bluuebunny/crossref_metadata_2025 huggingface dataset:
Coagulation of homogenized milk particles by rennet
Authors: Robson Elizabeth W. , Dalgleish Douglas G.
Published: June 2009

The action of rennet on homogenized milk was studied using turbidimetric and light scattering techniques, and compared with results obtained previously for skim milk. The time required for the onset of coagulation was shorter for homogenized milk than for skim milk. The rate of coagulation of fully renneted particles increased with increasing temperature, and with increasing Ca2+ concentration, but was only slightly influenced by changes in ionic strength. The von Smoluchowski rate constant for the coagulation reaction was two orders of magnitude smaller for homogenized milk than for skim milk. Results suggest that coagulation of homogenized milk is controlled in general by the same factors as skim milk, and that the reaction may be inhibited owing to a reduction in the amount of casein available for mutual interaction, rather than to disruption of the micelles on homogenization.
Importance of the calving interval to milk yield in the following lactation of British Friesian cows
Authors: Wood Peter D. P.
Published: June 2009

The records of 453260 British Friesian cows, accumulated by the Milk Marketing Board of England and Wales in 1981/82, were used to estimate the effect of the calving interval on milk production in the subsequent lactation. There was a clear relationship between the length of the dry period and the calving interval in which it occurred, such that the dry period was extended by 2·5 d for every 10 d extension of the calving interval. The relationship between the interval and milk production in the following lactation appeared more likely to be due to variation in the dry period than to variation in the calving interval itself. A dry period between 50 and 60 d was associated with maximum production of milk, fat and protein. Among cows with dry periods shorter than 55 d, fat and protein production increased by 8 and 3·5 kg/d respectively. For cows with dry periods longer than 55 d, production of fat and protein was reduced by 0·2 and 0·12 kg/d respectively. The modal calving interval was 355 d including a dry period of 51 d. The interval tended to increase with the age of the cow, at the rate of 3 d/month of age within parity. The best estimate of future calving intervals was the mean of all previous intervals of the cow.
Chemical composition, rennet coagulation properties and flavour of milks from cows grazing ryegrass or white clover
Authors: Grandison Alistair S. , Manning Donald J. , Thomson David J. , Anderson Malcolm
Published: June 2009

Milks from two groups of dairy cows grazing either white clover or ryegrass swards were compared to determine whether their acceptability in terms of flavour, composition and rennet coagulation properties was affected by these differences in the cows' diet.

The concentrations of Ca and Mg were slightly higher and that of inorganic phosphorus was slightly lower in milks from the animals on the ryegrass pasture compared with those grazing clover, but the levels of Na, K and citrate were the same. The clover milks contained more αs- and β-casein and a greater proportion of small micelles but had similar contents of κ-casein to the ryegrass milks. Following addition of rennet at pH 6·4, the clover milks gave rise to firmer curds but the clotting times and rates of syneresis were not consistently different from the ryegrass milks. The clover milks contained a greater proportion of short-chain (C4–C10) fatty acids, but lower proportions of long-chain (C18+) and unsaturated acids than the ryegrass milk.

The different pastures did not give rise to any differences in the flavour of the milk.
Evaluation of a porous silica-based ion-exchange medium for the production of protein fractions from rennet- and acid-whey
Authors: Skudder Paul J.
Published: June 2009

The use of a silica-based ion-exchange medium for the recovery of protein from wheys prepared by treatment with rennet or with acid has been investigated. The protein capacity of the medium whilst maintaining an adsorption greater than 75% during the passage of rennet-and acid-whey was 0·079 and 0·053 g/g respectively. Bovine serum albumin (BSA), α-lactalbumin (α-la) and β-lactoglobulin (β-lg) adsorbed from acid-whey were mostly recovered in yields greater than 93% in an undenatured form essentially free of lactose and milk salts by elution using 0·1 M-HC1. With rennet-whey, BSA and part of the α-la were not recovered in the native form, probably because of proteolysis during elution by enzymes originating in the rennet used in the manufacture of the whey. There was, however, no effect on the recovery of native β-lg adsorbed by the medium. An unidentified proteinaceous fraction, thought to be of casein origin, was also adsorbed and recovered from rennet-whey. Fractions of the adsorbed proteins could not be obtained by eluting with a gradient increase in NaCl concentration. Nevertheless, purified β-lg was obtained by passing a large quantity of whey through the medium. This protein had a high affinity for the functional groups of the medium, to the extent that other proteins initially adsorbed were subsequently displaced. Unidentified proteinaceous material in rennet-whey also had a high affinity for the functional groups of the ion exchanger but most of this fraction could be removed by a pretreatment procedure which involved passing the whey through the medium at pH 5·0; unidentified material was selectively adsorbed at this pH. The medium could also be used to produce a fraction containing a mixture of BSA and α-la but it was not possible to separate these proteins.
Cheddar cheesemaking with recombinant calf chymosin synthesized in Escherichia coli
Authors: Green Margaret L.
Published: June 2009

The cheesemaking properties of recombinant chymosin from Escherichia coli were compared with those of standard rennet in parallel trials with three single strain starters. For each pair of cheeses the cheesemaking characteristics, recoveries of milk solids in the curds and compositions were similar. The rates and types of proteolysis and texture development during ripening between cheeses made with the two coagulants were not significantly different.
Particle size distribution and calcium content of batch-precipitated acid casein curd: effect of precipitation temperature and pH
Authors: Jablonka Mark S. , Munro Peter A.
Published: June 2009

