bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of milk fat from β-hydroxybutyrate and acetate in lactating goats
Authors: Smith G. H. , McCarthy S. , Rook J. A. F.
Published: June 2009

The relative importance of β-hydroxybutyric acid (BHBA) and acetate as precursors for milk-fat synthesis was studied in lactating goats by infusing separately tracer quantities of [3−14C]DL-BHBA and [1−14C]acetate into the jugular vein, and [1−14C]butyrate into the portal vein. The concentrations and specific radioactivities of blood plasma constituents, the yields and specific radioactivities of individual milk fatty acids and the relative radioactivities of individual carbon atoms of milk fatty acids were determined.

The infusion of [1−14C]butyrate resulted in the appearance of labelled BHBA in the blood plasma which behaved almost identically with infused [14C]BHBA as a precursor for milk fatty acids.

The relative radioactivity of carbon atoms of the fatty acids of milk fat following the infusions provided direct evidence that BHBA had provided an intact 4-carbon unit at the methyl end of each fatty-acid chain. Acetate provided 2-carbon units both for the elongation of the 4-carbon units and for completede novosynthesis. BHBA also provided 2-carbon units which behaved in a similar fashion to those from acetate.

Acetate and BHBA together accounted for all of the C4–C12acids of milk fat, about 75% of the C14, 45% of the C16and 10% of the C18.

The total contributions of the various precursors to the fatty acids of milk fat were: acetate 42%, BHBA 9·4% and other plasma precursors (by difference) 48·6%.
Some factors associated with the late-winter decline in the lactose content of herd bulk milks
Authors: Dawson R. R. , Rook J. A. F. , Wood P. D. P.
Published: June 2009

A survey of the composition of the milk of individual cows in 6 commercial herds in the North of England was undertaken from October 1968 to July 1969. In all herds there was a decline in solids-not-fat (SNF) content; in 4 of the herds this was mainly the result of a fall in protein content, although in all herds there was a decline in lactose content in association with an increase in udder infection and an advance in average stage of lactation. Between-herd differences in the minimum value for lactose content were related to differences in udder infection, stage of lactation and lactation number.

Two of the herds were selected for further study from October 1970 to April 1971. After a preliminary period each herd was divided into 2 matched groups. One group received the usual management, and the other was subjected to remedial changes of supplementary feeding and antibiotic therapy and improved udder hygiene. In both herds, treatment reduced udder infection and improved lactose content and in one of the herds there was also an increase in protein content.
Quantification of milk-clotting enzymes in 40 commercial bovine rennets, comparing rocket immunoelectrophoresis with an activity ratio assay
Authors: Rothe G. A. L. , Harboe M. K. , Martiny S. C.
Published: June 2009

The enzymes chymosin, bovine pepsin A and bovine pepsin B in 40 commercial rennets were assayed by rocket immunoelectrophoresis, using monospecific antibody preparations against the 3 enzymes. Concentrations found were chymosin, 0–1208 mg/l; bovine pepsin A, 359–3818 mg/l; bovine pepsin B, 0–320 mg/l. Bovine pepsin B was found to be a minor enzymic component in bovine rennets, representing maximally 2·9 % of the milk-clotting activity or 9·7 % of the weight of the enzymes. The sensitivity for the quantification of the 3 enzymes was 0·5–1·0 mg/l. The coefficient of variation was 3·7 %. The sum of the immunochemical data converted into milk-clotting activities was in good agreement with the directly observed milk-clotting activity, indicating that there was no immunochemical overestimation due to the presence of non-enzymic active antigens. A high correlation was found between the enzymic composition determined immunochemically and by activity ratio assay.
An improved method for the quantitative fractionation of casein mixtures using ion-exchange chromatography
Authors: Davies D. T. , Law A. J. R.
Published: June 2009

A method for the quantitative analysis of casein mixtures is described. The method uses ion-exchange chromatography at 4 °C on DEAE cellulose, Whatman DE52 in the presence of tris-chloride-urea buffer (pH 8·6), and a NaCl gradient to fractionate the alkylated casein mixtures and a micro-biuret technique to determine protein concentrations. Values for fractions representative of (1) γ-caseins, (2) κ-casein plus some unknown proteins, (3) β-casein, (4) minor αs-caseins and (5) αs1- plus αs0-caseins were obtained, and whole casein from herd bulk milk was found to consist on average of about 2, 13, 36, 11 and 38% respectively of these fractions. Agreement between duplicate fractionations was satisfactory and the recovery of material varied between 94 and 98%.
Milk-fat globule membranes: chemical composition and phosphoesterase activities during lactation
Authors: Diaz-Mauriño Teresa , Nieto M.
Published: June 2009

The morphology, protein and glycoprotein composition, amino-acid analysis, phospholipid and carbohydrate contents and 3 phosphoesterase activities of the milk-fat globule membranes were studied in 4 cows during their whole period of lactation. No differences were found in the morphology and the overall chemical composition. However, glycoprotein composition varied with the cow and, for each cow, with the stage of lactation. The differences were more marked for membranes obtained from colostrum. Acid phosphomonoesterase was practically unchanged during the whole period of lactation, while alkaline phosphomonoesterase and phosphodiesterase increased as lactation proceeded.
The oxidation of lipids by components of bovine milk-fat globule membrane
Authors: Allen J. C. , Humphries Catherine
Published: June 2009

Bovine milk-fat globule membrane was solubilized with a zwitterionic surfactant and subjected to chromatography on agarose, with the surfactant in the eluant. Fractions were tested for their effects on the oxidation of buffered linoleate. The maximum oxidative capability was greatly enhanced by the addition of Cu, and became associated with the phospholipids.

