bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dipeptide utilization by starter streptococci
Authors: Law B. A. 
Published: June 2009

SummaryOf 8 strains ofStreptococcus cremoristested, 5 grew almost as well in defined media in which various essential amino acids were supplied in dipeptides as they did in media containing the equivalent free amino acids. The remainder grew poorly or not at all in the peptide-containing media. Growth of peptide-utilizing strains was inhibited by also including structurally-related dipeptides in the medium, presumably due to competition for uptake by transport system carriers. Both types of starters produced cell-free dipeptidases recoverable from the medium of exponential phase cultures. Addition of the partly-purified extracellular dipeptidases to dipeptidecontaining test media initiated growth in strains unable to use peptides.Str. lactisgrew in defined peptide media, but the further addition of structurally-related dipeptides did not inhibit growth, either bcause each dipeptide was transported by a specific carrier or because peptides were hydrolysed extracellularly. The presence of cell-bound extracellular dipeptidase was indicated by the hydrolysis of dipeptides with washed whole cells in buffer. This was not observed withStr. cremorisstrains.
Detection and quantification of non-milk fat in mixtures of milk and non-milk fats
Authors: Timms Ralph E. 
Published: June 2009

SUMMARYThe triglyceride compositions of 76 Australian milk fats obtained from 3 factories during a whole year were determined by gas-liquid chromatography. It was shown that all the data fitted the equationwith a S.D. of of 0·7088 where C40, C42 and C44 are the weight percentages of triglycerides with carbon numbers 40, 42 and 44. The triglyceride compositions of 10 samples of milk fat from countries other than Australia were also shown to fit the equation. If the equation is assumed to define pure milk fat, it is shown that as little as 5% of any non-milk fats can be detected with > 99% confidence. The amount of non-milk fat in mixtures of milk and non-milk fats can be quantified to better than ±2% with > 95% confidence. Also, the identity of the non-milk fat can usually be deduced by calculation of its triglyceride composition. Analyses of known mixtures and of chocolate and a table spread comprising butter and vegetable oil showed an agreement between observed and expected results well within the predicted confidence limits.
The effect of the chemical structure of additives on the coagulation of casein micelle suspensions by rennet
Authors: Marshall Richard J. , Green Margaret L. 
Published: June 2009

SummaryCasein micelles in milk-salts solution adsorbed charged detergents and highly-charged polypeptides strongly, neutral detergents less strongly and low molecular-weight amines weakly. A tetra-amine was adsorbed more strongly than a tri-amine. The extent of adsorption of proteins tended to rise as the molecular weight increased. Glycerol and lactate were adsorbed to a limited extent but dextran and α-ketoglutarate were not adsorbed at all. Proline was partly adsorbed, indicating that hydrophobic binding sites were available, and caused some disruption of the casein micelles. Additives were bound to approximately the same extent by casein micelles and rennet coagula. The proportions adsorbed were constant over at least 10-fold ranges of concentration. Additives which increased the rennet clotting time (RCT) acted by binding Ca2+. Most additives decreased the RCT, the extent increasing with the amount adsorbed and the positive charge on the additive. The greatest reduction in RCT was observed with those additives which had positively-charged and hydrophobic moieties and bound most strongly to casein micelles. Of the additives tested, only sodium dodecyl sulphate affected the enzymic action of rennet. The reduction in RCT may have resulted from the neutralization of the negative charge of the micelles or enhancement of their hydrophobicity, favouring hydrophobic interactions between the particles.
Influence of storage of milk on casein distribution between the micellar and soluble phases and its relationship to cheese-making parameters
Authors: Ali Ali E. , Andrews Anthony T. , Cheeseman Gordon C. 
Published: June 2009

SummaryThe influence of storage time and temperature on the distribution of individual milk proteins between the micellar and soluble phases has been examined. Storage at 4 or 7 °C is accompanied by a dissociation of micellar caseins, particularly β-casein, into the soluble phase during the first 48 h, but on further storage there is a partial reversal of this process. At higher storage temperatures (10–20 °C) the contents of all the individual caseins in the soluble phase decrease throughout storage. During cheese–making, losses of fat and curd fines in whey were greater with increased soluble phase casein and clotting times were prolonged. Curd structure was weaker, curds were more moist and slightly lower cheese yields were obtained in stored milks with elevated soluble–phase casein. When milks were stored for up to 3 d at 4 °C cheese gradings were virtually unaffected by storage, but higher temperatures (10–15 °C) led to cheeses being downgraded, largely for body and texture defects but also for flavour after 3 d.Attempts to reverse the pattern of casein dissociation and to minimize the detrimental effects of milk storage on subsequent cheese-making showed that a heat treatment of 30 min at 60 °C was the most beneficial.
Effect of atropine on plasma amino acid levels and milk secretion of cows
Authors: Roets Eddy , Peeters Georges 
Published: June 2009

