bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth of an extracellular proteinase-deficient strain of Pseudomonas fluorescens on milk and milk proteins
Authors: Torrie Joan P. , Cholette Hilaire , Froehlich Debbi A. , McKellar Robin C. 
Published: June 2009

SummaryAn extracellular proteinase-and lipase-deficient mutant of a psychrotroph, Pseudomonas fluorescens strain 32A, has been isolated and the absence of the proteinase enzyme confirmed by growth on differential media, enzyme assay and polyacrylamide gel electrophoresis. Competition between the parent and the mutant was observed when equal numbers of the 2 strains were inoculated together into raw skim-milk at 6 °C. Bitterness was detected at 6 °C in pasteurized skim-milk inoculated with the parent cells concurrent with the detection of proteolytic activity. In the case of the mutant, slight bitterness which did not increase with increasing cell numbers was detected in the absence of proteolysis. Mutant cells failed to grow on Na caseinate as the sole source of carbon. It was concluded that the extracellular proteinase, while not essential for growth in milk, does provide a selective advantage to the producer organism. This enzyme is, however, essential for growth on milk proteins and contributes to the development of bitterness in pasteurized milk.
Purification and characterization of porcine κ-casein
Authors: Cerning-Beroard Jutta , Zevaco Claude 
Published: June 2009

Summaryκ-casein from porcine milk was isolated and purified by affinity chromatography on thiopropyl Sepharose followed by hydroxyapatite chromatography. The amino acid composition of this protein is similar to that of bovine κ-casein. The sugar composition was established and sow κ-casein was found to be highly glycosylated. It contains 12 N-acetylneuraminic acid, 10 N-acetylgalactosamine, 2 N-acetylglucosamine and 22 galactose residues.
An automatic method for measuring the heat coagulation time of milk powder solutions
Authors: Foissy Helmut , Kneifel Wolfgang 
Published: June 2009

SummaryAn apparatus for the objective determination of the heat coagulation time of milk powder solutions is described. In the apparatus a chromium plated iron piston is moved by means of a ring magnet, driven by a control mechanism, through a heated cylinder containing a small sample of milk. When the milk coagulates, the increased impedance between the inner wall of the cylinder and the metal piston overcomes the magnetic strength of the ring magnet and the magnetic coil moves away from the piston core, resulting in a momentary change in coil current, which after amplification is used to stop a digital clock. The method was tested with 10 and 20 % milk powder solutions at various pH values, at temperatures of 120 and 140 °C. The results are comparable with those obtained using a traditional method involving visual determination of coagulation (Davies & White, 1966).
Heat stability of milk: the mechanism of stabilization by formaldehyde
Authors: Singh Harjinder , Fox Patrick F. 
Published: June 2009

SUMMARYThe increase produced by formaldehyde (HCHO) in the heat stability of milk did not occur when milk was treated with HCHO at temperatures up to 60°C followed by dialysis at 5°C. However, the minimum in the heat coagulation time (HCT)–pH curve was irreversibly removed if the milk was preheated at 80–C for 10 min in the presence of 5 mM-HCHO. Although this treatment blocked the ε-amino groups of lysyl residues, the stabilizing mechanism is considered to be due to the cross linking action of HCHO which reduced the level of non-sedimentable, κ-casein-rich protein dissociated from the micelles on heating. The specific crosslinking agent, dimethyl suberimidate, modified the HCT-pH profile of milk in a manner similar to preheating at 80°C for 10 min with 5 mM-HCHO, supporting the crosslinking hypothesis. The results of this study appear to lend some support to the proposal of Kudo (1980) that the minimum in the HCT-pH curve of milk is due to the dissociation of κ-casein from the micelles on heating at high temperatures at pH values greater than 6η7.
Inhibition by chelating agents of the formation of active extracellular proteinase byPseudomonas fluorescens32A
Authors: Mckeller Robin C. , Cholette Hilaire 
Published: June 2009