Further chromatography of the retarded protein peak from agarose on Sephadex G-200, again in the presence of surfactant, gave 2 protein peaks. Oxidative effectiveness resided almost entirely in the first peak, which was devoid of phospholipid, but high in xanthine oxidase activity. This fraction was subjected to isoelectric focusing, and the xanthine oxidase from this was highly pro-oxidative. Furthermore, its oxidative capability was almost doubled on heat treatment.
A calorimetric study of the thermal denaturation of whey proteins in simulated milk ultrafiltrate
Authors: Rüegg M. , Moor Ursula , Blanc B.
Published: June 2009

Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: β-lactoglobulin, α-lactalbumin, serum albumin, γ-globulin, apo- and Fe-lactoferrin, lysozyme, ribonuclease, α-chymotrypsin and xanthine oxidase. Denaturation enthalpies (ΔHD), denaturation temperatures (TD) and the half width of the denaturation peaks in DSC thermograms (ΔT½D) were determined and the degree of renaturation was estimated by rescanning previously denatured samples. A fair correlation between the results obtained by DSC and other more classical methods was found in general. However, for some proteins (α-lactalbumin, lysozyme, ribonuclease and xanthine oxidase), which have so far been considered relatively thermostable, calorimetry reveals conformational changes starting at temperatures as low as about 45 °C. In these cases thermostability observed after heat treatment of milk should be interpreted in terms of renaturation and not of high temperatures of denaturation.
The acceleration by cationic materials of the coagulation of casein micelles by rennet
Authors: Green Margaret L. , Marshall R. J.
Published: June 2009

Three cationic materials markedly reduced the rennet clotting time of casein micelle suspensions, the efficacy of each being primarily dependent on the charge and the amount absorbed by the micelles. The reduction in coagulation time was unaffected by components of the milk serum other than salts. No enzymic action by lysozyme on casein micelles was detected. All materials acted by the same mechanism, increasing the affinity of rennet for the micelles and accelerating the aggregation phase. Coagulation did not occur until a minimum amount of κ-casein had been hydrolysed to para-κ-casein. All additives increased the proportion of added rennet retained by the casein in the coagulum. The results indicated that coagulation occurs by specific interactions between micelles modified by rennet.
Relative importance of pre-partum and post-partum factors in the control of milk yield in the guinea-pig
Authors: Davis Stephen R. , Mepham T. Ben , Lock Kathryn J.
Published: June 2009

Examination of data pertaining to milk yield and litter growth rate of guinea-pigs at peak lactation showed that milk yield increased with increasing number of pups carried by the dam during pregnancy and also with increasing maternal weight. There was a significant linear correlation (P < 0.05) of mammary gland weight (expressed per unit of maternal body weight) with litter size. Increasing litter size, within 18 h of parturition, from 1 pup to 5 pups did not elicit a response in milk yield. Decreasing litter size from 5 pups to 1 pup reduced milk yield to the level expected of a monotocous dam. Data are presented showing the ability of the guinea-pig pup to survive from birth without access to milk and the inadequacy of milk supply to meet litter requirements when the litter size is more than 2 pups. The mechanisms controlling lactation in the guinea-pig are discussed in relation to data obtained in other species.
Application of reverse osmosis to the manufacture of dried whole milk and skim-milk
Authors: Abbot James , Glover Frank A. , Muir Donald D. , Skudder Paul J.
Published: June 2009

Powders were prepared from whole and skim-milk using reverse osmosis (RO) as a first stage followed by either evaporation and spray drying or spray drying alone. They were compared with powders made by the conventional method of evaporation and spray drying. Measurements were made of powder solubility, free fat content, whey protein denaturation, vitamin content, powder morphology and bacterial count. The free fat contents of powders prepared from whole milk concentrated by RO were high; otherwise, there were no significant differences in the properties of powders made from milks concentrated initially by RO and those prepared by conventional evaporation. The results indicate that it is feasible to use RO for the manufacture of skim-milk powder and for dried whole milk production where higher free fat levels are not detrimental.
Post-milking iodine teat skin disinfectants: 1. Bactericidal efficacy
Authors: Sheldrake Richard F. , Hoare Roderic J. T. , Hutchinson Jo-Anne E.
Published: June 2009

An iodine teat skin disinfectant tested in lactating cows over a range of concentrations, 100 to 10 000 mg available iodine/1 (mg avI/l) was found bactericidally effective against Staphylococcus aureus when containing 1000 mg avI/l or greater. Against Streptococcus dysgalactiae 5000 mg avI/l or greater was bactericidally effective.