SummarySubcutaneous injections of 30 mg atropine into lactating cows induced a 20–40% decrease of free amino acid (AA) levels in arterial plasma. Minimum levels were observed after 30–50 min. The decline persisted for more than 6 h. The greatest fall in concentration was noted for tyrosine, methionine, lysine, arginine, phenylalanine and threonine. Arterial glucose levels remained unaffected. The effect of atropine on milk secretion was studied in 2 cows which were milked every hour with the aid of oxytocin. Maximal effects were observed after 3–4 h. They included reduction in concentration of casein and ±-lactalbumin (±-la) and a decline in production of milk (20%), casein (35%), ±-la (45%) and lactose (18%). Uptake by the lactating udder over a period of about 1 h after injection of atropine was studied in 2 cows. Mammary blood flow and glucose uptake remained unaffected. There was a positive correlation between arteriovenous differences of essential AA and arterial plasma concentrations. The uptake of essential AA decreased by approximately 50 %. There was no evidence that atropine has a direct inhibiting effect on the udder. It is suggested that the decrease of ±-la synthesis might induce an inhibition of lactose synthesis and milk production.
The pyruvate test for monitoring the bacteriological quality of raw silo tank milk
Authors: Cousins Christina M. , Rodrigues Ubaldina M. , Fulford Rosemary J. 
Published: June 2009

SummarySamples of milk from silo tanks were stored at refrigeration temperatures and examined at intervals for pyruvate content and total colony count. Significant relationships between pyruvate, μg/ml, and log colony forming units (cfu)/ml were established for samples stored at 2°C for 2, 3 and 4 d (3, 4 and 5 d of age respectively) but at 5 and 7°C the relationships after 2-d storage (3 d of age) were not significant. From an overall relationship it was predicted that 4 μg pyruvate/ml would correspond to a bacterial content of 3·7 x 106cfu/ml with 95% confidence limits of 6·6 x 10 cfu/ml. 2·1 x 107cfu/ml.
Mechanism of aggregation of casein micelles in rennet-treated milk
Authors: Green Margaret L. , Morant Steven V. 
Published: June 2009

SummaryThe frequency distribution of aggregates of casein micelles was determined inelectron micrographs of rennet-treated skim-milk. The average degree of aggregation was constant until after 60% of the coagulation time, then increased linearly to 100% of the coagulation time and subsequently rose more slowly. The observations indicated that the rate of aggregation of casein micelles was determined by the random collision of particles, with no preference for the formation or reaction of aggregates of any particular size. The linking together of micelles was not rate-determining.
Factors affecting the ethanol stability of bovine milk
Authors: Horne David S. , Parker Thomas G. 
Published: June 2009

SummaryChanges in the ethanol (EtOH) stability/pH profile of skim-milk induced by forewarming have been investigated as a function of temperature and duration of forewarming and of milk pH prior to heating. Forewarming increased the EtOH stability of a milk in the mid-pH range, shifting the profile laterally to more acid pH values, with little effect being observed on the maximum and minimum EtOH stabilities. No significant changes in forewarming effects were obtained on adding the sulphydryl-blocking agent, N-ethylmaleimide, indicating the lack of involvement of serum protein interactions in the stabilizing effects of forewarming. It is suggested that the observed effects of forewarming are due to a heat-induced precipitation of colloidal calcium phosphate. This suggestion is supported by measurements of Ca2+ levels in forewarmed and untreated skim-milk as a function of pH and is in agreement with the previously suggested mechanism for the EtOH-induced coagulation of skim-milk. The effects of permitted additives (citrate, phosphate and Ca) on the EtOH stability of forewarmed milk paralleled their effect on untreated milk. A comparison is made of the effects of forewarming on the heat and EtOH stabilities of skim-milk.
Casein compositional studies: II. The effect of secretory disturbance on casein composition in freshly drawn and aged bovine milks
Authors: Barry J. Gerard , Donnelly William J. 
Published: June 2009

