bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proteolysis in milk: the significance of proteinases originating from milk leucocytes and a comparison of the action of leucocyte, bacterial and natural milk proteinases on casein
Authors: Grieve Paul A. , Kitchen Barry J. 
Published: June 2009

SUMMARYThe caseinolytic activities at pH 6·8 of polymorphonuclear (PMN) and mononuclear leucocyte homogenates (equivalent to a level of 106cells/ml milk) were less than the levels of natural milk proteinase activity found in milk from healthy cows. Bulk milks contained ∼ 4 times more milk proteinase activity than the composite milks from individual healthy cows. Isolated blood leucocytes, when added to raw milk of good bacteriological quality and stored at 5 °C, did not readily degenerate and had no detectable effect on the milk proteins even when these cells were completely disrupted by homogenization of the milk. Pasteurization of milk which contained leucocytes caused loss of cell vitality. Extracellular proteinases of psychrotrophic bacteria growing in milk were not detected until the early stationary phase of growth. The total viable count at which this occurred varied greatly. Proteinase production by a pure culture ofPseudomonas fluorescenswas not detected in milk stored at 5 °C until a viable count of ∼ 109colony forming units (c.f.u.)/ml was obtained, whilst normal bulk milks stored at 5 °C produced detectable levels of extracellular proteinase(s) when the psychrotrophic flora reached 107–108c.f.u./ml. Casein proteolysis by PMN and mononuclear leucocyte homogenates resulted in similar polypeptide maps, but plasmin and bacterial proteinase isolated from a strain ofSerratia marcescensresulted in polypeptide maps different from each other and from that produced by the leucocyte proteinase(s). The rate of proteolysis of caseins by the different proteinase sources appeared to be in the order αsl- > β- > > κ-casein for the leucocyte extracts, β- > αsl- > > > κ-casein for bovine plasmin and β- ≈ κ- > αsl-casein forS. marcescensproteinase.
Effect of variation in the composition of milk supply on the composition and quality of farmhouse Cheshire cheese
Authors: Grandison Alistair S. , Anderson Malcolm , Ford Graeme D. , Newell Lavinia , Lyon-Smith Pauline 
Published: June 2009

SUMMARYThe composition of the diet fed to cows, the composition and coagulating properties of the milk produced by them and used for cheesemaking, the cheesemaking methods and the chemical composition, texture and grade of Cheshire cheese obtained from four farmhouse producers during the period December to June 1982–83 were investigated. The presence of pockets of loose fat in the cheese structure, which can lead to downgrading in the late winter and spring, was not related to the chemical composition of the milk and may arise from the handling of the milk before cheesemaking. Generally the composition of the forage and the milk varied with date, but not between the different farms, whereas the composition and properties of the cheese were dependent on the manufacturers but were fairly constant during the period of study.
Effect of pH on the formation of deposit from milk on heated surfaces during ultra high temperature processing
Authors: Skudder Paul J. , Brooker Brian E. , Bonsey Andrew D. , Alvarez-Guerrero Norman R. 
Published: June 2009

SUMMARYInvestigation of the effect of pH on the formation of deposit from milk during ultra high temperature treatment using a plate-type plant showed that deposit formation was greatly increased when the pH of whole milk was reduced to 6·54, irrespective of whether the adjustment was made through the addition of HCl or lactic acid. Most of the increase in deposition took place in the higher temperature sections of the plant. Conversely, an increase in milk pH to 6·8 using NaOH resulted in considerably less deposit being formed during heat treatment. Reducing the pH of whole milk increased the deposition of both protein and fat, but reduced the deposition of minerals. Despite very high concentration of fat in the deposits, it is unlikely that fatper sewas responsible for increased deposit formation. Deposition also increased when the pH of skim milk was reduced to 6·51 before processing. Electron micrographs of the milks after heat treatment indicated that pH reductions caused the formation of large aggregates containing casein micelles during heating. Fat globules were also present in aggregates formed in whole milk with reduced pH. Slight reductions in the pH of milk before processing appear to enable the pH during heat treatment to fall below a critical value at which coagulation of milk takes place at the heated surfaces.
Salt distribution between the colloidal and soluble phases of ewes' milk
Authors: Polychroniadou Anna , Vafopoulou Anna 
Published: June 2009

