bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat stability of milk: the mechanism of stabilization by formaldehyde
Authors: Singh Harjinder , Fox Patrick F.
Published: June 2009

The 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

The 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

The 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

Changes 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

The 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

The 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

Fibronectins 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

Several 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

The 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

The 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

Permeation 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

Changes 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

A 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

The 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

Reducing 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

The 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

Effects 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.
A model heat-exchange apparatus for the investigation of fouling of stainless steel surfaces by milk I. Deposit formation at 100 °C
Authors: Foster Carole L. , Britten Michel , Green Margaret L.
Published: June 2009

A model heat-exchange apparatus was used to investigate the factors affecting deposit formation from milk on a stainless steel surface at 100 °C. The structure and composition of the deposits were determined by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and chemical analysis after solution in alkali. The effects of changing the pH, preheating and skimming of the milk were similar to those observed in a small-scale continuous ultra high temperature plant. The time course of deposit formation showed that a lag phase did not occur, but the deposit which formed after more than 45 min was more porous than that formed after shorter times. Most (50–90%) of the fresh deposit was readily removed by sonication, leaving a sublayer richer in minerais than the original. The results provide evidence for the two-layer model for deposit formation proposed by Tissier & Lalande (1986).
Effects of β-lactoglobulin and κ-casein genetic variants and concentrations on syneresis of gels from renneted heated milk
Authors: McLean Douglas M. , Schaar Johan
Published: June 2009

Milk protein genetic polymorphism has a major influence on the composition of milk, and on its processing properties, including yield of cheese (see Schaaret al.1985; McLeanet al.1984, 1987; McLean, 1987). However, there appears to be little information on the effects of milk protein genetic variants on syneresis of cheese curd. The effect of casein composition on syneresis was studied by Pearseet al.(1986), who found that syneresis was affected only by the level of β-casein. Syneresis is an essential requirement in cheese making from renneted or acidified milk, but is undesirable during the storage of products such as yogurt. Milk for yogurt manufacture is preheated to minimize syneresis and to give maximal firmness of the yogurt coagulum (Tamime & Deeth, 1980). Pearseet al.(1985) showed that the reduction of one-third in the extent of syneresis caused by heating artificial micelle milk (AMM) containing βlactoglobulin (β-lg) in natural concentrations was due to sulphydryl-mediated complex formation between β-lg and micellar κ-casein which appeared to interfere with the micelle–micelle interactions responsible for syneresis. The results presented here were part of a study which investigated the effects of κcasein and κ-lg genetic variants and concentrations on syneresis of curd formed from renneted heated AMM.
Effects of chromatographically pure bovine chymosin and pepsin A on cheese curd firmness
Authors: Andrén Anders , von Reedtz Christina
Published: June 2009

The effects of chromatographically pure bovine chymosin and pepsin A on cheese curd firmness have been investigated. The enzymes were studied in parallel experiments, using a Formagraph, under which the following parameters were tested and varied: reconstituted skim milk powder, bulk raw milk, CaCl2 addition, enzyme concentration and temperature. Chymosin had a slightly better rate of curd firming (P ≤ 0·001) and better curd firmness 30 min after gelling point compared to pepsin under all of the conditions investigated. However, as regards curd firmness in cheese manufacture, this difference is only a question of time, since pepsin will give the same degree of curd firmness of the cheesemilk as chymosin after some minutes. The biggest disadvantage with pepsin is its strong pH dependence, which can lead to very long gelling times and weak curd if the pH is too high and the rennet is dominated by pepsin.
Milk yield and mammary function in dairy cows milked four times daily
Authors: Hillerton J. Eric , Knight Christopher H. , Turvey Alan , Wheatley Stephen D. , Wilde Colin J.
Published: June 2009