SummaryWhole casein preparations obtained from paired quarters (one healthy and one subclinically infected) of each of 6 individual cows were fractionated quantitatively by column chromatography on hydroxyapatite. Infection was associated with an apparent decrease in the αs- and β-casein fractions and increase in the γ- and κ-casein fractions. The increase in the κ-casein fraction was attributable mainly to enrichment with chymosin-resistant minor components of casein.The profile produced by column chromatography on DEAE-cellulose of casein isolated from a healthy quarter of a single cow differed significantly from that from a subclinically infected quarter of the same cow. These differences were increased by incubation of the quarter milks at 37 °C for 8 h. Extensive fragmentation of [14C]methylated αs2- and β-casein, and less extensive fragmentation of [14C]methylated αs1-casein, occurred during incubation of these proteins in milk from an infected quarter. Fragmentation was almost entirely inhibited by soybean trypsin inhibitor. From a consideration of the chromatographic behaviour of the radiolabeled fragments on DEAE-cellulose, and other data presented, it was concluded that proteolysis of caseins by a plasmin-like enzyme was sufficient to account, in qualitative terms, for most of the compositional changes exhibited by casein from subclinically infected quarters.
Effect of cheese-making temperatures on the interactions of lactic streptococci and their phages
Authors: Mullan W. Michael A. , Daly Charles , Fox Patrick F. 
Published: June 2009

SummaryThe interactions of 23 bacteriophages on strains of lactic streptococci at 30, 38 and 40 °C were studied in reconstituted skim-milk and broth media. In milk, 3 different temperature mediated responses were observed. Extensive phage replication at 30, 38 and 40 °C with inhibition of acid production by infected cultures was observed for 8 phages; extensive phage replication at 30 and 38 °C, but not at 40 °C, was observed for 4 phages, while 11 phages replicated at 30 °C but not at 38 or 40 °C. Studies in broth media revealed that failure of phage to replicate at 38 and 40 °C was not due to lack of host growth in most cases, but due to a temperature sensitivity on the part of the phage. In one phage–host system, phage replication continued after growth of the host had ceased. The significance of these findings to starter selection for cheese manufacture is discussed.
Effects of dietary supplements of protected lipids on the concentration and transport of β-carotene and cholesterol in bovine blood and milk: unusual chromatographic behaviour of the high-density lipoprotein with high levels of β-carotene
Authors: Ashes John R. , Burley Ralph W. , Davenport James B. , Sidhu Gurcharn S. 
Published: June 2009

SUMMARYThe effects of feeding lipids protected against microbial degradation in the rumen, on the metabolism of β-carotene and cholesterol in the blood and milk of cows were studied. The diets fed to the cows consisted of a basal mixture of crushed oats and lucerne hay with a protected vitamin supplement containing α-tocopheryl acetate and β-carotene fed in conjunction with either (i) protected sunflower oil-seed rich in linoleic acid (PO), (ii) protected tallow (PT), or (iii) formaldehyde-treated casein (C) as a control. Diets PO and PT raised the concentrations of β-carotene and cholesterol in the blood plasma over that observed for diet C. Milk cholesterol concentrations were not affected by dietary supplements, but the level of β-carotene in milk of cows on diet PO showed a tendency to fall compared with milk from cows fed PT or C. The properties of the high density lipoprotein (HDLP) of the blood plasma which contained the β-carotene were affected by the PO diet. As a result of feeding this diet, the fatty-acid composition of the HDLP was altered and it emerged from a gel-filtration chromatographic column earlier than the control. This change in chromatographic behaviour was used as a measure of the effect of the diet, which, for some cows, was apparent long after the diet was changed. It is suggested that the altered lipid composition resulting from the PO diet affected the distribution of particle sizes of the HDLP and might interfere with the transfer of β-carotene from plasma to milk.
Surface properties of milk fat globules: interfacial tension studies
Authors: Phipps Leslie W. , Temple Dilys M. 
Published: June 2009