SUMMARYThe effect of chelating agents on extracellular proteinase production byPseudomonas fluorescens32A was examined. Increasing concentrations of orthophosphate slightly stimulated growth while inhibiting proteinase synthesis. Fifty percent inhibition was found at 35 and 28 mM-orthophosphate at 5 and 20 °C respectively. Extracellular protein concentration was reduced by 30% when cells were grown with 100 mM-orthophosphate. Polyacrylamide gel electrophoresis of the cell-free supernatants suggested that reduced enzyme synthesis had taken place as evidenced by the decrease in staining intensity of the protein band corresponding to the proteinase. Other phosphate compounds could replace orthophosphate as an inhibitor. Extent of inhibition was related to chain length; polyphosphates with 4–6 or 13–18 phosphorus atoms were the most effective inhibitors. EDTA (0·5 mM) completely inhibited proteinase synthesis. This inhibition could be partly reversed by Ca2+and, to a lesser extent, Mn2+. Proteinase production at 5 °C in skim milk was completely inhibited by phosphate glass (P13–P18). Control experiments showed that loss of activity with chelators was not due to inhibition of preformed enzyme. The results suggest a possible role for polyphosphates in controlling proteinase production in stored milk.
Partial purification and some properties of øC2(W) lysin, a lytic enzyme produced by phage-infected cells ofStreptococcus lactisC2
Authors: Mullan W. Michael A. , Crawford Robert J. M. 
Published: June 2009

SUMMARYThe lytic enzyme present in øC2(W) lysates was isolated by means of ion-exchange chromatography and further purified by gel filtration and ultrafiltration. The phage enzyme had an apparent pH optimum of 6·5–6·9 and was rapidly inactivated at temperatures > 47°C. The apparent temperature optimum was 37°C and Q10and Eavalues over the range 22–32°C were 2·5 and 69·2 kJ/mol respectively. Monovalent and divalent cations activated the enzyme. Reduced -SH groups on the enzyme were required for lytic activity. Gel filtration revealed a mol. wt of ˜ 46000. Strain-dependent differences in sensitivity of group N lactic streptococci to lysin were found. Group D streptococci were also lysed. Strains of three species ofLeuconostoc, two species ofLactobacillus, one strain ofEscherichia coliand ofMicrococcus lysodeikticuswere apparently resistant. Analysis of cell wall degradation products gave results which were consistent with the lysin having the specificity of an N-acetylmuramidase.
Mammary uptake of amino acids and glucose throughout lactation in Friesland sheep
Authors: Fleet Ivan R. , Mepham T. Ben 
Published: June 2009

SUMMARYChanges in mammary blood flow, arterial and venous plasma concentrations of glucose and individual amino acids, udder volume, and milk yield and composition were measured at intervals throughout lactation in four Friesland ewes. Milk yields peaked 50–80 d post partum and declined by 40% within 3 months. Neither mammary blood flow (43·3 ± 5·8 (s.e.m.) ml/100 cm3, min) nor udder volume changed significantly throughout the period of study, but for three ewes the ‘mammary blood flow:milk yield’ ratio increased from 300 (peak yield) to 570 (late lactation). Mammary glucose uptake remained essentially constant throughout lactation despite a 50% decline in lactose output. Arterial concentrations of glucose were much lower at peak yield than in late lactation. Mammary amino acid uptake conformed quite closely to ‘essential’ and ‘non essential’ categories previously defined for goats and cows, the degree of balance with output in milk protein being similar at all stages of lactation. For several amino acids arterial concentrations and arteriovenous differences were significantly positively correlated: the changes in arterial concentrations with lactation stage were also correlated for some amino acids. Apart from the intrinsic value of such studies on a breed of ewe increasingly used for dairy purposes, the Friesland ewe appears well suited for use in quantitative metabolic studies on lactation.
Plasmin activity and proteose-peptone content of individual milks
Authors: Schaar Johan 
Published: June 2009

SUMMARYThe variation in plasmin activity and proteose-peptone (PP) content in milks from 81 cows of four breeds was statistically analysed. Plasmin activity increased with parity and stage of lactation and differed between breeds, but the breed effect was removed when adjustment was made for differences in milk casein content. The negative correlation found between plasmin activity and casein content seemed to be expressed only under assay conditions and was thus probably an artefact. The linear regressions of proteose-peptones in fresh (PP) and cold-stored milks (ΔPP) on plasmin activity were highly significant (P< 0·001). However, the variation in plasmin activity explained only 38 and 33%, respectively, of the variation in PP and ΔPP. At apparent zero plasmin activity, PP and ΔPP were significantly different from zero (P< 0·001) and the intercepts represented 77 and 46%, respectively, of the averages. PP and ΔPP were significantly higher in milks containing the BB genotype of ²-lactoglobulin than in milks with the AA genotype.
Effects of genetic variants of κ-casein and β-lactoglobulin on cheesemaking
Authors: Schaar Johan , Hansson Bo , Pettersson Hans-Erik 
Published: June 2009

