bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimizing clarified whey ultrafiltration: influence of pH
Authors: Daufin Georges , Labbe Jean-Pierre , Quemerais Auguste , Michel Françoise , Merin Uzi 
Published: June 2009

SummaryWhey clarification can be achieved by using a lipid aggregation step followed by microfiltration. The results from using an M5 Carbosep membrane to ultrafilter defatted sweet whey at pH values in the range 8·0–1·5 furnished understanding of the fouling process so that fouling may be minimized. The conventional method of aggregation, allowing the pH to decrease naturally, has been compared with a modified aggregation process in which the pH was maintained constant. These two methods differed significantly in their influence on the subsequent ultrafiltration (UF), with respect to the UF hydraulic characteristics, i.e. reversible, irreversible and overall fouling resistance. Optimal UF performance was obtained at a pH equal to or slightly higher than the aggregation pH (7·5) owing to the limited fouling contribution of proteins and calcium phosphates. The modified process permitted UF at fluxes in the range 50–115 1 h-1 m-2, with moderate transraembrane pressure, even with a protein content two to five times higher than that of regular whey.
Effect of heat treatments on the incorporation of milk serum proteins into the fat globule membrane of homogenized milk
Authors: Sharma Shri K. , Dalgleish Douglas G. 
Published: June 2009

SummaryThe incorporation of serum proteins into the synthetic fat globule membrane in milks that had been heated and subsequently homogenized has been quantitatively determined using electrophoresis and densitometry. The results indicated that the amounts of serum proteins present in the fat globule membrane were smaller in milk that was heated before homogenization than in milk that had been homogenized and then heated. The thickness of the adsorbed layer of protein on the surfaces of the fat particles, measured using photon correlation spectroscopy in dissociating and non-dissociating buffer solutions, was also lower in the former case (∼ 20 nm) compared with the latter (∼ 34 nm). The kinetics of adsorption of both β–lactoglobulin and α-lactalbumin in heated homogenized milk on the vacant ‘sites’ on the synthetic fat globule membrane followed similar trends at 75 and 90 °C.
Detection of powerful odorants in heated milk by use of extract dilution sniffing analysis
Authors: Moid Luigi , Etievant Patrick , Langlois Dominique , Dekimpe Jocelyne , Addeo Francesco 
Published: June 2009

SummaryThe odour impact compounds of raw, pasteurized and UHT bovine milk were investigated using vacuum extraction and extract dilution sniffing analysis using CharmAnalysis™. Fifteen odour peaks with Charm values between 10 and 3443 were detected. Of these peaks, twelve were identified as hexanal, ethyl butanoate, 2-heptanone, heptanal, dimethyl sulphone, l-octen-3-ol, ethyl hexanoate, 2-nonanone, nonanal, benzothiazole, 2-undecanone, indole and one as a mixture of 2-tridecanone and δ-decalactone. Dimethyl sulphone, indole and one unknown compound (retention index 1154) were the only ones detected as odour impact compounds in all three types of milk. Ethyl butanoate and ethyl hexanoate were found as powerful odorants only in raw milk. A further predominant odorant for this milk was dimethyl sulphone, which was the most important odorant in pasteurized milk. 2-Hexanone and 2-nonanone were identified as the most intense volatile flavour compounds of UHT milk. The powerful odorants described can be used as indicators of the aroma quality of heated milk.
Detection of proteolysis in raw milk stored at low temperature by an inhibition ELISA
Authors: Picard Catherine , Plard Isabelle , Rongdaux-Gaida Dominique , Collin Jean-Claude 
Published: June 2009

