bluuebunny/crossref_metadata_2025 huggingface dataset:
Lipolysis and the distribution of lipase activity in bovine milk in relation to stage of lactation and time of milking
Authors: Ahrné Lennart , Björck Lennart
Published: June 2009

The increase in levels of free fatty acids (FFA) in morning and afternoon milk after 48 h cold storage at 5 °C was determined at two stages of lactation in milk from 96 cows. Lipolysis was positively correlated to day of lactation (r= 0·6,P< 0·001), while the correlations between lipolysis and milk yield and fat content respectively were due to these factors being related to day of lactation. In afternoon milk the level of FFA increased almost three times above that in morning milk. Lipolysis was closely related to the lipoprotein lipase (LPL) activity associated with the cream fraction (r= 0·8,P< 0·001). Afternoon milk had higher LPL activity in the cream fraction than morning milk. Lipase activity in the cream increased with increasing stage of lactation. Cooling of milk increased LPL activity associated with the fat phase. This effect was greater in afternoon milk from late lactation than in morning milk from early lactation. When heparin was added to milk the LPL activity associated with the fat increased substantially; again, this effect was greater in afternoon milk from late lactation than in morning milk from early lactation. Lipolysis was higher in heparinized milk than in normal milk, and there was a close correlation between lipolysis and LPL activity associated with the fat (r= 0·82,P< 0·001). Characteristics of the milk fat globule influencing the attraction of LPL were found to be fundamentally important to lipolysis.
Role of oxygen radicals in the bacteriostatic effect of whey and production of bacterial growth by free radical scavengers
Authors: Mattila Tiina
Published: June 2009

The involvement of toxic oxygen intermediates in the bacteriostatic effect of milk was determined by producing bacterial growth curves using turbidimetry in the presence and absence of oxygen radical-scavenging substances. Using whey as substrate, catalase, haemoglobin combined with ascorbic acid and xanthine oxidase inhibitors all provided protection against oxygen toxicity for a strain ofStaphylococcus aureusand ofStreptococcus agalactiae. Superoxide dismutase and mannitol were less effective. This was evident in whey alone and in the presence of oxygen radicals produced exogenously by the t-butylhydroperoxide, H2O2and xanthine/xanthine oxidase systems.
Comparison of the structure of micellar calcium phosphate in milk from six species by extended X-ray absorption fine structure spectroscopy
Authors: Irlam James C. , Holt Carl , Hasnainj S. Samar , Hukins David W. L.
Published: June 2009

Extended X-ray absorption fine structure spectra, above the Ca K absorption edge, were recorded from lyophilized casein micelles obtained from the milk of cow, pig, goat, rabbit and rat. A spectrum was also obtained from the calcium phosphate prepared from the casein micelles of human milk. Comparison of these spectra showed that the short-range environment of calcium in the micellar calcium phosphate was the same in all six species. Furthermore, these spectra closely resembled that of brushite (CaHP04. 2H20). However, X-ray diffraction showed no evidence for an extensive crystal lattice in micellar calcium phosphate.
Products of the heat-promoted reaction between urea and the protein fraction of bovine milk
Authors: Manson William , Carolan Thomas , Annan W. Douglas
Published: June 2009

Enzymic digests of samples of heated skimmed milk were found to contain small amounts of S-carbamyl-L-cysteine. This material was concluded to have arisen from reaction of a cysteinyl residue in βlactoglobulin (β-lg) with cyanate derived from the native urea of bovine milk. After heating at 75 or 90 °C for 20 min skimmed milk contained 0·009 and 0·029 μmol/ml respectively of protein-bound S-carbamyl-cysteine. Evaporated milk contained 0·058 μmol/ml. The S-carbamylcysteine contents of samples of β-lg heated under similar conditions in equimolar 0·17 mM-KCNO at pH 6·6 were 0·016 and 0·062 μmol/ml respectively. At 60 °C no formation of S-carbamyl-cysteine was detected. Samples of evaporated milk and skimmed milk which had been heated for 20 min at 60, 75 or 90 °C were examined, after acid hydrolysis, for the presence of homocitrulline. None was found. Similarly αs1- and β-caseins heated at 60 and 75 °C in 4 mM-urea at pH 6·6 yielded no homocitrulline, but after treatment at 90 °C for 20 min αs1-casein contained 68 μg/g and β-casein contained 73 μg/g protein-bound homocitrulline. This was concluded to have been the product of reaction of cyanate and ε-amino groupings of lysyl residues of the caseins. The relative importance of carbamylation involving ε-amino groups or sulphydryl groups in milk is discussed.
Centrifugal fractionation of homogenized milks
Authors: Dalgleish Douglas G. , Robson Elizabeth W.
Published: June 2009

A set of 12 fractions was isolated from homogenized cows' milk by a method of successive centrifugation steps. The fractions were analysed in terms of fat and protein contents and the diameters of the particles in them were also measured. Detailed comparisons of the turbidities of the samples and their light scattering properties allows comparison between them. It is concluded that the separation is less effective than a similar technique applied to casein micelles, but nonetheless that the different fractions do contain particles with different properties.
Complementary action of dipeptidyl peptidase IV and aminopeptidase M in the digestion of β-casein
Authors: Heymann Eberhard , Mentlein Rolf
Published: June 2009

