for hydrolysis when the reaction pH was reduced. Proteolytic specificity was also modified by NaCl.
Activation of milk lipase by serum proteins: possible role in the occurrence of lipolysis in raw bovine milk
Authors: Clegg Roger A.
Published: June 2009

The increase in unesterified fatty acid content of unpasteurized bulk milk in storage at 4 °C in the presence of known effectors of bovine milk lipoprotein lipase originating from bovine serum was studied. Bovine serum and high density lipoprotein (HDL) caused an increase in developed unesterified fatty acid levels whilst lipoprotein-free serum, apo-HDL, all individual apo-HDL tested, and the unfractionated C-peptide fraction were without lipolytic effect. In the presence of HDL-lipids, 2 C-peptides stimulated considerable lipolysis, as did the combination of HDL-lipid with unfractionated C-peptides. These characteristics of unesterified fatty acid development could be duplicated in milk whose endogenous lipolytic activity had been destroyed by heat treatment (75 °C for 5 min) and then restored by addition of purified bovine milk lipoprotein lipase. Radioactively labelled glycerol trioleate in milk was not hydrolysed in the same way as milk fat on the addition of serum liproproteins.
The content and composition of protein in creamery milks in south-west Scotland
Authors: Davies D. Thomas , Law Andrew J. R.
Published: June 2009

SUMMAARY

The content and composition of protein in milk samples from creameries in south-west Scotland were determined over a period of 12 months. The composition of the whole casein was expressed in terms of αsl-, β-, κ-, αs2- and γ-caseins, and that of the total milk serum protein in terms of β-lactoglobulins (β-lg), α-lactalbumins, bovine serum albumin, and a mixture of immunoglobulins, proteose-peptone component 3 and lactoferrin (IPL). Concentrations of the individual caseins varied appreciably and for most, concentration was closely correlated with and showed the same seasonal pattern as total casein concentration. Concentrations of the milk serum proteins also varied but only those of β-lg and the IPL fraction were closely correlated with that of total milk serum protein and seasonal trends were not marked. Relative amounts of the individual proteins, on the other hand, showed smaller variations and so throughout the experimental period the milks contained a protein complex of comparatively constant composition. Because of this comparative constancy it would appear that seasonal variations in milk properties in south-west Scotland are unlikely to be determined to a major extent by milk protein composition, but could be more affected by protein concentration.
Formation of lysinoalanine from individual bovine caseins
Authors: Manson William , Carolan Thomas
Published: June 2009

The formation of lysinoalanine, N-є-(2-amino-2-carboxyethyl)-L-lysine, by treatment of αs0-, αsl- and β-casein with alkali, has been studied. In all 3 proteins lysinoalanine was formed by reaction of lysyl residues with dehydroalanyl residues produced by alkaline degradation of those phosphoseryl residues which occupy isolated positions in the proteins' structures. The contribution to lysinoalanine production made by phosphoseryl residues which were arranged in clusters, as occurs in the sequence -Ser(P)-Ser(P)-Ser(P)-, was not significant.
Effect of milk concentration on the rennet coagulation time
Authors: Dalgleish Douglas G.
Published: June 2009

Measurements have been made of the coagulation times (CT) of concentrated and diluted milks when treated with chymosin. After dilution, milks showed a large increase in CT: conversely, concentrated milks showed a similar CT to unconcentrated milk. The results are discussed in terms of a mechanism which reduces to a form similar to that proposed by Holter (1932).
Characterization and response to mitogens of mammary lymphocytes from the bovine dry-period secretion
Authors: Concha Carlos , Holmberg Olof , Morein Bror
Published: June 2009

From bovine mammary secretion during the dry period, the total number of cells was between 1·2 and 5·9 Ǻ 106/ml. A mean of 35% of these cells were classified as lymphocytes and ∼ 85% of them could be isolated by the Ficoll-isopac method. Centrifugation separated 6% of the cells into the fat; 5% of them were lymphocytes. About 47% of the lymphocytes boundHelix pomatiaagglutinin, a T-cells marker, while the proportion of Ig-bearing cells was ∼ 28%. The mammary lymphocytes were stimulated by the lectins phytohaemagglutinin, pokeweed mitogen, concanavalin A and by lipopolysaccharide fromSalmonella typhimurium. The stimulation indices of mammary lymphocytes were generally lower than those for peripheral blood lymphocytes from the same animals. The background values, i.e. counts/min of lymphocytes incubated without mitogen, were often higher for lymphocytes isolated from mammary secretion than from blood.
Heat-induced association of β-lactoglobulin and casein micelles
Authors: Smits Petrus , Brouwershaven Johan H. Van
Published: June 2009