The first stage in acid casein manufacture is the isoelectric precipitation of casein from skim milk. This stage controls the particle size of the casein curd which is important in the later washing, dewatering and drying stages. Casein was precipitated batchwise from 9% total solids skim milk using 0·3 M-H2SO4 at temperatures from 25 to 53 °C and at pH (measured in the whey) from 3·6 to 5·1. A wet sieving method has been developed for measuring the particle size distribution of the casein curd. Ferric ammonium sulphate was added to the curd/whey mixture to toughen the curd particles and to reduce their stickiness. For given precipitation conditions the particle size distribution could generally be modelled by a normal distribution. The mean particle size generally increased with increasing temperature and pH. The increase in particle size with pH was pronounced at 53 °C, while at 25 and 35 °C particle size varied little with pH. The calcium contents of washed casein curd samples were low at all precipitation pH at a precipitation temperature of 35 °C, but increased markedly above pH 4·4 at precipitation temperatures of 45 and 53 °C.
Nutrient content of milk and milk products: water soluble vitamins in baby milk formulae
Authors: Scott K. John , Bishop Dinah R.
Published: June 2009

A study of the content of water soluble vitamins in the 12 baby milk formulae available in the UK in April 1983 showed that levels of vitamins in the individual brands were generally in excess of those declared by the manufacturer. For cows' milk based formulae the mean excess of vitamins over the declared level was 94%. Vitamin levels in prepared formulae averaged three times the minimum recommended level. The average level of B vitamins in prepared cows' milk based formulae was six times higher than in mature human milk. For the two soya based products, the levels of vitamins were generally in excess of the declared level and levels of vitamin B12, biotin and, in one sample, vitamin B6 were considerably in excess of those found in mature human milk.
Fractionation of bovine caseins by reverse phase high performance liquid chromatography: identification of a genetic variant
Authors: Carles Christophe
Published: June 2009

Samples of reduced whole casein from genetically typed individual cows were quantitatively separated into their main components, αsl-, αs2-, β- and κ-caseins by reverse phase high performance liquid chromatography (RP-HPLC) using a mobile phase of phosphate-buffered aqueous propan-2-ol containing sodium dodecyl sulphate and an octadecylsilyl stationary phase. One casein sample was found to give two peaks of β-casein of approximately equal areas. RP-HPLC of tryptic digests of the two separated peak fractions gave identical patterns with the exception of one peptide peak with different retention times. Amino acid analyses performed on both fractions showed that they corresponded to peptide 114–169 of β-casein A1. The atypical β-casein differed from the typical one by a Pro→Leu substitution in region 114–169.
Irreversible heat denaturation of bovine α-lactalbumin
Authors: Chaplin Lesley C. , Lyster Richard L. J.
Published: June 2009

The irreversible heat denaturation of α-lactalbumin (α-la) in 0·1 M-phosphate, pH 7·0, at 100 °C was studied using polyacrylamide-gel electrophoresis (PAGE). PAGE revealed two groups of bands, one moving faster than native α-la and one slower, in addition to some denatured protein which remained at the origin and some residual native α-la. The faster group had unchanged molecular weight, but an increase in charge, partly due to hydrolysis of glutamine and asparagine residues. The slower group was shown by two-dimensional sodium dodecyl sulphate-PAGE to be oligomers of denatured α-la; formation of the smaller oligomers preceded the larger ones. The oligomers reverted to monomers in the presence of dithiothreitol, showing that they were disulphide-linked aggregates of denatured α-la. Immuno-blots of the gels showed that both fast and slow groups of bands had irreversibly lost most of the antigenicity of the native protein.
Determination of tensile strength of gels prepared from fractionated whey proteins
Authors: Langley Keith R. , Millard David , Evans E. William
Published: June 2009

A novel method for measuring tensile strength of heat-setting gels is described and is applied to whey protein gels. Contributions made by β-lactoglobulin and α-lactalbumin individually to the tensile strength of the gel are calculated. The tensile strength can be found from power law equations related to concentration of α-lactalbumin and β-lactoglobulin in whey protein mixtures.
Phage typing of Staphylococcus aureus associated with subclinical bovine mastitis
Authors: Mackie Dermot P. , Pollock David A. , Rodgers Sean P. , Logan Ernest F.
Published: June 2009

Six hundred and seventeen isolates of Staphylococcus aureus from sub-clinical mastitis cases in 63 dairy herds in Northern Ireland were typed using a set of 25 phages. Ninety-four per cent of the isolates were typable, with nine phages, predominantly from groups I and III, being responsible for almost all of the lysis. Although 68 phage patterns were found, six of them typed 47·2 % of the isolates. One strain accounted for 14·7% of the isolates, but the largest number of strains (44) was restricted to individual farms. The epidemiological significance of these findings for on-farm mastitis control is discussed.
Metabolism of the lactating cow: I. Animal elements of a mechanistic model
Authors: Baldwin R. Lee , France James , Gill Margaret
Published: June 2009

A mechanistic model of dairy cow metabolism is described. The model was constructed as part of a programme directed toward quantitative and dynamic analysis of concepts and data regarding factors which influence the partition of nutrients in lactating dairy cows. Sensitivity and behavioural analyses undertaken using the model indicate that concepts and data arising from tissue level experiments conducted in vitro can be used to structure and parameterize whole-animal models since the quantitative and dynamic behaviour of such a model is acceptable. These analyses indicate further that such models can be used to evaluate factors which influence patterns of nutrient utilization. By way of illustrating the model's utility regarding evaluation of concepts relating to the interpretation of energy balance experiments, results of a simulated energy balance experiment are presented. Apparent costs of milk synthesis are partitioned among biosynthetic costs, physiological costs, ion transport costs and the reductions in energy expenditures in synthesis of body components which accompany increasingly negative energy balances due to feed restriction.
Formation of volatile aroma compounds and carbon dioxide in yogurt starter grown in cows' and goats' milk
Authors: Rysstad Gunnar , Abrahamsen Roger K.
Published: June 2009