SUMMARYThe effects of κ-casein and β-lactoglobulin (β-lg) genetic variants on cheesemaking were examined in two laboratory scale experiments. Variants of κ-casein had highly significant (P < 0·001) effects on milk citrate content (A > B) and rennet clotting time (A > B). When curds were cut at constant firmness there were only minor effects of κ-casein variants on milk component recoveries and cheese yield and composition. A tendency to higher fat recoveries from milks containing κ-casein B was reflected in significantly (P < 0·05) higher fat contents in cheese after 3·5 months of ripening. Genetic variants of βlg had highly significant (P < 0·001) effects on casein number (B > AB > A) and protein recoveries (B > AB > A) and significant (P < 0·05) effects on yield of cheese dry matter (B > AB > A). Green (unripened) cheeses made from the different milks also differed in fat, protein and moisture contents, probably in part due to differences in fat/casein ratios of the cheesemilks. The compositional differences were reflected in differences in the extent of proteolysis during ripening (A > AB > B). In the experiment with β-lg genetic variants the effect of time of cold storage of the cheesemilk was also investigated. No differences were found in milk composition and component recoveries or cheese yield, composition and quality when milks were cold-stored for 24, 48 or 120 h before cheesemaking.
Purification and characterization of bovine milk fibronectin
Authors: Sato Thomas N. , Hayashi Masao 
Published: June 2009

SUMMARYFibronectins were isolated from both bovine colostrum and fresh milk, and they were found to be very similar to plasma fibronectin. The concentration of fibronectin in milk decreased post partum: 30 µg/ml after 0 d and 2 µg/ml after 7–851 d. No fibronectin could be detected in any brands of ultra heat treated liquid milk on the market (≤0·006 µg/ml).
Relationship between ethanol stability of bovine milk and natural variations in milk composition
Authors: Donnelly William J. , Horne David S. 
Published: June 2009

SUMMARYSeveral ionic components of ultrafiltrate were measured in bulk and individual cow milks and an assessment was made of their relationship with the parameters of the corresponding ethanol (EtOH) stability/pH profiles. From linear regression analysis the strongest relationships (P < 0·001) were between soluble salt balance [expressed as (Ca+Mg) minus (Pi+Cit) or as the ratio to (Pi+Cit)] and pK (correlation coefficient, γ ∼ 0·82) or Smax, the maximum stability at high pH (γ ∼–0·72), and between Pi and pK(γ = –0·84)or Smax (γ = –0·61). These relationships agree with the view that the parameters of the EtOH stability/pH profile are determined by pH-induced changes in concentration of divalent cations. Natural variations in these parameters may be attributed to variations in relative concentrations of divalent cations and their chelators. EtOH stabilities at the natural pH of bulk milks from winter/spring- and autumn-calving animals were lowest in early and late lactation. The most important contributory factors appeared to be a high salt balance ratio in late lactation and a low natural milk pH in early lactation. The main component responsible for variable salt balance ratio was usually soluble Pi. Decrease in EtOH stability at the natural pH of late lactation milks reflected a more general change in the characteristics of the EtOH stability/pH profile, seen as an increase in pK and, in extreme cases, a decrease in Smax and profile gradient.
Physicochemical properties of proteinases from selected psychrotrophic bacteria
Authors: Mitchell Gregory E. , Ewings Ken N. , Bartley John P. 
Published: June 2009

SUMMARYThe physicochemical properties of eight extracellular proteinases secreted by psychrotrophic bacteria of dairy origin have been studied. Seven of these proteinases were able to withstand ultra heat treatment (UHT) with D values at 140 °C ranging from 2 to 300 s. The sixPseudomonas fluorescensproteinases were glycoproteins of mol. wt 47000–49500. The twoSerratia marcescensproteinases, of mol. wt of 51000, did not contain carbohydrate but in other respects were similar to the Pseudomonas proteinases. The proteinases were inhibited by various metal chelators and all contained Ca and Zn in similar proportions. Their amino acid compositions were similar, with alanine as the N-terminal group, cysteine completely absent and very low levels of methionine. Isoelectric points ranged from 5·10 to 8·25. Their physical and chemical properties enabled them to be classified as alkaline metalloendopeptidases. A similarity index (S▵n) was used to predict sequence homology between ten proteinases of known amino acid composition. Comparisons of S▵n of these proteinases showed only minor sequence differences except for those ofPs. fluorescensMC60. Heat resistance could not be related wholly to similarities in protein sequence, but could be related both to the strength of stabilizing Ca2+–protein interactions and to the randomness inherent within the folding of the peptide chain.
The bovine teat canal: information from measurement of velocity of milk flow from the teat
Authors: Williams David M. , Mein Graeme A. 
Published: June 2009