Heat-induced association of β-lactoglobulin (β-lg) and casein micelles, mainly at 85–90 °C, was studied by means of preparative ultracentrifugation, using [3H]-labelled β-lg. Qualitative aspects were studied by gel electrophoresis and electron microscopy. In this association, the formation of intermolecular S–S bonds between β-lg and κ-casein plays a role, but hydrophobic bonds are also involved.

After heating mixtures containing 25 g/kg casein and 4 g/kg β-lg at 90 °C for 20 min, the amount of β-lg sedimented with the casein micelles by ultracentrifugation decreased by approximately 30% when the milk salt buffer system was reduced to 0·25 of its normal concentration; it decreased by about 20% when the pH was increased from 6·8 to 7·3 and increased by 15% when the pH was reduced from 6·8 to 5·8. When the β-lg concentration was decreased from 4 to 2 g/kg, the amount of sedimented β-lg decreased by 25% after heating at 90 °C for 6 min. After heating in milk salt buffer, the amount of sedimented β-lg was 15% higher than after heating in a salt solution which contained neither Ca nor citrate ions.

Although α-lactalbumin (α-la) is involved in the heat-association of β-lg and casein micelles, no influence of α-la on the amount of associated β-lg was found. In addition to the heat-association product of β-lg and whole casein micelles, an association product consisting mainly of β-lg and κ-casein was also formed. This product was observed by electron microscopy as noodle-like particles. The size of these particles depended on the β-lg/κ-casein ratio.
Factors influencing casein distribution in cold-stored milk and their effects on cheese-making parameters
Authors: Ali Ali E. , Andrews Anthony T. , Cheeseman Gordon C.
Published: June 2009

In assessing the performance of milk for cheese-making, the influence of a number of factors in addition to cold storage time and temperature of the milk on the equilibria between the soluble and micellar phases and on cheese-making parameters has now been examined. An important factor was pH and although not apparent in fresh unstored milk, after storage at 4 °C there was a minimum in the soluble casein concentration at about pH 6·6, largely due to variations in β-casein concentration. As expected, addition of Ca reduced soluble casein concentrations while treatment with EDTA caused increases, and in most cases the cyclic pattern of casein dissociation from the micellar phase followed by a partial reassociation was again observed during storage at 4 °C over a 3-d period. Addition of low levels of urea (up to 75 mg/100 ml milk) led to some dissociation of all casein components, Ca and phosphate into the soluble phase while treatment of milk with urease caused small decreases. Additions of purified casein components to milk were accompanied by only small alterations to the composition of the soluble phase and added casein was largely incorporated into the micellar phase. In spite of this, most added casein was not recovered in curds, and cheese yields were not greatly enhanced by quite considerable additions of caseins to the milk. The effects of pH adjustment, addition of Ca, EDTA, urea, cyanate, purified αs1-, β- or κ-casein and urease treatment on rennet clotting time, curd strength, curd moisture and cheese yield are presented.
Acid-soluble nucleotides of cow's, goat's and sheep's milks, at different stages of lactation
Authors: Gil Angel , Sanchez-Medina Fermin
Published: June 2009

The acid-soluble ribonucleotides of cow's, goat's and sheep's milks were measured by enzymic and ion-exchange chromatographic procedures at different stages of lactation. Colostra and milk from ruminant species contained orotic acid and 13 well-identified nucleotides: AMP, CMP, GMP, UMP, UDP, GDP, UDP-glucose, UDP-galactose, UDP-N-acetyl-glucosamine, UDP-N-acetyl-galactosamine, UDP-glucuronate, GDP-mannose and GDP-fucose. Cow's, goat's and sheep's colostrum contained significant amounts of nucleotides, which increased in amount from the moment of parturition, to reach a maximum 24–48 h later. The nucleotide concentration decreased thereafter with advancing lactation. Cow's milk contained substantial amounts of orotic acid, which increased during lactation, whereas in goat's and sheep's milk no increase took place. The cytidine and adenosine derivatives in ruminants' milk did not change significantly during lactation. The UDP-glucose/UDP-galactose ratio was measured in ruminants' milk at different stages of lactation.
Effects of adding potassium iodate to milk before UHT treatment: II. Iodate-induced proteolysis during subsequent aseptic storage
Authors: Skudder Paul J.
Published: June 2009