Yogurt starter B3 was grown in cows' milk, goats' milk I (obtained 2–3 weeks after parturition) and goats' milk II (8 months after parturition), and a number of biochemical and bacteriological parameters were recorded at intervals during incubation for 8 h at 43°C. No appreciable differences between the milks were observed for total viable count, bacteriological ratio of rods to cocci, or decrease in pH. Production of acetaldehyde, however, was considerably lower in goats' milk I (6·2 ppm) and goats' milk II (8·9 ppm) than in cows' milk (18 ppm). Formation of diacetyl and acetoin showed similar patterns in all three milks. The highest production of α-acetolactic acid was observed in goats' milk II, apparently coincident with the highest production of CO2 in this milk.
Heat stability of milk: influence of modifying sulphydryl-disulphide interactions on the heat coagulation time–pH profile
Authors: Singh Harjinder , Fox Patrick F.
Published: June 2009

Addition of reducing agents such as 2-mercaptoethanol (2-ME), dithio-threitol and Na sulphite to milk markedly reduced its heat stability at pH values below 7·1. 2-ME reversibly destabilized milk or serum protein-free casein micelle dispersions and promoted the release of κ-casein-rich protein from the micelles. Reduction of either casein micelles or β-lactoglobulin (β-lg) with 2-ME and subsequent blocking of the newly formed –SH groups with N-ethylmaleimide irreversibly reduced the maximum to minimum ratio in the heat stability profile. 2-ME disrupted κ-casein/β-lg complexes and stripped κ-casein from the micelles on heating. The milk or caseinate systems were thus destabilized. Addition of KBrO4or iodosobenzoate to milk at 5 HIM eliminated the minimum but destabilized milk in the region of the maximum. However, KIO3at 5 mm had a strong stabilizing effect throughout the pH range 6·5–7·3.
Microbiological quality and composition of two types of Spanish sheep's milk cheeses (Manchego and Burgos varieties)
Authors: García María Camino , Otero Andrés , García María Luisa , Moreno Benito
Published: June 2009

Thirty six samples of Manchego and 36 of Burgos cheese from retail outlets were examined. The mean log microbiological counts/g in Manchego cheese were 2·6 coliforms, 3·76 enterococci, 7·07 lactic acid bacteria, 8·02 mesophiles, 3·84 psychrotrophs 4·47 yeasts and moulds and 4·11 staphylococci, and in Burgos cheese were 7·17, 3·45, 7·25, 8·89, 8·18, 5·09 and 5·12 respectively. Coagulase-positive staphylococci were detected only in three samples of Manchego cheese, one of these isolates producing enterotoxin A. Staphylococcal thermonuclease was detected in eight samples of Manchego and 12 of Burgos cheese, the mean values of enzyme detected being 0·29 and 0·32 ng/g cheese respectively. Staphylococcal enterotoxins were not detected in any of the cheeses tested. Possible relationships between microbial counts and physicochemical characteristics were investigated by regression analysis.
Histochemical localization and possible antibacterial role of xanthine oxidase in the bovine mammary gland
Authors: Collins Robert A. , Parsons Keith R. , Field Terry R. , Bramley A. John
Published: June 2009

Xanthine oxidase (XO) was demonstrated to be present in the teat canal and secretory tissue of the bovine mammary gland by histochemical techniques. Homogenates of these tissues were able to replace XO in an antibacterial assay with Streptococcus uberis. The action of XO on its substrate hypoxanthine was shown to provide an essential component for anti-streptococcal activity mediated by lactoperoxidase. A mechanism is proposed whereby the interaction of XO, lactoperoxidase and thiocyanate may provide antibacterial activity in the teat canal.
Partial purification and characterization of an extracellular proteinase fromAeromonas hydrophilastrain A4
Authors: Alichanidis Efstathios
Published: June 2009

An extracellular metalloproteinase fromAeromonas hydrophilastrain A4, isolated from milk, was purified by a factor of 300 by chromatogrpahy on DEAE-cellulose and Sephadex G-150. The enzyme had a mol. wt of 43000 and contained 2 g atom Ca/mol. It was active over a pH range 4·8–9·5 and had optimum activity on casein at pH 7·0 withKm= 0·17 mM. It was strongly inactivated by metal chelators and the apoenzyme was fully reactivated with Ca2+, Mn2+or Co2+. Heavy metal ions such as Ag+, Hg2+, Fe2+, Zn2+, Cd2+, Ni2+and Cu2+totally or partly inactivated the enzymic activity at 5 mM concentration. The enzyme was not inactivated by diisopropylfluorophosphate, soyabean trypsin inhibitor or sulphydryl group reagents. It was optimally active at 45 °C; above 50 °C activity declined rapidly, but significant activity persisted at 4 °C. It was heat labile in phosphate or Tris-maleate buffer but exogenous Ca2+afforded protection.
Uptake of glutamic acid byStreptococcus salivariussubsp.thermophilusCNRZ 302
Authors: Bracquart Patrice , Le Deaut Jean-Yves , Linden Guy
Published: June 2009

