bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of lipoprotein lipase activity in bovine milk
Authors: Anderson Malcolm
Published: June 2009

The effects of temperature, dilution, dialysis and the presence of heparin on the stability of lipoprotein lipase (LPL) in milk, skim-milk, milk serum and casein micelles were investigated. At 4 and 20 °C milk serum was the source of the least stable LPL and casein was that of the most stable. There was little difference between LPL stability in milk and skim-milk at these temperatures, or between serum and casein LPL at 50 °C. Heparin (5 µg/ml) increased stability although the effect was less for casein LPL than for serum LPL. A 40-fold dilution of serum LPL with either simulated milk ultrafiltrate (SMUF) or 0·01 M-Tris-Cl pH 8·3 increased the loss of serum LPL, but not of casein LPL. Dialysis of skim-milk against deionized water or SMUF increased stability at 4 or 20 °C but not at 37 °C. LPL activity was more stable in diluted samples of dialysed skim-milk than in diluted samples of the same milk which had not been dialysed. Dialysis against deionized water increased lipolysis but against SMUF it did not increase. Solutions prepared by dialysing water against some milks were found to inhibit lipolysis and this effect was overcome by heparin. The possibility that milk serum contains a factor which influences LPL stability is discussed.
Influence of milk proteins on lipid oxidation in aqueous emulsion: II. Lactoperoxidase, lactoferrin, superoxide dismutase and xanthine oxidase
Authors: Allen John C. , Wrieden Wendy L.
Published: June 2009

The milk-related model system described by Allen & Wrieden (1982) was used to assess the effects of a number of purified milk metalloproteins, at concentrations relevant to those in milk and dairy products, on triglyceride oxidation in emulsions. Oxidations were monitored by the rate of O2utilization (ROU) and by the thiobarbituricacid (TBA) assay. The proteins lactoferrin, lactoperoxidase, superoxide dismutase and xanthine oxidase were used either on their own or in conjunction with 10 μM-Cu2+or Fe2+. Lactoferrin alone had little effect on oxidation, although both the iron-free and iron-saturated protein were able to protect the lipid to some extent from Fe2+-catalysed oxidation. Cu2+-catalysed oxidation was slightly promoted. Lactoperoxidase was pro-oxidative in the absence and presence of added Cu2+or Fe2+. Heat treatment at 72°C/20 s had little effect, but oxidation was greatly reduced by treatment at 80°C/20 s. Superoxide dismutase strongly reduced the rate of lipid oxidation in the absence of added metals, but had no effect in the presence of 10 μM-Cu2+. xanthine oxidase had little effect on lipid oxidation in the absence of added metals, but was strongly pro-oxidative in the presence of 10 μ-Cu2+. Similar effects were observed down to 1 μM-Cu2+. The enzymic activity of xanthine oxidase was rapidly eliminated by 10 μM-Cu2+, but not by 10 μM-Fe2+. A moderate pro-oxidative effect was observed in the presence of 10 μM-Fe2+. Heat treatment of xanthine oxidase at 80°C/20 s reduced its lipid pro-oxidative effect in the presence of Cu2+more effectively than treatment at 72°C/20 s.
Homogenizing valve design and its influence on milk fat globule dispersion: II. High rate of flow (1000 1 h-1, 6000 < Re < 15000)
Authors: Phipps Leslie W.
Published: June 2009

The performance characteristics of a valve accepting a high rate of milk flow and operating at Reynolds’ numbers (Re) of 6000–15000 have been studied. Features of valve design which improved homogenizing efficiency were identified. As with small valves operating at lower Re numbers, efficiency increased as D0/D increased beyond 0·5; for D0/D ≈ 0·7, a 15% reduction in mean globule size was obtained. Changes of face angle up to 45° had virtually no effect on milk fat globule dispersion. The use of impact rings produced only small improvements in dispersion. The incorporation of perforated insets led to substantial globule size reductions of 15–25% or the equivalent in reductions of homogenizer energy consumption of 12–35%.
Hormonal control of casein synthesis in organ culture of the bovine lactating mammary gland
Authors: Gertler Arieh , Weil Anat , Cohen Nava
Published: June 2009

Explants from lactating bovine mammary gland were culturedin vitroin serum-free medium through 1–9 d. Casein synthesis was determined by [32P] incorporation into newly synthesized Ca rennin precipitable fraction. High correlation (γ = 0·98) was found between incorporation of [32P] and [3H]amino acids in explants cultured under different hormonal regimes, thus indicating that post-translational phosphorylation is not a rate-limiting step in casein synthesis.