SUMMARYA method capable of determining the interfacial tension (γ) of individual emulsified liquid drops has been investigated and applied to a study of the surface properties of milk fat globules. Measurements on several organic liquids in bulk against water were made to validate and standardize the technique. With one exception, results agreed well with literature values, but the reproducibility of measurements was not as good as that of other, standard, methods. Measurements performed on small drops were affected by several factors and precision was not high.The influence of different milk treatments upon the interfacial tension of milk fat globules was studied. Agitation of milk had the effect of increasing γ while the effect was reversed upon allowing agitated milk to stand. Dilution of normal milk with water resulted in an increase in γ while acidification and alkalization produced a decrease. Pasteurization of raw milk caused a slight, non-significant decrease. Values of γ were low, 1–2 mN m-1, irrespective of the nature of the milk treatment and were an order of magnitude smaller than those obtained for interfaces of butter oil and milk protein solutions. The results support the concept of a 2-layer membrane and suggest that changes in γ follow mainly the adsorption/desorption of surface active components in the outer hydrophilic layer of the globule membrane. An inner, firmly bound lipophilic layer, resistant to many different milk treatments, appears to determine the overall low γ value under most conditions.
A viscometric study of the flocculation of the components in stored homogenized ultra-heat-treated cream
Authors: Phipps Leslie W. 
Published: June 2009

SUMMARYThe apparent relative viscosity (ηr) of stored homogenized ultra-heat-treated ‘coffee’ cream increased with time (t) at a rate which was a function of mean fat globule diameter (d) and fat volume fraction (ø); the rate was also influenced by Na2CO3and Na citrate when present as stabilizing additives. Viscosity increases were attributed to the progressive flocculation of fat globules and to the strengthening of the structure formed by the gradual accretion of casein micelles on to globule surfaces and their points of contact (bridging). The expressionwheretis in days anddin μm, was found to hold over a 12-week storage period for a batch of creams (ø = 0·143) of differentdvalues prepared from the bulk cream containing carbonate and citrate stabilizers; η0is the relative viscosity att= 0 andkis a rate parameter. In the absence of stabilizers the parameterkassumed a smaller value and so appeared to be a function of chemical composition of the cream and of forces of particle interaction; seasonal factors were also suspected of influencingk. The effect of the fat volume fraction on storage behaviour was not fully resolved, but there was some evidence that the proportionality log ηrα1/ø½ was appropriate.
Effect of milking machine factors on the somatic cell count of milk from cows free of intramammary infection: II. Vacuum level and overmilking
Authors: Olney George R. , Mitchell Robert K. 
Published: June 2009

SummaryThe effect of milking vacuum levels and overmilking on the somatic cell count of milk from cows free of intramammary infections was determined. In the first experiment, 4 levels of vacuum ranging from 35 to 70 kPa were compared in a Latin square design with 20 cows being milked at each of the 4 vacuum treatments for periods of 19 d. In the second experiment 40 cows were milked for 16 weeks at either 50 or 70 kPa with or without 5 min overmilking. Neither vacuum level nor overmilking affected somatic cell count and it is concluded that these factors do not cause stress or irritation that will lead to an increase in somatic cell count in the absence of mastitis infections.
Effect of milking machine factors on the somatic cell count of milk from cows free of intramammary infection: III. Pulsator rate
Authors: Olney George R. , Scott George W. 
Published: June 2009

SummaryThe effect of pulsator rates on the somatic cell count of milk from cows free of intramammary infections was determined. Four pulsator rates ranging from 30 to 120 cycles/min were compared in a Latin square design with 20 cows being milked at each of the 4 pulsator rates for periods of 19 d. Somatic cell count was not affected by any of the pulsator rates and it is concluded that varying pulsator rates will not cause stress or irritation that will lead to an increase in somatic cell count in the absence of mastitis infections.
Thermal stability of an extracellular proteinase fromPseudomonas fluorescensAFT 36
Authors: Stepaniak Leszek , Fox Patrick F. 
Published: June 2009