Groups of lactating cows and heifers were milked four times daily in two diagonally opposed glands for 4 weeks, and the effects on milk yield studied relative to twice-daily milked glands as controls. Mammary enzyme activities, in vitro synthesis rates of milk constituents and histological scoring were determined in mammary biopsy samples obtained at the end of this period. These were used for assessment of mammary function. Frequent milking increased milk yield only in the treated glands, the contralateral control glands continuing to decline in yield at ~ 2%/week. There was no significant difference in response between cows and heifers; the mean increase in yield was 10·4%. The rate of decline in milk yield tended to decrease with frequent milking, to ~ 1%/week. Consequently the yield of the treated glands continued to be elevated above that of the controls for some time after reversion to overall twice daily milking. Milk protein content was increased slightly by frequent milking. Mammary enzyme activities were ~ 18% higher in the treated glands than in the controls. Synthesis rates of lactose, casein and total protein were unaffected by milking frequency, but were all lower in the gland selected for the second biopsy, reflecting the reduction in milk yield caused by the first biopsy. DNA synthesis was increased by milking frequency, as were the size and number of epithelial cells in histological sections.
Effect of methionyl bovine somatotropin in a prolonged-release vehicle on milk production, hormone profiles and health in dairy cows
Authors: Škarda Josef , Markalous Evžen , Slaba Josef , Krejčí Petr , Škardová Olga , Zedník Jiří
Published: June 2009

Milk production of dairy cows in 14 herds was increased by 3·8–32·1% by the administration of recombinant methionyl bovine somatotropin (bST) in a sustained-release vehicle at 14 d intervals at 40–94 d post partum. A greater response in multiparous than in primiparous cows was found in cows turned out to graze spring pasture. Administration of recombinant bST resulted in elevated plasma bST during the first 9 d after injection. Clinical characteristics such as respiration, heart rate and body temperature were unaffected by bST treatment, as were blood erythrocyte and leucocyte counts, haemoglobin concentrations and haematocrit values. Plasma levels of glucose, free fatty acids, urea and P, and serum alanine aminotransferase and aspartate aminotransferase were not affected by bST treatment, and acetone was not detected. No adverse effects of bST on general health, infection status of mammary glands, mastitis incidence and reproduction were found.
High-fat spreadable processed cheese for people with high blood cholesterol
Authors: Abou-Zeid Nadia A.
Published: June 2009

Part of the raw cheese base used for manufacturing high-fat processed cheese spread Was replaced by cows' (C) or buffalo (B) butter residue at levels of up to 20%. These residues were produced during the conversion of butter to butter oil by traditional moderate (T) or severe (M) heat treatments. The hypocholesterolaemic properties of butter residues incorporated into processed cheese were tested with rats (serum and liver cholesterol) and human beings (serum cholesterol). When rats were given the control cheese with no butter residue there were significant increases in both serum and liver cholesterol compared with rats given stock diet. However, when part of the raw cheese base was replaced by butter residue these rises were reduced by amounts proportional to the level of butter residue. The hypocholesterolaemic properties of the residues were in order CT > BT, CM > BM, and incorporations of 10% CT, 15% BT, 15% CM and 20% BM were found to nullify the hypercholesterolaemic effects of control cheese and restore cholesterol levels to their normal values. A small human trial gave similar results. Incorporation of butter residue slightly affected the chemical composition of the cheeses. Fat content and pH were little different; however, cheeses with butter residue tended to have higher total protein but lower soluble protein, tyrosine and tryptophan, and total volatile fatty acids. Rheological properties were not altered significantly. Incorporation of butter residue improved the organoleptic properties, particularly flavour intensity. Storage at 5 °C for 2 months did not alter the organoleptic properties and changes in chemical composition followed the normal pattern.
Comparative study of the separation of casein from bovine, ovine and caprine milks using HPLC
Authors: Kaminarides Stelios E. , Anifantakis Emmanuel M.
Published: June 2009

The separation of cows', sheep's and goats' milk casein components by HPLC on a strong anion-exchange (P.L-SAX 8μ 1000A) column is described. During HLPC, whole caseins of the three kinds of milk behaved differently from conventional separations. The casein components of the three kinds of milk were well resolved under the Chromatographie conditions used. HPLC resolved the κ-caseins better than did ion-exchange chromatography on DEAE cellulose, and was particularly efficient in the case of goats' milk. Goats' and sheep's milks had almost similar Chromatographie profiles but these differed considerably from that of cows' milk. Caseins from the sheep and the goat were also similar in that a shallower NaCl gradient was required for the separation of casein components than for cows' milk.
Evaluation of khoa as a milk solids source in ice cream
Authors: Shakeel-Ur-Rehman  , Upadhyay Kunjbihari G. , Pandya Ajit J.
Published: June 2009