Purified bovine β-casein was digested in vitro with varying mixtures of purified proteinases and peptidases including trypsin, chymotrypsin, dipeptidyl peptidase IV (DP IV), aminopeptidase M and prolidase. In digestion mixtures without DP IV the yield of free amino acids was considerably lower than in the corresponding assays with this peptidase. Especially, the release of proline increases drastically from almost zero to the theoretical amount in the presence of DP IV. Quantitative results indicated that the specificities of the two microvillar peptidases (aminopeptidase M and DP IV) optimally complemented each other. This effect elucidates the hitherto obscure physiological role of intestinal DP IV. A similar effect may also apply to other caseins and nutritional proteins.
Keeping quality of milk in relation to the copper content and temperature of pasteurization
Authors: Ford John E. , Schröder Monika J. A. , Bland Michael A. , Blease Kim S. , Scott K. John
Published: June 2009

For milk from four herds of cows, maintained under different conditions of feeding and management, the natural Cu content and the stability of the ascorbate were highly correlated. Low Cu levels in milk from cows at pasture at farms A and B during the summer were associated with low storage losses of ascorbate. During this period, the milk of cows at farms C and D (on forage and Cu-supplemented concentrate) was richer in Cu, and losses of ascorbate were high. Heat treatment of the milk stabilized the ascorbate. Thus, in ‘high Cu’ milk (60 µg Cu/l), loss of ascorbate in the raw milk was 58% at 2 d, as against 17% after pasteurization at 72 °C and no loss after treatment at 82 °C. Storage of milk in light caused rapid destruction of ascorbate, equally with 72 and 82 °C heat treatments. The effects were examined of milk pasteurization temperature (72–82 °C) on flavour stability, bacteriological quality and vitamins of the B-complex. Heat treatment at 82 °C increased the susceptibility of vitamin B12to destruction by light, but otherwise caused no greater losses of B-complex vitamins than did treatment at 72 °C. Taste panel ratings showed an initial preference for milk heated at 72 °C, but on storage of this milk in darkness the flavour score fell progressively and at 5 d it was judged ‘stale’. Treatment at 82 °C gave a faint ‘cooked’ flavour although, unlike that of the 72 °C-treated milk, the flavour remained stable throughout 14-d storage and after d 8 was increasingly preferred. On exposure to light after treatment at 72 °C milks rapidly acquired an unpleasant‘oxidized’ flavour, but after treatment at 82 °C, exposure to light had no such adverse effect on flavour during the early days of storage. Pasteurization at ∼ 80 °C offers a potential for improvement in the oxidative stability of milk and its contribution of vitamin C to the diet.
Effects of milk protein genetic variants and composition on heat stability of milk
Authors: McLean Douglas M. , Graham E. R. Bruce , Ponzoni Raul W. , Mckenzie Hugh A.
Published: June 2009

Skim milk samples from 126 Friesian and 147 Jersey cows in eight commercial herds were preheated at 85 °C for 30 min and concentrated to 200 g l−1 total solids. A heat coagulation time–pH curve was determined at 120 °C for each treated sample. Heat coagulation times ranged from 1 to 50 min at the non-adjusted pH and 1 to 60 min at the pH of maximum stability. The following statistically significant effects were found. Maximum heat stability was affected by genetic variants of κ-casein (B > AB > A; P < 0·001) and β-lactoglobulin (B, AB>A; P < 0·05) whereas natural heat stability was affected only by κ-casein genetic variants (B > AB > A; P < 0·001). Maximum and natural heat stability were corre-lated positively with β-casein and κ-casein concentrations and were negatively correlated with αs1-casein and β-lactoglobulin concentrations. Milk from Jersey cows had greater maximum and natural heat stability than milk from Friesian cows. Differences were found between herds within breed for natural heat stability, but not for maximum heat stability. Maximum heat stability declined with age of the cow. The heat stability of skim milk samples taken from 40 Jersey cows in one of the herds was determined at 140 °C. A considerable variation was found in the coagulation time–pH curves. There was a difference in natural heat stability between κ-casein variants (B > AB; P < 0°05). Natural and maximum heat stability were correlated positively with urea concentration. No relationship was found between the heat stability of preheated concentrated skim milk and the heat stability of the original skim milk. The pH of skim milk samples was associated with αs1-casein genetic variant, age of cow, stage of lactation and concentration of γ-casein.
Peptidases from two strains ofPseudomonas fluorescens: partial purification, properties and action on milk
Authors: Shamsuzzaman Kazi , McKellar Robin C.
Published: June 2009

Pseudomonas fluorescensstrains 240 and 32A expressed cell-associated peptidase activity which was shown by subcellular fractionation to be primarily intracellular. Two peptidases were partly purified from strain 32A. One specifically hydrolysedN-α-benzoyl-DL-arginine-4-nitroanilide and was termed endopeptidase and the other hydrolysed L-lysine- and L-leucine-4-nitroanilide and was termed aminopeptidase. The endopeptidase had very low activity on bovine serum albumin compared with that of trypsin and probably was not a proteinase. The endopeptidase had a mol. wt of 33000 and a pH optimum of 8·0. The enzyme was stimulated by Ca2+and Mg2+and inhibited by Co2+, Mn2+, Hg2+, Zn2+and leupeptin. Soya bean trypsin inhibitor and phenylmethane sulphonyl fluoride (PMSF) had no effect on its activity. The aminopeptidase had a mol. wt of 44000 and a pH optimum of 8·0. It was inhibited by all the metal ions mentioned above and by PMSF. Little proteolysis was found when ultra high temperature (UHT) sterilized milk was treated with cell-free extract from strain 32A. It was concluded that the cell-associated peptidases fromPseudomonasstrains normally present in raw milk may not contribute significantly to the deterioration of UHT sterilized milk.
Influence of pH, type of enzyme and ultrafiltration on the retention of milk clotting enzymes in Camembert cheese
Authors: Garnot Pascaline , Molle Daniel , Piot Michel
Published: June 2009