Hormonal effects on casein synthesis were studied by supplementing the incubating medium with insulin (I), prolactin (PRL), cortisol (F), thyroxine (T4) and triiodothyronine (T3). It was found that both PRL and I were required absolutely for maximal synthesis and almost maximal effect was achieved with 50 ng/ml. The effect of F was less clear, but some increase was achieved at the 200–1000 ng/ml range. T4and T3did not affect casein synthesis at a range of 10-11–10-7M while a significant inhibition was observed at 2 × 10-5M. A time-course study of casein synthesis further substantiated the dominant role of PRL in maintenance or even elevation of the initial rate of casein synthesis in the explants, through the first 4 d of incubation.
Effect of aspartyl proteinases ofPenicillium caseicolumandPenicillium roquefortion caseins
Authors: Trieu-Cuot Patrick , Archieri-Haze Marie-Jose , Gripon Jean-Claude
Published: June 2009

The aspartyl proteinases ofPenicillium caseicolumandP. roquefortiacted identically on β-casein; both enzymes split at least 3 bonds: Lys29–Ile30, Lys97–Val98and Lys99–Glu100. From αsl-casein, these proteinases released 6 main degradation products which arose from the splitting of 4 bonds;P. roquefortiaspartyl proteinase was found to cleave 1 bond at a higher rate thanP. caseicolumaspartyl proteinase. A hypothetical sequential hydrolysis mechanism of αsl-casein by these 2 enzymes is proposed from a study of the degradation by isoelectric focusing and by 2-dimensional electrophoresis.
Milk proteins: molecular, colloidal and functional properties
Authors: Fox Patrick F. , Mulvihill Daniel M.
Published: June 2009

The proteins of bovine milk are the best-characterized food-protein system. Lactoproteins, which have high biological value, contribute ∼25% of dietary protein in North West Europe, North America and Oceania. However, in protein-rich western diets, milk proteins are frequently more highly valued for their functional properties than for their nutritional qualities. The remarkably high heat stability of the caseinate system permits the manufacture of a range of sterilized, concentrated and dehydrated products while its gelation on very limited proteolysis is the basis of cheese manufacture. Skim-milk powders, caseinates and whey protein concentrates are the most flexible and widely used functional proteins in food processing.

This communication reviews recent studies on milk proteins with respect to molecular and colloidal properties; coagulation by Ca2+, heat and ethanol; and functional properties and their chemical and enzymic modification.
An evaluation of the Charm Test – a rapid method for the detection of penicillin in milk
Authors: Thorogood Shirley A , Wood Peter D. P. , Prentice George A
Published: June 2009

Using the Charm radioactive assay technique as a rapid test for the determination of penicillin in milk in experiments with milks containing known concentrations of penicillin, the coefficient of variation was found to be 15 and 11% for raw whole and reconstituted skim-milks respectively. Storage of reagents for up to 4 d increased the variance of the test by more than 20% and the estimated penicillin concentration 0·4 %/d of storage up to 25d. In comparison with the Bromocresol Purple Test, which was capable of 100% accuracy in defining a threshold of 0·02 i.u. penicillin/ml milk, the Charm Test falsely classified 15·6% of the samples.
Milk trypsin-inhibitor capacity as an indicator of bovine mastitis – a novel principle which can be automated
Authors: Sandholm Markus , Honkanen-Buzalski Tuula , Kangasniemi Reima
Published: June 2009

As mastitis is associated with leakage of small molecular weight plasma proteins, such as α1-antitrypsin, into milk, this antitrypsin can be used as an indicator of mastitis. A colorimetric procedure was developed for large scale monitoring of milk antitrypsin activity, using microtitration plates and the Multiskan system. The effect of stage of lactation and age of the cow on the antitrypsin concentration and its interrelationship with other mastitis indicators (bovine serum albumin (BSA), somatic cell count) was analysed by computer programs on 1029 cows. Milk antitrypsin activity was high after parturition owing to colostral inhibitors. After the first month of lactation the assay measures only blood-derived antitrypsin and is a good indicator for detecting an increased permeability between blood and milk due to mastitis. Increasing lactation number only slightly affected the antitrypsin and BSA concentrations whereas somatic cell content was markedly affected.
Origins and levels of post pasteurization contamination of milk in the dairy and their effects on keeping quality
Authors: Schröder Monika J. A.
Published: June 2009

Bacterial post pasteurization contamination with psychrotrophic Gram-negative rods (GNR) was measured in commercial milks before and after transfer to retail containers. The tanks of pasteurized milk feeding the filling units contaminated milk less often (39% of samples) but usually at a higher level than the filling units (92% of samples). The number of GNR present had a considerable influence on the shelf life of milk, and the range found in commercially pasteurized milk was reflected in a wide range of shelf lives.
Isolation and composition of milk fat globule membrane material
Authors: McPherson Avis V. , Dash Mary C. , Kitchen Barry J.
Published: June 2009

The material surrounding the fat globules in commercial pasteurized homogenized milk was isolated by centrifugation of the freeze – thaw extract of the fat globules through a 52·5% (w/v) sucrose solution in simulated milk ultrafiltrate. The purified membrane material contained higher neutral lipid levels than fresh raw milk fat globule membrane (MFGM) material. Caseins and whey proteins, mainly β-lactoglobulin (β-lg) were found to be the major protein components of homogenized milk membrane material. Native MFGM polypeptides comprised only a small proportion of the total protein in these membranes. The total amount of membrane material isolated from homogenized milk was substantially higher than that from fresh raw milk. Analysis of homogenized milk membrane material by linear sucrose density gradient centrifugation showed a different pattern to that found with other milks, indicating the presence of new lipoprotein complexes. Commercial ultra heat treated (UHT) milks were also examined, but it was difficult to obtain isolated MFGM material free from core fat. However, fat globule fractions were isolated from these products by high speed centrifugation and these were analysed intact. Membrane material in these milks contained caseins and whey proteins (mainly β-1g). Natural MFGM polypeptides were present at extremely low levels. Phospholipid levels in UHT milk membranes were greatly reduced compared with membrane material isolated from other milks.
Observations onCorynebacterium bovisinfection of the bovine mammary gland. II. Experimental infection
Authors: Honkanen-Buzalski Tuula , Bramley A. John
Published: June 2009