SUMMARYEwes' milk from two breeds of Greek sheep, Karagouniki and Serron, was analysed throughout mid and late lactation to investigate the salt distribution between colloidal and soluble phases. Separation of the phases was obtained by centrifugation at 48000 g. Effect of stage of lactation was significant only for total Mg in both breeds (P < 0·05) and for colloidal citrate in Serron ewe milk (P < 0·01). Breed differences were not significant (P < 0·05), except for colloidal casein.In the colloidal phase there was a strong positive correlation of casein with Ca and P, but correlation with Mg was poor. Molar sums of [Ca + Mg] and [P + Cit] were also significantly correlated. The Ca to P molar ratio averaged 2·00 and was higher than that reported for cows' milk. The inclusion of Mg as well as citrate in the colloidal calcium phosphate is indicated. In the aqueous phase there was a strong negative correlation of Ca with pH and a positive one with citrate. Correlation with phosphate was less. It seems that citrate is the main factor influencing Ca concentration in the soluble phase.
Effect of nature of forage on spontaneous lipolysis in milk from cows in late lactation
Authors: Chazal Marie-Paule , Chilliard Yves , Coulon Jean-Baptiste 
Published: June 2009

SummaryLevels of free fatty acids (FFA) were determined in milk from cows after 7 months of lactation and 4 months of pregnancy immediately after milking (initial FFA) and after 22 h storage at 4 °C (FFA-22). During the pre-experimental period, cows were at pasture. When housed indoors (experimental period) they were fed hay or grass silage for 3 weeks. Then all cows received grass silage for 3 weeks (post-experimental period). Feeding hay did not increase FFA-22 content in milk compared with pasture, but grass silage feeding enhanced FFA-22 content in milk compared with pasture (+130 %) or hay (+93 %). Increased lipolysis with grass silage was not due to underfeeding of the cows because grass silage and hay were both of high nutritive value. As pasture, hay and grass silage were of the same type (native mountain grassland), the high level of lipolysis occurring with grass silage probably resulted from the method of forage conservation.
A study of the heat stabilities of a number of indigenous milk enzymes
Authors: Andrews Anthony T. , Anderson Malcolm , Goodenough Peter W. 
Published: June 2009

SummaryHeat stability profiles of a number of indigenous bovine milk enzymes were examined with the object of being able to monitor heat treatments slightly more severe than typical pasteurization conditions by measurements of residual enzyme activity after heating. Assay procedures were limited to simple fluorimetric, or preferably colorimetric, methods that would be most likely to form the basis of a quick, simple and inexpensive test. Both lipoprotein lipase and α-fucosidase were relatively sensitive to heat and were totally inactivated at temperature/time combinations below those of pasteurization, but the latter may be satisfactory for studying temperatures in the range 55–65°C. Rather more heat stable wereN-acetyl-β-glucosaminidase and γ-glutamyl transpeptidase, which may be most appropriate for 65–75°C and 70–80°C respectively. Higher temperature treatments between 80 and 90°C could best be investigated by following α-mannosidase or xanthine oxidase activity.
A modified ultra high temperature treatment for reducing microbial lipolysis in stored milk
Authors: Bucky Anthony R. , Hayes Patrick R. , Robinson David S. 
Published: June 2009

SummaryCultures ofPseudomonasP46 grown in whole milk to contain ∼ 2 × 107or 1 × 108viable cells ml−1before ultra high temperature (UHT) treatment (140°C for 5 s) demonstrated near linear increases in the concentration of short-chain free fatty acids (FFA) during storage at 20°C. However with 5 × 106cells ml−1before UHT heat treatment there was no detectable increase in these FFA levels over a 6-month storage period. A novel heat treatment (140°C for 5 s followed by 60°C for 5 min) reduced the rate of production of volatile FFA to < 10% of the rates achieved after the normal UHT treatment.
Effect of manipulation of milk composition and curd-forming conditions on the formation, structure and properties of milk curd
Authors: Green Margaret L. 
Published: June 2009

