bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions of temperate bacteriophages ofStreptococcus salivariussubsp.thermophiluswith lysogenic indicators affect phage DNA restriction patterns and host ranges
Authors: Fayard Blandine , Haefliger Moritz , Accolas Jean-Pierre
Published: June 2009

After treatment with mitomycin C, 12 of the 120 strains of the French Collection of Lactic Acid Bacteria (CNRZ) belonging to the speciesStreptococcus salivariussubsp.thermophiluswere found to be inducible and lysogenic. The corresponding temperate phages were multiplied on indicator strains and further characterized. It is noteworthy that some of the indicators were themselves lysogenic. The temperate phages belonged to Bradley's group B, or to theSiphoviridaefamily of the International Committee on Taxonomy of Viruses. Seven of them were shared among the two protein profiles previously established for virulent phages ofStr. salivariussubsp.thermophilus. Seven different DNA restriction profiles were found for ten native temperate phages examined just after mitomycin C induction. Genome sizes varied from 40 to 45 kb and were classified into four related homology groups by DNA cross-hybridization, but there was no clear-cut relationship with the protein clusters previously shown. DNA homology with representatives of virulent phages was also found. The DNA restriction profiles of seven native temperate phages, examined just after mitomycin C induction of the lysogenic hosts, were noticeably different from those of the corresponding phages once they had been propagated on lysogenic indicators. Moreover, the host range of the latter phages was extended to a greater number of sensitive strains. The possible role of lysogenic strains ofStr. salivariussubsp.thermophilusin the occurrence of phage outbreaks affecting this dairy streptococcal species is discussed.
Milk removal in familiar and unfamiliar surroundings: concentrations of oxytocin, prolactin, cortisol andβ–endorphin
Authors: Bruckmaier Rupert M. , Schams Dieter , Blum Jürg W.
Published: June 2009

Eight cows were machine milked either in an operating theatre or in their familiar barn. During the experiments, milk flow curves were recorded and blood samples were taken for determination of concentrations of oxytocin, prolactin, cortisol andβ–endorphin. The milking cluster was attached without udder preparation. After cessation of milk flow, air was blown into the vagina for 2 min. When milk flow had stopped again, 1 i.u. oxytocin and finally 10 i.u. oxytocin were injected to remove the remaining milk. After the start of milking, oxytocin remained basal in unfamiliar, but increased in familiar surroundings. Therefore, during normal milking only 9% of total milk was removed in unfamiliar, whereas 79% was available in familiar surroundings. In response to subsequent vaginal stimulation in the operating theatre, oxytocin increased transiently in five cows and 15–71% of the milk was removed in these animals. In the other three cows in the operating theatre, oxytocin remained basal during vaginal stimulation, and no more milk was available. After injection of 1 i.u. oxytocin, 56 and 11%, and after injection of 10 i.u. oxytocin, 13 and 8% of milk was removed in unfamiliar and familiar surroundings respectively. Concentrations of prolactin increased during the course of milking in both treatments. Premilking concentrations of cortisol andβ–endorphin were elevated in unfamiliar as compared with familiar surroundings. During the course of milking, cortisol increased slightly andβ–endorphin decreased in unfamiliar, whereas both hormones increased markedly during milking in familiar surroundings. We conclude that disturbed milk removal in unfamiliar surroundings is due to central inhibition of oxytocin release during normal milking and partly also to a response to vaginal stimulation. This blockade is possibly associated with elevated concentrations ofβ–endorphin.
Influence of pH and sugars on the growth and production of diarrhoeagenic toxin byBacillus cereus
Authors: Sutherland Alastair D. , Limond Ann M.
Published: June 2009

Broth cultures supplemented with high levels of sugars, particularly glucose at > 50 g/1, did not support diarrhoeagenic toxin production by psychro-trophicBacillus cereusdespite growth to high counts ( ∼ 107/ml) over a 4 d period of incubation at 21 °C. In contrast, starch levels of 10 and 50 g/l actually enhanced toxin production. Toxin production was also affected by pH levels of broth cultures, and was concomitant with alterations in bacterial growth. These findings help to explain variations in toxin levels previously found in some dairy desserts, which were thought to be associated with pH and sugar content (Sutherland, 1993).
Changes in the gelation mechanism of whey protein concentrate with pH and temperature
Authors: Taylor Stephen M. , Gladden Lynn F. , Fryer Peter J.
Published: June 2009

The percolation model of Steventon et al. (1991) successfully detected changes in the mechanism of whey protein concentrate gelation with pH and temperature by comparing simulated with experimental gelation times. The results demonstrated that at 71 °C and pH 5·2 the formation of an aggregate from two denatured protein molecules (initiation) was the rate-determining step in the gelation process, while at pH 7·0 the addition of denatured protein molecules to an aggregate (propagation) was rate-determining. At pH 5·9, the gelation process was also initiation limited, with the rate being slower than for pH 5·2 solutions, probably owing to electrostatic effects. Analysis of the temperature dependence of the gelation time, and percolation analysis both showed that there was a change in the rate-controlling reaction at 73 °C for gelation at pH 5·2 and 7·0. In the case of pH 7·0 gelation, this change in rate-controlling reaction was not due to a change from denaturation- to aggregation-controlled gelation, but was probably due to a change in the relative rates of interactions between protein molecules. Gelation at pH 5·2 was aggregation-controlled at temperatures below 73 °C, and denaturation-controlled at higher temperatures; there appeared to be another change in rate-limiting reaction at 80–85 °C without a change in mechanism (i.e. it remained denaturation-limited). The activation energies of the rate-limiting reactions determined from analysis of the temperature dependence of gelation time and from percolation analysis were in agreement. This is evidence that the changes in the rate-controlling reaction of whey protein concentrate gelation with temperature and pH were real.
Arsenic content of Spanish cows' milk determined by dry ashing hydride generation atomic absorption spectrometry
Authors: Cervera M. Luisa , Lopez J. Carlos , Montoro Rosa
Published: June 2009