Experiments are described in which lactating cows were exposed toCorynebacterium boviseither by dipping the teats in a suspension of the bacteria or by inoculating the bacteria into the teat duct or the teat sinus. All three methods readily led to ‘infection’ being established. The effect of these infections on somatic cell count was minor and no clinical mastitis resulted during the course of the experiments although some cases occurred subsequently. There was evidence that 44% of these infections were confined to the teat duct. Quarters excretingC. bovisin milk continued to do so during endotoxin-induced inflammation and showed a similar cellular response to that of uninfected quarters.
β-Casomorphin immunoreactive materials in cows' milk incubated with various bacterial species
Authors: Hamel Ulrike , Kielwein Gerhard , Teschemacher Hansjörg
Published: June 2009

To obtain information about the possible release of β-casomorphins from β-casein under in vitro conditions, cows' milk was incubated with 13 strains of Gram-negative or Gram-positive bacterial species isolated from bovine milk. After incubation periods of 1–24 d, milk samples were assayed for β-casomorphin-4, -5, -6 or -7 immunoreactive materials. In general, no β-casomorphin immunoreactive material was found in samples incubated with non-caseolytic strains, e.g. Pseudomonas putida or Streptococcus faecalis subsp. faecalis; however, high levels were found in several samples incubated with caseolytic strains, e.g. Ps. aeruginosa or Bacillus cereus. When such materials were present, the amounts of β-casomorphin-4, -6 or -7 greatly exceeded β-casomorphin-5 immunoreactivity. It was concluded that while some of these materials probably represented authentic β-casomorphins, others were more likely to be β-casomorphin precursors.
Influence of processing temperature and seasonal change in diet on lipase activity and lipolysis during the mechanical separation of bovine milk
Authors: Needs Eric C. , Anderson Malcolm , Payne Stuart J. , Ridout Elizabeth A.
Published: June 2009

The effect of separating conditions on lipase activity and free fatty acid levels in preheated milk, cream and skim milk was measured on nine occasions during a 12-week period covering the seasonal change from winter feeding to summertime grazing. This change consisted of four periods each representing a different type of forage intake, namely: silage, kale, daytime grazing and 24 h grazing. Milk was separated at 30, 40, 50 and 60°C with preheating times of 10, 25 and 55 s. Results were expressed both as absolute values and in terms of changes relative to the original unheated milk. Lipase activity and free fatty acid concentration were significantly reduced as separation temperature increased but were not influenced by holding time. The loss of activity in cream was progressive so that at 60°C only 40% of the original activity remained. Up to 50°C little change occurred in preheated milk or skim milk activity, while at 60°C 83 and 76% respectively of the original activity remained. The amount of activity calculated to be associated with the fat fraction of the cream also decreased with temperature. Activity varied significantly with date; maximum values were observed during the first 3 weeks of summertime grazing. Relative activity values indicated that the susceptibility of milk lipase to heat inactivation also varied with date. Lipolysis was also significantly affected by date. Cream free fatty acid levels were lower during the period of daytime grazing and were significantly higher than those in preheated milk. The correlation between lipase activity and free fatty acid levels was generally poor, accounting for between 0 and 34% of the variance. Possible reasons for the effect of separating temperature on lipolysis in cream are discussed.
An examination of teat drying with disinfectant impregnated cloths on the bacteriological quality of milk and on the transfer of Streptococcus agalactiae before milking
Authors: McKinnon Charles H. , Higgs Trevor M. , Bramley A. John
Published: June 2009

Total bacterial counts of the milk from individual cows were measured for three groups of ten winter housed cows at three milkings. The teats were either (i) left unwashed or (ii) washed with disinfected water (60 ppm available iodine) and dried with individual paper towels or (iii) washed with plain water and then dried with a single fabric cloth impregnated with a polymeric bisguanide and a quaternary ammonium compound. The mean total bacterial counts/ml for the groups were 5820, 2108 and 1116 respectively. Treatments (ii) and (iii) were also compared for their ability to prevent the inter-teat transfer of bacteria. Before teat washing and drying, one teat of each cow was deliberately contaminated with Streptococcus agalactiae. Significantly fewer teats (5/30) became contaminated with Str. agalactiae when treatment (iii) was used for teat washing and drying compared with treatment (ii) (20/30).
Anaerobic digestion of deproteinated cheese whey
Authors: Haast Johannes De , Britz Trevor J. , Novello Johannes C. , Verwey Emilige W.
Published: June 2009