SummaryMilks whose compositions had been altered by deliberate manipulation or by contact with various environmental conditions relevant to cheesemaking were treated with rennet in such a way as normally to give a constant coagulation time. Rates of curd formation and whey loss, curd structure and fat retention were determined. Ca depletion in concentrated milks reduced firming and syneresis rates and gave curds with finer protein networks. Increased temperature of curd formation increased the curd-firming rate and curd coarseness, but decreased the syneresis rate at 30 °C. Prior treatment of concentrated milk with rennet in the cold gave a much finer protein network which retained fat better than curd formed normally. Despite increasing firming and syneresis rates, acidified milk gave a slightly finer curd with a better fat retention than normal. Addition of cationic materials stimulated aggregation and the curd retained fat better than normal, although the curd structure was unaffected. The results indicate that the processes of firming and syneresis have related mechanisms, and that the curd structure is not simply dependent on curd-forming conditions, but on the number of aggregating particles and the forces between them.
Indirect assay of milk clotting activity of Mucor miehei proteinase (Fromase) in combined rennets
Authors: Beránková Eva , Rauch Pavel , Káš Jan , Hušek Vladimír , Paluska Eduard 
Published: June 2009

SummaryMilk clotting activity of Mucor miehei proteinase (commercial name Fromase) was determined in combined rennets as the difference between the total activity of combined rennet and the residual activity after inhibition of Fromase by the purified immunoglobulin fraction of a Fromase antiserum. The proposed method is simple, rapid, and makes possible the use of any arbitrary method for assaying milk clotting activity. The application of the immunoglobulin fraction, instead of the whole antiserum, is necessary owing to the presence of nonspecific proteinase inhibitors in blood serum.
Production of extracellular lipases and proteinases during prolonged growth of strains of psychrotrophic bacteria in whole milk
Authors: Stead Donald 
Published: June 2009

SummaryThree strains of psychrotrophicPseudomonasspp., each with different lipolytic and proteolytic phenotypes (including a proteinase-deficient mutant), were cultured separately in whole milk at 7°C. Growth rates were the same during logarithmic growth phase, but during early stationary phase the cell densities were related to the activities of lipase and proteinase in the cultures. Only one strain underwent pronounced death phase. Proteinase activity was not detected in the culture of the proteinase-deficient mutant, but in those of the other strains it increased to a plateau, or continued to increase linearly. Lipase activity of the culture of each strain reached a peak in early stationary phase; in late stationary phase activity was highest for the proteinase-deficient mutant strain where degradation of lipase by bacterial proteinase would have been least. The ability of psychrotrophic bacteria both to survive for long periods and to produce high levels of proteinases and lipases on prolonged incubation in milk emphasizes the spoilage potential arising from psychrotrophic bacteria in inadequately cleaned dairy equipment.
Influence of milking conditions and vacuum control on hydraulic milking performance
Authors: Grindal Robert J. 
Published: June 2009

SummaryChanges were made in milking conditions and vacuum levels to assess optimum parameters for hydraulic milking. A randomized block design was used for the trial, each result being the mean of data from four cows. The results confirmed that faster milking occurred at 50 kPa vacuum (pulsation and milkline) and showed that high vacuum levels created within the liner could be prevented by providing a higher vacuum to the pulsation chamber than the milkline (differential vacuum) without substantially reducing milking performance. The stimulation provided by hydraulic milking may be important in achieving rapid milking in the absence of udder preparation. Lipolysis of milk fat was reduced by hydraulic milking as was milk foam in the recorder jar, particularly when no air was admitted to the claw.
Effect of pH, calcium concentration and temperature on the evolution of the refractometric signal produced during rennet coagulation of milk
Authors: Korolczuk Jozef , Maubois Jean-Louis 
Published: June 2009

SummaryAn industrial refractometer connected to a microcomputer was used to study the rennet coagulation of milk. The amplitude of the refractometer's signal changes during coagulation was about 104 times more important than the resolution of the computerized refractometer. The signal v. time derivatives were calculated and the inflection point time (ti) was correlated with pH, Ca concentration and temperature. The inflection point time was inversely proportional to the rennet and Ca concentrations and the logarithm of the proportionality factor (k) was linearly correlated with pH. The relation between ti and temperature was curvilinear. It is concluded that the refractometer tested could be used for research on the coagulation process.
A multi-valved milking machine cluster to control intramammary infection in dairy cows
Authors: Griffin Tony K. , Grindal Robert J. , Bramley A. John 
Published: June 2009