The addition of glycerine to a disinfectant containing 5000 or 1000 mg avI/l at levels of 225 ml/1 and 105 ml/1, respectively, resulted in a reduction in bactericidal efficacy of the disinfectant. Emulsified paraffin added at concentrations of between 50 and 500 ml/1 had no effect on the efficacy of the 5000 mg avI/l disinfectant, but the addition of 200 ml/1 emulsified paraffin to a 1000 mg avI/l disinfectant significantly reduced its efficiency. Iodine disinfectants containing emulsified paraffin phase separated rapidly during storage, and the bactericidal efficacy of the phases differed significantly and diminished with time.
Post-milking iodine teat skin disinfectants: 2. New intramammary infection rates
Authors: Sheldrake Richard F. , Hoare Roderic J. T.
Published: June 2009

Use of an iodine teat dip containing 5000 mg available iodine/l (mg avI/l) resulted in a significant reduction in the number of new Staphylococcus aureus infections in a lactating herd, while no significant reduction was found with a disinfectant containing only 1000 mg avI/l. When Streptococcus dysgalactiae was used as the challenge organism, the rate of new infection was extremely low, and no reduction in levels of new infection were found with either disinfectant. The pathogenicity of the Str. dysgalactiae strain was high, as 60 % of the quarters becoming infected produced clinical symptoms.
Identification, properties, and differential counts of cell populations using electron microscopy of dry cows secretions, colostrum and milk from normal cows
Authors: Lee Chee-Seong , Wooding F. B. Peter , Kemp Patrick
Published: June 2009

Differential counts of electron microscope sections of cell pellets isolated from bovine udder secretions showed that no secretory epithelial cells and very few ductal epithelial cells were present at any stage. The predominant cell type was the macrophage in dry and lactating cows or the polymorphonuclear leucocyte (PMNL) in colostrum. Lymphocytes were also present but no plasma cells were found. The macrophages took up polystyrene latex particles (as did the PMNL) and adhered toglass in culture. Neither macrophage-nor PMNL-rich cell suspensions produced any increase in free fatty acid levels when incubated with fresh milk.
Isolation and characterization of the principal caseins in rat milk
Authors: Pelissier Jean-Pierre , Yahia Ahmed , Chobert Jean-Marc , Dumas Bruno Ribadeau
Published: June 2009

The 4 major caseins, A1, A2, B1, B2, from rat milk have been isolated and analysed. From molecular weight determination, amino acid and phosphorus analyses and N-terminal sequence determination, A1 and A2 are concluded to possess similar peptide chains as do B1 and B2, with the individual fractions within each of these 2 groups differing only in their sialic acid content.

Mol. wts of approximately 22000 and 38000 were found for A1–A2 and B1–B2 respectively. The amino acid sequence of the first 13 residues of A1–A2 has been partly established. Components A1 and A2 appeared to be homologous with bovine β-casein, whereas B1 and B2 were different from any known casein, especially in their molecular weight.
Binding of calcium ions to bovine αsl-casein and precipitability of the protein–calcium ion complexes
Authors: Dalgleish Douglas G. , Parker Thomas G.
Published: June 2009

Binding isotherms for the calcium ion–αsl-casein system have been measured, as functions of ionic strength, temperature, and pH, and the isotherms have been analysed in terms of binding constants modified by substitution effects. The results demonstrate that the strength of binding is increased with increasing temperature and decreased by increasing ionic strength or decreasing pH, all of which may be explained semi-quantitatively. Parallel studies on the precipitability of the αsl-casein–Ca2+complexes showed that there is considerable variation in the extent of calcium binding required to initiate precipitation of the protein, and in the calcium concentration necessary to achieve the required extent of ligand binding.
Determination of the proportion of κ-casein hydrolysed by rennet on coagulation of skim-milk
Authors: Chaplin Brian , Green Margaret L.
Published: June 2009

A method has been developed for quantitative determination of para-κ-casein, involving spectrophotometric scanning of stained protein bands following polyacrylamide gel electrophoresis. The rate of hydrolysis of κ-casein in skim-milk at pH 6·6 and 30 °C was compared with that in EDTA-treated skim-milk under the same conditions. This showed that at the visually observed clotting time, at least 90% of the total κ-casein in milk had been hydrolysed. The time course of the reaction was consistent with all the κ-casein molecules being hydrolysed with the same efficiency. The results strongly suggest that essentially all of the κ-casein in milk is equally accessible to rennet action. This is consistent with the casein micelle being porous, or having all the κ-casein on the surface.
Calculation by computer of individual concentrations in a simulated milk salt solution. I
Authors: Wood Geoffrey B. , Reid David S. , Elvin Roger
Published: June 2009

A modegl is proposed for the equilibria between the components of the salts in milk. The model includes complex formation between calcium ions and the various ionized forms of citric, lactic and phosphoric acids, and makes allowance for the effect of ionic strength. A computer program has been written to calculate the pH of the milk salt solutions and the concentration of each of the complexes formed. Calculated pH values agree with observed values for solutions of known composition.
Effect of the addition of extracts of thermophilic lactobacilli on acid production byStreptococcus thermophilusin milk
Authors: Hemme Denis H. , Schmal Véronique , Auclair Jean E.
Published: June 2009

Soluble extracts of 20 strains of thermophilic lactobacilli (Lactobacillus helveticus, L.lactisand L.bulgaricus) were prepared and added to milk for the culture of 10 strains ofStreptococcus thermophilus. Acid production was stimulated in 64·5% of cases for 9 of these 10 strains. The L.helveticusextracts were the most stimulatory, but the same extracts did not always strongly stimulate each strain ofStr. thermophilus. The stimulatory effects observed varied with the volume of extract and the strain ofStr. thermophilus. The exception wasStr. thermophilus385, which was never stimulated. The stimulatory effects observed were due to aminopeptidases present in the lactobacillus extracts and were not related to a general caseinolytic activity. The possible addition of such extracts to milk for cooked hard cheese is discussed.
Effects of feeding level in late pregnancy and dietary protein concentration during early lactation on food intake, milk yield, liveweight change and nitrogen balance of cows
Authors: Cowan Robert T. , Reid George W. , Greenhalgh James F. D. , Tait Charles A. G.
Published: June 2009