Whey and deproteinated whey preparations with different carbon: nitrogen (C/N) ratios ranging from 7·5 to 73 were digested anaerobically in a downflow stationary fixed-bed reactor at 35 °C with a hydraulic retention time of 5 d. Effluent and biogas parameters indicated that no decrease in digestion and stability occurred at the highest C/N ratio. Chemical oxygen demand (COD) removal averaged 88%, while volatile fatty acids were maintained at a low level (< 500 mg l–1). Biogas yield averaged 0·423 m3kg–1COD and the methane content of the biogas varied between 57 and 63%. Ammonia toxicity occurred at a C/N ratio of 7/5 in the substrate feed. Virtually no ammonia N was detected in the effluent when whey substrates with C/N ratios of 50 and 73 were fed. Titration curves showed that buffer intensities in the effluent were not affected by a decrease in ammonia level. A decrease in the biomass content of the effluent which occurred as a result of the increase in C/N ratio of the substrate did not cause any rate limiting effect on biogas production. The removal of protein from the whey caused a reduction in the ratio of COD: total carbon in the whey. On average 59% of the carbon in the substrate was converted to biogas.
Effect of elevated ripening temperatures on proteolysis and flavour development in Cheddar cheese
Authors: Aston John W. , Giles Janet E. , Durward Ian G. , Dulley John R.
Published: June 2009

The effect of storing Cheddar cheeses at elevated temperatures on proteolysis and flavour development was examined. Cheeses were stored under the following ripening conditions: (1) 8 °C for 32 weeks (control); (2) 15 °C for 8 weeks then 8 °C for 24 weeks; (3) 17·5 °C for 8 weeks then 8 °C for 24 weeks; (4) 20 °C for 8 weeks then 8 °C for 24 weeks; (5) 15 °C for 32 weeks; (6) 17·5 °C for 32 weeks; and (7) 20 °C for 32 weeks. The rates of build up of products of proteolysis and flavour increased in the order of the above treatments and substantial acceleration of ripening was achieved. However, after 32 weeks at 17·5 °C and 16 weeks at 20 °C, cheeses received significantly lower preference scores than the control cheeses (P < 0·05) mainly owing to the development of off flavours. The maximum temperature at which cheeses could be stored for 32 weeks without reduction in quality was 15 °C. Cheeses stored at this temperature for the entire period had levels of products of proteolysis at 12 weeks of age which were similar to those of controls at 32 weeks, and estimations of age at 20 weeks which were similar to those of controls at 32 weeks.
Residual milk in Friesland sheep and the galactopoietic effect associated with oxytocin treatment
Authors: Heap R. Brian , Fleet Ivan R. , Proudfoot Robert , Walters D. Eurof
Published: June 2009

Mature lactating Friesland ewes had a mean lactation yield of 293 ± 26 kg during a lactation period of 35 ± 2 weeks giving an average daily milk yield of 1·2 kg/d. Ewes were injected intravenously after normal milking with either saline (sham) or oxytocin and then remilked to determine the volume of residual (alveolar) milk. After a long milking interval of 16 h oxytocin treatment gave a significantly greater total daily milk yield than the sham treatment (oxytocin minus saline, morning milking, 0·199±0·038 kg, mean ±s.e.m., P < 0·01). Oxytocin had a small significant reverse effect after a short milking interval of 8 h (afternoon milking, –0·065±0·022 kg, P <0·05). The average increase in total daily yield over four stages of lactation was 0·133±0·029 kg (P < 0·01), or 11% of the average daily milk yield. The galactopoietic effect of oxytocin was associated with the efficient removal of residual (alveolar) milk. Residual milk accounted for 7·4 and 27·2% of the total daily milk yield in ewes treated with saline or oxytocin respectively. Residual milk expressed as a proportion of daily total milk yield remained steady in ewes studied between April and July, but declined in September when yields were less than 1 kg/d.
Seasonal changes in the fat composition and concentration of citrate and related metabolites in cows' milk
Authors: Faulkner Anne , Brechany Elizabeth Y. , Mabon Richard M. , Pollock Helen T.
Published: June 2009

Seasonal variations were observed in the proportion of long-chain (C18and over) and medium-chain (C6–14) fatty acids (FA) in milk fat. Long-chain FA were proportionately higher during the period June to October. Changes were also observed in the concentrations of citrate, isocitrate and 2-oxoglutarate in milk. Changes in [isocitrate]: [2-oxoglutarate] correlated positively with changes in the proportion of long-chain FA in milk fat and negatively with the proportion of medium-chain FA.
Influence of calcium chloride on the chymosin-initiated coagulation of casein micelles
Authors: Bringe Neal A. , Kinsella John E.
Published: June 2009