Camembert cheeses were made with pasteurized skim milk or with ultrafiltered milk concentrated 2-fold, using either rennet or Mucor miehei proteinase as coagulant. Using rennet, the rapid acidification during cheesemaking increased enzyme retention and 55% was retained after 24 h. With the M. miehei proteinase, acidification had no effect and only 17% of it was retained after 24 h. The use of ultrafiltered milk resulted in less rennet being retained in the curd.
Compressive load applied by the teatcup liner to the bovine teat
Authors: Mein Graeme A. , Williams David M. , Thiel Cliff C.
Published: June 2009

The magnitude of the cyclic load applied to the teat apex by the collapsed liner during milking was estimated by measuring the pressure required to cause retrograde flow of milk into the teat canal from a manometer attached to the external teat orifice. The study was extended by observation of the milk flow cycle within a transparent teatcup assembly and by pressure recordings within the teat canal using a catheter-tip transducer. The source of the force compressing the teat is the small airspace, within the collapsed liner, directly below the teat apex. The total force generated is determined mainly by the size of this airspace and the pressure difference (PD) acting across the opposing liner walls. When the PD reached 80–90% of the liner vacuum, the load was just sufficient to occlude the teat canal. Further increase in PD provided the compressive load capable of offsetting vascular congestion of the teat apex. Increasing liner tension increased the load applied. The narrow range of compressive loads applied by conventional liners (5–12 kPa above atmospheric pressure) may be sufficient to offset congestion and oedema in the teat. Loads greater than the mean arterial pressure within the teat apex might serve only to expose the tissues to non-productive compression.
Dissemination of staphylococci in mice with experimental mastitis
Authors: Anderson James C.
Published: June 2009

During the course of an acute, fatal mastitis in mice caused by intra-mammary injection of ∼ 105 cfu of Staphylococcus aureus, small numbers of staphylococci were detected in liver, spleen, kidney and heart. Transport from the mammary gland was by the venous blood system with no evidence of lymph node involvement. Intravenous injection of 100 times more staphylococci (∼107 cfu) than were fatal by the intramammary route failed to kill the mice and small numbers of staphylococci were found in the visceral organs. However, intravenous injection of ∼ 108 cfu of Staph. aureus was fatal and large numbers of staphylococci were found in the visceral organs. Treatment with cloxacillin (500 μg) by the intramammary or subcutaneous routes, or equally divided between these two routes, cleared the visceral organs of staphylococci; subcutaneous therapy had a limited and variable effect on numbers of staphylococci in the mammary gland while intramammary and divided treatments significantly reduced the numbers of staphylococci. Thus, staphylococci are disseminated to visceral organs during acute staphylococcal mastitis, but this makes a negligible contribution to the clinical disease.
Quantitative fractionation of casein mixtures by fast protein liquid chromatography
Authors: Davies D. Thomas , Law Andrew J. R.
Published: June 2009

Alkylation of whole casein samples by reaction with cysteamine and cystamine in a bis-tris-propane–urea buffer (pH 7·0) followed by fast protein liquid chromatography (FPLC) at 20°C on a Mono Q HR5/5 column in the same buffer and using a NaCl gradient led to good resolution of the whole casein into fractions representing (i) γ2- plus γ3-caseins, (ii) κ-caseins, (iii) β-casein, (iv) αs2-caseins and (v) αsl-caseins, together with small amounts of unidentified materials. Quantitatively the FPLC values agreed well with those for αs1-, β-, αs2- and γ2- plus γ3-caseins obtained by ion-exchange chromatography on DEAE cellulose, Whatman DE52 and with those for º-caseins obtained by gel-permeation chromatography on Sephadex G–150.
Heat-induced association-dissociation of casein micelles preceding coagulation
Authors: Mohammad Kais S. , Fox Patrick F.
Published: June 2009

Heating milk at 140 °C caused an initial increase in the percentage of total casein sedimented at 10000 g for 1 h and in the relative viscosity, but as heating continued both parameters decreased before increasing again just before the onset of visible coagulation. This suggests that heating milk at high temperatures caused an initial aggregation of casein micelles with a concomitant increase in particle size and weight, followed by dissociation of these aggregates with reaggregation just before coagulation. Chromatography of heated milk on controlled pore glass confirmed the above suggestion. Calcium appeared to play a major role in the initial association of casein micelles which was also influenced by the initial pH and total solids concentration but whey protein had no effect.
Comparison of a simple butterfat agar medium with other media used for isolation and enumeration of lipolytic bacteria from dairy products
Authors: Shelley Arthur W. , Deeth Hilton C. , MacRae Ian C.
Published: June 2009

A nutrient agar medium containing 0·1 % of a low melting point fraction of butterfat was shown to be suitable for detection, enumeration and isolation of lipolytic bacteria from milk. Bacterial growth was not inhibited by the butterfat and lipolytic reactions were clearly visible and easily interpreted. Lipolytic counts on the butterfat agar compared favourably with lipolytic counts obtained with other commonly used media.
Interspecies variation in milk composition among horses, zebras and asses (Perissodactyla: Equidae)
Authors: Oftedal Olav T. , Jenness Robert
Published: June 2009

