bluuebunny/crossref_metadata_2025_split huggingface dataset:
The roles of native milk proteinase and its zymogen during proteolysis in normal bovine milk
Authors: de Rham Olivier , Andrews Anthony T. 
Published: June 2009

SUMMARYProteolysis was measured quantitatively in normal bulk milk, either raw, pasteurized or heated (95 °C, 15 min). During incubation at 37 °C for 24 h, about 0·7 mM of peptide bonds were split in raw milk, and 1·8 mM after activation of the zymogen with urokinase. The same values were observed in pasteurized milk, and no significant activity was present in heated milk. When compared with a commercial plasmin preparation, these levels correspond to about 1·4 and 3·6μg/ml of plasmin respectively. Most of this activity was separated in the micellar fraction, and it was suppressed by addition of soyabean trypsin inhibitor (SBTI). The remaining activity in the serum phase was not inhibited by SBTI and gave a rather non-specific breakdown with few well-defined casein fragments being produced. Upon further incubation, after the first 24 h, the activity increased, indicating that activation of the zymogen (plasminogen) occurred spontaneously. The rate of this activation was independent of the addition of more plasminogen and was higher in pasteurized than in raw milk. In pasteurized milk, all the native milk proteinase was in the form of the zymogen at the time of secretion. β-Casein was the preferred substrate for the milk proteinase (plasmin) and produced γ-caseins and proteose-peptone components 5 and 8-fast; other fragments were clearly visible on polyacrylamide gel electrophoresis, and included degradation products of αs1-casein. The formation of all these fragments was enhanced by addition of urokinase alone, or of plasminogen and urokinase, or by increasing the incubation time. They were also produced by incubating the micellar fraction alone, but not the serum fraction. Additional fragments were produced when porcine plasmin was added presumably due to differences in specificity between the porcine and bovine enzymes or to contaminating enzymes. Proteolysis induced by additions of plasminogen alone, or of plasminogen plus urokinase, was closer to that observed for the native milk proteinase, and must be recommended for future work in which it is desired to enhance the level of proteinase without altering breakdown patterns, unless a very pure bovine plasmin is available.
Heat stability of milk: influence of cationic detergents on pH sensitivity
Authors: Shalabi Samweul I. , Fox Patrick F. 
Published: June 2009

SUMMARYThe heat stability–pH profile of milk is shifted to more acidic values by anionic compounds such as SDS, lysolecithin and β-lactoglobulin and to more alkaline values by cationic compounds such as quaternary ammonium compounds. Proline, which reduces the hydrophobicity of proteins, destabilized milk slightly. The results suggest that the heat stability of milk and the shape of the HCT–pH curve may be dependent on micellar charge effects.
Aspects of the formation of lysinoalanine in milk and milk products
Authors: de Koning Petrus J. , van Rooijen Peter J. 
Published: June 2009

SUMMARYTreatment of food proteins with heat and/or alkali may convert some of the constituent amino acids into the unnatural amino acid lysinoalanine (LAL), which has been found to cause kidney damage (nephrocytomegaly) when fed to rats. LAL may be produced by β-elimination of a phosphoseryl, of a glycosylated seryl or of a cystyl residue followed by a nucleophilic addition to a lysyl residue. The formation of LAL in αs0-, αsl- and β-casein is discussed in relation to the location of phosphoseryl residues immediately adjacent to lysyl residues. The influence of pH, temperature and exposure time on the formation of LAL in whole casein is described in detail. The formation of LAL can be prevented by the addition of reducing agents, dephosphorylation or chemical modification of the є-amino group of lysine. The LAL content of foodstuffs can be measured accurately by ion-exchange chromatography and a survey is given of the LAL content of commercial milk and milk products.The biological effects of free and protein-bound LAL are discussed. It seems that renal changes due to the presence of LAL in the diet are species-specific to the rat although recent findings have shown that no effect is observed in rats fed a mixed diet containing proteins with and without protein-bound LAL. When LAL is removed from the diet, nephrocytomegaly disappears. From these results it may be concluded that the health risks for man, connected with the eating of proteins which have been subjected to treatment with heat and/or alkali, are small.The decrease in lysine content of milk and milk products due to formation of LAL is small (0–1 or 2%) in comparison with the decrease in available lysine possibly caused by the Maillard reaction (0–24%) and so the decrease in nutritive value of food products due to LAL formation may be neglected.
Effect of milking machine factors on the somatic cell count of milk from cows free of intramammary infection: I. Vacuum fluctuations
Authors: Olney George R. , Scott George W. , Mitchell Robert K. 
Published: June 2009