SummaryAn inhibition ELISA (enzyme-linked immunosorbent assay) was developed for the determination of caseinomacropeptide (CMP) in order to estimate the proteolysis of κ-casein due to the enzymes of psychrotrophic bacteria in bulk raw milk. The CMP present in milk was quantified specifically by an antibody. The limit of detection was ∽ 0·1 μg/ml and the CV was < 10%. This method was used to study the proteolytic activity of three strains of psychrotrophic Pseudomonas fluorescens in raw milk and to analyse different raw milk samples supplied by four dairy plants. The proteolytic activity for different strains of psychrotrophs and for different milk samples varied considerably, but no correlation was established between the level of microbial flora and κ-casein proteolysis. It is thus not possible to determine the extent of proteolysis from the bacterial count alone. However, by CMP determination in bulk raw milk samples after 6 d storage at 4°C, the mean κ-casein proteolysis was ∽ 4%. Among the milk samples analysed that contained < 107 cfu psychrotrophs/ml, 30% exhibited a proteolysis of κ-casein < 0·5%, i.e. < 5μg CMP/ml.
Microfiltration performance: physicochemical aspects of whey pretreatment
Authors: Gesan Genevieve , Daufin Georges , Merin Uzi , Labbe Jean-Pierre , Quemerais Auguste 
Published: June 2009

SUMMARYClarification of whey by microfiltration (MF) can be achieved after appropriate pretreatment of the feed. A control pretreatment consists of a physicochemical process comprising increased ionic calcium and pH accompanied by heat (50 °C, 15 min) to cause aggregation of complex lipid–calcium phosphate particles, which are then separated by MF. This pretreatment process was modified by increasing the temperature to 55 °C and by maintaining the pH constant during heat treatment. This modification resulted in larger calcium phosphate particles and a lower content of soluble calcium and phosphate ions. As a consequence, a longer period of MF operation, better whey clarification and lower calcium and phosphate content of the filtrate were achieved. This suggests that a loosely structured deposit was formed on the membrane surface which was less resistant to filtration than that resulting from the control pretreatment. During MF, it was necessary to avoid zones of high shear in the retentate compartment that might cause physical alteration of the aggregates.
Changes in casein composition of goats' milk during the course of lactation: physiological inferences and technological implications
Authors: Brown Joanna R. , Law Andrew J. R. , Knight Christopher H. 
Published: June 2009

SummaryFive British Saanen goats were milk sampled during the first 39 weeks of lactation to determine changes in casein composition. Caseins were separated by anion- and cation-exchange FPLC to determine the relative amounts of the individual caseins. Acid, alkaline and SDS-PAGE were used to determine possible genetic polymorphisms and observe any lactational changes. Total casein nitrogen was determined using a micro-Kjeldahl method and this allowed the concentrations of individual caseins to be calculated. The milk of one animal, which had the deduced genotype αs1-CnAB, showed higher concentrations of both total and αs1-casein. The remainder of the group were either heterozygous αs1-CnBE or, more probably, homozygous αs1-CnE and produced milk of a generally lower protein concentration. Both FPLC and PAGE results showed that the relative amounts and concentrations of αs2-casein decreased with stage of lactation, consistent with its susceptibility to proteolysis. The relative amounts of the breakdown products of plasmin attack on β-casein, γ-caseins, were highly negatively correlated with milk yield (r = –0·942, P < 0·001) in the declining phase of lactation, reflecting the gradual involution of the gland at this time. The relative amount of κ-casein increased by ∼ 50% after peak lactation and its concentration almost doubled near the end of lactation. These compositional changes may alter the processing qualities of goats' milk in relation to cheese production.
Water-holding capacity and characterization of protein interactions in processed cheese
Authors: Marchesseau Sylvie , Cuq Jean-Louis 
Published: June 2009

SummaryIn order to predict the oozing susceptibility of heat-induced milk protein gels such as processed cheeses during storage, ultracentrifugation forces are required to accelerate the expulsion of water from the gel structure. Two predictive methods have been tested. Direct ultracentrifugation of processed cheese was used to study effects of centrifugal compression on the water-holding ability. The water release with optimal parameters (time, temperature and ultracentrifugation force) from a freshly manufactured processed cheese was correlated with visual assessment of oozing after 6 months storage. A second method was based on the susceptibility of gelled proteins to resist the dissociating action of solutions of chemical agents such as SDS, urea, EDTA and 2-mercaptoethanol. Most of the protein sedimented by ultracentrifugation in the presence of SDS represented that still in complexed form. This correlated with optimal water binding by the processed cheese. Response-surface methods, used to optimize the ultracentrifugation variables and the composition of the dissociation solutions, showed that the dissociation test was best with a dispersion of processed cheese in SDS solution (10 g/l) at a ratio of 1:6 (w/v) at 20°C, ultracentrifuged at 86000 g and 20°C for 25 min. Analysis of processed cheese cooked at 115°C and then dissociated in different solutions showed various protein–protein interactions in the gel network, whereas hydrophobic interactions were the most important stabilizers of the protein matrix of cheese cooked at higher temperature.
Interruption of machine milking in dairy cows: effects on intramammary pressure and milking characteristics
Authors: Pfeilsticker Hans-Ulrich , Bruckmaier Rupert M. , Blum Jürg W. 
Published: June 2009