Coagulation of para-casein micelles was monitored using a Platelet Aggregometer at 37·8 °C and pH 6·7. The macropeptide released by chymosin was determined quantitatively with fluorescamine. The aggregatability of para-casein micelles integrated over the complete hydrolysis of κ-casein was calculated from the amount of κ-casein hydrolysed during the clotting time (Tc). Low concentrations of CaCl2 enhanced the rate of κ-casein hydrolysis but increases in CaCl2 concentration above 8 mM caused marked decreases in this rate. Calcium chloride enhanced the ability of para-casein micelles to aggregate. Little aggregation of para-casein micelles occurred at 0·6 mM-CaCl2 even after all of the κ-casein was hydrolysed. As the concentration of CaCl2 was increased from 3 to 60 mM, aggregation of para-casein micelles took place at progressively lower levels of κ-casein hydrolysis and the percentage hydrolysis at the Tc decreased markedly from 71±7% to 26±8%. The combined influence of CaCl2 on the velocity of the chymosin-catalysed reaction and on para-casein micelle aggregatability accounted for its effect on the average rate of coagulation (calculated by the reciprocal of the Tc). Results are consistent with the hypothesis that electrostatic repulsions and ionic bonding are involved in the interaction between chymosin and κ-casein.
Studies on the heat stability of milk: I. Behaviour of divalent cations and phosphate in milks heated in a stainless steel system
Authors: Dalgleish Douglas G. , Pouliot Yves , Paquin Paul
Published: June 2009

Skim milk was heated rapidly to 130 °C in stainless steel tubing, and was then held at this temperature for periods of up to 1 h in a stainless steel holding vessel. Samples taken at intervals during the holding period were analysed for cations, inorganic and organic phosphate and protein in the total sample and in the supernatant after centrifugation at 60 500g. The cation and total phosphate (organic+inorganic) contents of the sedimentable material remained constant throughout the heating, although the caseins became extensively dephosphorylated. Dephosphorylated protein dissociated from the casein micelles during the first 20 min of heating, after which its concentration in the serum began to decrease, perhaps indicating the onset of the heat coagulation reaction.
Metabolism of the lactating cow: II. Digestive elements of a mechanistic model
Authors: Baldwin R. Lee , Thornley John H. M. , Beever David E.
Published: June 2009

The structure and characteristics of a model suitable for estimating digestion within the rumen and rates and patterns of nutrient entry in lactating cows are presented. The model consists of 12 state variables comprising a large particle pool, small particle pools representing insoluble dietary nutrients, soluble pools representing soluble dietary nutrients, and fermentation intermediates and end products. The model was constructed assuming continuous feeding, using Michaelis–Menten or mass action kinetics. The computer program was written in ACSL to run on a VAX computer. A fourth-order Runge–Kutta procedure was used for numerical integration.

Sensitivity and behavioural analysis demonstrated that overall stability and sensitivity of the model to individual parameters was generally satisfactory, but the need to improve the description and parameterization of aspects such as particle size in relation to availability, rate and affinity constants for amino acid degradation and rate constants for particle outflow from the rumen was established. Adjustments of the model to examine discontinuous feeding regimes were undertaken and initial results with respect to changes in fermentation rates, rumen acetate levels and microbial metabolism were considered realistic.

Comparisons with experimental data were considered satisfactory on forage-based and medium concentrate-containing diets, but with diets comprising 90% cereal, some inconsistencies, especially with respect to predictions of volatile fatty acid production rates, were observed. Reasons for this are put forward and suggestions for improvements in the model are discussed.
Purification of goats' milk casein by reversed-phase high-performance liquid chromatography and identification of αs1-casein
Authors: Mikkelsen Jan , Højrup Peter , Knudsen Jens
Published: June 2009

Goats’ milk caseins were separated into four components in a single run using reversed-phase gradient high-performance liquid chromatography. The purity of the isolated components was checked by sodium dodecyl sulphate polyacrylamide gel electrophoresis, amino acid analysis and determination of the N-terminal residue. By a comparison with previously published results for goats’ milk caseins the four peaks were identified as κ-, αs1-, αs2- and β-casein. In order to confirm the existence of αsl-casein in goats’ milk, this component was sequenced for 44 steps, revealing a sequence homologous to bovine αsl-casein and almost identical to the N-terminal sequence previously published by Boulangeret al.(1984).
Heat stable proteinase fromPseudomonas fluorescensAH-70: purification by affinity chromatography on cyclopeptide antibiotics
Authors: Azcona Juan I. , Martín Rosario , Asensio Miguel A. , Hernández Pablo E. , Sanz Bernabé
Published: June 2009

A heat stable extracellular proteinase from the psychrotrophPseudomonas fluorescensAH-70 was purified to electrophoretic homogeneity by affinity chromatography on a gramicidin S–Sepharose-4B column. Bacitracin linked to Sepharose-4B was unable to retain any proteolytic activity, whereas the same antibiotic bound to AH-Sepharose-4B retained ~ 25% of the total activity. The purification procedure on the gramicidin S–Sepharose-4B column was easy to perform, fast and reproducible; it resulted in a 207-fold increase in the specific activity and a yield of 41% of the original activity. The purified enzyme was a monomer with a mol. wt of 33000. The enzyme hydrolysed whole casein and its fractions whereas no activity was observed against bovine serum albumin. The enzyme was a metalloproteinase. It was heat stable, havingD-values at 121, 135 and 150 °C of 3·8, 1·9 and 0·6 min respectively.
Increased secretion of insulin-like growth factor I into milk of cows treated with recombinantly derived bovine growth hormone
Authors: Prosser Colin G. , Fleet Ivan R. , Corps Anthony N.
Published: June 2009