The performance of khoa, a local heat-concentrated milk product, as a milk solids source in ice cream was tested by replacing 250, 500, 750 and 1000 g/kg of the condensed whole milk in control ice cream. Proximate composition was little affected by the inclusion of khoa at any level tested. At levels of inclusion > 250 g/kg the viscosity of both fresh and aged experimental mixes was significantly (P < 0·05) increased compared with controls. Some mixes containing khoa appeared slightly off-white, but there were no overall differences from control. Control and experimental mixes were identical in whipping capacity and overrun. In organoleptic evaluation, the colour score of the ice creams declined significantly (P < 0·05) when 750 or 1000 g/kg of the condensed milk was replaced with khoa. Ice creams containing khoa were equivalent or superior to controls in flavour. In objective tests, the experimental ice creams showed significantly (P < 0·05) faster meltdown compared with control, but no differences were found in subjective assessments. We conclude that khoa can be used successfully as a milk solids source for ice cream without any serious adverse effects on quality, the only problem being the dull colour.
Triacylglycerol fatty acid composition of milk from periparturient cows during acute Escherichia coli mastitis
Authors: Massart-Leën Anne-Marie , Burvenich Christian , Massart D. Luc
Published: June 2009

Changes in fat concentration and triacylglycerol fatty acid (TGFA) composition were studied in milk from six periparturient cows 1 d before and 20 d after an experimentally induced Escherichia coli mastitis in the fore and rear homolateral quarters. Opposite fore and rear heterolateral quarters remained uninfected and were used as controls. Milk was collected from all individual quarters during the experiment. The fat concentration in milk from infected quarters did not change, but total fat production decreased owing to reduced milk production after the Esch. coli challenge. In milk from the heterolateral uninfected quarters fat concentration rose significantly 48 and 72 h after induction of mastitis, the rise being concomitant with a decrease in milk production. Throughout the experiment similar changes in TGFA composition were observed for both infected and uninfected quarters. There was an increase in all the even, odd-numbered, iso and anteiso short-chain TGFA from day +6 on after induction of mastitis. There was little change in the composition of 16:0 and 18:0 fatty acids, while the long-chain unsaturated fatty acids decreased. Using multivariate analysis, the results are presented visually. The observed changes in the TGFA can be ascribed to changes normally observed in cows' milk soon after parturition.
Heat stability of homogenized milk: role of interfacial protein
Authors: McCrae Catharina H. , Hirst David , Law Andrew J. R. , Muir D. Donald
Published: June 2009

The role of interfacial protein in determining the heat stability of recombined milk was investigated by removing serum protein prior to homogenization and reincorporating it after homogenization. In addition, the surface protein composition of recombined fat globules was probed by analyses of protein load and by quantification of the individual surface protein components using FPLC. In the absence of serum protein, substantially more casein was bound to the fat surface during homogenization. Despite this, the detrimental effect of homogenization on heat stability did not occur when serum protein had been removed from the system. Reincorporation of serum protein after homogenization caused the heat coagulation time–pH profile to revert to a form very similar to that observed without removing serum protein from the system. Thus, adsorption of serum protein did not affect heat stability. It is more likely that heat-induced interactions of serum protein with surface-adsorbed casein promoted heat coagulation. Fat surface area rather than casein load affected these interfacial protein-protein interactions during heating.
Use of California Mastitis Test,N-acetyl-β-glucosaminidase, and antitrypsin to diagnose caprine subclinical mastitis
Authors: Maisi Päivi , Riipinen Inna
Published: June 2009