Thirty-nine British Friesian cows and 17 British Friesian heifers were used to measure the effects on milk yield, food intake and digestion, and N balance of increasing the protein concentration in the diet from 111 to 147 g crude protein/kg dry matter during the first 16 weeks of lactation. The comparison was made for animals given food either ad lib. or at a level which allowed them to gain 0·5 kg/d during the 8 weeks before parturition, and for animals given ad lib. diets of either 60:40 or 40:60 hay: concentrate ratio during early lactation. Milk yield was increased by a higher protein concentration in the diet (P < 0·01) and the increase was evident from the first week of lactation. Mean increases over the first 8 weeks of lactation were 3 kg/d for animals on the diet of high roughage content and 7 kg/d for animals on the diet of low roughage content. A higher crude protein content in the diet also increased food intake (P < 0·05) and digestion (P < 0·05), and the increases were greater for animals given the diet of low compared with high roughage content. Level of feeding before parturition did not influence food intake or milk yield and there were no differences between cows and heifers in their response to treatments. N balance over the first 10 weeks of lactation averaged –13 g/d for cows and 6 g/d for heifers (P < 0·025). and was not significantly altered by treatments. Mean N balance of all animals was estimated to increase from –37 g/d immediately after parturition to zero at 8 weeks of lactation. The results demonstrate that an increased protein concentration in the diet during early lactation is associated with increased food intake and digestibility of food, which are in turn largely responsible for higher levels of milk production.
Inhibition of lipolysis in bovine milk by proteose peptone
Authors: Anderson Malcolm
Published: June 2009

The ability of total milk proteose peptone and individual proteose peptone components to inhibit lipolysis in milk was examined. Proteose peptone (1·5 mg/ml) when added to milk inhibited lipolysis, and component 3 was a more effective inhibitor than component 5 or component 8-fast. Inhibition by proteose peptone also occurred when the milk was treated with between 2 and 20% v/v bovine blood serum or with 5 μg/ml heparin. In vitro activity of milk lipoprotein lipase and its stability were not affected by proteose peptone. It was concluded that proteose peptone does not interact with lipase or its activator and that the mechanism of inhibition involves the substrate.
Milk coagulation by cationic polyelectrolytes
Authors: Gregorio Francesco Di , Sisto Raffaello
Published: June 2009

Positively charged materials, polyethyleneimine, poly-L-lysine and partly estcrified proteins (i.e. methyl bovine serum albumin, methyl casein and ethyl casein), in aqueous solution at the natural pH of milk, caused milk coagulation. This occurred at pH 6–6·7 at ≤ 30 °C using a defined amount of coagulant, which was quantitatively recovered in the curd. The protein and fat recovery yields were higher than with acid and rennet coagulation; the (Ca + Mg) partition between whey and curd was very similar to rennet milk clotting: the curd obtained showed high syneresis rate.
In vivo studies on the digestion of bovine caseins in the rat stomach
Authors: Miranda Guy , Pelissier Jean-Pierre
Published: June 2009

The action of gastric proteinases on bovine caseins was studied in vivo on rats fed skim-milk, or whole casein in water or whole casein in mineral solution, by analysing the gastric content after 30 min digestion. Clotting of the diet in the stomach greatly reduced the rate of gastric emptying. The proteolysis of caseins observed by gel electrophoresis appeared to follow a different pathway for the 3 different diets. The amino acid compositions of the trichloracetic acid sediments of the stomach contents did not differ between the 3 diets. The presence of free amino acids in the stomachs at significant levels (0·8–5 % of the total amino acid content) was observed.
Induction of some enzymes of citrate metabolism inLeuconostoc lactisand other heterofermentative lactic acid bacteria
Authors: Mellerick Dervla , Cogan Timothy M.
Published: June 2009

Citrate stimulated growth, totally induced citrate lyase, partly induced acetolactate synthase activity and partly repressed both diacetyl and acetoin reductases inLeuconostoc lactisNCW1. Similar results were obtained with 2 other leuconostocs and a heterofermentative lactobacillus. In 2 of the 3 leuconostocs tested, diacetyl reductase and acetoin reductase were NADPH specific, while in the 2 heterofermentative lactobacilli, they were NADH specific.
Positional distribution of fatty acids in the triglyceride classes of milk fat
Authors: Parodi Peter W.
Published: June 2009

A sample of milk fat was fractionated into high, medium and low molecular weight triglycerides by silicic acid column chromatography. Each fraction was further separated by silver ion adsorption thin-layer chromatography into triglyceride classes which were subjected to stereospecific analysis.Trans-monoene fatty acids were incorporated into triglycerides in the same manner as their cis-isomer. The specific positional distribution for fatty acids in intact milk fat triglycerides was not always maintained in the molecular weight fractions or in the various classes of unsaturation. The significance of these findings is discussed in relation to biosynthetic mechanisms for milk fat synthesis.
Influence of milk proteins on lipid oxidation in aqueous emulsion: I. Casein, whey protein and α-lactalbumin
Authors: Allen John C. , Wrieden Wendy L.
Published: June 2009

