bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of intravenous supplements of L-methionine on milk yield and composition in cows given silage-cereal diets
Authors: Chamberlain David G. , Thomas Phillip C.
Published: June 2009

Eight cows in mid lactation and receiving a diet of perennial ryegrass silage and barley (70:30 on a DM basis) were given intravenous supplements of l-methionine (8 g/d). The methionine treatment had no significant effect on milk yield, protein content or lactose content, but increased milk fat content and yield by approximately 10% (P < 0·05).
Effect of oxygen on the keeping quality of milk: II. Effect of available oxygen on bacterial spoilage and oxygen uptake
Authors: Schröder Monika J. A.
Published: June 2009

The effect of limiting the amount of O2 present in commercially pasteurized milk on bacterial growth and on the keeping quality of the milk was investigated. No increase in bacterial count of laboratory pasteurized milk during storage for 9 d at 5 °C was observed and O2 consumption due to bacterial activity was low. In commercial pasteurized milk containing post-pasteurization contamination (PPC) growth of strict aerobes was encouraged by high O2 content while that of coliforms was less dependent on O2 level. The amounts of headspace (HS) O2 consumed in milk with PPC growth were large. Reducing the dissolved O2 content of commercial pasteurized milk stored in O2-impermeable containers without HS had little effect on bacterial activity and shelf-life.
Factors affecting the ethanol stability of bovine milk: V. Effects of chemical modification of milk protein
Authors: Horne David S. , Parker Thomas G.
Published: June 2009

The effect of chemical modification of milk protein on the ethanol (EtOH) stability of skim-milk has been investigated. Modification of lysine residues by reaction with anhydrides increased the EtOH stability whereas amidation of carboxyl groups destabilized the milk. Lysine modification also counteracted destabilization induced by Ca2+ addition. By using multiple linear regression techniques these latter effects can be accounted for in terms of the changes they bring about in micellar charge. These results provide a further verification and an extension of the previously proposed mechanism for EtOH-induced coagulation of skim-milk.
Some factors affecting the post clotting development of coagulum strength in renneted milk
Authors: Storry John E. , Ford Graeme D.
Published: June 2009

Effects of pH, added Ca, rennet concentration, temperature, concentration and dilution of milk, on rennet clotting and coagulum development have been investigated. Rennet clotting time (RCT) was decreased by reduced pH, by increased temperature and by increased concentrations of rennet or added Ca. Only extremes of concentration or dilution of milk increased RCT. Strength of milk coagulum at 1 h after RCT was increased by reduction in pH and by increased concentrations of added Ca. Increased temperatures decreased coagulum strength whereas increased rennet concentrations had little effect. A curvilinear relationship between total casein concentration and coagulum strength was found for Friesian and Jersey milks. Two phases of coagulum development after clotting were observed. Changes in pH particularly affected the first phase whereas changes in temperature particularly affected the second. Effects of rennet, casein and Ca were similar for both phases.
Detection by Warburg manometry of compounds stimulatory to lactic acid bacteria
Authors: Webb Leslie E.
Published: June 2009

The effect of aqueous algal extract, yeast extract casein peptone and meat peptone on acid production by 4 strains of lactic acid bacteria was tested manometrically using a milk–bicarbonate medium. A strain-dependent stimulation of the bacteria was detected after 4 h incubation. After fractionation of an aqueous extract of the green algaScenedesmus obliquuson a Sephadex G25 column, 2 fractions with stimulatory activity were found usingStreptococcus lactisas the test organism. One of the peaks of activity, confined to shortening of the lag phase, was due to hypoxanthine which, however, had only a slight stimulatory effect in conventional milk souring tests. The manometric method provides a sensitive and rapid test for detecting compounds with biological activity in µg amounts, but it should be accompanied by milk souring tests for interpretation of the type of stimulation involved.
Effect of teat washing on the bacteriological contamination of milk from cows kept under various housing conditions
Authors: McKinnon Charles H. , Fulford Rosemary J. , Cousins Christina M.
Published: June 2009

The effect of different methods of teat washing on bacterial contamination and sediment levels of the milk of cows kept under 3 housing conditions was studied. By use of an in line milk sampler and steam sterilized clusters the bacterial contamination from the teats after udder preparation was determined directly.

The results show that, even under the same housing conditions and teat washing treatments, considerable variation in bacterial counts and sediment level occurred. Overall, washing with hypochlorite (600 mg/1 available Cl) and drying with a paper towel gave total counts that were significantly lower than were obtained with the other 4 treatments. The aerobic spore count, in which thermoduric flora predominated, was greatly reduced by drying the teats, but the inclusion of hypochlorite in the wash water had little effect. Coliform contamination was very low (∼ 1/ml) even where the cows' teats were heavily soiled and were not washed.