Milk samples of four species of wild equids (onager, Equus hemionus onager; mountain zebra, E. zebra hartmannae; plains zebra, E. burchelli; Przewalski horse, E. caballus przewalskii) and two domesticated equids (ass, E. asinus; pony, E. caballus) were analysed. At mid to late lactation the milks of all species were very similar, containing on average 10–12% total solids, 1–2% fat, 1·6–1·8% true protein, 6–7% ‘lactose’, 0·3–0·5% ash, 0·08–0·12% calcium, 0·04–0·07% phosphorus and a calculated energy content of 2·0–2·4 kJ/g. Milk samples collected in the first 2 weeks after birth showed elevated levels of total solids and protein, and some had reduced ‘lactose’ levels, but there were no observable trends in milk composition during mid to late lactation (1–12 months post partum). It was concluded that these closely related species produce milks that are nearly identical in gross composition and that the domestic horse is a representative model for the study of equid lactation.
Dissociation during dialysis of casein aggregates cross-linked by colloidal calcium phosphate in bovine casein micelles
Authors: Aoki Takayoshi , Yamada Nagisa , Kako Yoshitaka , Imamura Tsuneaki
Published: June 2009

Casein micelles separated by ultracentrifugation of raw skim milk were dispersed at a casein concentration of 2·5% in simulated milk ultrafiltrate and dialysed against 10 mM-imidazole buffer (pH 7·0) at 5 °C. The amounts of colloidal Ca and inorganic P decreased from 77 to 11 mg and from 31 to 2 mg respectively in 100 ml during 72 h of dialysis. Micellar casein content was reduced to 43 and 11% after 48 and 72 h of dialysis respectively. In high-performance gel chromatography of casein micelles in the presence of 6 M-urea, fraction 1, consisting of the casein aggregates cross-linked by colloidal Ca phosphate (CCP) decreased during dialysis and the retention time of the peak of fraction 1 was prolonged, suggesting that the cross-linkage between CCP and casein molecules was disrupted. The dissociation rates of the individual casein constituents from the casein aggregates cross-linked by CCP during dialysis were in the order β-> αs1 - > αs2-casein. The higher the ester phosphate content, the slower was the dissociation rate of the individual casein constituent. It is suggested that the strength of interaction between CCP and casein molecules depends on the ester phosphate content.
Inorganic constituents of cheese: analysis of juice from a one-month-old Cheddar cheese and the use of light and electron microscopy to characterize the crystalline phases
Authors: Morris Howard A. , Holt Carl , Brooker Brian E. , Banks Jean M. , Manson William
Published: June 2009

A method of extracting cheese juice is described. Juice from a single one-month-old Cheddar cheese was used to investigate the relationship between the composition of the cheese juice and the occurrence of crystalline aggregates in the cheese. Two classes of crystalline aggregates were identified by light microscopy and also by electron microscopy in combination with X-ray microanalysis: the larger class contained both Ca and P whereas the smaller class contained Ca but not P. Concentrations of ions in the cheese and cheese juice were determined and corrected for the excluded volume of co-solutes and other phases present. When this was done, comparison of the concentrations of Na, K, Cl and lactate in the cheese and the cheese juice indicated that they were virtually entirely in solution, whereas appreciable amounts of the total Ca, P and P1 in the cheese were not extracted in the cheese juice. The amounts of the non-extractable salts were consistent with the volume fractions of the crystalline aggregates found by microscopy; calculations of the ion equilibria in the cheese juice showed that it was supersaturated with respect to various Ca phosphate salts and to tricalcium citrate. It is concluded that the physicochemical origin of the crystalline aggregates was the nucleation and growth of crystals from a supersaturated solution, though the sites of nucleation may have been formed by the microbial activity in the cheese. Of the free amino acids found in the juice, none was at a sufficiently high concentration to form a saturated solution, indicating that in this relatively young cheese the crystalline aggregates were not formed from amino acids.
Effect of a shielded liner on new mastitis infection
Authors: Binde Martin , Melby Hans Peter , Ask Asbjørn , Lund Andreas , Vangdal Svein AA.
Published: June 2009

Results from a field trial involving 23 Norwegian dairy herds support the theory that deflector shields inserted into the teatcup liner can reduce the risk of intramammary infection. However, the effectiveness of this measure is questionable in cows already infected and in problem herds.
Catecholamines, oxytocin and milk removal in dairy cows
Authors: Blum Jürg W. , Schams Dieter , Bruckmaier Rupert
Published: June 2009

Experiments were designed to study the effects of catecholamines on oxytocin responses and milk removal in dairy cows. Adrenalin, noradrenalin, dopamine, isoproterenol (a β-adrenoceptor agonist), phentolamine (an α-adrenergic blocker) and propranolol (a β-adrenergic blocker) were infused intravenously. In addition, adrenalin was infused together with phentolamine and/or propranolol. Infusions started 8 min before milking and lasted until the end of milking. In some cases electroshocks (for 5 s) were applied immediately before milking in the absence and presence of phentolamine and propranolol. Adrenalin, noradrenalin and dopamine reduced milk removal, but only if administered in supraphysiological amounts. The effect of adrenalin and electroshocks on milk removal could be inhibited by α-, but not by β-adrenergic blockade. The effect of dopamine could be inhibited only partly by phentolamine. Inhibition of milk removal was not mediated by reduced oxytocin responses. Enhanced local release of catecholamines from sympathetic nerves was presumably responsible for lowered milk removal in response to electroshocks. Milk removal was facilitated during α-adrenergic blockade and during β-adrenoceptor stimulation.
Observations on the heat-induced salt balance changes in milk I. Effect of heating time between 4 and 90°C
Authors: Pouliot Yves , Boulet Marcel , Paquin Paul
Published: June 2009