Glutamic acid uptake inStreptococcus salivariussubsp.thermophiluswas energy dependent, the source of energy and adaptation to sugar being important to efficiency of uptake. The disaccharides, lactose and sucrose, stimulated uptake, but cells grown in glucose were more active. Optimum temperature was ˜ 40 °C and pH ˜ 7·0. NaCl was strongly inhibitory to the uptake of glutamic acid although not to that of isoleucine. High specificity existed because only L-aspartic acid was inhibitory.
Purification and thermostability of β-galactosidase (lactase) from an autolytic strain ofStreptococcus salivariussubsp.thermophilus
Authors: Chang Byeong-Seon , Mahoney Raymond R.
Published: June 2009

β-Galactosidase from an autolytic strain ofStreptococcus salivariussubsp.thermophiluswas purified 109-fold to near homogeneity. The yield of purified enzyme was 41% and the specific activity was 5920-nitrophenylβ-D-galactopyranoside U/mg at 37 °C. Two isozymes were present, but only one subunit was detected, having a mol. wt of 116000. Enzyme stability was 37–83 times greater in milk than in buffer in the range 60–65 °C. At 60 °C the half-life in milk was 146 min. Denaturation in buffer was first-order, but in milk the overall reaction order with respect to enzyme concentration was ˜ 0·5. The activation energy for denaturation was 453 kJ/mol in milk and 372 kJ/mol in buffer. In milk the activation energy for lactose hydrolysis was 35·1 kJ/mol.
Proportion of phage-insensitive and phage-sensitive cells within pure strains of lactic streptococci, and the influence of calcium
Authors: Tesfaigzi Johannes , Süssmuth Roland
Published: June 2009

It is of industrial importance to investigate the interaction ofStreptococcus lactiswith phages. Although it has been long recognized that in phage–bacterial relationships the phage-carrier state can occur (Hunter, 1947), relatively little study has been done on this subject. The terras ‘phage-carrier state’ and ‘pseudolysogeny’ have been used synonymously to describe bacterial cultures which are persistently infected with a virus (Barksdale & Arden, 1974, Lawrenceet al.1976). The phagecarrier state differs from lysogenesis in that the bacteria are easily separated from the bacteriophage by a simple plating and re-isolation procedure (Grahamet al.1952). Süssmuth & Tayran (1986) showed that after lysis of one single strain, phage and phage-insensitive bacteria coexist. This work investigates the proportion of phage-insensitive bacteria remaining after lysis of otherStr. lactisstrains, the effect of calcium on this proportion, and the number of generations required to return to a normal sensitive population.
Low resolution NMR spectroscopy: a tool to study protein denaturation: I. Application to diamagnetic whey proteins
Authors: Lambelet Pierre , Berrocal Rafael , Ducret Francine
Published: June 2009

A method using low resolution NMR spectroscopy is described for investigating whey protein thermal denaturation. The method is based on measuring at 20 °C changes in water proton transverse (T2) relaxation parameter following the denaturing treatment. This parameter is shown to be sensitive to protein denaturation and not to other phenomena such as gelation. Examples are given for the qualitative study of protein thermal denaturation in whey protein concentratc, β-lactoglobulin, α-lactalbumin, bovine serum albumin and immunoglobulins aqueous solutions and for the quantitative determination of thermal denaturation in whey protein concentrate solutions.
Influence of chromatographically pure bovine chymosin and pepsin A on cheese curd syneresis
Authors: Andersson Hans , Andrén Anders
Published: June 2009

The influence of chromatographically pure bovine chymosin and pepsin A on cheese curd syneresis has been studied. The enzymes were compared in experiments using a microscale syneresis assay, where the light absorbance of the released whey was used as a measurement of the syneresis. The following parameters were investigated: reconstituted skim milk powder (RSM), bulk raw milk, CaCl2 addition and cutting time of the curd. The gelling (clotting) time was held constant under all experimental conditions to eliminate its influence on syneresis. The differences in influence on syneresis of the two enzymes were neither obvious nor uniform. As regards the syneresis of RSM, the influence of chymosin and pepsin seemed to be very similar, while the syneresis of bulk raw milk seemed to be more enhanced by chymosin. However, results were not sufficiently clear to prove any distinct differences between the enzymes. As long as the cheese curd is cut at a proper firmness, there are probably no practical problems in using bovine rennets with varying chymosin: pepsin ratio.
Ultraviolet spectroscopic studies and the prediction of the feathering of cream in filter coffees
Authors: Hamboyan Lucie , Pink David
Published: June 2009

Cream feathering was studied in sixteen samples made from six brands of filter coffee. We have used a predictive rule, deduced from our studies of instant coffees, to determine the likelihood of feathering occurring in filter coffee samples upon the addition of coffee cream. The predictive rule makes use of 1,3,4,5-tetra-hydroxycyclohexane carboxylic acid-3-[(3,4) dihydroxycinnamate] (chlorogenic acid) concentration in the coffee, and the ratio of ultraviolet absorbances at 261 nm and 340 nm. We found good agreement between the predicted and observed behaviour of samples of filter coffee and conclude that the predictive rule is reliable for both instant and filter coffees. The effect of increased fat content in the cream was also studied.
A model heat exchange apparatus for the investigation of fouling of stainless steel surfaces by milk II. Deposition of fouling material at 140 °C, its adhesion and depth profiling
Authors: Foster Carole L. , Green Margaret L.
Published: June 2009