The addition of potassium iodate to milk at 0·1 mm before UHT treatment resulted in rapid breakdown of αs- and β-casein during subsequent aseptic storage. Maximum rates of proteolysis were observed at storage temperatures of 37–45 °C, but the reaction was strongly inhibited by storage at 55 °C and by increased holding time at 140 °C during the UHT sterilization. Iodate-induced proteolysis of purified αs1-and β-casein was detected only with solutions in the serum phase of raw milk; no proteolysis occurred with solutions in 01·M-phosphate buffer (pH 6·7) or in milk ultrafiltrate, irrespective of whether whey proteins and lactose were also added. Thus, it appears that iodate increased the activity of one or more proteolytic components which were present in milk and were unable to pass through an ultrafiltration membrane. However, it is unlikely that iodate acts by increasing the activity of proteinases produced by contaminant bacteria; the presence of iodate did not affect the activity of a proteolytic enzyme isolated from Pseudomonas fluorescens PM-1. Furthermore, iodate promoted protein breakdown during storage of milk drawn aseptically from the cow and subsequently UHT processed. It is suggested that iodate increased the activity of native milk proteinases, other than plasmin which was inactivated by UHT treatment, possibly by preventing thiol-disulphide exchange reactions during the heating process.
Derivation of a mathematical model for the mechanism of casein micelle coagulation by rennet
Authors: Darling Donald F. , Van Hooydonk Antoon C. M.
Published: June 2009

The action of rennet on the stability of casein micelles has been described theoretically by combining Michaelis–Menten enzyme kinetics with von Smoluchow-ski's theory for slow coagulation. The casein micelle is considered to be stabilized by stcric interactions arising from a highly hydrated surface protein layer. The stability factor, in von Smoluchowski's theory, is then considered as a variable and determined by the concentration of unhydrolysed κ-casein.

The theoretical approach describes semi-quantitatively experimental observations on clotting time (CT) as a function of temperature, rennet concentration, and total protein concentration. The model also predicts that, under certain circumstances, the CT is inversely proportional to the enzyme concentration. Furthermore, the model agrees with other workers' experimental observations on the effect of κ-cascin concentration, the presence of a lag phase, and that the lag phase is commonly about 60% of the CT.
Rapid membrane filtration epifluorescent microscopic technique for the direct enumeration of somatic cells in fresh and formalin-preserved milk
Authors: Pettipher Graham L. , Rodrigues Ubaldina M.
Published: June 2009

A rapid method for the direct enumeration of somatic cells in fresh and formalin-preserved raw milk is described. Heat treatment at 80°C for 10 mn fixed somatic cells sufficiently to prevent lysis and subsequent dilution allowed the equivalent of at least 0.5 ml milk to be filtered through a 1.0 μm pore size Nuclepore membrane filter. The somatic cells were concentrated on the membrane and, after staining with acridine orange, fluoresced green, yellow or orange under an epifluorescent microscope. Three different types of cell could be distinguished on the basis of nuclear structure and cell size. These were monocytes, polymorphonuclear leucocytes and the larger epithelial and/or secretory cells. For both fresh and preserved milks the count of somatic cells on the membrane correlated well (r≽ 0·93) with the Coulter count. Differences between counts obtained by different operators were not significant. The technique is rapid, taking about 20min, and is suitable for milks containing between 2 × 104and 1 × 107somatic cells/ml.
The relationship between the levels of free fatty acids, lipoprotein lipase, carboxylesterase, N-acetyl-β-D-glucosaminidase, somatic cell count and other mastitis indices in bovine milk
Authors: Fitz-Gerald Carolyn H. , Deeth Hilton C. , Kitchen Barry J.
Published: June 2009

A large-scale survey of milks from healthy and mastitic bovine quarters was undertaken to establish the influence of mastitic infection on milk lipase activity and free fatty acid (FFA) level. Mastitic milks tended to have higher FFA levels, but lower lipoprotein lipase activities compared with milk from healthy quarters. These effects became significant at relatively severe levels of infection. The elevated FFA was attributable to higher FFA levels on secretion and to greater lipolysis during storage. Levels of carboxylesterase activity increased with severity of mastitis and showed high positive correlation with mastitis indices.