SummaryA milking machine claw incorporating valves to prevent movement of milk between teats during milking, and its contribution to the prevention of udder infection under experimental and field conditions, is described. Under experimental conditions a suspension of Streptococcus agalactiae and Str. dysgalactiae was introduced into the milking cluster during milking; 11 of 40 quarters became infected using a conventional claw piece whereas none of 40 quarters milked with the multivalve claw developed intramammary infection. In a 12-month experiment in ten commercial herds, each split into two equal susceptibility groups, the multi-valved cluster reduced the incidence of new infection with coliforms and Str. uberis by 17% (P < 0·1). The incidence of all new infections and new clinical cases was 14 and 25% lower compared to conventional clusters but these reductions were not significant.
Rennet coagulation of heated milk: influence of pH adjustment before or after heating
Authors: Singh Harjinder , Shalabi Samweul I. , Fox Patrick F. , Flynn Albert , Barry Anne 
Published: June 2009

SummaryThe rennet coagulation times of infant milk formulae or fresh skim milk (milk) samples heated at temperatures in the range 70–140 °C for 1–10 min decreased on acidification, usually to pH < 6·0. Heated milk samples acidified to pH 5·5 and reneutralized to pH 6·6 retained good rennet coagulability. Acidification of such milk samples before heating also reduced the adverse effect of severe heat treatment (95 °C for 1 min) on rennet coagulation. Addition of low concentrations of CaCl2 to heated milks offset the adverse effects of heating. Acidification of heated milks increased the [Ca2+], and reneutralization of acidified milk only partly restored the [Ca2+], i.e. acidified/reneutralized milk had a higher [Ca2+] than normal milk, suggesting this as the mechanism via which acidification/neutralization improves the rennet coagulability of heated milk. Approximately 50% of the whey protein can be incorporated into rennet gels in heated milks while retaining good coagulability and curd tension; this may be a useful technique for increasing cheese yield.
Accelerated cheese ripening with heat treated cells of Lactobacillus helveticus and a commercial proteolytic enzyme
Authors: Ardö Ylva , Pettersson Hans-Erik 
Published: June 2009

SummarySynergic effects of proteolytic enzymes from two different microbial sources on the ripening of Swedish hard cheese were studied. When extracellular proteolytic enzymes from Bacillus subtilis (Neutrase) and/or heat treated cells of Lactobacillus helveticus (now L. delbrueckii subsp. helveticus) were added to the cheese milk, cheese ripening was accelerated; Neutrase effectively hydrolysed casein to give a softer body. Addition of heat treated lactobacilli did not accelerate hydrolysis of casein, but accelerated the breakdown of peptides which increased the amount of amino acid N in the cheese and also enhanced the intensity of cheese flavour. A bitter taste which developed in cheeses with added Neutrase could be eliminated by the simultaneous addition of heat treated lactobacilli.
Metabolic adaptations in goat mammary tissue during long-term incomplete milking
Authors: Wilde Colin J. , Blatchford David R. , Knight Christopher H. , Peaker Malcolm 
Published: June 2009

SummaryLactating goats were milked incompletely in one gland and normally in the other gland twice daily for 24 weeks. Yields of the incompletely milked glands were adjusted so that a calculated 100 ml milk remained in the gland at the end of milking. On average this residual volume was greater by 7·6% of the total milk volume than that left after normal milking and was 25·9% greater than the capacity of the alveoli. After 24 weeks, the weekly milk yield of the incompletely milked gland was 23·8% lower than that of the other gland (P < 0·001) when expressed in relation to cell number. The metabolic capacity of secretory cells in the two glands was measured in serial tissue biopsies. Two weeks of incomplete milking had no effect on enzyme activities or metabolic fluxes in the incompletely milked gland, but after 24 weeks the activities of several key enzymes were significantly lower in this gland. This was associated with a reduced rate of synthesis of total protein and casein in expiants freshly prepared from the tissue. The rate of lactose synthesis also tended to be lower in expiants from the incompletely milked gland. Secretory cell number in the two glands was similar at the end of incomplete milking. The data indicate that incomplete milking over a long period caused partial secretory cellular involution via a local chemical feedback mechanism in the gland.
A mathematical model for the description of chymosin action on casein micelles
Authors: Merin Uzi , Talpaz Hovav , Fishman Svetlana 
Published: June 2009