The arsenic content of cows' milk consumed in Spain was determined. A procedure using dry ashing hydride generation atomic absorption spectrometry was developed for the purpose. Experimental conditions for the destruction of organic matter were established and an interference study was carried out. The method developed has a detection limit of 0·1 ng/g, a relative SD of 5%, and a recovery (mean ± CSI) of 100 ± 4%. The accuracy of the method was checked by analysis of a certified sample of IAEA milk powder (mean ± CSI: certified, 4·85 ± 0·32 ng/g; found, 5·04 ± 0·81 ng/g). The proposed procedure was used to analyse cows' milk samples. The extremely low arsenic levels found do not present toxicological problems.
Identification of the unsaturated oxo fatty acids in cheese
Authors: Brechany Elizabeth Y. , Christie William W.
Published: June 2009

The nature and composition of the unsaturated (monoenoic) oxo fatty acids in Cheddar cheese have been re-evaluated. Following isolation by column chromatography and silver ion HPLC, the fatty acids were identified in the form of their picolinyl ester derivatives by gas chromatography–mass spectrometry. For confirmation, they were analysed similarly following deuteration of the double bonds with deuterium and Wilkinson's catalyst. Fifteen fatty acids were identified fully, only five of which corresponded to those reported in an earlier study. Isomers with double bonds in positions 5, 7, 9 and 11–15 were identified, with oxo groups in positions 8, 9, 10, 13, 16 and 17, and with chain-lengths varying from C14 to C18, but with C18 predominating.
Thermal gelation and denaturation of bovine β-lactoglobulins A and B
Authors: McSwiney Mary , Singh Harjinder , Campanella Osvaldo , Creamer Lawrence K.
Published: June 2009

Heat-induced gelation, an important functional property of β-lactoglobulin, was studied by measuring the rheological properties of both the A and B variants of the protein during and after heat treatment within a range of pH, temperature and concentration. Gel electrophoresis was used to determine the extent of denaturation and disulphide bond crosslinking of some samples. Both variants formed gel networks on heating at temperatures > 75 °C, and under most conditions the storage modulus (G′) of βlactoglobulin A gels was higher than the G′ of β-lactoglobulin B gels, in particular after cooling to 25 °C. A minimum protein concentration of 50 g/1 was required for gel formation at pH 7·0 in 0·1 M-NaCl by both variants at 80 °C. Increasing the protein concentration above 50 g/1 increased G′, the extent of increase being much greater for the A variant than the B variant. G′ of variant A gels was not much influenced by pH whereas G′ of variant B gels decreased slightly from pH 3 to pH 6 and increased between pH 6 and pH 9. When mixtures of the two variants were gelled G′ increased at the temperature of heating (80 °C) and after cooling (25 °C) as the relative quantity of variant A was increased. Comparisons of the loss of discrete protein bands from electrophoretic gels (native-PAGE, SDS-PAGE and SDS-PAGE of reduced samples) showed that heating β-lactoglobulin solutions of 100 g/1 at pH 7 in 0·1 M-NaCl and at 75, 80 and 85 °C caused a faster loss of both native and SDS-soluble β-lactoglobulin A than of β-lactoglobulin B. It was concluded that the loss of native β-lactoglobulin structure from these solutions during heating was faster than the formation of disulphidelinked aggregates, which was faster than gel formation for both β-lactoglobulin A and β-lactoglobulin B, and that each of these reactions was faster for β-lactoglobulin A than for β-lactoglobulin B. This contrasts with conclusions drawn from some previous studies and may arise from the differences in protein concentration between the present study (∼ 100 g/1) and the previous ones (< ∼ 10 g/1).
Production of volatile compounds in model milk and cheese media by eight strains of Geotrichum candidum Link
Authors: Jollivet Nathalie , Chataud Jean , Vayssier Yves , Bensoussan Maurice , Belin Jean-Marc
Published: June 2009

Eight strains of Geotrichum candidum isolated from cheese were compared for aroma production. Twenty-four components, including alcohols, methyl ketones, fatty acids and esters, were identified by gas–liquid chromatography and gas chromatography–mass spectrometry of the volatile compounds produced by G. candidum cultures. Strains could be differentiated by their ability to produce dimethyldisulphide, phenol, phenylethanol and methyl ketones.
Autolysis and proteolysis in different strains of starter bacteria during Cheddar cheese ripening
Authors: Wilkinson Martin G. , Guinee Timothy P. , O'Callaghan Daniel M. , Fox Patrick F.
Published: June 2009