Marked increases in carboxylesterase, N-acetyl-β-D-glucosaminidase and phospholipase occurred following the induction of mastitis by intramammary infusion of Escherichia, coli endotoxin, in parallel with changes in somatic cell count and other mastitis indices. Relatively little change in lipoprotein lipase activity was observed.
Factors affecting the ethanol stability of bovine milk.: I. Effect of serum phase components
Authors: Horne David S. , Parker Thomas G.
Published: June 2009

By resuspending casein micelles in whey and dialysate it is shown that the role of whey proteins in the ethanol (EtOH)-induced coagulation of skim-milk is minimal. Experiments involving the interchange of milk sera indicated that the position of the EtOH stability/pH profile along the pH axis was governed by the diffusible constituents of the milk serum phase. The identities of those serum components governing the shape and position of the EtOH stability/pH profile were investigated. The addition of Ca2+ caused a shift in the entire profile to higher pH. Reduction of the available Ca2+ by addition of EDTA (up to 5 ran) shifted the profile to lower pH. The addition of phosphate (up to 5 mM) or citrate (up to 1 mM) had no effect on the profile, though higher concentrations of citrate (up to 5 mMi) caused slight shifts to lower pH. When equimolar amounts of Ca and phosphate were added, the system showed a shift in profile approximately equivalent to that of the free Ca introduced. Increasing the ionic strength of a milk by the addition of NaCl did not shift the profile, but decreased the maximum EtOH stability of the high pH arm of the sigmoidal profile. The EtOH stability/pH profile retained the same sigmoidal shape in all cases.
Electrofocusing and two-dimensional electrophoresis of bovine caseins
Authors: Trieu-Cuot Patrick , Gripon Jean-Claude
Published: June 2009

The main components of bovine whole casein were characterized by electrofocusing; pi values of αs1-, β-, κ-, γ1-, γ2- and γ3-caseins were determined. A further identification of casein components was achieved by a 2-dimensional electrophoresis study. 2-Dimensional patterns of γ-caseins obtained from a hydrolysate of β-cascin by bovine plasmin are in good agreement with those of γ-caseins naturally present in whole casein.
Mineral and protein equilibria between the colloidal and soluble phases of milk at low temperature
Authors: Pierre Alice , Brule Gerard
Published: June 2009

Mechanisms controlling exchange and partition of minerals and β-casein between micellar and soluble phases during cooling have been studied using suspensions of milk proteins of varying concentrations in the presence of aqueous phases having varying mineral compositions. In these studies the final equilibrium between Ca and phosphate was found to be regulated by formation of Ca phosphates of varying solubilities. The effect of the total casein level on mineral and protein equilibria was also studied. In milk, part of the β-casein content is bound to micelles by hydrophobic bonds; the proportion present in this form was increased by spontaneous micellar demineralization during cooling as well as by addition of a complexant to milk. At low temperatures, an equilibrium between the micellar and the monomeric states was reached which depends upon the total casein level and on the hydrophobic-bonded β-casein content. Not all of these hydrophobic bonds were broken when milk was cooled.
Effect of nutrition on fertility and blood composition in the milk cow
Authors: Bogin Eitan , Avidar Yaacov , Davidson Menachem , Gordin Salli , Israeli Bit-Ami
Published: June 2009

The relationship between nutrition, fertility and blood composition was studied in 400 cows from commercial farms. Fertility evaluated by overall conception rate (OCR) was shown to be significantly related to the relative proportion of concentrate and roughage feeds in the diet, and to its content of dry matter, digestible protein, Ca and P. The ratio of serum total lipids to glucose and a newly introduced parameter, ΔPi(a calculated value, obtained by subtracting whole blood levels of Pifrom those of the blood serum), showed a highly significant relationship to OCR. No significant relationship was found between OCR and serum, total lipids, cholesterol, urea, Ca, Mg, organic and inorganic phosphate. The values and significance of the 2 blood parameters which showed a relationship to fertility are discussed.
Inorganic constituents of milk III. The colloidal calcium phosphate of cow's milk
Authors: Holt Carl
Published: June 2009