SummaryA metalloproteinase, isolated from a shaken milk culture ofPseudomonas fluorescensAFT 36 by chromatography in DEAE and CM-cellulose and Sephadex G-150, was very unstable in 0·1 m-phosphate buffer, pH6·6, being completely denatured above 70 °C in 1 min. It was also unstable in a Ca-containing buffer (synthetic milk salts, SMS) between 50 and 60 °C (minimum at 55 °C), but stability was very high above 80 °C in this buffer. D-values were determined at 10 °C intervals in the range 70–150 °C in SMS from which a Z value of 31·9 °C and anEaof 8·82 × 104J mol-1were calculated; the half-life at 150 °C was 9 s.Instability at 55 °C was due to autolysis as evidenced by gel electrophoresis, gel filtration and increase in 2,4,6-trinitrobenzenesulphonic acid-reactive amino groups. The extent of inactivation experienced at 80 °C was inversely related to the rate of heating to 80 °C,i.e.length of time spent in the neighbourhood of 55 °C. Addition of increasing concentrations of caseinate substrate reduced inactivation of the enzyme at 55 °C, presumably due to substrate binding. Attempts to stabilize the enzyme at 55 °C by addition of EDTA or by adjusting the reaction pH to 4·2, at which the enzyme has little proteolytic activity, were unsuccessful, although autolysis was prevented.Unlike the proteinase fromPs. fluorescensMC 60, AFT 36 proteinase did not inactivate itself on cooling to 55 °C from 80, 100 or 150 °C, but did regain autolytic activity on cooling to below 50 °C to an extent dependent on the duration of holding at the lower temperature. It is suggested that on heating to ∼ 55 °C, a conformational change occurs which renders the enzyme susceptible to proteolysis by still active enzyme; at higher temperatures the enzyme, although susceptible to autolysis, is inactive; an active conformation is restored on cooling to below 50 °C.
A method for the quantitative determination of individual free fatty acids in milk by ion exchange resin adsorption and gas-liquid chromatography
Authors: Needs Eric C. , Ford Graeme D. , Owen A. Jane , Tuckley Brian , Anderson Malcolm 
Published: June 2009

SummaryA quantitative method for rapid routine analysis of individual free fatty acids (FFA) in milk was developed. Lipid was extracted from milk in ether and FFA were recovered by shaking the extract with anion exchange resin Amberlyst 26. The resin-bound FFA were methylated directly and the individual acids quantified, using internal standards, by gas-liquid chromatography. The properties of the resin were measured. The validity of the method was established by extraction of FFA mixtures and milk. Individual acids were, on average, found to be within 6% of the actual concentration present in the mixture. An average coefficient of variation of 4·3% was achieved for the major individual fatty acids on repeated extraction of a single milk sample.
Behaviour ofStreptococcus lactisin heat treated (80 °C for 30 min) or sterilized cow's and ewe's milk
Authors: Chavarri Francisco J. , Nuñez Jose A. , Nuñez Manuel 
Published: June 2009

SummaryGeneration times and acid production after 6 and 24 h by 20 strains ofStreptococcus lactisof dairy origin were determined in heat treated (80 °C for 30 min) and sterilized cow's and ewe's milk. Ewe's milk enhanced growth of the streptococci, with significantly (P< 0·001) shorter generation times and higher acid production after 6 h incubation than cow's milk, probably due to its higher vitamin content. The stronger buffer capacity of ewe's milk allowed a higher (P< 0·001) acid production after 24 h than cow's milk. A stimulatory effect of sterilization on generation time and acid production after 24 h was observed in cow's milk. However, the heat treated ewe's milk was shown to be a better substrate than sterilized ewe's milk forStr. lactis.
Use of chemical additives to improve the palatability of low fat milk
Authors: Green Margaret L. , Ridout Elizabeth A. 
Published: June 2009

SummaryMilk with 1·5% fat was treated to increase its viscosity to that of whole milk on the assumption that the sensation produced in the mouth, its mouthfeel, would be improved. Selected treated 1·5% fat milks were assessed for similarity to whole milk in taste panel trials. Panelists were chosen because of their ability to distinguish between whole milk and that containing 1·5 % fat by taste in at least one of two tests. Only 34% of the persons screened were suitable. Throughout the trials, the proportion of panelists able to distinguish between the two milks served alone and in tea remained at about 50%, but rose to 80–90% for the milks in coffee. In general, addition of KOH to 1·5% fat milk to pH 7·4 and of 6 mM-citrate overcame about 75 and 50%, respectively, of the difference in mouthfeel between whole and 1·5% fat milk. Whole and 1·5% fat milks were easily distinguishable visually, but the appearance of the latter was improved by adjustment to pH 7·4.