SummaryThe effect of vacuum fluctuations during milking on the somatic cell count of milk from cows free of intramammary infections was determined. Four vacuum fluctuation treatments were compared using a Latin square design with 20 cows being milked at each of the 4 treatments for a continuous period of 12 d. The vacuum fluctuations were designed to simulate the depressions in vacuum that occur when applying teatcups during milking. In the most severe treatment the vacuum level fell from 50 to 14 kPa. The somatic cell count was not affected by vacuum fluctuation treatment and it is concluded that vacuum fluctuations will not cause an increase in the somatic cell count of milk in the absence of mastitis infections.
Surface tension of whole and skim-milk between 18 and 135 °C
Authors: Bertsch Antonio J. 
Published: June 2009

SummaryThe surface tension (γ) of whole milk (4% fat) and skim-milk was determined in the temperature range 18–135 °C by the drop number method. Measurements were carried out in a temperature-controlled chamber under pressure. Above 90 °C, the mean residence time of the milk at the test temperature was 15 s. Surface tension values were calculated by the Harkins and Brown method, corrections being made to account for the kinetic energy of the drops. The results for whole and skim-milk were not significantly different and the combined data (66 values) could be represented by the equation:γ =1·8 10-4θ2–0·163θ+55·6,(where γ is in mN. m-1 and θ is the temperature in °C) with a residual s.d. of 2·1 mN. m-1 (mean relative error 9·6 % at the 5 % level of significance).
Effect of homogenization on the heat stability of milk
Authors: Sweetsur A. W. Maurice , Muir D. Donald 
Published: June 2009

SummaryThe effect of homogenization on the heat stability characteristics of milk was examined. The heat stability of homogenized milk, as determined by the time taken for protein clots to form when heated at 140 °C, was reduced with increasing pressure in the range 3·5–34·5 MPa. The heat stability of homogenized milks was greater for samples obtained in the summer months than for those obtained in the winter. The general destabilizing effect of homogenization could be partly offset by 2-stage homogenization (20·7 MPa followed by 3·5 MPa), addition of phosphate stabilizers (0·08% w/v) or homogenization at a high temperature (65 °C). Whilst homogenized and unhomogenized milks reacted similarly to the addition of Ca, phosphate stabilizers, sulphydryl-blocking and oxidizing agents, the effects of season, addition of urea or formaldehyde were different for homogenized milk.
Stimulation of Streptococcus thermophilus growth in mastitic milk
Authors: Marshall Valerie M. , Bramley A. John 
Published: June 2009

SummaryGrowth of Streptococcus thermophilus was faster in mastitic milk, aseptically collected following intramammary infusion of Escherichia coli endotoxin, than in normal aseptically collected milk. The contribution of polymorphonuclear leucocytes (PMN), of plasma and plasmin to this stimulation has been investigated. Addition of plasmin to low cell count milk stimulated growth of the streptococcus to the same degree as mastitic milk. However, addition of plasma or PMN from blood or from milk were less stimulatory. The part played by these components in providing casein breakdown products for the weakly proteolytic Str. thermophilus in mastitic milk is discussed.
Nutrient content of liquid milk
Authors: Scott K. John , Bishop Dinah R. , Zechalko Alicja , Edwards-Webb John D. 
Published: June 2009