Autolysis of and proteolysis by variousLactococcus lactissubsp.cremorisstrains were monitored in cheese ‘juice’ extracted by hydraulic pressure up to 63 d ripening. Viability was lowest for strain AM2 (non-bitter), intermediate for strain HP (bitter) and highest for the defined mixed strains G11/C25 (non-bitter). Autolysis monitored by the levels of the intracellular marker enzymes lactate dehydrogenase (EC 1.1.1.27), glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and post-proline dipeptidyl aminopeptidase proceeded in the order AM2 > G11/C25 > HP. Differences in autolysis between strains did not appear to be due to differences in stabilities of the marker enzymes, populations of non-starter lactic acid bacteria or levels of the marker enzymes in the strains. Proteolysis, as measured by gel permeation FPLC and free amino acid analysis of the cheese juice was highest for AM2, intermediate for G11/C25 and lowest for HP. The results of this study provided some evidence that differentLactococcusstrains used for cheesemaking had different autolytic patterns during ripening, the effects of which on ripening and flavour development have not yet been clearly demonstrated.
Machine milking of dairy goats during lactation: udder anatomy, milking characteristics, and blood concentrations of oxytocin and prolactin
Authors: Bruckmaier Rupert M. , Ritter Chantal , Schams Dieter , Blum Jürg W.
Published: June 2009

Forty-four goats were milked and milk flow recorded without or with 1 min manual prestimulation in early, mid and late lactation. Ultrasound measurements of cross sections of the whole mammary gland were performed in a water bath. In additional experiments with 15 goats, milk flow was recorded and frequent blood samples were taken for the determination of oxytocin and prolactin concentrations. Milk yield increased from the first to the third lactation and decreased markedly during the course of lactation. Average and peak milk flow rates were closely related to the actual milk yield. The ultrasound cisternal area was 27·4±1·5% of the entire udder half cross section. Milking characteristics were scarcely different without or with prestimulation, although oxytocin was released within 30 s after the start of prestimulation, whereas oxytocin concentrations without prestimulation increased only after the start of milking. Concentrations of prolactin were higher during July and August than in April, and increased similarly with or without prestimulation during milking. In contrast to dairy cows, prestimulation and an opportune release of oxytocin during milking does not significantly influence the course of milk flow in goats, and this is probably because large amounts of cisternal milk allow milk ejection to be induced only after the start of milking without causing bimodal or otherwise reduced milk flow.
Rennet coagulation of milk in the presence of sucrose
Authors: Famelart Marie-Hélène
Published: June 2009

The aim of this work was to test the diffusion-controlled hypothesis of milk coagulation kinetics by reducing the diffusion coefficient of casein micelles. This has been achieved by increasing the solvent viscosity of milk through sucrose addition. Milk was reconstituted from skim milk powder and sucrose added at 100–300 g kg–1. Hydrolysis and coagulation were followed by chromatographic determination of caseinomacropeptide content and optical, thermal and viscoelastic measurements. Soluble and ionic calcium were determined by atomic absorption spectrophotometry and ionometry and micelle size was measured by dynamic light scattering. Addition of sucrose resulted in a substantial retardation of both enzymic and aggregation steps, a re-equilibration of calcium because of water reduction, and a micelle size increase. The enzymic rate constant was inversely proportional to the viscosity, according to a diffusion-controlled model, and the lag or characteristic times for the aggregation reaction were inversely proportional to the viscosity. These results are consistent with the involvement of diffusion-controlled steps in the sequence of reactions.
Variability of reduced glutathione levels in Massese ewes and its effect on daily milk production
Authors: Rizzi Rita , Caroli Anna , Bolla Patrizia , Acciaioli Anna , Pagnacco Giulio
Published: June 2009

The variability of the erythrocyte concentration of the tripeptide glutathione was studied in four flocks of Massese sheep. A relationship was found between glutathione level and stage of lactation in which the second month showed the lowest content. Genotype at transferrin and haemoglobin loci was associated with glutathione levels. Homozygotes at the transferrin locus yielded higher levels, while the D allele at the same locus was associated with lower concentrations. Animals with haemoglobin AA showed higher contents of glutathione. Also, a negative correlation was found between daily milk production and glutathione level.
Distribution of cholesterol in milk fat fractions
Authors: Arul Joseph , Boudreau Armand , Makhlouf Joseph , Tardif Rene , Grenier Benoit
Published: June 2009

Milk fat was fractionated into liquid (m.p. ⋍ 12 °C), intermediate (m.p. ⋍ 21 °C) and solid (m.p. ⋍ 39 °C) fractions by three different processes—melt crystallization, short-path distillation and supercritical CO2extraction—and the cholesterol content of these fractions determined. Cholesterol was enriched in the liquid fractions from all three processes, in particular about 80% of the cholesterol being found in the liquid fraction obtained by short-path distillation. The basis of migration of cholesterol into various milk fat fractions was explained by its affinity to various triglycerides (melt crystallization) and by vapour pressure and molecular weight (short-path distillation). It was more complex in the supercritical CO2extraction process; the interplay of cholesterol affinity toward CO2and its molar volume, and its vapour pressure enhancement under applied pressure play a role.
Opioid antagonist peptides derived from κ-casein
Authors: Chiba Hideo , Tani Fumito , Yoshikawa Masaaki
Published: June 2009