The sediment levels in the milk again showed wide variation and occasional high values (3 mg/l) were recorded for washed cows. In marked contrast to its effect on the bacteriological results, drying had little effect on reducing the sediment.
Relationship between the level of N-acetyl-β-D-glucosaminidase (NAGase) in bovine milk and the presence of mastitis pathogens
Authors: Kitchen Barry J. , Kwee W. Seng , Middleton Gordon , Andrews R. Jeffrey
Published: June 2009

Changes in the level of the tissue damage marker enzyme, N-acetyl-β-D-glucosaminidase (NAGase) in quarter fore milks were found to be related to the presence and types of pathogenic bacteria present and to somatic cell counts (SCC). Minor pathogens (coagulase-negative staphylococci, Corynebacterium bovis) elicited a mild SCC increase (from a mean of 243 × 103/ml in healthy quarters to 504 × 103/ml in infected quarters) with marginal tissue damage (mean NAGase activity increased from 21 in healthy quarters to 28 in infected quarters). Major pathogens (i.e. Staphylococcus aureus, Streptococcus agalactiae, Str. dysgalactiae and Str. uberis) caused more severe tissue damage (mean NAGase of 48) and SCC increases (mean, 2803 × 103/ml). The NAGase test could also be used effectively on composite milk samples where regular monthly NAGase analysis was able to identify correctly 74% of animals having infected quarters. The possibility of combining SCC and NAGase data in order to give a more definite diagnosis of bovine mastitis is discussed.
Milk yield in rats in relation to activity and size of the mammary secretory cell population
Authors: Knight Christopher H. , Docherty Ann H. , Peaker Malcolm
Published: June 2009

An attempt was made to partition changes in milk yield during lactation in the rat between changes in the size of the secretory cell population and changes in cellular activity. Groups of rats were studied on d 2, 7, 14, 21 and 28 of lactation. Milk yield increased between d 2 and 7, less markedly between d 7 and 14 and decreased between d 14 and 21. Milk secretion had apparently ceased on d 28. Total mammary DNA (DNAt) and RNA (RNAt) increased from d 2 to 14. It is concluded that of the increase in milk yield between d 2 and 14, an increase in cell population accounted for 75% and an increase in cellular activity for 25%. A decrease in activity appeared to be entirely responsible for the decrease in yield between d 14 and 21.
Isolation of bovine milk fat globule membrane material from cream without prior removal of caseins and whey proteins
Authors: McPherson Avis V. , Dash Mary C. , Kitchen Barry J.
Published: June 2009

Bovine milk fat globule membrane (MFGM) material was isolated from cream by a new technique which did not involve removal of caseins and whey proteins before destabilization of the fat globules. These components were removed by centrifugation of the membrane material extract through a concentrated sucrose solution (52·5% (w/v) sucrose in 10 mM-Tris HCl buffer, pH 7·5). Membranes collected at the sample–sucrose interface, while whey proteins remained in the supernatant and caseins migrated into the concentrated sucrose solution. The yield of membrane material using this procedure was 25% less than that from conventional methods. This reduced yield was due mainly to lower levels of lipid material, in particular triglyceride. Electrophoretic analysis showed that the polypeptide composition of ‘unwashed’ membrane material was similar to that of conventionally prepared MFGM. This method is particularly suitable for the isolation of membrane material from milks and dairy products in which the fat globule stability is reduced or unknown.
Some observations on the behaviour of dairy cattle using cow-activated out-of-parlour concentrate dispensers
Authors: Little William , Harrison Roger D.
Published: June 2009