Experiments involving the depletion of milk calcium phosphate (MCP) with EDTA have shown that it has a Ca to phosphate ratio of 1·61±0·04, close to that of dental enamel. The calcium phosphate also contains small amounts of citrate (citrate/Pi = 0·097±0·011) and Mg (Mg/Pi = 0·044 ± 0·011). These experiments and model calculations indicate that the Ca binding capacity of casein is not reduced by mineralization with calcium phosphate and hence that ion binding sites and nucleation sites are distinct, or nearly so. Calculations of the ionic equilibria in the aqueous phase of milk show that there is an invariant ion activity product for a molecular formula close to that of dicalcium phosphate. It is suggested that MCP is a mixture of salts, with dicalcium phosphate a precursor of more basic salts such as octacalcium phosphate and hydroxyapatite.
Application of the plastein reaction to caseins and to skim-milk powder: II. Chemical and physical properties of the plasteins and the mechanism of plastein formation
Authors: Sukan Gonca , Andrews Anthony T.
Published: June 2009

Chemical and physical properties of plasteins derived from caseins and skim-milk powder have been investigated. Plasteins were very similar in properties regardless of starting material or of the proteinase used in their production. Plastein formed from Na caseinate hydrolysate at pH 5 was stable over the pH range 1·5–9·0 and had the properties of a thixotropic gel. More extreme pH values caused dissolution as did various chaotropic reagents. 8 M-urea disrupted plastein structure almost entirely, as did various organic acids at concentrations of 50% (v/v) and strongly ionic detergents. Non-ionic or weakly cationic detergents and 6 M-guanidine hydrochloride were less effective. Treatment with strong salt solutions, Ca2+ and EDTA had no effect. Gel filtration experiments demonstrated that plasteins were completely disrupted under dissociating conditions and peptide mapping confirmed that all the peptides originally present in the hydrolysate were also present in plastein. Amino group contents were unchanged on plastein formation. These experiments together with gel electrophoresis studies clearly showed that only hydrophobic and ionic bonding mechanisms were involved in plastein formation and no detectable peptide bond formation or transpeptidation occurred. In accordance with this, amino acid analysis suggested that hydrophobic peptides were preferentially incorporated. Implications for use of plasteins in food products are discussed.
Homogenizing valve design and its influence on milk fat globule dispersion: I. Low rate of flow (100 1 h–1, Re ≤ 3000)
Authors: Phipps Leslie W.
Published: June 2009

The efficiencies of small capacity homogenizing valves of the high pressure type have been studied in relation to their design. The performance of a valve was strongly affected by the magnitude of the effective inlet diameter D0 of the seating for a given exit diameter D when D0/D > 0·5. The indications are that narrow mating faces situated such that D0/D → 1 should maximize performance. Milk fat globule dispersion varied regularly with a valve's face angle; optimum angles for maximum disruptive effect were about +35° and –30°. Perforated metal insets interposed between flat faces of a valve piece and its seat noticeably improved fat dispersion; reductions in mean globule diameter of up to 25% were obtained.

Variations in the sensitivity of different milks to homogenization were observed but avoided by appropriate experimental procedures.
An improved method for measurement of the syneresis of curd formed by rennet action on milk
Authors: Marshall Richard J.
Published: June 2009

In this method, the curd, formed in a beaker, was retained after cutting by means of a wire grid placed on top of it. This enabled the whey to be poured off easily at timed intervals for measurement of its volume. The method gave results reproducible within 1·5%. Increasing the amount of rennet added to the milk increased the rate of syneresis of the curd slightly. Adding CaCl2 to the milk, raising the temperature and decreasing the pH, all increased the rate of syneresis. Addition of fat, as cream, to skim-milk decreased the rate of syneresis proportionally. The rate of syneresis was decreased if the milk was concentrated by ultrafiltration and increased if the milk was diluted with permeate. In all instances the early stages of syneresis followed first-order kinetics, the rate depending on the amount of whey remaining within the curd. The later stages of syneresis appeared to depend on hydrophobic forces. Probably, the increasing aggregation of the casein within the curd caused the whey to be squeezed out.
Sources ofStreptococcus uberisin the dairy herd: I. Isolation from bovine faces and from straw bedding of cattle
Authors: Bramley A. John
Published: June 2009