Opioid antagonists were sought in the fragments of κ-casein which were obtained by chemical synthesis and enzymic digestion. A synthetic bovine κ-casein peptide (35–41), Tyr-Pro-Ser-Tyr-Gly-Leu-Asn (casoxin A) showed opioid antagonist activity at 200 μM in the guinea pig ileum assay. A synthetic peptide Tyr-Pro-Tyr-Tyr (casoxin B) which is found in bovine and human κ-casein, also showed opioid antagonist activity at 100 μM. Another opioid antagonist peptide (casoxin C) was isolated from tryptic digests of bovine κ-casein by reverse-phase HPLC. The structure of the peptide was Tyr-Ile-Pro-Ile-Gln-Tyr-Val-Leu-Ser-Arg, which corresponded to κ-casein (25–34). Casoxin C was active at 5 μM in the guinea pig ileum assay. Thus, bovine κ-casein contains three potential opioid antagonist sequences.
Hydrophobic interactions in human casein micelle formation: β-casein aggregation
Authors: Slattery Charles W. , Sood Satish M. , Chang Pat
Published: June 2009

The association of non-phosphorylated (0-P) and fully phosphorylated (5-P) human β-caseins was studied by fluorescence spectroscopy and laser light scattering. The tryptophan fluorescence intensity (FI) level increased between 20 and 35 °C, indicating a change in the environment of that residue. A similar transition occurred when ANS was used as a probe. Transition temperatures were slightly lower in 10 mM-CaCl2 but were not affected by an equivalent increase in ionic strength caused by NaCl. The magnitude of the FI change was less for the 5-P than the 0-P protein but was increased for both by CaCl2 addition. These FI data were characteristic of a conformational change and this was supported by fluorescence polarization which indicated that with CaCl2, tryptophan and ANS mobility increased at the transition temperature even though the extent of protein association also increased. Light scattering suggested that protein association proeeeded with the primary formation of submicellar aggregates containing 20–30 monomers which then associated further to form particles of minimum micelle size (12–15 submicelles), and eventually larger. The temperature of precipitation of the 5-P form in the presence of CaCl2 was lower than the conformational transition and suggested that both hydrophobic interactions and Ca bridges between phosphate esters on adjacent molecules are important in micelle formation.
Surface active properties at the air–water interface of β-casein and its fragments derived by plasmin proteolysis
Authors: Wilson Michael , Mulvihill Daniel M. , Donnelly William J. , Gill Brian P.
Published: June 2009

β-Casein, was enzymically modified by incubation with plasmin to yield γ-caseins and proteose peptones. Whole γ-, γ1-, γ2/γ3-caseins and whole proteose peptone (pp) were isolated from the hydrolysate mixture. The time dependence of surface tension at the air-water interface of solutions of β-casein and its plasmin derived fragments, at concentrations of 10−1 to 10−4% (w/v) protein, pH 7.0, was determined, at 25 °C, using a drop volume apparatus. The ranking of the proteins with respect to rate of reduction of surface tension, during the first rate determining step, at 10-2% (w/v) protein, was γ2/γ3 ≫ pp > whole γ- > γ1- > β-casein. The ranking of the proteins with respect to surface pressures attained after 40 min (π40) was concentration dependent. γ2/γ3-Caseins were found to be very surface active, decreasing surface tension rapidly and giving a high π40. γ1 Casein decreased surface activity somewhat faster than β-casein, but generally reached a lower π40. Whole γ-casein reflected the properties of both γ1 and γ2/γ3-caseins. Proteose peptone was found to decrease surface tension rapidly during the initial rate determining step; it gave a relatively high π40 at a bulk phase concentration of 10−3% (w/v) protein, but, it was the least surface active protein at 10−1 and 10−2% (w/v) protein.
Rheological properties of casein gels
Authors: van Vilet T. , Roefs S. P. F. M. , Zoon P. , Walstra P.
Published: June 2009

The rheological properties of rennet-induced skim milk gels at 30 °C are compared with casein gels formed by acidification to pH 4·6 at 2 °C and subsequent heating to 30 °C. Both types of gels are viscoelastic. However, the gels formed by rennet action are relatively more viscous over time scales longer than 1 s. This implies that on average the protein-protein bonds in these gels are relatively more mobile than in the acid casein gels. It is thought that this is primarily due to differences in the structure of the casein particles and in the type of the main interaction forces in and between the casein molecules and particles.
Incorporation of individual casein constituents into casein aggregates cross-linked by colloidal calcium phosphate in artificial casein micelles
Authors: Aoki Takayoshi
Published: June 2009

Artificial casein micelles were prepared at a casein concentration of 2·5% with 10–40 mM-Ca, 12–27 mM-phosphate and 10 mM-citrate and cross-linking of casein by colloidal Ca phosphate (CCP) was examined. No casein aggregates cross-linked by CCP were formed at 10 mM-Ca, 12 mM-phosphate and 10 mM-citrate, which are the approximate concentrations found in the soluble phase of bovine milk. Although the amounts of casein aggregates cross-linked by CCP and of colloidal inorganic phosphate increased with increasing Ca and phosphate concentrations, the effect was not uniform. The incorporation rates of individual casein constituents into casein aggregates cross-linked by CCP were in the order > > β-casein. This was the reverse of the order of dissociation rates during dialysis of casein aggregates cross-linked by CCP reported previously.
Determination of chymosin and bovine pepsin A activity in combined rennets on the basis of immunochemical inhibition
Authors: Beránková Eva , Rauch Pavel , Káš Jan
Published: June 2009