Six lactating, non-pregnant Jersey cows were given subcutaneous injections of recombinantly derived bovine growth hormone for 7 d. Milk yield was increased by 4·5 kg/d on d 7, compared with the average yield of 10·7 ± 0·4 kg/d (mean ± s. e. m.) for the 7d preceding treatment. Concentrations of insulin-like growth factor I (IGF-I) in the milk increased from 0·44 ± 0·04 nmol/1 (mean ± s. e. m.) during the 7 d preceding treatment to 1·6 ± 0·2 nmol/1 on d 7 of treatment. Taking the increase in milk yield into account the total increase in the secretion of IGF-I into milk of one udder half was 6-fold. Plasma concentrations of total IGF-I rose from 15·5 + 1·3 nmol/1 (mean ± s. e. m.) on the day preceding treatment to 56·9 ± 3·6 nmol/1 (mean ± s. e. m.) on d 7 of treatment. Mammary plasma flow increased from 1·6 ± 0·09 to 2·2 ± 0·06 1/min udder half over the same time. Estimates of the amount of IGF-I that reached the mammary gland gave values of 24 and 116 nmol/min udder half before and during treatment respectively. IGF-I in milk of treated cows was associated predominantly with proteins ranging from 40000 to 150000 mol. wt, but a significant proportion (19%) of the total IGF-I was present in the free unbound form. IGF-I crosslinking studies revealed the presence in milk of one specifically labelled band at 31000 mol. wt.
Anaerobic digestion of deproteinated cheese whey in an Upflow Sludge Blanket reactor
Authors: Schröder Emilige W. , De Haast Johannes
Published: June 2009

Two l·9 1 Upflow Anaerobic Sludge Blanket (USAB) reactors, operated at 35 °C, were used for the digestion of deproteinated cheese whey substrate. The C/N ratio was 19, and the alkalinity requirements of the two reactors were satisfied by adding Ca(OH)2 and Na2CO3 in two different ratios respectively. Gas and effluent parameters indicated that reactor 1 (receiving a higher level of calcium) was superior and eventually a loading rate of 7·1 kg COD m−3 d−1 could be obtained in this reactor, compared to a loading rate of 5 kg COD m−3 d−1 which was obtained in reactor 2. Pellets with good settling abilities formed in reactor 1, while the sludge in reactor 2 developed a granular slimy appearance and settled poorly. Investigation of the ultrastructure of the sludge particles revealed a difference in the types of bacteria present in the granules.
Compensatory milk production within the bovine udder: effects of short-term non-milking of single quarters
Authors: Hamann Jörn , Reichmuth Joachim
Published: June 2009

Daily quarter-milk yields of eight high-yielding cows (24–28 kg/d) and eight heifers (14–24 kg/d) were measured to examine compensatory changes in milk production between quarters within an udder. Either one, two or three quarters per cow were left unmilked for 12 d, in early or late lactation, and then all quarters of all cows were milked normally for a further period of 12 d. Concentrate feeding levels were constant throughout the experiment.

The mean daily yield per cow fell to 26, 59 and 75% during the period of milking either one, two or three quarters respectively. Twelve days after resumption of normal milking the total daily yield per cow was the same for cows continuously milked in two, three or all four quarters. Daily yield in cows with only one quarter milked continuously recovered to only 78% of the level of the pretreatment period.

During the treatment period, the mean daily yield of the continuously milked quarters increased by almost 14% for cows milked in one quarter only, by more than 10% for two quarters milked, and by 4% per quarter if three quarters were milked. Milk yields of these quarters remained above their pretreatment levels when milking was resumed in the adjacent quarters.

There was no difference in the compensatory effect between cows and heifers in early lactation, but the compensatory effects were lower in late lactation heifers.
Repression ofPseudomonas fluorescensextracellular lipase secretion by arginine
Authors: Fernandez Leonides , San Jose Carmen , McKellar Robin C.
Published: June 2009

The effect of arginine on the production of extracellular lipase byPseudomonas fluorescens32A was studied. Arginine repressed lipase production when N was supplied partially or totally as arginine. Proteinase production was unaffected under the same conditions. Arginine did not repress lipase secretion when cells were pregrown in an arginine-containing medium; however, repression was found with uninduced cells. Several arginine-analogues were tested for the ability to repress lipase secretion and. of these, L-homoarginine and L-canavanine were the most effective. D-Arginine, L-arginine methyl ester, and L-ornithine did not cause repression. With the exception of glutamic acid and methionine, those amino acids that supplied N but not C for growth were found to repress lipase secretion. It is suggested that the accumulation of metabolic intermediate(s) may cause repression of lipase production.
Proline-specific peptidases ofStreptococcus cremorisAM2
Authors: Booth Mary , Donnelly William J. , Fhaoláin Ide Ni , Jennings P. Vincent , O'Cuinn Gerard
Published: June 2009

The present study identifies proline-specific peptidases found inStreptococcus cremorisAM2. These activities were present prcdominantly in the cytoplasmic fraction of the cells with minor amounts in cell membrane fraction. No evidence vvas found for such activities in either the extracellular fluid used to grow the cells, in the wash fraction or in the cell wall fraction. The involvement of these enzymes in release of free proline from proline-containing peptides is considered.
Effects of added salts on the heat stability of recombined concentrated milk
Authors: Augustin Mary-Ann , Clarke Phillip T.
Published: June 2009