Analysis of 448 milk samples (11 herds) from caprine udder halves showed that microorganisms were isolated from 21·8% of the samples. California Mastitis Test (GMT) andN-acetyl-β-glucosaminidase (NAGase) were superior to antitrypsin in detecting subclinical infections. Coagulase-negative staphylococci and micrococci were the main species isolated from halves showing no clinical disease. Coagulase-positive staphylococcal infections were associated with a significant increase of all inflammatory parameters. Significantly increased CMT and NAGase occurred when streptococci, other staphylococci or micrococci were present. Infection within one half was reflected as an increase in the inflammatory parameters in the milk of the infected half as well as a slight increase in the inflammation parameters in the adjoining half.
Rapid separation of bovine caseins by mass ion exchange chromatography
Authors: Ng-Kwai-Hang K. F. , Pélissier J. P.
Published: June 2009

The rapid isolation of major bovine caseins in gram quantities was investigated. Whole casein was precipitated from individual cow's milk by adjusting the pH to 4·6 and the precipitated casein was suspended in 4·5 M urea (pH 8·0) containing 0·02 M imidazole and 0·03 M β-mercaptoethanol, and bound on a QAE Zeta Prep 250 cartridge. Stepwise elution with the urea/imidazole β-mercaptoethanol buffer and varying amounts of NaCl gave five well resolved peaks, which were identified by polyacrylamide gel electrophoresis and fast protein liquid chromatography to be pure γ-casein, κ-casein. β-casein, β-casein and αs-casein, respectively. The ion exchange cartridge was regenerated by flushing with buffer containing 0·50 Μ-NaCl followed by equilibration with starting buffer before separation of next sample. The time required to run each sample including cartridge regeneration and equilibration was 4 hours.
Characteristics of the autolysis of variants ofLactococcus lactissubsp.cremoris
Authors: Niskasaari Kaarina
Published: June 2009

Two slime-forming strains (T5and MLS96) and a non-slime-forming strain (HA)of Lactococcus lactissubsp.cremoriswere investigated for autolysis and optimal conditions for the autolytic process were developed. The rate of autolysis was maximal in exponential phase cells in 0·01 M-Na phosphate buffer, pH 6·5–7·5, at 30–45 °C. Autolysis of the native exponential phase walls was activated by trypsin and inhibited by lipoteichoic acid and cardiolipin. Decreased trypsin activation was found in intact exponential phase cells and no activation in stationary phase cells.N-acetylmuramylhydrolase action in the autolytic system ofLc. lactissubsp.cremorisstrains was indicated by the progressive release of reducing groups. No amidase or endopeptidase action was found. Great variation in the rate of autolysis of whole cells was observed between the two slime-forming strains. Intact cells of strain T5exhibited decreased autolytic activity, but a higher rate of autolysis of isolated exponential phase walls. Autolysins from strain T5walls exhibited lower hydrolytic activity against sodium dodecyl sulphate-treated walls of the other two strains as compared with strains MLS96 and HA. Quantitative analysis revealed higher protein and phosphorus and lower hexosamine and rhamnose in cell wall preparations of strain T5compared with the other two strains. Results suggest that the decreased rate of autolysis of strain T5cells may at least in part be caused by cell surface components other than cell-wall peptidoglycan. It is proposed that the difference in autolytic characteristics should be used as a criterion when selecting starter strains of lactococci (streptococci).
Formation of galactose during heat treatment of milk and model systems
Authors: Calvo Marta M. , Olano Agustin
Published: June 2009

The formation of galactose, lactulose and epilactose during heating of milk was studied. The concentration of these carbohydrates increased with pH and the severity of heat treatment. The presence of proteins reduced the amount of lactulose formed whereas it increased that of epilactose and galactose. The galactose in heated milks was derived from lactose degradation. Under the conditions studied, degradation of the Amadori rearrangement product did not result in the formation of galactose. The interaction between proteins and galactose increased the thermal stability of the monosaccharide.
Intracellular proteinase ofLactococcus lactissubsp.lactisNCDO 763
Authors: Muset Graciela , Monnet Véronique , Gripon Jean-Claude
Published: June 2009