Milk permeate was separated at various temperatures by means of a hollow fibre ultrafiltration unit coupled to a stainless steel heat exchanger. Milk samples conditioned at 4°C were heated to 20, 40, 60, 80, 85 or 90°C prior to ultrafiltration. Ca, P, Mg, Na, K and citrate concentrations were measured in the permeate samples. Ca and P contents of the permeate decreased as the temperature increased. The pH was measured after cooling the permeate to room temperature. Smaller losses of Mg and citrate were also observed with increase in temperature. Na and K levels were not affected. A two-step time-concentration relationship was apparent for the species under study. An initial sharp decrease in concentration occurred in the first minute of holding time and was followed by a slower reaction. The possible occurrence of a two-step mechanism in the heat-induced salt balance changes is discussed. Dicalcium phosphate precipitation is believed to be coupled with tricalcium citrate precipitation upon heating.
Observations on the heat-induced salt balance changes in milk II. Reversibility on cooling
Authors: Pouliot Yves , Boulet Marcel , Paquin Paul
Published: June 2009

Milk which had been heated to 85°C for 40 min was examined for changes to milk salts taking place upon cooling to 4, 20, 40 and 60°C. The time-concentration curves showed a two-step reaction for Ca, Pi and pH. The effect of the heat treatment in milk heated to 85°C for 40 min was to produce greater changes in the second step of the reaction. Because of the variability of the results for other species (Mg and citrate), the reversibility was calculated only for Ca and P. It was 90–95% and 93–99% respectively depending on the cooling temperature. The reversibility of the heat-induced changes and especially of the possible dissolution equilibrium between Ca phosphate and citrate precipitates on cooling are discussed.
Fatty acid composition and milk quality related to feeding Ca-saponified palm acid oil to different breeds of dairy cows
Authors: Hermansen John E. , Lund Pia
Published: June 2009

The effect of supplementing a normal dairy feed ration (3–4% fatty acid of DM) with saponified palm acid oil (soap) was investigated in two experiments. The first experiment was carried out in eight herds (four Jersey, four heavy breeds), where the diet was supplemented with 1·0 and 0·5 kg soap for cows in the first and last part of lactation, respectively. Taste and acid degree of milk were not affected, and no breed × soap interaction was found. Fatty acid composition in milk was only slightly but significantly affected. The content of short and medium chain fatty acids was reduced (3·5% unit) and was followed by an increase in the content of 16:0 and 18:1. The increase in 16:0 by the soap supplementation was smaller in Jersey cows than in the other breeds. In the second experiment the effect of supplementing diets either with 0·5 or 1·0 kg Ca-soap to cows in the first part of lactation was investigated in two herds of Danish Black and White cows. Acid degree and time for curd formation on renneting (K20) were significantly lowest at the highest soap inclusion. No general effect on the proportion of short and medium chain fatty acids in the milk fat was observed as a function of level of Ca-soap, but the proportion of 16:0 was increased. It is assumed that the very small effect on milk fatty acid composition obtained when the daily allowance of fatty acids was increased from 600 to ~ 1400 g per cow, is more or less a specific effect of dietary fat rich in palmitic acid and given in excess to the basic diet.
Detection of cows' milk in ewes' milk and cheese by an indirect enzyme-linked immunosorbent assay (ELISA)
Authors: Rodríguez Elena , Martín Rosario , García Teresa , Hernández Pablo E. , Sanz Bernabé
Published: June 2009

An indirect enzyme-linked immunosorbent assay was successfully developed for the detection of defined amounts of cows' milk (1–50%) in sheeps' milk and cheese. The assay used polyclonal antibodies raised in rabbits against bovine caseins (BC). The anti-BC antibodies were recovered from the crude antiserum by immunoadsorption and elution from a column containing BC. The antibodies were biotinylated and rendered cows' milk specific by mixing them with lyophilized ovine and caprine caseins. ExtrAvidin-peroxidase was used to detect the biotinylated anti-BC antibodies bound to BC immobilized on 96-well plates. Subsequent enzymic conversion of substrate gave clear absorbance differences when assaying mixtures of sheeps' milk and cheese containing variable amounts of cows' milk.
An improved method for determining the nitrogen solubility of caseinates
Authors: Kneifel Wolfgang , Beurel Anne
Published: June 2009

The nitrogen solubility index (NSI) method for the examination of caseinates was evaluated. It was found that widely scattering NSI values are mainly due to ineffective centrifugation and filtration of the caseinate dispersion. In order to avoid this, an improved combined centrifugation–filtration procedure was developed as an alternative to the original NSI method, using an Amicon micropartition system MPS-1 equipped with discs of filter paper. The micropartition devices can be centrifuged in a Gerber centrifuge of the type used for butyromctric fat determination. Several types of caseinates were evaluated with the new method and yielded a markedly smaller range of single values than were obtained with the NSI method.
Prolidase activity ofLactococcus lactissubsp.cremorisAM2: partial purification and characterization
Authors: Booth Mary , Jennings Vincent , Fhaolain Ide Ní , O'Cuinn Gerard
Published: June 2009