SUMMARYThe velocity of milk flow from the teat during the peak flow rate period of milking was estimated to be ∼ 8·5 m/s with a liner vacuum of 50 kPa and 7·5 m/s at 40 kPa. These results confirm the applicability of the Bernoulli theorem for estimating velocity of milk flow through the teat canal during milking. Concurrent measurements of mass flow rate and velocity indicate that the effective diameter of the open teat canal is ∼ 2 mm. Further calculations indicate that the shear force due to milk flow acting to debride the surface of the open teat canal is about 1·8 × 10-2 N. The opposing surfaces of the ‘closed’ teat canal may be ∼ 100 µm apart immediately after milking. If so, bacteria present in the milk residue within the teat canal would never be more than 50 µm from a surface.
Optimization of porous glass chromatography for size-fractionation of bovine casein micelles
Authors: McNeill Gerald P. , Donnelly William J. 
Published: June 2009

SummaryPermeation chromatography on porous glass was carried out with skim milk at 20 or 30 °C using CPG-10 (50 nm) or a dual column system of CPG-10 (50 nm) followed by CPG-10 (300 nm). On columns of CPG-10 (50 nm) casein micelles were eluted at the void volume and were rapidly and efficiently resolved from non-micellar protein without micelle dissociation. The dual column system resulted in the additional resolution of the micelles into different size ranges. Examination of the resolved micelle fractions by electron microscopy showed a gradual decrease of weight average diameter (Dw) from 228·4 nm in the void volume fraction to 86·3 nm in the smallest micelle fraction. The translucent upper layer of a micelle sediment obtained by ultracentrifugation of skim milk at 30 °C consisted of casein aggregates intermediate in size between monomeric protein and the bulk micelle fraction as shown by its elution behaviour on CPG-10 (50 nm). These aggregates were enriched more than 2-fold with κ-casein relative to skim milk, were devoid of αs2-casein and had an estimated value of Dw of 33 nm. The ultracentrifugate serum contained ∼ 2·5% of total milk casein which had the elution characteristics of monomeric protein on CPG-10 (50 nm). It was concluded that the translucent sediment consisted of the smallest micelle fraction of skim milk and represented the minimum size range for casein polymerization in the natural milk environment. Overall, the results show that porous glass chromatography is an effective and convenient tool for the isolation and study of casein micelles.
Effect of elevated ripening temperatures on the microflora of Cheddar cheese
Authors: Cromie Susan J. , Giles Janet E. , Dulley John R. 
Published: June 2009

SummaryChanges in the composition of the microflora in Cheddar cheese ripened at elevated temperatures were examined. Cheeses were stored under the following ripening conditions: (i) control, 8°C for 32 weeks; (ii) 15°C, (iii) 17·5°C or (iv) 20°C, all for 8 weeks, then followed by 8°C for 24 weeks; (v) 15°C, (vi) 17·5°C or (vii) 20°C, all for 32 weeks. Generally, the total bacteria, lactic acid bacteria, lactobacilli and ‘undesirable lactobacilli’ (producing off flavours and CO2) counts in cheeses stored above 8°C were higher than in the control cheese. This effect seemed to be dependent on continued storage at the elevated temperature. Streptococcal counts rose slightly during ripening at elevated temperatures and fell slightly during ripening at the control temperature. Numbers of non-lactic acid bacteria were unaffected by elevated storage temperatures. In the only treatments where off flavours developed (17·5°C for 32 weeks, 20°C for 16 weeks or more) there was no apparent relationship between any bacterial group and the off flavours.
Purification and characterization of a cell wall proteinase fromStreptococcus lactisNCDO 763
Authors: Monnet Véronique , Le Bars Dominique , Gripon Jean-Claude 
Published: June 2009

SummaryA proteinase was purified from a cell wall extract of a culture ofStreptococcus lactisNCDO 763 grown in skim milk. Being active at a low pH (at pH 4·8 on haemoglobin and pH 6·–6·5 on casein) and completely inhibited by diisopropylfluorophosphate, it was considered to be a serine proteinase partly inhibited by EDTA; the mol. wt was ∼ 80000.
Closing forces of the bovine teat canal
Authors: Williams David M. , Mein Graeme A. 
Published: June 2009