SummaryA mathematical model for chymosin action on casein micelles is presented in a two-stage equation which results in a single curve demonstrating the lag time from enzyme addition to the end of coagulum firming. The model uses the Michaelis–Menten enzyme kinetics equation for the first reaction followed by an nth order reaction for the casein micelles agglomeration stage. The computer output using these equations shows that lag time is elongated as enzyme concentration is lowered. Regression analysis of time of gelation against l/E0 shows good correlation. Viscosity of the milk drops at the beginning of the κ-casein hydrolysis and increases thereafter, when the coagulum is being formed.
Release of cholesteryl esters by the mammary gland of the pre-partum cow
Authors: Thompson Gordon E. 
Published: June 2009

SummaryIn five cows that were regularly milked before parturition, cholesteryl esters were continuously released into the mammary fluid; their concentration in the fluid was initially high, but decreased a few days before parturition when mammary secretion of fluid and triglyceride was increasing. The composition of fatty acids in the cholesteryl esters of mammary fluid and in blood plasma was different, suggesting mammary synthesis of cholesteryl esters.
Estimation of casein micelles' surface energy by means of contact angle measurements
Authors: Britten Michel , Boulet Marcel , Paquin Paul 
Published: June 2009

SummaryThe surface energies of highly hydrated casein micelle layers isolated from variously pretreated skim milks have been determined by means of contact angle measurements. The long range Lifshitz-Van der Waals (LW) and the short range hydrogen bonding (SR) components of surface energy were determined using α-bromonaphthalene and water for contact angle measurements. Casein micelles isolated from untreated and heat treated milks showed similar surface energy values of about 63·5 mJ.m-2 with an LW component of 19·2 mJ.m-2 and an SR component of 44·3 mJ.m-2. The calculated attraction potential energy was − 0·7 mJ.m-2. Casein micelles isolated from renneted milk showed a surface energy of 33·0 mJ.m-2 with an LW component of 30·7 mJ.m-2 and an SR component of 2·3 mJ.m-2. The attraction potential energy of renneted micelles was nearly two orders of magnitude higher than those of micelles from other milks ( − 63·3 mJ.m-2). The SR component of interfacial energy accounted for 98% of this attraction potential. The importance of attractive forces in relation to casein micelle stability is discussed.
Milk protein polymorphism in Danish dairy cattle and the influence of genetic variants on milk yield
Authors: Bech Anne-Marie , Kristiansen K. Rotvig 
Published: June 2009

SummaryIn milk samples from 549 cows of the breeds Danish Jersey, Red Danish Dairy Cattle (RDM), and Black and White Danish Dairy Cattle (SDM) the genetic polymorphisms of the αs1, β andK-cascin and β-lactoglobulin (β-Lg) loci were determined by isoelectric focusing in agarose gels. The results of the screening were comparcd with results obtained by Larsen & Thymann (1966). In addition, the genetic linkage of the three casein loci was studied, and the association between milk protein genotypes and yields in first and second lactations of milk, fat and protein were investigated.The distribution of genotypes of all four milk protein Systems was different from breed to breed.For Jersey cows, significant differences in the gene frequencies from the results of the 1966 investigation were found for αs1andK-casein and β-Lg. For SDM cows a change in theK-casein frequency had occurred whereas for RDM cows no changes were found.Linkage between some of the casein loci was found within ail three breeds. For the RDM breed the possible linkage between αs1-casein and the other caseins could not be tested bccause nearly ail thc cows were homozygous for the αs1-cascin-B genotypes.β-Casein genotypes were associated with yield parameters in ail breeds. The A2A2genotype of this protein gave higher yields of milk, fat, and protein in the second lactation than thc A1A1genotype.