SummaryConcentrations were measured of different vitamins in milk as delivered to the home and after storage in the domestic refrigerator, during summer and winter periods. Vitamin C concentrations varied greatly, ranging from 0·1 to 18·4 εg/ml. Most of the lower vitamin C values were associated with known exposure of the milk to daylight and there was a clear tendency for the concentrations to fall with increased time of refrigerated storage especially when associated with prior exposure of the milk to daylight. Riboflavin values were mostly in the range 1·35–1·92εg/ml, but occasional lower values were associated with low content of vitamin C and in some instances with prolonged exposure to daylight on the doorstep. Concentrations of the other vitamins (εg/m1) were: folic acid 0·041–0·074, thiamin 0·38–0·48, vitamin B12 0·0032–0·0044 and vitamin B6 0·56–0·71. All fell within the normal ranges and were not significantly influenced by exposure of the milk to daylight or subsequent storage in the refrigerator.
Studies on micellar calcium phosphate: composition and apparent solubility product in milk over a wide pH range
Authors: Chaplin Lesley C. 
Published: June 2009

SummaryCalcium and phosphate concentrations in milk ultrafiltrate prepared at 37 °C over the pH range 4.0–8.0 have been measured and used to calculate the apparent solubility products for various calcium phosphates in milk. Micellar calcium phosphate had a constant Ca/Pi= 1·58·10·03 at all pH values and a near-invariant ion activity product for CaHP04. Apparent solubility products have also been obtained for brushite, hydroxyapatite and amorphous tricalcium phosphate in milk salt solution over a similar pH range. No evidence was found for a hydroxyapatite or amorphous tricalcium phosphate phase in milk.
Factors affecting the volume of milk delivered by a standard loop in the plate loop method for bacterial count
Authors: King Joseph S. , Mabbit Leonard A. 
Published: June 2009

SummaryOf the various factors influencing the volume transferred by the loop in the automated plate loop technique for enumerating bacteria in milk, the speed of the loop as it emerged from the milk sample was the most important. Increasing this speed from 3 to 6 cm/s resulted in a 23% increase in volume transferred by a standard loop of internal diam. 1·45 mm. The depth of dip was also important, but changes in temperature of the sample from 5 to 20 °C caused no significant change in volume transferred. The results indicate that if the transfer of 1 µl milk is required at speeds commonly used in the automated plate loop technique, the internal diam. of the loop should be reduced from the present standard 1·45 to 1·3 mm.
Assessment of the suitability for Cheddar cheesemaking of purified and commercial chicken pepsin preparations
Authors: Green Margaret L. , Valler Martin J. , Kay John 
Published: June 2009

SummaryCommercial and pure chicken pepsin preparations were compared with rennet as cheesemaking coagulants. From the milk clotting and caseinolytic activities and enzymic stabilities, predictions were made of the relative activities of the chicken pepsins and rennet during cheese ripening. By this means mixtures of chicken and pig pepsins for cheesemaking trials were formulated. These and mixtures of chicken pepsins with rennet were approximately additive in coagulating activity provided they were used immediately. The amounts of chicken pepsins used in laboratory scale Cheddar cheesemaking trials were minimized by acidification and calcification of the milk. The nature of the coagulant did not affect the cheesemaking conditions, yields or cheese composition. Cheeses made with chicken pepsins alone showed faster proteolysis, more intense flavour, off-flavours and bitterness and were softer than those made with rennet. Cheeses made with chicken pepsin/rennet mixtures were intermediate and those made with chicken pepsin/pig pepsin mixtures were similar to those made with rennet. It was concluded that neither of the chicken pepsin preparations was suitable for Cheddar cheesemaking and that the predictive tests had led to correct assessments.
Changes in milk yield and composition at oestrus in dairy cows
Authors: Horrell R. Ian , Macmillan Keith L. , Kilgour Ron , Bremner Kaye 
Published: June 2009

SUMMARYA New Zealand dairy herd of 73 cows was observed at pasture during the breeding season. Individual cow milk yields and composition analyses were obtained before, during and after oestrus. There was an overall reduction in yield at the first, and a rebound enhancement at the second milking after onset of oestrus. Changes in fat content followed the same time course and there was a slight increase in lactose content. Protein and somatic cell content were unaffected. There were considerable individual differences in both the duration and intensity of oestrous behaviour on the one hand, and the extent and timing of the effects on milk production on the other. However no relationship was found between the degree of behavioural excitement shown by a cow in oestrus and its change in milk production.
Preservation of West African soft cheese by chemical treatment
Authors: Aworh Ogugua C. , Egounlety Moutairou 
Published: June 2009