SummaryThe magnitude of the forces causing closure of the bovine teat canal was estimated by measuring the pressure required to cause retrograde flow of milk into the canal from a manometer attached to the external teat orifice. Before milking, the hydrostatic pressure required to cause retrograde flow was 12 kPa or greater. Retrograde flow occurred at a pressure of 4–6 kPa once the teat canal surface had been wetted. This 2- or 3-fold fall in the closing forces presumably resulted from the combined effects of fracturing the teat canal epithelium and loss of initial resting tension in the smooth muscle fibres surrounding the teat canal. After milking, retrograde flow into any teat canal occurred at a pressure ∼ 1 kPa lower than the wetted, pre-milking value. This small drop, and subsequent recovery ∼ 30 min after milking, reflects the change in tonicity of the smooth muscle fibres which are stretched during milking. At hydrostatic pressures below 7–9 kPa, retrograde flow could be arrested momentarily by the occurrence of a teat contraction. At 4–7 kPa, the wave of contraction was also capable of expelling 4–14 μl milk from the teat canal indicating the outwardly directed, peristaltic nature of the phasic muscular activity.
Heat stability of milk: influence of colloidal and soluble salts and protein modification on the pH-dependent dissociation of micellar κ-casein
Authors: Singh Harjinder , Fox Patrick F. 
Published: June 2009

SummaryReducing the colloidal calcium phosphate (CCP) content of milk by 40% or increasing it by 20% did not significantly affect the heat-induced pH-dependent dissociation of micellar κ-casein. However, changes in soluble Ca and phosphate affected the dissociation of κ-casein markedly; decreasing the phosphate concentration or increasing the Ca concentration reduced the formation of non-sedimentable N (NSN) and non-sedimentable 12% TCA-insolubleN-acetyl-neuraminic acid (NANA). Dialysis of milk against water for short periods (∼ 5 h) reduced the formation of both NSN and non-sedimentable 12% TCA-insoluble NANA, as did NaCl at concentrations above 0·05 M. Modification of protein amino groups by succinylation promoted the release of κ-casein while amidation of carboxyl groups had the opposite effect. It appears that the pH-dependent dissociation of κ-casein produced on heating milk above 90°C is controlled by electrostatic interactions. The effects of soluble ions such as Ca2+or Na+appear to be due to shielding of such negatively-charged groups as seryl phosphate and carboxyl on the protein, thus reducing the release of κ-casein.
Effect of hydraulic milking on milking performance, teat condition and lipolysis
Authors: Grindal Robert J. , Griffin Tony K. 
Published: June 2009

SummaryThe term ‘hydraulic milking’ describes a new milking concept in which liner movement is restricted and the liner is flooded with milk beneath the teat. This condition, achieved with a multi-valve claw without air admission to the cluster, reduced milking time by 26% and increased milk flow rate by 20%. Four experiments describe the discovery of hydraulic milking and investigate its potential using equal or different levels of vacuum in the milkline and pulseline. Benefits from hydraulic milking include decreased lipolysis (≤36%) and milk foam (75%), improved teat condition and a high degree of protection against machine-induced infections. Evidence of increased milk yield is inconclusive. Cluster removal is impeded by hydraulic milking and the multi-valve cluster requires modification to facilitate the process. Pulsation characteristics and vacuum levels developed for conventional milking appear adequate for hydraulic milking. Unorthodox vacuum conditions may be needed, however, to exploit fully this novel milking concept.
Solubilization of spray-dried lactalbumin by Alcalase
Authors: Smith Craig G. , Munro Peter A. , Otter Donald E. , Brauer Ralph M. 
Published: June 2009

SummaryEffects of the reaction variables pH, temperature, time, enzyme concentration and solids concentration on the hydrolysis and solubilization of lactalbumin slurries by Alcalase have been determined. Reaction progress curves, solubilization v. time, were very unusual with a maximum solubilization of 96% occurring at a short reaction time corresponding to a degree of hydrolysis of 11–12%. Further hydrolysis beyond this point produced a rapid decrease in solubilization to about 67%, followed by a further gradual increase in solubilization with prolonged hydrolysis. The unusual solubilization profile was also produced by increasing enzyme concentration at fixed reaction time. The effects of pH, temperature and solids concentration were similar to those found in the hydrolysis and solubilization of other insoluble proteins. The implications of the results for the design and operation of an enzymic hydrolysis process are discussed.