Formation and adhesion of fouling deposit during heating of milk at a stainless steel surface were studied separately using a model apparatus. The amount of deposit and proportion of minerals present increased with increase in surface temperature. At 140 °C, the amount of deposit formed increased linearly with heating time, becoming more uneven in appearance. The variations of deposit formation at 140 °C with pH of the milk, with fat removal and with preheating were similar to those observed in the final heating section of continuous UHT plants. Deposits containing a higher proportion of protein were easier to remove. The remaining inner layer had a smoother appearance and contained a higher proportion of minerals than the original deposit. Depth profiling, using secondary ion mass spectrometry, showed that protein was concentrated on the outside of deposits with calcium phosphate being concentrated closest to the steel surface.
Acidic coagulation of casein micelles: mechanisms inferred from spectrophotometric studies
Authors: Bringe Neal A. , Kinsella John E.
Published: June 2009

The acidic coagulation of casein micelles was monitored turbidimetrically at 400 nm using a Cary 219 spectrophotometer. Following acidification with HCI, the rate of coagulation during the initial stage of coagulation was proportional to the rate during the immediate subsequent stages, indicating that progressive stages of coagulation were controlled by similar factors and the slope at any portion of the reaction profile could be used to characterize the kinetics of the coagulation reaction. The rate of coagulation following acidification by glucono-δ-lactone was proportional to the reciprocal of the rate of acidification. The effects of environmental factors on the rate of the acidic coagulation of casein micelles over a range of pH values were evaluated from the smooth, hyperbolic profiles of pH v. coagulation rate. Determination of the pH required to initiate coagulation of casein micelles in skim milk ultrafiltrate at 5–25 °C, together with the maximum rates of coagulation at 5–25 °C, suggested that repulsive forces are reduced by acidification and con-sequently facilitate hydrophobic interactions resulting in the coagulation of casein micelles.
Characterization and kinetics of gastric emptying of peptides derived from milk proteins in the preruminant calf
Authors: Scanff P. , Yvon M. , Thirouin S. , Pelissffir J.-P.
Published: June 2009

The gastric emptying kinetics of peptides derived from milk protein were studiedin vivoin preruminant calves by collecting and characterizing the whole effluent leaving the stomach for 12 h after ingestion of crude skim milk. Peptides were isolated by reversed-phase HPLC and identified. Particular attention was paid to biologically active peptides and to peptides that could be precursors of biologically active sequences. A gastrin inhibitor, the caseinomacropeptide, was emptied from the stomach only during the first 0·5 h of digestion and rapidly hydrolysed. Precursors of immunostimulatory peptides from αs1- andβ-caseins were emptied throughout digestion in the gastric effluent. A precursor ofβ-casomorphins (peptide 58–93 ofβ-casein) was emptied from the stomach 3·5 h after the meal when it was taken on an empty stomach. From this precursor, peptides that may be resistant to hydrolysis by intestinal peptidase were obtained afterin vitrohydrolysis by pancreatic enzymes. A phosphopeptide (fragment 110–142 of αs1-casein) was also found in digesta after a few hours of digestion. When the meal was not taken on an empty stomach, these peptides were emptied in the first digesta at a low concentration. The potential activity of these peptides is discussed. The results support the hypothesis that active sequences could still be present in the gut after the action of pancreatic enzymes.
Effect of breed, protein genetic variants and feeding on cows' milk coagulation properties
Authors: Macheboeuf Didier , Coulon Jean-Baptiste , D'Hour Pascal
Published: June 2009

One hundred and thirty-seven (Holstein (41), Montbéliarde (42) and Tarentaise (54)) dairy cows in first or second lactation received during winter one of two levels (high, H; low, L) of energy intake, and were later fed identically at pasture. Thrice in winter and twice at pasture, the chemical composition and coagulation properties of individual milks were measured. Milk from Holstein cows had lower casein and calcium contents, and poorer coagulation properties (curd firming time and curd firmness) than that from Montbéliardes and Tarentaises (P< 0·01). These differences practically disappeared when taking into account the distribution of the differentκ-casein variants and milk casein content.κ-BB milks had coagulation properties 20–50% superior, according to characteristic, to those of AA milks. In the three breeds, animals from the H group had casein contents higher by 1·4 g/l than those of the L group, which induced a significant improvement in curd firming time, curd firmness and cheese yield. Turning out to pasture induced an increase of 0·02 in milk pH, and improved milk coagulation properties. These changes did not appear to result entirely from the parallel increase in milk casein content.
Effect of heat treatment and other milk proteins on the interaction of lactoferrin with monocytes
Authors: Oria Rosa , Ismail Maznah , Sánchez Lourdes , Calvo Miguel , Brock Jeremy H.
Published: June 2009

The interaction of lactoferrin from human and bovine milk with the human promonocytic cell line U937 has been studied. Both human and bovine Fe-lactoferrins bound to the cells. Binding of bovine lactoferrin was inhibited by excess bovine lactoferrin but not by human lactoferrin, suggesting that the binding mechanisms for the two proteins are different. Binding of human but not bovine lactoferrin was inhibited by bovine lactoperoxidase, while a 20-fold excess of human IgA inhibited binding of human but not bovine lactoferrin. Human and bovine α-lactalbumins, bovine β-lactoglobulin, and human lysozyme had no effect on binding of lactoferrin from either species. Samples of bovine Fe- and apolactoferrin in capillary tubes were exposed to temperatures of 72 °C for 20 s, 85 °C for 20 min or 137 °C for 8 s. All the heated samples inhibited binding of native Fe- and apolactoferrin, though to a lesser extent than the native proteins. Both heated and native lactoferrins enhanced [3H]thymidine incorporation by U937 cells, except for Fe-lactoferrin heated at 85 °C for 20 min, which was inhibitory. These results suggest that heat treatment of lactoferrin under conditions used for industrial processing does not greatly affect its ability to interact with and stimulate monocytic cells, and that other milk proteins in general do not interfere with lactoferrin–monocyte interactions. It may thus be feasible to incorporate biologically active lactoferrin into infant formulas.
Polyclonal antibodies with predetermined specificity against bovine αs1-casein: application to the detection of bovine milk in ovine milk and cheese
Authors: Rolland Marie-Paule , Bitri Lotfi , Besançon Pierre
Published: June 2009