During an outbreak of mastitis due toStreptococcus uberisthe organism was frequently isolated from samples of straw bedding used by the cattle. More than one millionStr. uberis/g straw were isolated from 36% of samples. The organism was also recovered from 34% of samples of bovine faeces, but usually in low numbers. An examination of straw samples collected from cattle yards on 32 other dairy farms demonstrated that this was not an isolated occurrence sinceStr. uberiswas found in 24% of samples from 56% of the herds. No correlation was found between counts ofStr. uberisand coliforms. The significance of these observations is discussed.
Effect of oxygen on the keeping quality of milk: I. Oxidized flavour development and oxygen uptake in milk in relation to oxygen availability
Authors: Schröder Monika J. A.
Published: June 2009

Oxidized flavour developed in whole milk only through the catalytic effect of either Cu or light. The O2 requirement for the 2 processes differed as did the characteristics of the off-flavours produced. Cu-induced oxidized flavour was described as ‘cardboardy’ and light-induced oxidized flavour was ‘painty’. Light-induced oxidized flavour increased in intensity with O2 loss, and could be prevented in stored milk by restricting access of O2. In UHT milk with a dissolved O2 content of 6·6 mg/1, and in the absence of access of further O2, light-induced oxidized flavour did not develop; similarly, O2 uptake of 7·5 mg/1 in in-bottle sterilized milk exposed to fluorescent light did not result in flavour formation. When light-induced oxidized flavour developed consistently in whole milk none developed in skim-milk, indicating the lipid source of the flavour. In contrast Cu-induced oxidized flavour development was not associated with high O2 uptake. Although nearly complete deoxygenation of whole pasteurized milk contaminated with Cu prevented the formation of the flavour, moderate deoxygenation resulted in even greater flavour intensity than non-deoxygenation. The 2 oxidized flavours also differed in relation to ascorbic acid (AA) oxidation. Light-induced oxidized flavour developed only after AA oxidation was complete, whereas Cu-induced flavour developed with AA still present. AA oxidation was greatly accelerated through the effects of both Cu and light. In milk free from Cu contamination and protected from light, after AA oxidation (plus SH group oxidation in the case of UHT milk) was complete, no further loss of O2 occurred, even during prolonged storage at 5°C, despite the presence of large O2 concentrations. However, at 20°C, a small consumption of O2 was measured, and this was associated with stale flavour.
Effect of psychrotrophic post-pasteurization contamination on the keeping quality at 11 and 5 °C of HTST-pasteurized milk in the UK
Authors: Schröder Monika J. A. , Cousins Christina M. , McKinnon Charles H.
Published: June 2009

The keeping quality of commercial HTST-pasteurized milk and laboratory pasteurized milk from a common bulk raw supply has been investigated for 5 dairies. Spoilage occurred at levels of total bacterial counts around 107 colony forming units/ml, but with a slightly higher off-flavour threshold for the commercial milks than the laboratory pasteurized milks. The predominant microflora at spoilage and the type of off-flavour produced differed between the 2 types of milk. Raising the storage temperature from 5 to 11 °C caused a slight shift in the spoilage microflora and led to an average reduction in the shelf life of the laboratory pasteurized milk from 28 to 6 d and of the commercial pasteurized milk from 13 to 5 d. Changes in the level of post-pasteurization contamination (PPC) were reflected in changes in keeping quality, particularly at 5 °C. However, the greatest improvements were found in the absence of PPC.
A survey of sources of heat-resistant bacteria in milk with particular reference to psychrotrophic spore-forming bacteria
Authors: McKinnon Charles H. , Pettipher Graham L.
Published: June 2009

Samples of winter bedding and summer pasture, rinses of teats and milking equipment, and milk samples from bulk tanks from 4 farms were analysed bacteriologically for total count (TC), thermoduric count, total spore count (TSC) and psychrotrophic spore count (PSC).

In bedding and pasture samples the TSC comprised the main component of the thermoduric flora but was less than 0·1 % of the TC. The PSC formed ∼ 1 % of the TSC in winter bedding and ∼23 % of the TSC in pasture. For pasture, the PSC: TSC ratio was highest for the upper layer of soil and lower for the grass and deeper layer of soil. The TSC formed 5% of the thermoduric flora in rinses of milking equipment and only a very low PSC was obtained. The TSC of farm bulk tank milks was higher in the winter than the summer but the PSC was similar in both seasons. This was due to an increase of ∼9 times in the PSC:TSC ratio for milks in summer compared with winter. The PSC in raw and commercially pasteurized milks from a local creamery showed a similar seasonal trend.