The milk clotting activity of chymosin in combined rennets was determined as the difference between the total and residual activity after specific inhibition of chymosin with the purified immunoglobulin fraction of chymosin antiserum. The milk clotting activity of bovine pepsin A was assessed in a similar manner. In bovine rennets milk clotting activity of chymosin was measured directly after immunochemical inactivation of bovine pepsin A. Any method may be used for the determination of milk clotting activity. High correlation was found between the proposed method, which is simple and rapid to perform, and Chromatographic assay.
Effect of udder preparation on transmission of Staphylococcus aureus while milking with a multi-valved cluster
Authors: Grindal Robert J. , Bramley A. John
Published: June 2009

With two groups of 12 cows, a procedure involving foremilking, teat washing and drying before milking was compared with no premilking preparation for its effects on mastitis and teat contamination. Half the cows in each group were deliberately infected in a single udder quarter with Staphylococcus aureus and milked alternately with uninfected cows for 9 weeks. To minimize transfer during milking all cows were milked with the use of a multi-valved claw.

Five new staphylococcal infections developed in the 12 animals in the teat preparation group compared to one in the control group. A significantly higher incidence of teat orifice colonization developed in the prepared cows compared to the control cows (17 v. 7). Foremilking and teat preparation led to transfer of staphylococci between quarters (within cow) but this was effectively prevented by the multi-valve claw in the absence of teat preparation.
pH-Induced dissociation of bovine casein micelles. II. Mineral solubilization and its relation to casein release
Authors: Dalgleish Douglas G. , Law Andrew J. R.
Published: June 2009

Measurements of the release of Ca, Mg and inorganic phosphate(Pi) from the casein micelles of bovine milk have been made, as functions of the pH, in the range 4·9–6·7, and at temperatures of 4, 20 and 30 °C. The results are in general agreement with earlier published studies in giving a value of 1·75–1·84 for the micellar Ca:Pi ratio. Mg appeared to behave similarly to Ca, although the amounts of micellar material were much smaller. The results on the acid-solvation of calcium phosphate are considered in relation to published quantitative studies of the pH-induced dissociation of the different types of caseins from the micelle, and of the micellar dissociation caused when micellar calcium phosphate is dissolved at neutral pH. It is evident from this that at present it is not possible to derive a universal relation between the dissociation of minerals and of caseins from the micelles at different temperatures and under different conditions.
Measurement of machine-induced changes in thickness of the bovine teat
Authors: Hamann Jörn , Mein Graeme A.
Published: June 2009

Machine milking induced repeatable, short-term changes in thickness of the teat apex. These changes were measured with a spring-loaded caliper instrument under milking conditions that imposed differing forces on the teat apex. The mean percentage changes in teat end thickness (relative to the premilking values for individual teats) varied from 10% decrease up to 20% or more increase depending on the particular milking system used. The overall decrease in teat end thickness associated with cannula milking, milking at very low vacuum levels or milking with positive pressure pulsation may result from: (i) decrease in the intramammary pressure; and/or (ii) small changes in tone of teat musculature; and/or (iii) changes in the distribution of interstitial fluids in the teat apex. The overall increase in teat thickness caused by conventional or PKME milking systems results mainly from oedema (the extravascular accumulation of fluid). It is likely that milking equipment can, and should, be designed to minimize circulatory impairment resulting in oedema of the teat.
Enhancement of proteolysis in bovine skim milk by heat and chemical treatments
Authors: Igarashi Yasuo
Published: June 2009

Effect of heating and of some chemical treatments on the proteolysis of skim milk caused by its major proteinase system, plasmin, was investigated. Degree of proteolysis was expressed as the increase in γ-casein content of skim milk (mg/ml) after incubation with 0·02% (w/v) NaN3 at 37 °C for 20 h. Apart from reduced proteolysis in skim milk heated at > 70 °C for 10 min or at 75 °C for ∼ 5 min, some enhancement (10–80%) was observed on heating at 55–63 °C for 10 min or at 60–65 °C for 15 s. Heating at pasteurization conditions (63 °C/30 min or 72 °C/15 s) had no apparent effect on the amount of proteolysis. Addition of ascorbic acid (0·2 mg/100 ml) or H2O2 (1/100 ml) to unheated skim milk also increased the amount of proteolysis by 38 and 28%, respectively. However, the extent of this increase diminished with increasing amounts of both chemicals. Furthermore, there was a steady increase (∼ 33%) in proteolysis with time of exposure to light for up to 3 h. These results suggest that oxidative conditions lead skim milk to enhanced proteolysis by inactivating an inhibitor(s) operating in the plasmin system in milk.
The cheesemaking potential of milk concentrated up to four-fold by ultrafiltration and heated in the range 90–97 °C
Authors: Green Margaret L.
Published: June 2009

Properties of interest to cheesemaking were investigated with milks concentrated by ultrafiltration and heated at 90 °C or 95–97 °C for 15 s. The effects of light homogenization before concentration and of addition of CaCl2 after heating were assessed. No changes in casein–fat or casein–whey protein interactions were detected by electron microscopy. The heat denaturation of whey protein increased linearly as the milk became more concentrated. Coagulability by rennet after heat treatment increased with concentration to close to the unheated value in 3·5 to 4-fold concentrates. The decrease in curd firming rate by heat treatment was slightly affected by concentration and addition of CaCl2 restored some of the difference. Heat treatment reduced the rate of whey loss and slightly improved the curd structure but did not affect fat losses. Light homogenization slightly reduced heat denaturation of whey protein and whey loss.
Proteinase, peptidase and esterase activities of cell-free extracts from wild strains ofLactobacillus delbrueckiisubsp.bulgaricusandStreptococcus salivariussubsp.thermophilusisolated from traditional Greek yogurt
Authors: Kalantzopoulos Georgios , Tsakalidou Efthimia , Manolopoulou Eugenia
Published: June 2009