Changes in heat stability and Ca2+activity of recombined concentrated milk (18% solids non-fat:8% fat) induced by the additions of 0·011–0·217 mol phosphate/kg skim milk solids (SMS), 0·022–0·217 mol citrate/kg SMS, 0·011–0·022 mol Ca/kg SMS and 0·016–0·067 mol EDTA/kg SMS were evaluated. Heat stability was assessed using an objective method which involved determination of viscosity after heating under controlled conditions. Low levels of added phosphate and citrate generally effected an acid shift of the viscosity–pH profile, while higher levels caused a broadening of the profile. Addition of CaCl2at a level of 0·011 mol/kg SMS resulted in a narrowing of the viscosity–pH curve; additions of higher levels resulted in a non-heat stable recombined milk concentrate. EDTA also caused a narrowing of the viscosity–pH curve. The results highlight the importance of pH control for effective stabilization of recombined milk concentrates by additions of phosphate and citrate.
Firmness values of three-phase, milk fat-based table spreads as determined by composition and temperature
Authors: Foley John , Moran Michael A. , Cooney Cornelius M.
Published: June 2009

Physical properties of aerated, high moisture and low calorie table spreads are considerably influenced by the phase volumes of the mix components. Using a statistical approach developed for mixture experiments, the firmness values of milk fat-based table spreads at three different temperatures were quantified in terms of the phase volumes of the fat, water and gas present. A simple equation was found which related changes in relative firmness values with composition at any temperature. Absolute firmness values may be obtained from relative values by multiplying by a factor, F, which is the firmness value of the similarly treated milk fat. This factor is related to the solid fat content by the formula F = 10ks+c, where F is the firmness value in kg cm–2 of milk fat having a percentage solids content, s, k is the slope of a semi-logarithmic plot and c is a constant.
Effect of pre-milking teat dipping on clinical mastitis on dairy farms in England
Authors: Hillerton J. Eric , Shearn Martin F. H. , Teverson Rachel M. , Langridge Susan , Booth James M.
Published: June 2009

Two trials were conducted to investigate the effect of pre-milking teat dipping (PMTD) on mastitis caused by environmentally associated pathogens. The first trial showed considerable variation in effect between herds, so a second, larger trial was conducted. In this second trial a comparison of the rate of clinical mastitis was made between nine matched pairs of dairy herds over 24 weeks of the winter housed period. All herds were near the national average incidence of mastitis before the trial. One member of each pair used their normal method of udder preparation throughout the trial and disinfected all teats after milking with an iodophor disinfectant. In the other nine herds the preparation of all teats, at all milkings, included dipping in a 0·25% available iodine disinfectant, which was left on the teat for 30 s. Every teat was then wiped with a paper towel before cluster attachment. There was no difference in the overall rate of mastitis or the incidence of mastitis caused by any particular type or group of pathogens between the trial groups of herds. Both groups showed a reduction in mastitis compared with the previous winter. Although there were apparent benefits in some pairs of herds there was no overall benefit. In comparison with the previous winter the control herds reported a greater reduction in mastitis than the PMTD herds. The effect of trial supervision on normal practice gave a benefit which overwhelmed any effect of PMTD. There appeared to be no effect of PMTD on the total bacterial count, cell count or iodine content of bulk tank milk. There appears to be no justification for wholesale use of PMTD although most farms and risk groups could benefit from better attention to conventional mastitis control.
Changes in milk on heating: viscosity measurements
Authors: Jeurnink Theo J. M. , De Kruif Kees G.
Published: June 2009

Skim milk was heated at 85 °C for different holding times. As a result of such heating, whey proteins, in particular β-lactoglobulin, denatured and associated with casein micelles. This led to an increase in size of the casein micelles but also to a different interaction between them. Both these changes could be described by using a quantitative model which was developed for the viscosity of so-called adhesive hard spheres. We applied the model successfully to skim milk and were able to describe on a quantitative basis the changes due to the heat treatment of milk. It was shown that after heating the casein micelles became larger and acquired a mutual attraction. The unfolding of the whey proteins and their subsequent association with the casein micelles appeared to be responsible for these changes. How this reaction influences the fouling of heat exchangers is discussed.
Influence of processing on the molecular modifications of milk proteins in the course of enzymic coagulation
Authors: Iametti Stefania , Giangiacomo Roberto , Messina Giorgio , Bonomi Francesco
Published: June 2009

The formation of hydrophobic sites on the surface of casein micelles as a consequence of enzymic coagulation of industrially heat-treated milk was studied by following the distribution of a fluorescent hydrophobic probe between a free and an aggregated protein fraction. Results were compared with those obtained when coagulation of the same milk samples was followed rheologically in a Gelograph apparatus and by tristimulus colorimetry. Thermal treatment of milk appeared to affect the accessibility of casein to enzyme action, while homogenization influenced the rate of cooperative aggregation of casein subjected to proteolysis.
Neutral volatile compounds in the raw milks from different species
Authors: Moio Luigi , Dekimpe Jocelyne , Etievant Patrick , Addeo Francesco
Published: June 2009