An intracellular proteinase was purified fromLactococcus lactissubsp.lactisNCDO 763 after spheroplast formation from cell wall proteinase-deficient variants. The proteinase was active at pH 7·5 and 45 °C and affected by metalloenzyme inhibitors. Its specificity, determined on B-chain of insulin, was thermolysin-like. The B-chain of insulin was hydrolysed rapidly while hydrolysis of β-casein was slower. This enzyme has aMrof ∽ 93000.
Ovine lactoferrin: isolation from colostrum and characterization
Authors: Buchta Richard
Published: June 2009

Highly purified lactoferrin was isolated from ovine colostrum by sequential purification on CM-Sephadex C-50 and Blue-Sepharose, with overall yield of 55%. The ovine lactoferrin was characterized by SDS-PAGE, its amino acid composition and N-terminal sequence to residue 30. Homology with bovine and human lactoferrins was greater than 80 and 50% respectively. Antibodies to ovine lactoferrin were raised in rabbits and used to develop an enzyme-linked immuno-sorbent assay (ELISA). The antiserum was not cross reactive with other colostrum proteins.
In vitroproteolysis and functional properties of reductively alkylated β-casein derivatives
Authors: Chobert Jean-Marc , Touati Abdelmadjid , Bertrand-Harb Catherine , Dalgalarrondo Michele , Nicolas Marie-Georgette , Haertle Tomasz
Published: June 2009

β-Casein amino groups were modified with aldehydes and dialdehydes via reductive alkylation at pH 8·0. The degree of alkylation was controlled by the amount of the alkylating reagent applied. The initial rates of α-chymotrypsin-catalysed hydrolysis of alkylated β-casein were inversely related to the size of the modifying group. Proteolysis of modified β-casein with trypsin (18 h) or with α-chymotrypsin (48 h) depended on the nature and size of the substituent applied. The measurements of tryptophan fluorescence indicate that the modifications also induced conformation change. Solubilities of methyl-, ethyl- or benzyl-β-casein slightly increased; solubilities of β-casein dialdehyde derivatives were significantly lower than that of native β-casein. Emulsion stability of methyl- or ethyl- β-casein was higher than that of native β-casein in the acidic pH range. After modification with glyoxal, the emulsifying activity and the emulsion stability of β-casein decreased. The emulsifying activity of benzyl- β-casein was lower than that of native β-casein. Phthalylated β-casein displayed the poorest emulsion stability.
Size distribution and average size parameters of casein micelles determined by electron microscopy in bovine milk between pH 5·5 and 6·7. A comparison of several evaluation methods
Authors: Vreeman Henk J. , van Markwijk Bas W. , Both Paula
Published: June 2009

The conversion of the two-dimensional size distribution of casein micelles, observed by electron microscopy in a plane section, to the three dimensional distribution is discussed and the average size parameters evaluated by several methods are compared. It is shown that parameters containing the −1 moment of the two-dimensional distribution, i.e. Dn, the number of micelles per unit volume and the width of the size distribution, are sometimes uncertain. The occurrence of negative numbers in some of the classes of the distribution is discussed and remedies are suggested. Sections were made by freeze-fracturing skim milk samples; the pH of the milk was between 5·5 and 6·7.
Antioxidant activity of casein and Maillard reaction products from casein-sugar mixtures
Authors: McGookin Barry J. , Augustin Mary-Ann
Published: June 2009

The antioxidant activity of casein and Maillard reaction products obtained by reaction of casein with glucose or lactose was studied. Antioxidant activity was evaluated in a model System containing methyl linoleate with haemoglobin as a pro-oxidant. Casein was antioxidative and heating casein in the presence of glucose or lactose resulted in enhancement of antioxidant activity. The development of antioxidant activity in reacted casein–sugar mixtures was determined as a function of initial casein and sugar concentration. The observed antioxidant activity of reacted casein–sugar mixtures was due to casein itself and Maillard reaction products resulting from reacting casein with sugar.
Effect of recombinant chymosin on ewes' milk coagulation and Manchego cheese characteristics
Authors: Nuñez Manuel , Medina Margarita , Gaya Pilar , Guillen Ana M. , Rodríguez-Marín M. Asunción
Published: June 2009