A milk-related model system, 2 mM-trilinolein in 0·1 M-piperazine-N, N′-bis-2-ethanesulphonic acid buffer, pH 6·8, stabilized by lysophosphatidylcholine was used to assess the effect of milk proteins on lipid oxidation in emulsion, catalysed by Cu2+ions. In some experiments the trilinolein was replaced by sunflower oil (2 g 1-1). Oxidation at 25°C was assessed by measurement of the rate of O2-utilization and by the thiobarbituric acid assay. The features, relevance and reliability of the model are described in terms of the observed effects in the absence and presence of added protein. Casein was antioxidative at concentrations relevant to those in bovine milk, human milk, infant milk formulations and ‘high linoleic acid’ milk. Whole whey protein was a less effective inhibitor of lipid oxidation at similar concentrations. Purified α-lactalbumin was also marginally antioxidative, and its effect was independent of the molar Cu2+: protein ratio between 1:1 and 3:1.
Studies on salivary and pancreatic lipases of the pre-ruminant calf
Authors: Toothill Joyce
Published: June 2009

Salivary and pancreatic lipases of the pre-ruminant calf have been studied using ion-exchange chromatography and gel filtration. In addition, pancreatic lipase has been fractionated using concanavalin A-affinity chromatography. The effects of 5,5′-dithiobis(2-nitrobenzoic acid), organic solvents and trypsin on pancreatic lipase have also been investigated. The effect of taurodeoxycholate on the lipolytic activity of the 2 lipases has been compared. Salivary lipase behaved as a single enzyme on ion-exchange chromatography, and gel filtration gave a mol. wt value of 52000 for the enzyme. Although pancreatic lipase appeared to be a single enzyme on gel filtration, with a mol. wt of almost 80000, the lipase was shown by ion-exchange and affinity chromatography to consist of at least 2 enzymes of mol. wts 72000 and 60000, and did not require colipase for maximum activity in the presence of high concentrations of bile salts. Colipase-dependent lipase, mol. wt about 45000, and probably amounting to not more than 10% of the total activity, was also present. This was the predominant form only after large losses in total lipolytic activity had occurred, as after treatment with a mixture of ether, ethanol and deoxycholate, or prolonged action of trypsin. When the concentration of taurodeoxycholate was increased from zero to 1 mM in a tributyrin substrate, the lipolytic activites of calf salivary and pancreatic lipases, and pig pancreatic lipase, increased. At a concentration of 4 mM-taurodeoxycholate, calf salivary lipase activity was higher, that of calf pancreatic lipase slightly lower and pig pancreatic lipase activity markedly lower.
Recent aspects of the chemistry of lactose
Authors: Thelwall Leslie A. W.
Published: June 2009

Regioselective esterification and acetalation reactions of lactose have produced partly protected derivatives which have significant value in the further modification of lactose and as precursors for the synthesis of higher oligosaccharides.
A note on the lactation performance of twin-bearing cows
Authors: Broster William H. , Clements A. June , Hill Randolph E.
Published: June 2009

Seven pairs of cows were chosen at parturition. In each pair, 1 member had had a twin pregnancy (T) and the other was a comparable cow with a single calf pregnancy (S). All cows were offered the same amount of feed over the first 28 weeks of lactation. In early lactation, intakes were equal; in mid-lactation the T group ate more. The T cows had a lower peak yield of milk than the S cows, but rates of decline in yield in mid-lactation were equal for the 2 groups. Lactose concentrations in the milk were equal throughout lactation, but the fat and protein concentrations were greater for the T group in early lactation. The T group yielded smaller amounts of milk solids. The T group lost less weight in early lactation and gained more weight subsequently. Three of the T group, but only 1 of the S group, did not conceive during the test lactation.
Serum lipoprotein stimulation of lipolysis and its relevance to free fatty acid development in bovine milk
Authors: Anderson Malcolm , Needs Eric C.
Published: June 2009

The role of blood serum lipoproteins in stimulating milk lipolysis was investigated by adding blood serum and heparin to the milk of normal cows and cows in which elevated somatic cell counts were induced by intramammary infusion ofEscherichia coliendotoxin andStaphylococcus aureus. There was considerable variation between individual milks in the extent to which lipolysis was stimulated. In some milks there was almost no response. For values obtained from 29 cows during the first 6 months of lactation a relationship was observed between free fatty acid (FFA) levels in the untreated and serum-stimulated samples (r= 0·776). FFA values were higher after 18 h at 4 °C in milks from infused quarters than in those from control quarters, but this difference was not entirely due to higher values from the infused quarters at 0 h. Both blood serum and heparin stimulated lipolysis in high cell count milks and control milks. The response to heparin was greater than that to blood serum, but the response to both was highly correlated with FFA levels in the untreated milks. There were no differences in the ability of skim-milks prepared from infused and control quarters to promote lipolysis in recombined milks containing sterilized homogenized milk fat globules as a source of substrate. Incubation of blood serum with 2 μg/ml trypsin for 1 h at 37 °C reduced the ability of the serum to promote lipolysis. The importance of lipase activation by blood serum lipoproteins in relation to milk lipolysis is discussed.
Coagulation of renneted bovine casein micelles: dependence on temperature, calcium ion concentration and ionic strength
Authors: Dalgleish Douglas G.
Published: June 2009