Housed dairy heifers (62 cows) were fed concentrates exclusively through variable-time, out-of-parlour dispensers. They were observed to visit the dispensers on average 20·4 times/d but significantly less frequently (13·9 times/d) shortly after calving. The dispensers were occupied for 25·8% of the night (22.00–06.00 h) compared with 30·4% of the day (06.00–22.00 h). This difference was small but significant, whereas the differences between the proportion of night and day spent standing (32·5 v. 66·2%) or eating silage (4·8 v. 24·7%) were noticeably greater. In a herd of ∼ 80 cows in which the daily average number of visits to the dispenser was 20·5/cow there was a significant decrease in the number of visits/d (y) with increasing time after calving (x) where y = 23·4–0·030x (r = 0·88). Some cows repeatedly visited the dispensers more frequently than others (range 13·2–34·9±5·3 visits/d, giving a repeatability of 0·58). Cows in a grazing herd (∼ 60) visited the dispensers on average 14·6 times/d during an average 3·6 visits to a cubicle house to which they had continuous access. The number of visits to the dispensers (y) again decreased with increasing time after calving (x) where y = 22·7–0·072x (r = 0·45). The average time spent in the cubicle house (z) also decreased as the days after calving (x) increased (z = 8·4 – 0073x+0·000203x2, r =–0·66). All cows, however, stayed in the cubicle house during periods of heavy rainfall.
Some attributes of twin-bearing British Friesian and Canadian Holstein cows recorded in England and Wales
Authors: Wood Peter D. P.
Published: June 2009

The production of milk, fat and protein of 37216 mothers of twins was compared with that of 1691 127 mothers of single calves of Black and White breeds of cattle recorded in England and Wales. At every parity, the mothers of twins produced more milk, fat and protein than the mothers of single calves. The proportion of twin-bearing cows retained increased with parity, from 0·67% at first calving to ∼ 4·0% at the tenth or eleventh calving. More mothers of twins achieved 305 d of lactation subsequently than mothers of single calves, although their inter-calving intervals were not generally longer.
Effects of κ-casein genetic variants and lactation number on the renneting properties of individual milks
Authors: Schaar Johan
Published: June 2009

The effects of κ-casein genetic variants, lactation number, pH and casein content on the renneting properties of individual milks were studied. Rennet coagulation time (RCT) and curd firmness were determined with the aid of a lactodynamograph and the results statistically analysed. Renneting properties were strongly related to κ-casein variants and lactation number, with κ-casein B and higher lactation numbers giving shorter RCT and increased curd firmness, the effects on curd firmness being more pronounced. The effect of κ-casein variant on RCT could be eliminated by reducing pH and adding CaCl2 to the milk samples. The effect on curd firmness was not altered by this treatment, however. The results show that the renneting properties of individual milks are to a considerable degree genetically controlled.
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

The 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

The 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

Investigation 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

Ewes' 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

Levels 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

Heat 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

Cultures 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

Milks 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

Milk 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

Three 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

Changes 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

An 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

A 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

The 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

Synergic 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

Lactating 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

A 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

In 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

The 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

In 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.
A survey of the microflora of raw and pasteurized milk and the sources of contamination in a milk processing plant in Addis Ababa, Ethiopia
Authors: Mahari Tadesse , Gashe Berhanu A.
Published: June 2009

The microorganisms present in raw and pasteurized milk and the sources of contamination in the milk after it had arrived at the processing plant in Addis Ababa were studied. The lowest count registered for raw milk samples was 4 × 107cfu/ml while the highest was 1 × 109cfu/ml. Pasteurized milk had mesophilic aerobic counts of 7 × 105cfu/ml as it left the pasteurizing unit, but the population increased 2- to 4-fold as a result of subsequent contamination. Of the total counts in raw milk, psychrophilic, thermoduric and thermophilic organisms made up 98·l, 1·4 and 0·5% respectively. In pasteurized milk, the amounts were 53·0, 39·5 and 7·5% respectively. Samples of milk pasteurized in the laboratory contained only 74·5% thermoduric and 25·5% thermophilic organisms. The isolates mostly belonged to the generaBacillus, Streptococcus, Lactobacillus, Arthrobacter, Alcaligenes, AeromonasandPseudomonas. Cocci were more predominant than rod-shaped bacteria. Of the rod-shaped bacteria, 73% were Gram-negative. The utensils holding the raw and pasteurized milk and the plastic sheets used for bagging the pasteurized milk contributed unusually high numbers of bacteria which were either thermoduric or thermophilic. More isolates were obtained from the pasteurized than the raw milk. The keeping quality of the pasteurized milk was found to be much lower than that of the laboratory-pasteurized milk.
A 43Ca and 31P NMR study of the calcium and phosphate equilibria in heated milk solutions
Authors: Wahlgren N. Magnus , Dejmek Petr , Drakenberg Torbjörn
Published: June 2009