Proteinase, peptidase and esterase activities were detected in cell-free extracts of fourLactobacillus delbrueckiisubsp.bulgaricusand fourStreptococcus salivariussubsp.thermophilusstrains. Post-electrophoretic detection was based on hydrolysis of L-leucine-βnaphthylamide and α-naphthylacetate. The substrates L-leucine-p–nitroanilide,N-acetyl-L-alanine-p–nitroanilide, 2-nitrophenylbutyrate and 4-nitrophenylbutyrate were used for the spectrophotometric detection of the enzymes. Estimation of total proteolytic activity was based on hydrolysis of bovine whole casein. Interesting differences were observed between the two French strains and those isolated from traditional Greek yogurt.
In-vivo magnetic resonance imaging studies of mammogenesis in non-pregnant goats treated with exogenous steroids
Authors: Fowler Paul A. , Knight Christopher H. , Foster Margaret A.
Published: June 2009

Mammogenesis and lactation were induced in five multiparous, non-pregnant goats by treatment with oestrogen and progesterone for 11 d, followed by dexamethasone for 3 d. Reserpine was administered during the last 5 d. All five goats lactated, although milk yield was less than had been achieved in previous natural lactations. Mammary development was assessed in vivo, using magnetic resonance imaging. Although parenchyma volume increased by more than 6-fold overall, only 25% of this increase occurred during steroid treatment. Most development took place after the cessation of treatment, when milking commenced. Maximum size was not achieved until week 8 of the induced lactation, and was only 70% of normal parenchyma volume. After 18 weeks lactation the activities of three key milk synthetic enzymes were very similar to values previously found in natural lactations, and secretion efficiency (milk production per unit volume of parenchyma) was also similar to that of natural lactations. We conclude that the lower than normal milk yields were associated with incomplete proliferation of mammary tissue, rather than inadequate differentiation of individual secretory cells.
Potential value of photoacoustic spectroscopy for determining iron content of milk protein concentrates
Authors: Dóka Ottó , Kispéter József , Lörincz András
Published: June 2009

Photoacoustic and proton-induced X-ray emission measurements were performed on iron-enriched milk protein concentrates. The possibility of measuring Fe content by photoacoustic measurements in the visible region of the spectrum is discussed.
Effect of heat treatment on the proteolytic/peptidolytic enzyme system of aLactobacillus delbrueckiisubsp.bulgaricusstrain
Authors: López-Fandiño Rosina , Ardö Ylva
Published: June 2009

Lactobacillus delbrueckiisubsp.bulgaricuscells heat treated at 67 or 68 °C for 15·5–16 s had significantly less acidification capacity and much lower endopeptidase activity than untreated cells, while they still retained high aminopeptidase activities against amino acids commonly found in bitter peptides. A stimulatory effect of heat treatment on the leakage of aminopeptidases from cells was observed at pH 5·4. These properties make them suitable as extra sources of important ripening enzymes in cheesemaking.
Detection of propionic acid bacteria in cheese
Authors: Drinan Finbarr D. , Cogan Timothy M.
Published: June 2009

Mesophilic lactic starters and thermophilic lactobacilli but notStreptococcus salivariussubsp.thermophilusgrew on the sodium lactate agar (SLA) used for estimating the numbers of propionic acid bacteria (PAB) in cheese. The addition of cloxacillin (4 μg/ml) to SLA inhibited the starter bacteria but had no effect on the PAB. It was possible to count low numbers of PAB in the presence of high numbers of starter bacteria. A correlation coefficient of 0·9 was obtained between the level of propionic acid and the counts of PAB in cheese (n= 40). A disadvantage of the medium is that other bacteria found in cheese (mesophilic lactobacilli, enterococci,Clostridium tyrobutyricum) also grow on it; however, these bacteria are easily distinguishable from PAB on the basis of size, colour and absence of catalase.
Milk yield responses to sequential treatments with recombinant bovine somatotrophin and frequent milking in lactating goats
Authors: Knight Christopher H.
Published: June 2009

Lactating goats routinely milked twice daily were used. Starting at peak lactation, two groups of five goats were milked three times daily unilaterally (right gland) for 6 weeks, then one group received recombinant bovine somatotrophin (BST) by daily injection for 6 weeks, and finally both groups were returned to unilateral thrice-daily milking (left gland) for 6 weeks. Thrice-daily milking increased milk yield significantly by 10·4%. As thrice-daily milking finished and BST treatment began there was a small (2·7%) but significant increase in whole-udder milk yield in the treated goats and a decline in the control goats; throughout the BST treatment period treated goats produced 14·3% more milk than controls. The effect of BST was the same in glands previously milked thrice daily as in those previously milked twice daily. Milk yield declined as BST treatment finished, but this decline was less in the glands that then began thrice-daily milking. The effect of milking frequency was similar in this period to that obtained earlier in the experiment, and was not different between goats that had previously received BST and those that had not. The results are discussed in relation to the proposed modes of action of BST and frequent milking, and possible interactions between the two.
Separate and additive stimulation of bovine milk yield by the local and systemic galactopoietic stimuli of frequent milking and growth hormone
Authors: Knight Christopher H. , Hillerton J. Eric , Kerr Marian A. , Teverson Rachel M. , Turvey Alan , Wilde Colin J.
Published: June 2009