The rates of coagulation of completely renneted casein micelles have been measured as functions of ionic strength, temperature, and concentration of Ca2+. At 25 °C and below, the rate constants for the coagulation were found to be low, but increased with temperature so that at 60 °C the particles were coagulating at almost maximum rate permitted by diffusion. This maximal rate at 60 °C was achieved at nearly all of the ionic strengths and concentrations of Ca2+ used. At lower temperatures the rate constant decreased with increasing ionic strength, the dependence being more marked at lower temperatures. Increasing concentration of Ca2+ also increased the rate at low and moderate temperatures. The implications of these results are discussed in terms of specific and non-specific ionic interactions and of hydrophobic bond formation.
Effect of calcium on the hydration of casein. I. Water vapour sorption and fine structure of calcium caseinates compared with sodium caseinates in the pH range 4·6–8·0
Authors: Rüegg Max , Moor Ursula
Published: June 2009

Hydration of Ca and Na caseinates which were prepared from whole casein at different pH levels (range 4·7–8·0) was determined by means of water vapour sorption measurements in the water activity (aw) range 0·58–0·95. Water uptake of Ca caseinates was systematically lower than that of Na caseinates prepared at equal pH, the differences increasing with increasing pH and aw. Plots of the water content ν. the amount of added hydroxide at constant aw revealed a linear relationship between water uptake and cation content, suggesting that the increase in water uptake is mainly determined by the amount and type of cations associated with the caseins. In the aw range tested, Ca2+ adsorbed about 2–7 and Na+ 3–18 mol water/mol of cation. This implies that replacement of one mol of casein-bound Na+ by Ca2+ is accompanied by a displacement of 1–11 mol water at aw 0·58–0·95. The loss of water is a consequence of conformational changes induced by the chelating and cross-linking effects of Ca2+, which also lead to micelle formation.
N-acetyl-β-D-glucosaminidase (NAGase) levels in bulk herd milk
Authors: Kitchen Barry J. , Middleton Gordon , Kwee W. Seng , Andrews R. Jeffrey
Published: June 2009

N-acetyl-β-D-glucosaminidase (NAGase) levels and somatic cell counts (SCC) were determined monthly for 6 months in the bulk milk of 181 suppliers (1063 samples). A highly significant correlation (r = 0·74; P < 0·001) was found between supplier's bulk herd milk geometric mean NAGase activity and SCC. Monthly trends which grouped suppliers into various categories defined by different NAGase and SCC thresholds showed that a similar overall pattern was obtained with both SCC and NAGase. However, further analysis indicated that 18% of the bulk milk which had SCC < 500 × 103/ml had NAGase levels > 25 units. Also, 34% of samples with SCC > 500 × 103/ml had NAGase levels < 25 units. Overall, 24% of all samples did not have corresponding NAGase and SCC results. When the bulk milk of 2 commercial dairy herds was tested monthly over 12–18 months whilst the infection status of all quarters in the herds was regularly monitored, those herds with low incidence of mastitis (5% quarters infected) had significantly lower bulk milk SCC and NAGase levels than those with a high incidence of mastitis (22% of quarters infected). This suggests that NAGase measurement on bulk herd milk would be a simple means of monitoring infection status of dairy herds and of rapidly classifying a supplier's milk as being of low, medium or high SCC status. The possible combined use of SCC and NAGase levels in bulk milk monitoring schemes is discussed.
Viscosity and heat capacity of whey retentates from sheep's milk cheese
Authors: Fernández-Martín Fernando
Published: June 2009

Different concentrates from sheep's milk cheese whey, with up to 26·5% solids, were prepared in the laboratory by reverse osmosis, and their viscosities and heat capacities determined over the temperature range 5–80 °C. These products behaved like other liquid milk concentrates previously studied, so that similar analytical expressions could be used to predict these physical properties in cheese whey as a function of the temperature and solid content. A nomogram is also given for an easier computation of each property. The water in liquid dairy products and their concentrates up to 40% solid content appears to behave as pure, free water with respect to its partial contribution to the heat capacity of these products, its apparent heat capacity being 4·208±0·016 kJ. kg-1°C-1.
Effect of heat induced interaction between β-lactoglobulin and κ-casein on syneresis
Authors: Pearse Martin J. , Linklater Peter M. , Hall Robert J. , Mackinlay Antony G.
Published: June 2009

The effect of preheating skim milk and artificial micelle milk on curd syneresis was studied. The inhibition of syneresis caused by heat was dependent on the presence of β-lactoglobulin (β-lg) and to a lesser extent α-lactalbumin. The degree of inhibition increased with increasing amounts of added β-lg and preheating temperature. This agrees with the hypothesis that the detrimental effect of preheating on syneresis is due to complex formation between β-lg and κ-casein. This complex appeared to be mediated via thiol–disulphide exchange and its formation appeared to interfere with the micelle–micelle interactions responsible for syneresis.
Heat stability of plasmin (milk proteinase) and plasminogen
Authors: Alichanidis Efstathios , Wrathall Julia H. M. , Andrews Anthony T.
Published: June 2009