Comparing the primary sequences of bovine and ovine milk proteins, some short peptide fragments are cow-specific, in particular the 141–148 fragment of bovine αs1-casein, which is deleted in its ovine counterpart. The 140–149 peptide was chemically synthesized on a solid phase matrix and directly used as an immunogen to produce polyclonal monospecific antibodies in rabbits. These antibodies recognized this fragment both on the peptidyl resin and in the native protein. They appeared to be monospecific, since no antigen–antibody complex was formed with homologous ovine or caprine proteins. Subsequently, a competitive enzyme-linked immuno-sorbent assay was successfully developed for the detection of defined amounts of cows' milk in sheep's milk from 0·125 to 64% (v/v) and in cheese from 0·5 to 25% (v/v) that was not influenced by heat treatment of milk or the degree of ripening of cheese.
Preliminary stages of fouling from whey protein solutions
Authors: Belmar-Beiny M. Teresa , Fryer Peter J.
Published: June 2009

Fouling from milk fluids is a severe industrial problem which reduces the efficiency of process plant. The chemistry of fouling has been thoroughly investigated but the sequence of events that occur is not yet clear. Deposit contains both protein and minerals. Experiments have been carried out to determine the sequence of events in the fouling of stainless steel surfaces at 96 °C from turbulent flows of whey. Contact times between 4 and 210 s have been studied, and surface analysis techniques used to detect the distribution of elements. The first layer of deposit, formed after 4 s of contact between the fluid and the surface (fluid temperature 68 and 73 °C), consisted mainly of protein and was identified by X-ray photoelectron spectroscopy analysis. There was a lag phase of up to 150 s for a fluid temperature of 73 °C before deposit aggregates were observed to adsorb on to the surface. These aggregates were identified as protein and Ca by X-ray elemental mapping. No P was found in any experiments for this exposure. After 60 min contact time, however, both Ca and P were found at the interface between deposit and the stainless steel surface, irrespective of the Ca and P content of the test fluid.
Phosphorylation, glycosylation and amino acid sequence of component PP3 from the proteose peptone fraction of bovine milk
Authors: Sørensen Esben S. , Petersen Torben E.
Published: June 2009

Component PP3 is a phosphorylated glycoprotein with an apparent molecular mass of 28 kDa isolated from the proteose peptone fraction of bovine milk. The function of the protein is not known. The primary structure has been determined and shown to contain 135 amino acid residues (EMBL accession no. P80195). It was phosphorylated at Ser29, Ser34, Ser38, Ser40 and Ser46. Two O-linked carbohydrate groups were found at Thr16 and Thr86, while one N-linked carbohydrate group was present at Asn77. Thr16 was only ∼ 50% glycosylated. The amino sugar detected by the amino acid analyser at Thr86 was mainly galactosamine but a small amount of glucosamine was also present. The amino sugars found in the carbohydrate group linked to Asn77 were both glucosamine and galactosamine. A fragment of PP3 has been isolated from milk and shown to correspond to residues 54–135. This fragment was probably generated by plasmin hydrolysing the Arg53–Ser54 bond.
Growth of lactic acid bacteria and bifidobacteria on lactose and lactose-related mono-, di- and trisaccharides and correlation with distribution ofβ–galactosidase and phospho-β–galactosidase
Authors: Smart John B. , Pillidge Christopher J. , Garman Jean H.
Published: June 2009

Spectrophotometric assays ofβ–galactosidase (EC 3.2.1.23) and phospho-β–galactosidase (EC 3.2.1.85) activity were used to survey the lactose utilization pathways of lactic acid bacteria and bifidobacteria.β–Galactosidase activity was found in all six genera represented (Lactococcus, Streptococcus, Leuconostoc, Lactobacillus, PediococcusandBifidobacterium) while phospho-β–galactosidase was restricted to the lactococci, twoLactobacillusand twoLeuconostocspecies. A number of strains ofLactococcus lactis, Lactobacillus caseiandLeuconostocspp. contained both enzymes. Enzyme activities varied when cells were grown on different sugars, but in general were low or absent for cells grown on glucose compared with lactose. Two lactose-related compounds, lactulose and galactosyl lactose, believed to be specific growth factors for bifidobacteria, supported growth amongst a wide range of lactic acid bacteria in addition to bifidobacteria. Growth on galactosyl lactose was restricted to some but not all strains containingβ–galactosidase, implying that the presence ofβ–galactosidase is insufficient by itself to ensure utilization of galactosyl lactose. DNA fragments that encoded theLactococcus lactissubsp.cremorisphospho-β–galactosidase gene or theβ–galactosidase genes ofStreptococcus salivariussubsp.thermophilusorLactobacillus delbrueckiisubsp.bulgaricuswere isolated and used as probes in DNA-DNA hybridizations. Little or no hybridization was detected between these probes and plasmid or genomic DNA isolated from heterologous species, despite the presence of the corresponding enzyme activity in the strains probed.
Hormonal induction of α–lactalbumin and β–lactoglobulin in cultured mammary explants from pregnant pigs
Authors: Dodd Susan C. , Forsyth Isabel A. , Buttle Hugh L. , Gurr Michael I. , Dils Raymond R.
Published: June 2009