SUMMARYExperiments were designed to test the hypothesis that milk ejection rate decreases during milking, thereby causing insufficient refill of the cistern and decreasing milk flow rate towards the end of milking. In a first series of experiments machine milking of the left front quarters of 11 cows was interrupted for 2 min after removal of 25, 50 or 75% of expected total milk yield, while milking was continued in the other three quarters. Milk flow was recorded during machine-on times. Intramammary pressure (IMP) was recorded during premilking teat stimulation and during interruption of milking. IMP during interruption of milking decreased with decreasing amounts of milk remaining in the udder. The IMP did not change during these interruptions when they occurred after 25 and 50% of expected total milk yield was removed. Thus, the ejection rate could keep up with the milk flow or removal rate. However, IMP increased during interruption of milking following removal of 75% of total yield, although significantly so only in cows with a high milk flow rate. Obviously, more milk was removed than was transported to the cisternal cavity. It is likely that a reduced ejection rate caused the decreased milk flow rate. In a second series of experiments the pulsation ratio of the milking machine was changed from the usual 70:30 to 50:50 with the aim of reducing the milk flow rate and thus adapting to the ejection rate at the end of milking. The changed pulsation ratio caused a reduced peak flow rate and a prolonged high milk flow period, whereas the main flow rate did not change significantly.
Water-soluble peptides in Cheddar cheese: isolation and identification of peptides in the diafiltration retentate of the water-soluble fraction
Authors: Singh Tanoj K. , Fox Patrick F. , Healy Áine 
Published: June 2009

SUMMARYThe water-soluble extract of Cheddar cheese was fractionated by diafiltration using 10 kDa cut-off membranes. Peptides were isolated from the diafiltrate retentate by chromatography on DEAE-cellulose with a linear NaCl gradient in 50 mM-Tris-HCl, pH 8·6, and reversed-phase HPLC or electroblotting from urea-PAGE gels. Peptides were identified by determining N-terminal amino acid sequences and mass spectrometry. Most (45) of the total 51 peptides identified in the diafiltrate retentate originated from β-casein, especially from a short region in the N-terminal half of the molecule. Only six peptides originated from αs1-casein; β-lactoglobulin was also identified in the retentate. The origin of most of these peptides could be explained on the basis of known specificities of lactococcal cell envelope proteinases.
Evidence for an interaction between cationic and neutral amino acids at the blood-facing aspect of the lactating rat mammary epithelium
Authors: Calvert D. T. , Shennan D. B. 
Published: June 2009

SummaryThe transport of lysine by perfused lactating rat mammary tissue has been examined using a rapid, paired-tracer dilution technique. This experimental approach allowed the characteristics of lysine transport across the blood-facing aspect of the mammary epithelium to be studied. The clearance of lysine from the perfusate was influenced by the extracellular lysine concentration in a fashion consistent with the presence of carrier-mediated transport. Replacing extracellular Na+withN-methyl-D-glucamine had no significant effect on lysine transport. Lysine uptake was inhibited by extracellular leucine and glutamine but not by α-(methylamino)isobutyric acid. Leucine interacted with lysine transport under Na+-free conditions. It appears that the system for cationic acid transport which is situated in the blood-facing aspect of the lactating rat mammary epithelium may also accept neutral amino acids as substrates.
Immunomodulatory activities of whey fractions in efferent prefemoral lymph of sheep
Authors: Wong Chun W. , Regester Geoffrey O. , Francis Geoffrey L. , Watson Dennis L. 
Published: June 2009