SUMMARYThe effects of sorbic and propionic acids on shelf life and organoleptic characteristics of West African soft cheese stored at 7–9 °C were investigated. In cheeses treated with 0·1% sorbic acid spoilage was delayed and microbial growth, especially mesophilic bacteria, yeasts and moulds, was suppressed compared with untreated controls. Treatment with 0·05% sorbic acid or up to 10% propionic acid was less effective. An objectionable bitter flavour was reported for sorbate-treated cheese but other qualities were not adversely affected.
Effect of stage of lactation on transport of colloidal carbon orStaphylococcus aureusfrom the mammary gland lumen to lymph nodes in guinea pigs
Authors: Schenkman Daniel I. , Berman David T. , Yandell Brian S. 
Published: June 2009

SUMMARYGuinea pig mammary glands which were either lactating, involuting or dry were infused with colloidal carbon or killed staphylococci. At different time intervals following infusion, animals were killed and the superficial inguinal lymph nodes examined for the presence of carbon. Sides which had nodes with visible carbon were designated ‘positive’. The time intervals from infusion to positive for the three groups were compared using logistic regression. The times required for 50 % of the sides to be positive were estimated to be ˜4 h for lactating glands, 32 h for those in involution, and 13 min for dry glands. Histological differences in distribution of carbon in the mammary tissue suggest that differences in transit time may have been due to different mechanisms of transport through the glands in the three different physiological states. The distribution of bacteria was similar to that of the carbon in the corresponding tissues.
Effect of ripening cream with Streptococcus lactis subsp. diacetilactis on the flavour of ghee (clarified butterfat)
Authors: Yadav Jagjit S. , Srinivasan R. Appachar 
Published: June 2009

SUMMARYBovine milk cream (40% fat) was ripened under different time/temperature/inoculum conditions with Streptococcus lactis subsp. diacetilactis DRC-1 before converting by heat treatment into ghee (Indian clarified butterfat). Biochemical changes in cream, in terms of titratable acidity, volatile acids, diacetyl and acetaldehyde and flavour changes in the ghee made from it in terms of free fatty acids (FFA), total carbonyls (TC) and flavour score, were studied. Of the different combinations of ripening conditions, 30 °C, 18 hand 3% inoculum produced optimum changes in the cream which resulted in the development of the most desirable flavour in the ghee, being comparable to that of desi ghee (made by the indigenous method). The flavour characteristics as determined by FFA (% oleic acid), TC (μmol/g fat) and flavour score (out of 10) of the best ripened cream ghee were found to be 0·54, 6·756 and 8·83 respectively. The flavour of ghee became impaired after a particular level of acidity developed in cream after 18 h incubation. The optimum conditions of ripening standardized under laboratory conditions were also extended to a semi-industrial scale.
Effect of milk pretreatment and making conditions on the properties of Cheddar cheese from milk concentrated by ultrafiltration
Authors: Green Margaret L. 
Published: June 2009

SUMMARYCheddar cheeses were made from milks concentrated 3- to 6-fold by ultrafiltration. Modifications to the conventional cheesemaking process were designed to obtain the correct composition and pH value in the final curd, improve the fat and moisture retention and cheese texture, and increase the ripening rate. The compositions of all cheeses were similar to those of controls made with unconcentrated pasteurized milk. The curd and cheese structures and the textural properties of the cheeses were closer to those of the controls when made from milk concentrated 5-fold than when made from milk concentrated 3-fold. Light homogenization of the milk before concentration led to improved fat recovery and decreased graininess and crumbliness in the cheese. Lowering the coagulation temperature of concentrated milks gave improved curd structure and less grainy and more sticky cheeses. Addition of the bacterial proteinase, Neutrase, with the salt, stimulated proteolysis and flavour production in the cheeses and made them more sticky. Neither reduction of the mineral levels in the milk by acidification before concentration nor reduction of the lactose concentration by diafiltration had any significant effect on the composition or textural properties of the cheeses.
Analysis by fast protein liquid chromatography of variants of κ-casein and their relevance to micellar structure and renneting
Authors: Dalgleish Douglas G. 
Published: June 2009