Prolidase activity from cytoplasm ofLactococcus lactissubsp.cremoris (Streptococcus cremoris)AM2 was partially purified. The enzyme hadMr42000 and optimum activity between pH 7·35 and 8·25 in citrate, phosphate and borate buffers while in a universal buffer system an optimum pH between 8·3 and 9·0 was observed. The activity was strongly inhibited by the chelating agents E.DTA, 1,10-phenanthroline and 8-hydroxyquinoline. Inhibition was also noted with dithio-threitol,N-ethylmaleimide and bacitracin. The enzyme was active on all amino-acylproline substrates tested except Gly-Pro and Gip-Pro and also showed activity against Pro-Pro. While most prolyl amino acids tested were not hydrolysed, hydrolysis was noted with Pro-Ala and Pro-Val.Kmvalues of 20 mM and 10 mM were obtained with Phe-Pro and Met-Pro respectively; however, substrate inhibition was observed with Ile-Pro and Leu-Pro.
Preparation and consumer acceptability tests of fermented camel milk in Kenya
Authors: Farah Zakaria , Streiff Thomas , Bachmann Marc R.
Published: June 2009

There are estimated to be 600000 camels (Camelus dromedarius) in Kenya (Wandera, 1985). Almost 80% of these are kept by pastoral tribes living in arid areas in eastern and north-eastern parts of the country. In these regions, camels are important dairy animals. A camel in north-east Kenya can be expected to yield about 4 kg milk daily as compared with 0·5–1·5 kg for a cow in the same area. Most of the camel milk is consumed in the form of fermented milk. The milk is allowed to ferment naturally at ambient temperature and without prior heat treatment until it turns sour. The resulting fermented camel milk is known as Susa. Due to the spontaneous nature of the fermentation, this traditional method results in a product with varying taste and flavour and is often of poor hygienic quality, in addition, because of the limited scale of production, the product can be sold only in the immediate vicinity of the herd. For production of fermented milk under controlled conditions, thermophilic or mesophilic lactic acid cultures are normally used. In warm countries, mesophilic lactic cultured milk offers some advantages, as it can be incubated at ambient temperature (20–30 °C) and the fermentation stops at 1–1·2% lactic acid, eliminating the need for cooling to stop further souring as occurs in the case of yoghurt (Kurwijila, 1980).
The effect of udder preparation before milking and contamination from the milking plant on bacterial numbers in bulk milk of eight dairy herds
Authors: McKinnon Charles H. , Rowlands G. John , Bramley A. John
Published: June 2009

The effect of teat washing and drying on bacterial numbers in bulk milk was compared with that of no teat preparation in eight commercial herds over one year. Using in-line milk samplers, milk was collected at various points during its passage through the milking plant and the samples were used to establish the relative significance of the sources of contamination of raw milk. Teat washing and drying of cows housed during winter reduced the total counts by 40% and streptococcal and coliform counts by 50%. Bacterial counts were significantly lower in cows at pasture during the summer and there was no reduction in count due to teat washing and drying. Bacteriological counts increased at each stage as the milk passed through the milking machine. The milking equipment significantly increased the total colony count by between 2000 and 3000/ml, and the bulk tank added a further 1500 to 2000/ml. The mean rinse bacterial counts of the milking equipment were higher in summer than winter, averaging 4·4 x 107bacteria/m2compared with 3·5 x 107/m2respectively. Although this level of bacterial contamination of the equipment is high by current standards, very low bulk milk bacterial counts were nevertheless achieved, particularly in the summer. This confirms that organisms from this source are not a major contaminant of the bulk milk. There was a very poor correlation between rinse counts and the bulk milk bacterial count, but a strong correlation (0·98) between total and streptococcal counts of the bulk milk. The unreliability of the use of rinse techniques to assess the contribution of milking equipment to bacterial counts of raw milk is emphasized.
Changes in the concentrations of glucose and galactose in the peripheral blood of sucking piglets
Authors: Holmes Mark A. , Arthur Peter G. , Hartmann Peter E.
Published: June 2009

Changes in the concentrations of glucose and galactose were measured in the peripheral blood of ten piglets after they had ingested milk during a natural sucking. In addition, the mild stress associated with the experimental procedure was determined by sampling nine fasted piglets over a period of 9 to 12 min. During this period there was a significant increase in the concentration of glucose in the blood of the piglets but no change in the concentration of galactose. After milk ingestion during a natural sucking the concentrations of both glucose and galactose increased from 5·7 mM and 19μM to reach peak values of 7·7 mM and 122μM, respectively, by 30 to 35 min. The concentrations of glucose and galactose returned to initial values in 60–80 min and 80–100 min, respectively, after sucking. Since the change in the concentration of galactose in the peripheral blood was much lower than the change in the concentration of glucose, we conclude that galactose was rapidly removed by the livers of sucking piglets. However, after the ingestion of milk the percentage increase (from initial to peak values) in the concentration of galactose in the blood was much larger (650%) than the increase in the concentration of glucose (43%). Thus, we propose that the determination of galactose in the peripheral blood may provide a qualitative method for monitoring the digestion and absorption of milk lactose in sucking piglets.
Transepithelial potential difference in the goat mammary gland and its change during hand milking, and administration of oxytocin and catecholamines
Authors: Alekseev Nikolaj P. , Markov Alexander G. , Tolkunov Yuri A.
Published: June 2009