Casein micelle suspensions, colloidal Ca phosphate-free casein solution and simulated milk ultrafiltrate (SMUF) were studied using high-resolution 43Ca and 31P NMR in the temperature range 4–64 °C. Only one 43Ca and one 31P signal was obtained for each solution. Signal intensities and line widths varied with the environment and were affected by the redistribution of Ca and P during heating and cooling. Based upon the temperature-dependent broadening of the 43Ca signal, five different Ca environments were discerned in the heated milk fractions. The Ca state, induced by heating of a casein-containing milk salt solution, differed from both the state of Ca present in micellar colloidal Ca phosphate and from the state of Ca induced by the heating of SMUF.
Comparison of oestrone sulphate concentrations in mammary secretions during lactogenesis and lactation in dairy ruminants
Authors: Hamon Maureen , Fleet Ivan R. , Heap R. Brian
Published: June 2009

Oestrone sulphate is quantitatively a major oestrogen in pregnant goats rising gradually in concentration in milk and plasma as placental function develops (Heap et al. 1984). We report here that its concentration in mammary secretions increases sharply at the time of parturition. The results support the idea that oestrone sulphate in mammary secretions could be used as a predictor of the onset of parturition in dairy animals.
Characteristics of ruminant mammary epithelial cells grown in primary culture in serum-free medium
Authors: Winder Steven J. , Turvey Alan , Forsyth Isabel A.
Published: June 2009

Cells were obtained from the mammary glands of sheep and cows by collagenase–hyaluronidase digestion. Characterization of cells as epithelial was by reaction with a monoclonal antibody to cytokeratin. A subpopulation of spindle-shaped or stellate cells reacted with a monoclonal antibody to desmin and may be related to myoepithelial cells. The development is described of a simple serum-free culture system for these cells on gels of rat tail (type 1) collagen. A commercial medium (M199) was used, buffered with Hepes and with bovine serum albumin as the sole protein supplement, plus fibronectin for the first 18 h only as an attachment factor. The cell cultures showed stimulated DNA synthesis in response to mitogens on attached gels and also responded as floating cultures to lactogenic hormones with production of α-lactalbumin.
Isolation and characterization of 3-deoxypentulose and its determination in heated milk
Authors: Troyano Esperanza , Olano Agustin , Jimeno Maria Luisa , Sanz Jesus , Martínez-Castro Isabel
Published: June 2009

The presence of 3-deoxypentulose in heated milk is reported. This compound has been isolated from alkaline solutions of lactose and characterized by spectroscopic and Chromatographie techniques. Gas Chromatographic analysis of free monosaccharides of milk revealed two peaks corresponding to 3-deoxypentulose in commercial sterilized milk samples, in a concentration range of 30–50 mg/1. Its concentration increased with temperature and length of time of processing.
Multinuclear NMR study of the pH dependent water state in skim milk and caseinate solutions
Authors: Mariette François , Tellier Charles , Brule Gerard , Marchal Philippe
Published: June 2009

The effects of decreasing pH and micellar calcium concentrations of reconstituted skim milk and caseinate solution were studied by 1H and 17O NMR spectroscopy. The proton transverse relaxation rate 1/T2 of skim milk decreased as the pH decreased, reaching a minimum at pH 5·3. However, as the pH fell sodium caseinate solution showed a continuous increase in 1/T2, with no minimum. Analysis of proton relaxation as a function of the interpulse time in the CPMG (Carr-Purcell-Meiboom-Gill) sequence demonstrated that both the proton exchange mechanism and ‘bound’ water contributed to proton relaxation in skim milk. The study of 17O relaxation rate as a function of pH confirmed the change in protein hydration upon acidification. Increasing the amount of EDTA showed that the proton transverse relaxation rate of skim milk decreased until a plateau was reached when the micellar calcium was totally solubilized. With excess EDTA the relaxation rates of skim milk and caseinate solution were identical. A strong correlation was also found between the pH dependent relaxation rate and the solubilization of micellar phosphorus as detected by 31P NMR. Together, these results suggested that aggregation of caseins by calcium and colloidal calcium phosphate is mainly responsible for the excess hydration in skim milk micelles.
Process integration study of a milk powder plant
Authors: Robertson Lindsay J. , Baldwin Alan J.
Published: June 2009

A study was undertaken of the heat exchange possible in a milk powder plant consisting of milk treatment, a four-effect evaporator fitted with a thermovapour recompressor and a spray drier fitted with a fluidized bed secondary drier. The study utilized the techniques of process integration analysis and grand composite curve matching. Of particular interest was the optimum utilization of vapours within the evaporator. It was shown that with a minor redesign of the evaporator, and utilization of some vapour in the milk treatment section of the plant, a 6% reduction in total energy consumption of the milk powder plant was possible. If heat exchange between inlet and outlet air of the spray drier was not considered practical, preheating spray drier air with vapour from the evaporator resulted in a 10% reduction in energy consumption. Other minor heat exchange possibilities were also revealed. It was concluded that the use of vapour from the evaporator, and increased steam consumption in the evaporator, may lead in some designs to decreased plant thermal energy consumption overall. As well as the process integration study, formulae are presented for calculating the change in thermal economy of an evaporator when vapour is extracted for use in other sections of the plant. The use of process integration studies needs to be given consideration in overall design of energy-intensive dairy plant.
Yield and composition of milk from lactating mares: effect of body condition at foaling
Authors: Doreau Michel , Boulot Sylviane , Chilliard Yves
Published: June 2009