The effect of heating on plasmin activity in various media, including phosphate buffer pH 7·0, skim milk, blood plasma, solutions of casein and solutions of whey proteins were investigated. Plots of log residual activity υ. heating time were linear at all temperatures from 63 to 143 °C. In buffer solutions the presence of casein led to substantial substrate protection, the Arrhenius plots being linear both in the presence and absence of casein. The activation energy, Ea, for the inactivation reaction, was 62·4 kJ/mol in buffer alone and 58·4 kJ/mol with casein present at 25 mg/ml. In skim milk, despite the presence of casein at a similar concentration, plasmin was no more stable to heat than in buffer alone, and a curved Arrhenius plot was obtained indicating a more complex inactivation mechanism. Heating in the presence of proteins having free -SH groups accelerated the inactivation of plasmin. The role of -SH groups was confirmed by experiments with added α-lactalbumin, in which no free -SH groups occur, and reduced carboxymethylated β-lactoglobulin, both of which were without effect. In blood plasma, plasmin was less stable to heat than in buffer (pH 7·0) or in skim milk. Plasminogen behaved very similarly to plasmin either when activated to plasmin with urokinase before heating or when activated afterwards. A hypothesis is presented to describe the heat inactivation and denaturation of plasmin. Technologically important findings are that in skim milk plasmin was largely unaffected by pasteurization conditions and 30–40% of its activity remained even after ultra high temperature processing conditions.
Radioimmunoassay for measurement of bovine α-lactalbumin in serum, milk and tissue culture media
Authors: Akers R. Michael , McFadden Thomas B. , Beal W. E. , Guidry Albert J. , Farrell Harold M.
Published: June 2009

A sensitive, specific radioimmunoassay for bovine α-lactalbumin (α-la) suitable for measurement of serum, tissue culture media and milk was developed. α-La was not detected in serum from prepubertal male or female cattle, but was detected as early as 60 d of gestation in nulliparous Holstein heifers, the level being greatly increased during the last one third of gestation. Serum from cross bred beef heifers contained less α-la and it was not detected until late gestation. Concentrations of α-la in serum samples from pregnant multiparous Holstein cows decreased at drying-off and subsequently increased just before parturition. Secretion of α-la by mammary tissue explants from steroid-primed prepubertal Holstein heifers was induced by the addition of bovine prolactin, ovine prolactin or human growth hormone to tissue culture media.
Effect of different neutralizing treatments on the efficiency of an anaerobic digester fed with deproteinated cheese whey
Authors: Haast Johannes De , Britz Trevor J. , Novello Johannes C.
Published: June 2009

Deproteinated whey, prepared from sweet whey powder, was digested anaerobically in a downflow fixed-bed reactor at 35 °C. Different pH control treatments were applied over a period of 210 d. Initially NaOH was added at a concentration of 68 mequiv. l-1 substrate. This was successfully replaced by 80 mequiv. Na2CO3l-1 which resulted in a 15·5% increase in biogas production and a 6·7% increase in CH4 production. A decrease in the quantity of Na2C03l-1 added led to signs of instability and a drop in CH4 production. The stepwise addition of urea restored the stability, and a further increase of urea, to a level of about 20 mequiv. l-1, made it possible to replace Na2C03 completely. When all pH control measures were omitted, complete failure resulted within 10 d. Methane yields, under stable conditions, varied between 0·321 and 0·272 m3 kg-1 chemical oxygen demand (COD) removed which corresponds to 92 and 78% of the theoretical yields. Carbon balances indicated that between 60·8 and 68·5% of the carbon fed was converted to biogas. No toxicity was observed at a carbon: nitrogen (C/N) ratio of 7·7. This was in contrast to previous results where toxicity had occurred at the same C/N ratio but at a higher concentration of Na.
Effect of breed of cow (Friesian and Montbéliarde) on spontaneous and induced lipolysis in milk
Authors: Chazal Marie-Paule , Chilliard Yves
Published: June 2009

Levels of free fatty acids (FFA) were determined immediately after milking (initial FFA), and after 22 h storage at 4 °C, either without (FFA-22) or with a mechanical induction of lipolysis (FFA-22I), in milk from Friesian and Montbéliarde cows in the same herd, at identical stages of lactation and pregnancy and receiving the same feeding regimes. There was no difference between the two breeds in initial FFA and FFA-22 contents whatever the lactation period. This was also true during late lactation when lipolysis was further increased after feeding a poor quality grass silage. The observation that milk FFA-22I content from the Montbéliarde cows was higher than that from Friesian cows in summer, but not in winter, requires cautious interpretation as the activation treatments were not comparable, owing to the different ambient temperatures during activation in these two periods.
Microbiological assay of blood serum for the vitamin B12status of dairy cows
Authors: Carlos Gerard M. , Telfer Stewart B. , Johnson C. Lewis , Givens D. Ian , Wilkins Roger J. , Newberry Robert D.
Published: June 2009

Four vitamin B12assays were compared using blood sera from Friesian cows on winter diets or grazing. In herd 1, ten animals were blood-sampled three times at monthly intervals and the vitamin B12concentration of the sera determined by thePoteriochromonas malhamensisandLactobacillus delbrueckiiassays. At all three sampling dates the results produced by theP. malhamensisassay were significantly greater than those produced by theL. delbrueckiiassay. Cows in herd 2 were divided into two groups, each of 30 animals. One group was given a soluble glass bolus releasing cobalt and the other was unsupplemented. Milk yields were recorded throughout the experimental period and herbage samples were taken at intervals for cobalt determinations. Blood samples were taken at intervals from January to September 1983 and the vitamin B12concentration of the sera determined by four different assay methods: theP. malhamensisandL. delbrueckiimicrobiological assays and the Becton Dickinson and RIA Products ‘No-boil’ radioassays. The last of these failed to detect vitamin B12in any sample. There was a significant difference between the results obtained by the three other assays, with the Becton Dickinson radioassay consistently producing the lowest result and theP. malhamensisassay the highest result of the three. There was no significant effect of cobalt supplementation on milk yield.
Influence of somatic cell count on the whipping properties of cream
Authors: Needs Eric C. , Anderson Malcolm , Kirby Simon
Published: June 2009