The reaction of secretory epithelium and myoepithelial cells in the alveoli to hand milking and i.v. injection of oxytocin and catecholamines was studied in lactating goats. The reaction of secretory cells was assessed by changes in the transepithelial (blood–milk) potential difference (PD), and the contractile reaction of myoepithelial cells by the growth of intramammary pressure (IP). The initial value of PD was 24·6 ± 0·6 mV, that of IP 3·32 ± 0·08 kPa (24·9 ± 0·6 mmHg). Milking and oxytocin administration caused a rise in PD and an increase in IP. After noradrenaline and adrenaline injections two-phase PD changes and a short-term rise in IP were recorded. Isoproterenol, a β-agonist, caused a rise in PD but did not affect IP. Phenylephrine, an α-agonist, caused two-phase and one-phase changes in PD. Simultaneously, a rise in IP was recorded. The results show that the reaction of the mammary gland to the substances administered is complex. Myoepithelial and secretory cells respond differently to short-term rises in the level of mediators and hormones in the blood.
Ultrafiltration of defatted whey: improving performance by limiting membrane fouling
Authors: Daufin Georges , Michel Françoise , Labbé Jean-Pierre , Quemebais Auguste , Grangeon André
Published: June 2009

Defatted whey was obtained by aggregating residual fat to calcium phosphate precipitates and separating the precipitate by membrane microfiltration (pore diameter 0·2 μm). When ultrafiltering this defatted whey the performance of an inorganic membrane (molecular mass cut-off, 10 kDa) was limited by the large concentration of Ca and phosphates. Consequently, the influence of the aggregation pH (either decreasing or constant) on membrane fouling has been studied for ultrafiltration (UF) of defatted sweet whey and defatted whey UF retentates (protein content up to 30g l–1). In all experiments protein rejection was 100%. When pH was kept constant during the pretreatment, membrane fouling was significantly lowered. Hydraulic resistances ascribed to irreversible fouling were in good agreement with fouled membrane analyses performed by i.r. and X-ray photoelectron spectroscopies. They showed that provided a low Ca and phosphate content was maintained in the microfiltrate, which was achieved at constant pH, no apatite was detected within the membrane, and proteins were less fouling. On the other hand, the amount of fouling material depended on the transmembrane pressure gradient along the hydraulic path. On the membrane surface, the higher the pressure, the higher the fouling. In the membrane bulk, the fouling heterogeneity depended on the ability of the defatted whey to precipitate apatite. If it did, the higher the pressure, the higher the calcium phosphate and the protein fouling. With other phosphate structures, the bulk fouling depended on the barrier formed by surface fouling layers and the protein concentration polarization layer, which were more resistant to solute and solvent transfer under higher pressure, where they were thicker.
Powerful odorants in bovine, ovine, caprine and water buffalo milk determined by means of gas chromatography–olfactometry
Authors: Moio Luigi , Langlois Dominique , Etievant Patrick , Addeo Francesco
Published: June 2009

The main compounds responsible for the aroma of bovine, ovine, caprine and water buffalo freshly secreted milk have been identified by means of a gas chromatography–olfactometry technique. Of the fourteen odour-active volatile compounds detected, eight were present in all milks studied. Ethylbutanoate and ethylhexanoate (fruit-like aroma), among the neutral odorants, were the major contributors to the odour of bovine, ovine and caprine milk. The aroma of water buffalo milk was less dependent on ethylhexanoate and was also due to l-octen-3-ol (aroma of raw mushrooms), nonanal (freshly cut grass), indole (stable, animals) and an unidentified constituent, characterized by a retention index of 828, with a typical odour of warm milk and/or smoked cheese. Other aroma components were specific for some types of milk, contributing to the complexity and richness of flavour.
Influence of switch level of automatic cluster removers on milking performance and udder health
Authors: Rasmussen Morten D.
Published: June 2009

The effect of a switch level of 200 or 400 g/min for automatic cluster removers on milking performance and udder health was measured with 71 first lactation cows in their first 36 weeks of lactation and with 64 older cows in their first 12 weeks of lactation. Early removal of the milking unit decreased machine-on time by 0·5 min, increased average milk flow rate slightly, improved teat condition significantly and reduced the change in teat end thickness during milking of first lactation cows. Early removal of the milking unit did not affect milk yield or composition, and the incidence and prevalence of subclinical mastitis were the same in the two groups. Fewer older cows developed clinical mastitis in the group switched at 400 g/min, but this was not significant. It is concluded that the milking unit can be detached at a milk flow rate of 400 instead of 200 g/min without having a negative influence on milk yield. Machine-on time is shortened and teat condition improved, and udder health does not seem to be affected.
Proteolytic specificity of chymosin on bovine αs1,-casein
Authors: McSweeney Paul L. H. , Olson Norman F. , Fox Patrick F. , Healy Aine , Højrup Peter
Published: June 2009