The yield and composition of milk from nursing mares were studied during the first 2 months of lactation in two groups of six and five saddle mares respectively made thin or fat before foaling, then fed ad lib. post partum. Milk yield did not significantly vary with body condition (16·5 and 15·4 kg/d for fat and thin mares respectively). Milk from fat mares had a higher fat content than milk from thin mares; the reverse was found for protein. The composition of milk fat was modified: milk of fat mares was poorer in short- and medium-chain fatty acids (C8-C14). Milk fat output was affected by body condition: 252 and 187 g/d for fat and thin mares respectively. This can be explained by a difference in lipid mobilization, as shown by variations in non-esterified fatty acids.
Measurement of teatcup liner wall movement
Authors: Butler M. Clare , Adley Nicholas J. D.
Published: June 2009

A technique for monitoring the movement of the teatcup liner during milking, using video recordings, has been investigated. The liner was videoed through a transparent shell and the recordings were subsequently processed frame by frame by an image analyser. The width of the liner and its variation with pressure difference across the liner walls were calculated at several locations along the liner length, and analysis of these results allowed the pressures at which the liner buckled and the walls touched to be determined and some estimate of the degree and duration of liner collapse to be made.
Characteristics ofα–aminoisobutyric acid transport by lactating rat mammary gland
Authors: Shennan D. B. , McNeillie S. A.
Published: June 2009

The transport of α-aminoisobutyric acid (AIB) by lactating rat mammary tissue has been examined. AIB uptake by mammary tissue was via both Na+-dependent and Na+-independent pathways. AIB uptake via the Na+-dependent pathway was inhibited by (methylamino)isobutyric acid (MeAIB) whereas AIB uptake via the Na+-independent pathway was blocked by 2-aminobicyclo[2, 2, 1]-heptane-2-carboxylic acid (BCH). A small fraction of AIB influx persisted in the presence of both MeAIB and BCH. The Na+-independent moiety of AIB uptake was strongly inhibited by phenylalanine, tryptophan, leucine, isoleucine and methionine. AIB efflux from mammary tissue slices was found to be both Na+-dependent and Na+-independent. Trans-stimulation of AIB efflux by other amino acids was not observed; in contrast, external phenylalanine, tryptophan and leucine inhibited AIB efflux. The results are largely consistent with the presence of systems A and L in lactating rat mammary tissue. However, the Na+-independent fraction of AIB transport may represent transport via a tissue specific form of system L.
Retinol determination in milk by HPLC and fluorescence detection
Authors: Jensen Søren Krogh
Published: June 2009

A simple and rapid method for determination of retinol in whole milk is described. Milk (400 mg) was diluted with a water–methanol–ethanol mixture (55:9:36 by vol.) and saponified with potassium hydroxide in a culture tube. Retinol was extracted into 10ml heptane-di-isopropyl ether (3:1) of which 100 μl was injected into the HPLC. Fluorescence detection ensured the specificity and sensitivity. The critical points in the analysis were the extraction of retinol from fatty samples and the instability of retinol towards photo-oxidation and air oxidation in alkaline solvents. There was an average recovery of 98·5 ± 2·4% and a CV of 3·6%.
Thermal inactivation of γ-glutamyltranspeptidase and Enterococcus faecium in milk-based systems
Authors: Patel Shailam S. , Wilbey R. Andrew
Published: June 2009

Untreated whole milk, skim milk, sweetened milks, sweetened and unsweetened creams and ice-cream mixes were preincubated with a culture of Enterococcus faecium, then subjected to heat treatment in a pilot-scale plate heat exchanger using a hold of 15 s at 76°C. The liquids were examined for γ-glutamyltranspeptidase (GGTP) activity and total streptococcal count before and after heat treatment and the results plotted against water activity (aw). There was a good correlation between reduction in GGTP activity, destruction of streptococci and aw, demonstrating the potential of the enzymic assay for assessing the severity of HTST heat treatments above the minimum for pasteurization.