Mammary tissue from pigs on days 60, 80, 90, 100 and 100+ (days 106–111) of pregnancy has been cultured in vitro as explants. The total accumulation in tissue and culture medium of the whey proteins α-lactalbumin and β-lactoglobulin has been measured using specific radioimmunoassays. The control, uncultured tissue showed progressive morphological development from sparse, non-secretory epithelial tissue on day 60 to full lobulo-alveolar development with some accumulated secretion from day 100. In uncultured explants β-lactoglobulin could be detected consistently from day 90 (13 ± 12 ng/μg DNA, n = 4) and α-lactalbumin from day 100 (1·3 ± 0·5 ng/μg DNA, n = 11). At all stages of pregnancy, both whey proteins increased markedly during the period of culture (up to 7 d). Stimulation of α-lactalbumin appeared to be primarily under prolactin control. Prolactin increased α-lactalbumin accumulation to a similar extent alone, or in the presence of insulin and/or corticosterone. The response to prolactin was dose-dependent over the range 0·4–20 nM (10–500 ng/ml). Porcine prolactin was more potent than ovine prolactin. There was no effect of porcine growth hormone and no synergism detected between prolactin and tri-iodothyronine. By contrast, no specific hormonal requirements were established for accumulation of β-lactoglobulin, which appeared to increase in vitro if tissue remained viable in various combinations of insulin, corticosterone and prolactin. It was not stimulated by growth hormone. There was some indication of a prolactin-sensitive component in longer term cultures after day 4.
Milk accumulation and distribution in the bovine udder during the interval between milkings
Authors: Knight Christopher H. , Hirst David , Dewhurst Richard J.
Published: June 2009

The proportions of milk stored within the gland cistern (cisternal milk) and within secretory alveolar tissue (alveolar milk) were determined at various intervals after milking in peak lactation cows and late lactation cows. The rate of milk secretion remained constant up to 12 h in both groups. Cisternal milk remained low (600 g or less) until after 4 h in both groups, then increased gradually to values at 12 h of 5·08 (peak lactation) and 2·60 kg (late lactation). Alveolar milk exceeded cisternal milk in both groups and at all time points up to 12 h, and was greatest in the peak lactation cows. A further measurement was made at 20 h in the late lactation group. Milk secretion rate remained constant between 12 and 20 h and most of this additional milk accumulated in the cistern. Alveolar fraction, defined as alveolar milk as a proportion of total milk, ranged from 0·43 to 0·94 at 8 h. There was a highly significant correlation between 8 h and 20 h alveolar milk fraction results, but not between 1 h and 8 h values, nor between alveolar milk at 0 h (effectively residual milk) and alveolar fraction at any time point. The milk volume results were used to construct a mathematical model describing milk flow between cisternal and alveolar compartments, and hence the pattern of milk accumulation. The results are discussed in relation to current hypotheses regarding local autocrine control of milk secretion by a feedback inhibitor in milk.
Effect of milking interval on secretion rate and composition of camel milk in late lactation
Authors: Alshaikh Muhammad A. , Salah Mahmoud S.
Published: June 2009

The effect of milking interval on secretion rates of milk and milk constituents was studied in four milking camels during late lactation. An interval of 4 h produced the highest milk secretion rate compared with 8, 12 and 16 h intervals, and rates tended to decline with increasing milking intervals. Secretion rates of organic (lactose, SNF, fat and protein) and inorganic milk constituents (sodium, potassium, calcium and magnesium) generally followed similar patterns of decreasing secretion with increasing milking intervals. Many of the values for different intervals were significantly different.
Response to phage infection of immobilized lactococci during continuous acidification and inoculation of skim milk
Authors: Passos Flavia M. L. , Klaenhammer Todd R. , Swaisgood Harold E.
Published: June 2009

A laboratory scale bioreactor was used for continuous acidification and inoculation of milk with a proteinase-negative, lactose-fermenting strain,Lactococcus lactissubsp.lactisC2S. Calcium alginate-entrapped cells were immobilized on a spiral stainless steel mesh incorporated into a column bioreactor and used to acidify and inoculate reconstituted skim milk. Characteristics of the immobilized cell bioreactor (ICB) were compared with those of a free cell bioreactor (FCB) during challenge with a virulent phage. Steady state biomass and lactate productivities were respectively 25-fold and 12-fold larger with the ICB than with the FCB. The ICB and the FCB were inoculated with the prolate phage c2 at multiplicities of infection of 0·25 and 0·02 respectively. Within 90 min of the infection, the FCB viable cell concentration dropped by five orders of magnitude and never recovered, while the plaque forming units/ml increased dramatically. In the ICB, released cells decreased immediately after infection, but subsequently increased, while the plaque forming units/ml steadily declined, indicating that phage were being washed out of the bioreactor. Productivity of FCB decreased to zero, whereas productivity of the ICB only decreased ∼ 60% and subsequently recovered to its initial steady state value.
Enhanced inactivation of bacterial lipases and proteinases in whole milk by a modified ultra high temperature treatment
Authors: Bucky Anthony R. , Hayes Patrick R. , Robinson David S.
Published: June 2009