Lactating heifers were treated for 4 weeks with recombinant bovine growth hormone (bGH, n = 9) or were untreated (n = 9). In addition, two mammary glands of each heifer were milked four times daily rather than the normal twice daily for the same 4 weeks, and for the following 2 weeks. Over the 4 weeks, milk yield was increased 12·8% by bGH, 14·0% by frequent milking and 28·5% by the combined treatment. The effect of bGH as administered here was slower in onset than that of frequency, but eventually produced a higher peak yield. ANOVA revealed significant effects of each stimulus independently and an additive, but not synergic effect of the combined treatment. The effect of the combined treatment tended to persist beyond the end of treatment; most of this response was related to the milking frequency component rather than the bGH. Mammary differentiation was assessed in biopsies of mammary tissue obtained prior to and at the end of treatment. Mammary enzyme activities (expressed on a per cell basis) indicated minimal differentiative response to either treatment, but synthesis rates for lactose and casein determined in vitro were increased by bGH treatment. Histological examination revealed a stimulatory effect of milking frequency on epithelial cell size. The results indicate that these two galactopoietic stimuli operate through independent mechanisms, and neither stimulus alone is sufficient to maximize milk yield in dairy heifers.
Effect of calcium on the stability of mares' milk lysozyme
Authors: Lyster Richard L. J.
Published: June 2009

The three aspartic acid residues that form part of the Ca-binding site of mares' milk lysozyme have apparent pK values of 4·9, 4·3 and 4·1. The fluorescence of tryptophan has been used to compare the denaturation of mares' milk lysozyme by guanidinium chloride at various concentrations of Ca with that of hens' egg-white lysozyme (EC 3.2.1.17) and α-lactalbumin. Fluorescence revealed an intermediate stage in the denaturation of mares' milk lysozyme. The Ca-free form of mares' milk lysozyme is slightly more stable than that of α-lactalbumin, but its interaction with Ca is similar to that of α-lactalbumin, since only the native state binds Ca. Three-state models of denaturation can usefully be displayed on a ternary diagram.
Texture and microstructure of chhana and rasogolla made from cows' milk
Authors: Adhikari Amitava K. , Mathur Om N. , Patil Girdhari R.
Published: June 2009

The relationships between the composition, texture and microstructure of chhana (an Indian-style soft cottage cheese analogue) and rasogolla (a sweetened dairy product made from chhana) were analysed. Chhana contained a significantly higher proportion of fat, protein, lactose and minerals than did rasogolla. Cooking of chhana in 60% sucrose solution introduced sucrose and changed the texture and structure to that typical of rasogolla. As chhana was transformed to rasogolla, the Instron textural properties, hardness, gumminess and chewiness, fell significantly, whereas springiness increased dramatically. Market rasogolla had a slightly different composition from the laboratory-made samples, but both had similar Instron textural and sensory textural attributes. Scanning electron microscopy showed that chhana had a structure like cottage cheese or cream cheese, a compact, coalesced casein matrix with fat globules embedded in it. Rasogolla had a conglomerated, ragged and porous casein matrix with uneven surface and numerous large void spaces. The collapsed and ruptured fat globules were found embedded in the agglomerated protein particles of rasogolla. The textural attributes of both chhana and rasogolla could be explained by the microstructure.
Effects on milk yield, somatic cell count and milk conductivity of short-term non-milking of lactating quarters of cows
Authors: Hamann Jörn , Gyodi Peter
Published: June 2009

Compensatory changes in daily milk production between quarters within an udder were investigated, together with related changes in cell count and electrical conductivity of fore milk samples. Two quarters per cow were left unmilked for 2 d (Group 1, four cows) or for 4 d (Group 2, four cows), and then all quarters of all cows were milked twice daily for a further period of 16 d. The mean daily yield per cow fell 50% during the period of milking two quarters. Daily yield for cows in Group 1 decreased significantly only during the treatment period and the first post-treatment period of 4 d, whereas the daily yield for Group 2 was significantly reduced during the whole post-treatment period. The cell count for all continuously milked (control) quarters was stable during the experiment, but increased in the treated quarters during the first 4 d of the post-treatment period. Non-milking was accompanied by a significant increase in fore milk conductivity which persisted for an additional 4 d after the resumption of normal milking. Throughout the last 12 d of the post-treatment period milk from both control and treated quarters had significantly decreased conductivity levels compared with the pretreatment values.
High affinity (Na++ Cl-)-dependent taurine transport by lactating mammary tissue
Authors: Shennan David B. , McNeillie Sandra A.
Published: June 2009