SummaryStudies on the immunomodulatory activities of ruminant milk and colostral whey fractions were undertaken. By comparing with boiled colostral whey in a preliminary experiment, a putative heat-labile immunostimulatory factor for antibody responses was found to be present in ovine colostral whey. Studies were then undertaken in sheep in which the efferent prefemoral lymphatic ducts were cannulated bilaterally, and immune responses in the node were measured following subcutaneous injection in the flank fold of whey protein preparations of various purities. A significant sustained decline of efferent lymphocyte output was observed following injection with autologous crude milk whey or colostral whey preparations, but no changes were observed in interferon-gamma levels in lymph plasma. Two bovine milk whey fractions (lactoperoxidase and lactoferrin) of high purity were compared in bilaterally cannulated sheep. A transient decline over the first 6 h was seen in the efferent lymphocyte output and lymph flow rate after injection of both fractions. A significant difference was seen between the two fractions in interferongamma levels in lymph at 6 h after injection. However, no significant changes in the proportion of the various efferent lymphocyte phenotypes were seen following either treatment. Whereas both fractions showed a significant inhibitory effect in a dose-dependent manner on the proliferative response of T lymphocytes, but not B lymphocytes, to mitogenic stimulationin vitro, no similar changes were seen followingin vivostimulation with these two fractions.
Screening and characterization of fungal cultures for a milk-clotting enzyme for use in an oriental style dairy product
Authors: Lin Chin-Wen , Chen Hsiao-Ling 
Published: June 2009

SummaryThe aim of this work was to develop new oriental style dairy products coagulated with culture filtrates from lao-chao, a traditional fermented rice product. The fermenting fungal cultures screened wereRhizopus javanicus, Rhiz. oryzae, Rhiz. chinensis, Rhiz. oligosporus, Aspergillus oryzae, Mucor racemosusand chiu-yao, a commercial starter. All the inocula liquefied a steamed glutinous rice base and produced culture filtrates with both milk-clotting and proteolytic activities. Of the fungal products tested,Rhiz. javanicuswas the most successful, producing a good yield of culture filtrate with the desired milk-clotting activity, and the resultant yogurt-like product was more acceptable to consumers than any except that from chiu-yao. The firmness was less acceptable, but this could be improved by using mixed pure cultures ofRhiz. javanicusandM. racemosus.
Tocopherols, retinol, β-carotene and fatty acids in fat globule membrane and fat globule core in cows' milk
Authors: Jensen Søren Krogh , Nielsen Kirsten Nyholm 
Published: June 2009

SummaryMilk fat globule membranes (MFGM) were isolated from milk from cows injected intraperitoneally with dl-α-tocopherol acetate. The fatty acid composition and content, and the contents of tocopherols, retinol and β-carotene were determined and compared with the composition and content in the original cream sample. Intraperitoneal injection of 10 g dl-α-tocopherol acetate elevated the α-tocopherol content in the milk fat from 13–30 to 50–70 εg α-tocopherol/g milk fat 2–3 d after injection. The increase depended on the α-tocopherol status of the cow prior to injection. The concentrations of retinol and β-carotene in the milk fat were unchanged after the α-tocopherol injections. MFGM fatty acids made up 18–27 g/kg total fatty acids in the milk fat. However, the proportions of monounsaturated and polyunsaturated fatty acids were higher in MFGM than in total milk fat, while the proportion of saturated fatty acids was lower in MFGM (P < 0·001). Thus, the longchain polyunsaturated fatty acids in MFGM constituted ∼ 40–70 g/kg total milk fat. α-Tocopherol was the only fat-soluble vitamin detected in MFGM; γ-tocopherol, retinol and β-carotene were detected only in the cream. A significant relationship between α-tocopherol contents in cream and MFGM was found: (α-tocopherol in MFGM fatty acids) =–1652 × (1/ln(α-tocopherol in cream fatty acids)3)+ 97 (r = 0·857, P < 0·001) when the contents of α-tocopherol were expressed as εg/g fatty acid. According to this equation the upper limit for incorporation of α-tocopherol into MFGM is 97±5 εg/g MFGM fatty acids. Thus, under normal farming conditions the α-tocopherol content will be highest in MFGM. However, in cream with an α-tocopherol concentration < 15 εg/g cream fatty acids the concentration in MFGM will be lower and furthermore will decrease rapidly. The possible importance of this relationship in relation to the oxidation of milk fat is discussed.
Breakdown of caseins by proteinases in bovine milks with high somatic cell counts arising from mastitis or infusion with bacterial endotoxin
Authors: Andrews Anthony T. 
Published: June 2009