SUMMARYFast protein liquid chromatography was used to study the κ-casein fraction of casein micelles from bulk milk and from milk from individual animals homozygous for κ-caseins A and B. The extent of glycosylation of the κ-casein appeared to have no effect on its distribution in casein micelles of different sizes, nor did it affect the rate at which κ-casein was destroyed during renneting. The rate of breakdown of κ-casein during renneting was also almost independent of micellar size. The results may indicate a difference between methods which analyse for intact κ-casein or for the product macropeptide during renneting.
Determinants of bacterial replication rates in mastitic whey
Authors: Mattila Tuna , Syväjärvi Jouko , Jensen Niels-Einar , Sandholm Markus 
Published: June 2009

SUMMARYBacterial growth was measured by a turbidimetric microtechnique in the whey of milk samples from quarters of cows with subclinical mastitis. Samples were grouped according to bacterial isolates recovered and the effects of bacterial species and whey on bacterial growth rates were analysed. Different strains of bacteria and different whey samples gave highly significant differences in bacterial replication rates. Except for penicillin-resistantStaphylococcus aureus, bacteria grew better in whey from mastitic milk where the inflammation was caused by the same bacterial species than in other mastitic milk samples. Inflammation caused by major pathogens generally enhanced the growth in whey of any type of major pathogen. Since mastitis pathogens showed enhanced growth in whey prepared from the same milk from which they were isolated, specific antibacterial factors in the whey did not appear to restrict bacterial growth in whey. The nutritional quality of the medium seems to be the important determinant of bacterial growth.
Interaction of factors which influence the extent of lipolysis during milking and storage of raw milk
Authors: Needs Eric C. , Anderson Malcolm , Morant Steven V. 
Published: June 2009

SUMMARYThe effect of aeration and agitation during milking on free fatty acid (FFA) levels in raw milk was investigated by comparing (a) a dual vacuum system with a ‘round the barn’ installation and (b) a claw piece requiring high air bleed with conventional claw pieces. Reduced milk transfer pressure resulted in a reduction in lipolysis of 54%, while high air bleed led to a 21% increase. FFA values were related to milk yield, stage of lactation and to a lesser extent the incidence of mastitis. These relationships were largely independent of the type of milking equipment. Fat content and somatic cell count did not affect the level of lipolysis. Increases in FFA due to activation by added blood serum were strongly related to the initial FFA concentrations.
Chemical composition of milk from a herd of Norwegian goats
Authors: Brendehaug Johanne , Abrahamsen Roger K. 
Published: June 2009

SUMMARYThe chemical composition of Norwegian bulk collected goats' milk from the University herd was analysed during one lactation period (30 weeks, 20 samples during 1983). There was considerable variation in chemical composition during the year. Fat content decreased over the first 4 months of lactation and increased during the mountain pasture period. Protein concentration decreased during the first 4 months, and then increased until the end of lactation. Lactose concentration decreased throughout lactation. Casein nitrogen (casein N) was highest at mid lactation and lowest at the beginning and end of lactation. β-Lactoglobulin N showed the opposite trend. Citrate content showed a significantly quadratic decrease and total ash content an increase with advancing lactation. Mutual significant correlations between total P, K, Na, Ca and Mg were calculated, and all increased throughout lactation. There was significant positive correlation between concentrations of individual medium-chain fatty acids and stage of lactation. They remained more or less constant during the first part of the lactation, decreased to minima when the goats were on pasture, and increased during the last phase of lactation. Concentration of C16fatty acid was negatively correlated with C18and C18:1. Goat flavour intensity score and quality flavour score were highest at mid lactation, and positively correlated with the acid degree value.