The proteolytic specificity of chymosin (EC 3.4.23.4) on bovine αs1-casein at 30°C in phosphate buffer, pH 6·5 and at pH 5·2 in the presence of 5% (w/v) NaCl was investigated. Peptides (pH 4·6-soluble) were isolated by reversed-phase HPLC and identified from their amino acid sequence; the identity of some peptides was confirmed by mass spectrometry and/or amino acid composition. The small peptides produced at pH 6·5 were Arg1–Phe23, Phe24–Phe28, Phe24–Leu40(?), Phe150–Phe153, Phe150–Leu156, Tyr154–Tyr159, Tyr154–Trp164, Asp157–Trp164 and Tyr165–Trp199. The same peptides, except Tyr154–Trp164, were produced at pH 5·2 in the presence of NaCl and, in addition, the peptides Arg1–Leu11, Phe24–Phe32, Lys102–Leu142, Ala143-Leu149 and Tyr165-Phe179. The rates of production of individual peptides differed under the two conditions studied but Arg1-Phe23 and Tyr165–Trp199 were the first and second peptides produced under both conditions. Pathways are proposed to interpret the proteolysis of αs1-casein in solution under the conditions of this study.
Discovery of an ovine αs2-casein variant
Authors: Chianese Lina , Garro Giuseppina , Addeo Francesco , Lopez-Galvez Gloria , Ramos Mercedes
Published: June 2009

A novel ovine αs2-casein variant has been detected using discontinuons polyacrylamide gel electrophoresis at alkaline pH, two dimensional electrophoresis and immunoblotting. It is characterized by a greater negative net charge and a lower isoelectric point compared with the most common ovine αs2-casein variant. The phenotypic frequency in the Manchega breed is 5·5%.
Heavy coagulum formation in lactic casein manufacture: solids content, pH and gel strength variations through setting lactic coagulum
Authors: Weeks Michael G. , Gosling Eileen J. , Munro Peter A.
Published: June 2009

Samples of lactic coagulum were obtained from various depths in a lactic casein silo. The casein content at the base of the silo was in the range 38–62 g/kg compared with 25–30 g/kg in the bulk of the silo. This layer of higher casein concentration, called heavy coagulum, was up to l m deep and appeared long before the bulk milk had fully coagulated. It had a lower pH than the bulk, e.g. pH 4·35 when the bulk pH was 5·2. The heavy coagulum layer was removed from the silo last during pump-out. A laboratory coagulation tube was designed to permit more intensive study of heavy coagulum formation. Starter bacteria levels in the heavy coagulum were 10–160 times those in the bulk. Heavy coagulum had a visibly different curd structure (a much more granular gel), produced differently shaped extrusion curves, and had a higher gel strength than coagulum from the bulk. The heavy coagulum phenomenon had many similarities to minor sludge formation in Cottage cheese manufacture.
Detection of residual chymosin in cheese by an enzyme-linked immunosorbent assay
Authors: Boudjellab Nissab , Rolet-Repecaud Odile , Collin Jean-Claude
Published: June 2009

A simple and rapid competitive enzyme-linked immunosorbent assay method has been developed to detect the residual activity of chymosin in various types of cheese without extraction. In a cheese of the Saint-Paulin type, concentrations of chymosin detected at the end of cheesemaking in curd and whey represented 22·5 and 73·5% respectively of the total amount added to milk, so most of the chymosin was detected using this method. In a cooked pressed cheese of the Comté type, only 14% of the chymosin added to milk was detected in curd and all the chymosin in whey was inactivated. It was thus possible to demonstrate the presence of active residual chymosin in cooked pressed cheese. When measurements were carried out in 12 different cheeses, chymosin concentrations ranged between 384 ng/g in a Camembert cheese and 86 ng/g for an 8-month old Comté cheese. Chymosin appeared to be highly stable during cheese ripening.
Effect of freezing and frozen storage on the physicochemical, organoleptic and microbiological characteristics of a semi-hard ewes' milk cheese
Authors: Fontecha Javier , Peláez Carmen , Juárez Manuela , Martín-Hernández M. Carmen
Published: June 2009

Physicochemical, organoleptic and microbiological characteristics of semi-hard ewes' milk cheeses, frozen immediately after manufacture under two different conditions at −35 and −80°C and stored at −20°C for 4 months, were studied during subsequent ripening. Frozen storage after either freezing condition did not result in marked alterations in overall composition or rheological and sensory properties of the cheeses after 45 d ripening. Water activity decreased over the ripening period and this decrease was more pronounced in the frozen batches. The water-holding capacities of the protein in the frozen cheese batches were higher than for the control batch. The level of proteolysis, estimated from the level of amino groups, was higher in the previously frozen cheese. Freezing also reduced the viability of the microbial flora in the cheese. The differences in these characteristics for the two freezing conditions were not significant.
Modification of β–lactoglobulin by aliphatic aldehydes in aqueous solution
Authors: Stapelfeldt Henrik , Skibsted Leif H.
Published: June 2009

Each of the secondary lipid oxidation products pentanal, hexanal and heptanal was found to react with β–lactoglobulin (β–lg) in a two-phase model System (aqueous phosphate buffer–1-octanol) yielding fluorescent condensation products (emission maximum, 410 nm; excitation maximum, 350 nm). Protein polymers were detected by size-exclusion HPLC, and the rate of reaction paralleled the formation of fluorescent products, with the reactivity being pentanal > hexanal > heptanal. Simultaneously, the reaction also changed the intrinsic fluorescence of β–lg, and in particular pentanal reduced the intensity of tryptophan fluorescence (emission maximum, 332 nm; excitation maximum, 288 nm) by 30%. These findings are discussed with reference to the effect of peroxidizing lipids on the physical properties of whey proteins and the use of protein fluorescence (induced by the reaction with aldehydes) as marker for the oxidative status of milk and whey protein products.