Cultures ofPseudomonasspp. strains P10, P12 and P15 grown in whole milk which contained ∼ 1 × 108viable bacteria ml−1demonstrated near linear increases in the concentration of short-chain free fatty acids and trichloroacetic acid soluble free amino groups at 20 °C, following either ultra high temperature (UHT) treatment (140 °C for 5 s) or dual heat treatments (140 °C followed by either 57, 60 or 65 °C). The dual heat treatments reduced the rates of lipolysis and proteolysis compared to the UHT treatment by up to 25-fold. The dual heat treatment utilizing 60 °C for 5 min also effectively limited both lipase and proteinase activities in raw milk culture samples which had contained either 6 × 106, 5 × 107or 1 × 108viable bacteria ml−1. In this system enzyme activities were reduced by up to 10-fold following dual heat treatment compared to UHT treatment alone.
Study of calcium binding to phosphoserine residues of β-casein and its phosphopeptide (1–25) by 31P NMR
Authors: Baumy J.-J. , Guenot P. , Sinbandhit S. , Brulé G.
Published: June 2009

The effect of Ca2+. binding and ionic strength on the physicochemical characteristics of phosphoserine residues was studied on O-phospho-DL-serine, bovine β-casein and its phosphopeptide (1–25) using 31P NMR. pK in various experimental conditions were determined.

The pK of the phosphoserine residues of β-casein and its phosphopeptide (1–25) respectively ranged from 6·46 to 7·21 and from 6·57 to 7·10. pK of O-phospho-DL-serine, β-casein and its phosphopeptide decreased when Ca2+ was bound to the phosphoserine residue or when ionic strength was increased. The binding of Ca2+ to the phosphopeptide (1–25) took place at first on phosphoserine residues 17, 18, 19 which had the highest pK, then, when these were saturated, on residue 15 whose pK was the lowest. When the four sites had bound Ca2+, peaks corresponding to a different complex form appeared in the spectrum.
Short-term effects of frequent milking of dairy cows
Authors: Van Der Iest Renee , Hillerton J. Eric
Published: June 2009

When six cows were milked every 4 h over 48 h the average milk yield per cow increased by 1O·7% for the last 24 h period compared with the previous 5 d. Milk composition was similar to pre-experimental values although fat content was 0·5% lower in the last 24 h. The somatic cell count rose to twice the pre-experimental value over the first 24 h but was not significantly different by the second 24 h. It appears that cows responded quickly to an increased frequency of milking and milk of an acceptable composition was produced. This has implications for management of milk production where quotas are in operation and for robotic milking systems.
A method for determination of γ-casein and its use for investigating proteolysis in bovine milk
Authors: Igarashi Yasuo
Published: June 2009

A convenient and sensitive method for determining γ-casein content of skim milk is described. It is based on quantitative separation in which the soluble fraction obtained from skim milk (1·5 ml) in a solvent system consisting of 50% (v/v) ethanol, 0·4 M-Na thiocyanate and 0·15 M-CaCl2 was applied to a small column of DEAE-cellulose and eluted with 0·02 M-Tris-HCl buffer (pH 8·0) containing 0·03 M-NaCl and 6 M-urea. Protein in this fraction (5 ml) was measured from its absorbance at 280 nm. The method is applicable also to heated skim milk. Its availability for investigating proteolysis in milk is expected from the fact that incubation of skim milk with porcine plasmin at 37 °C for 3 h increased γ-casein content, an increase that was lowered by addition of soyabean trypsin inhibitor. Incubation of raw skim milk with 0·02% (w/v) NaN3 resulted in increase in γ-casein with time and with increasing temperature. This was accompanied by a time lag, the length of which increased with decreasing temperature. The degree of proteolysis in skim milk, expressed as the amount of increase in γ-casein after 20 h of incubation at 37 °C, showed two pH optima, one at pH 8·0 and the other at pH 7·2–7·5. These results suggested that the present method.of γ-casein determination can be used for more precise studies of the milk plasmin system in which important factors, such as plasminogen activator and inhibitors, are involved.
Serological identification of Streptococcus salivarius subsp. thermophilus
Authors: Nour Maher A. , Abdel-Tawab Gamal , Shalaby Samir , Mohamed Osama A.
Published: June 2009

Streptococcus salivarius subsp. thermophilus (Str. thermophilus) has no group-specific antigen. HC1 extracts of 551 strains of streptococci isolated from cheese or yogurt (123 Str. thermophilus and 428 Enterococcus faecalis – Ent. faecium spp.) were examined with three type-specific antisera prepared against representatives of Str. thermophilus and also with Lancefield group D antisera. All typical (80) or atypical (43) strains of Str. thermophilus reacted with at least one type-specific antiserum and none of the enterococci reacted. Only two strains reacted with both type-specific and group antisera.
Factors affecting the thermostability of β-galactosidase (Streptococcus salivariussubsp.thermophilus) in milk: a quantitative study
Authors: Chang Byeong-Seon , Mahoney Raymond R.
Published: June 2009

Enhanced stability of β-galactosidase (Streptococcus salivariussubsp.thermophilus) in milk is due to several milk components acting in concert. Milk salts stabilized the enzyme 3-fold compared to phosphate buffer. K+was a better stabilizer than Na+. Omission of divalent cations, especially Mg2+, caused a marked drop in stability. Lactose stabilized enzyme stored in the frozen state but destabilized enzyme stored unfrozen. Caseinate stabilized the enzyme 8-fold in phosphate buffer but it stabilized 144-fold in the presence of lactose. In the presence of milk proteins, lactose was 25 times as effective as galactose and 100 times as effective as glucose at promoting stability; sucrose slightly destabilized the enzyme. Stability rose with increasing lactose concentration but declined with increasing enzyme concentration. In milk, soluble casein was the primary stabilizer; whey proteins and peptides had much less effect. Micellar casein had no effect on stability.