SummaryMilk obtained from cows which were either infected by clinical mastitis or had been subjected to intramammary infusion of Escherichia coli endotoxin possessed high counts of somatic cells and very high levels of proteinase activity which hydrolysed the caseins almost completely in a few hours at 37 °C. The rate of hydrolysis of β-casein was slightly greater than that of αs1-casein, but in both cases hydrolysis was enhanced by 6 cycles of freezing and thawing to disrupt somatic cell membranes. A study of the relationship between proteinase activity and cell count suggested that only some of the proteinase activity originated in the somatic cells and also that the identity of the cells making up the total cellular population was important. Maximum proteolysis occurred at 50–60 °C, but the temperature-activity curve was a broad peak. Likewise the pH versus activity plot was very broad and was almost flat over the pH range 6–9. Experiments with a number of inhibitors of proteinases failed to give a clear cut pattern of inhibition. All evidence obtained was consistent with the view that several different enzymes with different pH and temperature optima and different specificities contributed to the overall hydrolysis of caseins in these milks. From electrophoretic band patterns one of these enzymes was clearly plasmin, but in high cell count milks other proteinases also became significant.
Casein compositional studies. III. Changes in Irish milk for manufacturing and role of milk proteinase
Authors: Donnelly William J. , Barry J. Gerard 
Published: June 2009

SUMMARYThe composition of casein in Irish milk for manufacturing was examined throughout the year. Large changes in composition were observed in the final quarter of the year as a result of the influence of late lactation when the proportion of αs- and β-caseins declined and the proportion of κ- and γ-caseins and of minor casein components increased. Similar changes in casein composition were induced by treatment of milk with porcine plasmin. The activity of plasmin-like milk proteinase in milk was quantified from the rate of conversion of added [14C]β-casein to [14C]γ-caseins. This activity was considerably higher in a late lactation milk than in a mid lactation milk and was ∼ 20 times higher at 37 °C than at 4 °C. It was concluded that casein compositional changes in late lactation were largely the result of proteolysis of individual caseins by plasmin-like milk proteinase.
Effect of fermentation sugar on hydrogen peroxide accumulation byStreptococcus lactisC10
Authors: Grufferty Roger C. , Condon Seamus 
Published: June 2009

SUMMARYHydrogen peroxide accumulated in aerated cultures ofStreptococcus lactisC10, the amount depending on the sugar being utilized. When the energy source was galactose or (to a lesser extent) lactose or maltose, H2O2reached autoinhibitory levels. With glucose, H2O2reached levels which did not cause obvious inhibition, and then declined. Washed cell suspensions utilized several media ingredients including glucose, galactose and yeast extract as substrates for O2uptake, but cell-free extracts utilized none of these. The only substrate which supported O2uptake by cell-free extracts was NADH. The activity of NADH oxidase was not affected by several intermediates of carbohydrate metabolism. Evidence was obtained to show that its synthesis was regulated via induction by O2with an overriding catabolite repression type control, when cells were grown at the expense of glucose.
Molecular weights of subunit components of bovine casein micelles
Authors: Ono Tomotada , Takagi Toshio 
Published: June 2009

SummaryUsing either Sephacryl S-300 or TSK-G4000SW gel chromatography, the larger of the two major components of bovine casein micelles (F2) was eluted at the same retention time irrespective of sample concentration and column temperature. Its mol. wt was estimated to be 500K by examination of the eluate from a TSK-gel G4000SW column using a low-angle laser light-scattering photometer and a precision differential refractometer. With the second component (F3), retention time in Sephacryl gel chromatography was significantly affected by both sample concentra-tion and volume applied. Limiting retention times for F3 could be obtained by extrapolation of these two parameters to higher and lower values, and corresponded to those of water-soluble protein with mol. wt 200K and 100K respectively. Approach to sedimentation equilibrium technique at the above limiting sample concentrations gave values of F3 consistent with the above molecular weight. Sephacryl gel chromatography at either low sample concentration or low column temperature resulted in a new component being eluted at a position of mol. wt 25K