Cows were infused with Escherichia coli endotoxin to provide a pool of milks with high somatic cell counts (SCC). This was mixed with bulk tank milk obtained from either of two Institute herds, producing a range of milks containing 0, 10, 20, 30 and 100% high SCC (HCC) milk. Creams containing 38% fat were produced from these milks on nine separate occasions; five times from winter milks and four times from summer milks. The SCC of the milks, the free fatty acid concentration of the unwhipped creams and the whipping time, stiffness and overrun of the whipped cream were measured. Whipping time and stiffness increased and overrun (volume increase) decreased as the proportion of HCC milk in the mixture increased. However, these changes were statistically significant only when comparing the 100% HCC milk with the other treatments containing lower levels of HCC milk. Creams produced in the summer took less time to whip and were less stiff than winter creams but there was no change in overrun. The source of bulk milk supply affected the stiffness and overrun of the whipped creams. Free fatty acid concentration appeared to have no direct effect on whipping characteristics.
Factors influencing the concentrations and yields of milk constituents and their interrelationships
Authors: Sharaby Mahmoud Abdelalim
Published: June 2009

Milk samples from 250 Jersey and Friesian cows were collected and used to investigate the pattern of interrelationships between milk constituents and to test the effects of breed, sire, parity, stage of lactation, season of calving and milking time on them. Breed and sire effects were significant for all constituents. Overall Jersey cows produced significantly higher milk constituent concentrations except lactose, but the test-day yields in Friesians were significantly higher. Milk constituents had varying responses to parity, days in milk and season of calving. Correlation between different constituents and their regression on each other suggested antagonistic relationships. The pattern of association between constituent concentrations in Friesian cows was similar to that between test-day yields, indicating an equilibrium between volume and content of milk.
Lack of correlation between milk glucose concentrations and rates of milk production in the rat
Authors: Grigor Murray R. , Carrington Janet M. , Arthur Peter G. , Hartmann Peter E.
Published: June 2009

Concentrations of lactose, α-lactalbumin (α-la), glucose and glucose-6-phosphate were measured in milk obtained from rats under conditions where the rates of milk production varied from 0 to 2·6 g/h. In the milk from rats fed a low protein diet where milk production was 0·9 g/h, the concentration of α-la was 1·5 mg/ml, being significantly lower than that in the milk of control rats at 2·9 mg/ml and where the rate of milk production was 2·6 g/h. No differences were detected in the glucose concentrations. When rats were fed restricted amounts of the control diet and where milk production varied from 0 to 1·7 g/h during the course of the day, no differences in the concentrations of either α-la or glucose were detected. These results suggest that considerable caution must be used in interpreting the significance of milk glucose in the rat.
Precision conductometry in milk renneting
Authors: Dejmek Petr
Published: June 2009

On renneting, the electrical conductivity of milk decreased as viscosity increased. The sigmoidal time course of the decrease resembled the time course of shear modulus, but was more rapid. The total amount of change was independent of the amount of rennet and proportional to milk conductivity and its casein content. The conductivity change was interpreted as a change in the way casein micelles obstructed the path of the charge-carrying ions.
Ultrafiltration of reconstituted skim milk
Authors: El-Salam Mohamed H. Abd , Shahein Nadia
Published: June 2009

The manufacture of Domiati cheese by ultrafiltration (UF) processing of recombined milk bas been described in several reports (El-Shibinyet al.1982; Bogaard, 1986). This method has several potential advantages in areas short in milk production. In Egypt, a new plant has been established recently for the manufacture of Domiati cheese on the basis of this technology.

The behaviour of fresh pasteurized skim milk during UF has been described (Glover, 1971; Setti & Peri, 1976; Patel & Reuter, 1985; Chiang & Cheryan, 1986). Similar studies are lacking for reconstituted skim milk or recombined milk. Skim milk powder is usually subjected to variable heat treatments during processing which are known to affect its properties. These heat treatments have been used as a basis for classification of skim milk powders. Therefore, studies on UF of reconstituted milks previously subjected to different heat treatments would be important in the adaptation of this technology to cheese manufacture.

We describe here results obtained for permeation rates of reconstituted skim milk during UF compared with fresh pasteurized skim milk.
Changes in the concentration of metabolites in milk from cows fed on diets supplemented with soyabean oil or fatty acids
Authors: Faulkner Anne , Pollock Helen T.
Published: June 2009

Cows were fed on diets supplemented with soyabean oil or soyabean fatty acids which in some cases were protected from rumen hydrogenation. The fat-containing diets reduced the output of short- and medium-chain fatty acids in milk. Associated with this fall in short- and medium-chain fatty acids was a decrease in the concentration of 2-oxoglutarate and an increase in that of isocitrate and citrate. Protection of polyunsaturated fat from rumen hydrogenation had no significant effect. Milk yields were unaffected by diet, but the variation in milk yield among cows correlated positively with the concentration of glucose in milk.