The transport of taurine by lactating rat mammary tissue has been examined. Taurine uptake was found to be dependent upon the presence of extracellular Na+and Cl-, which is consistent with (Na++ Cl-+ taurine) cotransport. TheKaandVmaxof taurine influx were respectively 43 μM and 37·5 μmol/kg cell water per 15 min. It is apparent that the mechanism responsible for taurine uptake is highly selective for β-amino acids. Taurine efflux consisted of a fast extracellular component and a slow membrane-limited component. The slow component was relatively insensitive to temperature, suggesting that it may represent simple diffusion. Mammary tissue was found to contain a high level of intracellular taurine: 7·29–7·44 mmol/kg cell water. We suggest that taurine is taken up and concentrated by the mammary gland by a (Na++ Cl-+ taurine) cotransport mechanism situated in the blood-facing aspect of the secretory epithelium and that a low outward permeability to taurine allows a high intra-to-extracellular concentration gradient to be maintained. Milk taurine may be derived from taurine diffusing from the cell cytosol across the apical membrane.
Hormone-dependent expression of the ovine β-lactoglobulin gene
Authors: Osborne Rebecca , Howell Michael , Clark A. John , Nicholas Kevin R.
Published: June 2009

The minimal hormonal requirements for inducing the ovine β-lactoglobulin gene have been investigated using mammary gland explants from ewes in the first half of pregnancy. Quantification of β-lactoglobulin mRNA showed that a combination of insulin, Cortisol and prolactin was required to stimulate the expression of the gene and that this response could not be enhanced by the addition of oestrogen and thyroid hormone to the culture medium. Explants cultured in the presence of insulin, Cortisol and prolactin also demonstrated the capacity to synthesize the protein. Progesterone did not inhibit the induction of the gene, which is consistent with the increase in β-lactoglobulin mRNA observed in vivo in the mammary gland during the final 2 months of pregnancy when the circulating level of progesterone is elevated.
Inhibition of mitogen-induced proliferative responses of lymphocytes by bovine κ-caseinoglycopeptides having different carbohydrate chains
Authors: Otani Hajime , Monnai Makoto , Kawasaki Yoshihiro , Kawakami Hiroshi , Tanimoto Morimasa
Published: June 2009

Bovine κ-caseinoglycopeptides (i.e. residues 106–169, CGP) were prepared from κ-casein digested with rennin and a commercial whey protein concentrate. CGP from whey protein concentrate was further divided into seven CGP fractions having different carbohydrate compositions using FPLC. Unfractionated CGP inhibited lipopolysaccharide (LPS)- and phytohaemagglutinin (PHA)-induced proliferative responses of mouse spleen cells and rabbit Peyer's patch cells. The unfractionated CGP also inhibited antibody responses to sheep red blood cells in mouse spleen cell cultures. However, seven CGP fractions having zero to fiveN-acetylneuraminic acid (NANA) residues had different inhibitory effects on both LPS- and PHA-induced proliferative responses of mouse spleen cells. The inhibitory effect on PHA-induced proliferative responses increased with increasing numbers of NANA residues, whereas that on LPS-induced proliferation was highest with the CGP fraction having two NANA residues. Both inhibitory effects decreased significantly after neuraminidase or chymotrypsin digestion. These findings indicate that both the carbohydrate (particularly the NANA residues) and the polypeptide portions are essential for inhibitory effects on LPS- and PHA-induced proliferative responses of mouse spleen cells.
Immunomodulatory effects of dietary whey proteins in mice
Authors: Wong Chun W. , Watson Dennis L.
Published: June 2009

Studies on the immunomodulatory properties of dietary whey proteins in mice are reported. Ingestion of bovine milk whey proteins, either as a supplement in an adequately balanced commercial diet or as the only protein source in a balanced diet, consistently enhanced secondary humoral antibody responses following systemic immunization with ovalbumin, when compared with other protein sources such as soyabean protein isolate and ovine colostral whey proteins. After 5–8 weeks of feeding, dietary milk whey proteins enhanced cell-mediated immune responses as revealed by footpad delayed-type hypersensitivity responses, and concanavalin A-induced spleen cell proliferative responses. To monitor nutritional effects of milk whey proteins, live weight, leucocyte counts and clinical changes of diet-fed mice were examined. The present results confirm other previous results that dietary bovine milk whey proteins have immunoenhancing properties in mice and these properties are unlikely to be related solely to the nutritional effects.
Effects ofStaphylococcus aureusproducts on growth and function of bovine mammary myoepithelial cellsin vitro
Authors: Zavizion Boris , John Bramley A. , Politis Ioannis
Published: June 2009

The effects of culture supernatants conditioned by the growth ofStaphylococcus aureusM60 onin vitrogrowth and functional properties of bovine mammary myoepithelial cells were examined. Myoepithelial cell proliferation was reduced byStaph, aurexisM60 culture supernatants. Exposure of myoepithelial cells to culture supernatants of isogeneic mutants ofStaph, aureusM60 that produced either α or β toxins reduced proliferation, but to a lesser extent than supernatants from the wild type strain. Thus, α and β toxins may play some role in affecting myoepithelial cell proliferation. Of the cells tested, 42% contracted following addition of oxytocin (10–7M) in the culture medium. Treatment of myoepithelial cells for 15 min withStaph, aureusM60 supernatants, prior to addition of oxytocin in the culture medium, increased the number of cells that contracted to 92%. Exposure of cells for 3 h to the same supernatant, prior to addition of oxytocin in the culture medium, abolished oxytocin responsiveness, had no effect on immunolocalization of actin and vimentin, but affected the localization of α-actinin within myoepithelial cells. Treatment of myoepithelial cells for 3 h with a combination of purified staphylococcal proteinases XVI and XVII-B abolished oxytocin responsiveness and mimicked the effect of theStaph, aureusculture supernatant. We conclude thatStaph, aureusM60 culture supernatant affected proliferation and functional properties of myoepithelial cells.