Ewes' milk coagulation was significantly influenced by the type of rennet when recombinant chymosin produced by Kluyveromyces lactis was compared with two commercial calf rennets with declared chymosin contents of 55 and 70%. Recombinant chymosin and calf rennet with 70% chymosin exhibited similar thrombelastographic characteristics, and coagulated milk more rapidly than calf rennet with 55% chymosin. The type of rennet had no effect on Manchego cheese dry matter, pH or recovery of dry matter in cheese. N soluble at pH 4·6 was the only N fraction influenced by the type of rennet, with slightly higher levels for cheese made with recombinant chymosin or with calf rennet containing 70% chymosin than for that made with rennet containing 55% chymosin. No significant differences in rheological or sensory characteristics between Manchego cheese made with recombinant chymosin and that made with the calf rennets were detected.
Effects of some calcium-chelating agents on the physical properties of acid-set milk gels
Authors: Johnston Donald E. , Murphy Robert J.
Published: June 2009

Acid-set milk gels containing up to 30 mM added hexametaphosphate, oxalate, citrate, EDTA or orthophosphate were prepared using gluconic acid-δ-lactone and their properties investigated. Increases in the apparent shear modulus were observed in the gels containing hexametaphosphate, oxalate, citrate and EDTA. The effect was maximum for hexametaphosphate-containing gels at ˜ 8 mM. Increases were also observed in the force required to break the gels, and for added hexametaphosphate the effect peaked at ˜ 5 niM. The ability of the gels to resist syneresis was investigated by a cut, tip and drain type test and by a centrifugation method. In both tests, resistance to syneresis was increased by added hexametaphosphate, oxalate, citrate and EDTA. The additions of anions were shown to cause disintegration of the micelles and release caseins to the serum. It is suggested that the improved homogeneity of casein distribution that results allows greater opportunity for protein-protein interaction during gel formation and leads to improved properties. Controlled micelle disintegration would therefore appear to offer promise for the development of improved or novel products.
Adherence of psychrotrophic bacteria to dairy equipment surfaces
Authors: Suárez Beatriz , Ferreirós Carlos M. , Criado Maria-Teresa
Published: June 2009

Psychrotrophic bacteria isolated from raw milk were tested for their ability to adhere to steel, two types of rubber, and glass, materials employed in the construction of milking equipment. The adherence assays were carried out by exposure of the materials to radioactively labelled bacteria in both a buffering solution (Ringer's) and milk. The degree of adherence of Gram-positive bacteria was lower (P< 0·001) than that of Gram-negative bacteria. Glass was the material least prone to bacterial adherence (P< 0·001); there were no significant differences between the other three materials. Milk was found to inhibit adhesion significantly (P< 0·05), this inhibition being more evident with the most adherent bacteria. There was no statistically significant correlation between bacterial surface hydrophobicity and adherence. Our results suggest that intrinsic bacterial adherence cannot be considered a relevant factor in the contamination of milking equipment.
Comparison between the EC plate count test at 21 °C and an accelerated plate count method for assessing the keeping quality of pasteurized milk
Authors: Langford Sarah A. , Kroll Rohan G.
Published: June 2009

The keeping quality of properly refrigerated pasteurized milk and cream is primarily determined by post-pasteurization contamination by Gram-negative psychrotrophic bacteria (Phillips et al. 1981; Schröder et al. 1982). Reliable and rapid methods of assessing the levels of contamination by these organisms are therefore of commercial interest.
Simple empirical and fundamental methods to determine objectively the stretchability of Mozzarella cheese
Authors: Apostolopoulos Christos
Published: June 2009

The ability of Mozzarella cheese to stretch and form long fibres was evaluated by two simple instrumental tests. The first test, which was basically a tensile test, resembled the way the consumer assesses the stretchability of cheese as a pizza topping. The extensibility measurements of the test correlated well with the sensory stringiness scores. The second, fundamental test was a compressive elongation of the melted cheese. The elongational viscosity of the melted cheese was calculated; this could be used as an index of the ability of the cheese to form strings when it is stretched.