A comparative study was carried out on the flavour constituents of bovine, ovine, caprine and water buffalo fresh raw milks. The volatiles were isolated from milks by means of vacuum distillation and liquid–liquid extraction. Eighty neutral volatile compounds were identified using high resolution gas chromatography (HRGC) and HRGC-mass spectrometry. About 30 of these components have not been detected previously in milk. The volatiles in milk were similar for the four species, although several quantitative differences might explain the different odours. The volatiles consisted mainly of ethyl esters, especially those derived from butyric and hexanoic acids. Dimethylsulphone alone comprised ~ 25% of the volatile components in bovine, caprine and ovine milk, but only 4% in buffalo milk. Among the aldehydes, pentanal and nonanal were the most representative. Other aldehydes were present selectively: 3-methylbutanal was found only in buffalo milk; phenylacetaldehyde and benzaldehyde were present in large quantities in caprine milk, and in trace amounts in the other milks. The content of ketones, mainly 2-methylketones, was higher in buffalo milk than in the other three types. Alcohols varied between species, from 1·5% (bovine) to 5% (buffalo). Among these, 1-octen-3-ol and phenylethanol could be particularly important for the aroma of milk. The level of l-octen-3-ol in the milks was: buffalo > ewe > goat ≫ cow. Phenylethanol was not found in ewes' and goats' milk and its concentration in buffalo milk was 100 times higher than in bovine milk. Finally, indole and 4-methylphenol, interesting because of their odorant properties, were present in higher quantities in buffalo, ewes' and goats' milks than in cows' milk.
Purification and some properties of proteinase fromPseudomonas fluorescensNo. 33
Authors: Kumura Haruto , Mikawa Katsuhiko , Saito Zenichi
Published: June 2009

The extracellular proteinase fromPseudomonas fluorescensNo. 33 was purified to electrophoretic homogeneity by a procedure including precipitation with HC1 and (NH4)2SO4, and column chromatography. The enzyme was purified 170-fold giving a yield of 7 % of the original activity. The molecular mass of the purified enzyme was 48000 by SDS-PAGE. The optimum pH and temperature for the hydrolysis of casein were 8·0–9·8 and 30–35 °C respectively. The enzyme was more thermostable in synthetic milk salts solution than in 0·1 M-sodium phosphate buffer, but was heat-labile at 50 °C in both buffer Systems. The activity was inhibited byo−phenanthroline, Hg2+, Cu2+, Fe2+and, to a lesser extent, Ni2+. Caseins were susceptible to the proteinase, but degradation patterns were dependent on the form of the casein.
Rheology of whey protein concentrate solutions as a function of concentration, temperature, pH and salt concentration
Authors: Tang Qingnong , Munro Peter A. , McCarthy Owen J.
Published: June 2009

Rheological properties of whey protein concentrate (WPG) solutions were studied in steady shear, using a Bohlin VOR Rheometer, as a function of concentration, temperature, shear rate, shearing time, pH, salt type, salt concentration and solution age. At 22 °C and pH 7, the WPC solutions exhibited Newtonian behaviour up to a concentration of 10% total solids, pseudoplastic behaviour between 10 and 30% and time-dependent shear thinning at 35% and above. The apparent viscosity of solutions at 22 °C and pH 7 was linearly related to concentration up to 8%. The effect of temperature on apparent viscosity in the range 5–60 °C was closely described by the Arrhenius equation. The viscosities of WPC solutions were independent of solution age in the pH range 4–8 at all concentrations up to and including 20%, the precise pH range narrowing as concentration increased. At pH values above or below this range apparent viscosity became dependent on both pH and solution age, the age effect becoming more marked at higher WPC concentrations. Apparent viscosity at pH 7 increased markedly with both CaCl2 concentration and solution age at concentrations above 0·6 M-CaCl2, the age effect in this case increasing with CaCl2 concentration. In contrast, NaCl concentrations of up to 0·8 M-NaCl had little effect on apparent viscosity. The rheological behaviour of WPC solutions changed from time-independent to time-dependent shear thinning at high concentration, at extreme pH values, at high CaCl2 concentration (after ageing) and on heating to above ∼ 60 °C. This change is considered to be caused by the formation of structure in solutions; a 40% solution (at 22 °C and pH 6·75) exhibited classic thixotropic behaviour in a step–shear rate experiment.
Toxin production byBacillus cereusin dairy products
Authors: Sutherland Alastair D.
Published: June 2009

Spores of a known toxigenic and psychrotrophic dairy isolate ofBacillus cereus(HRM 44) were unable to grow and produce diarrhoeagenic toxin at 6 °C in creams and dairy-based products. These findings suggest that the production ofB. cereusdiarrhoeagenic toxin is unlikely to occur in creams and dairy-based products maintained within the cold chain. Growth and toxin production were readily demonstrated in creams and some desserts stored at 21 °C. Growth in creams was associated with obvious spoilage. However, in the flavoured desserts, spoilage was not always obvious before significant growth ofB. cereusand toxin production had occurred. Dairy desserts with high sugar content and/or low pH did not support toxin production and these findings are discussed.
Milk whey proteins in plasma of sows: variation with physiological state
Authors: Dodd Susan C. , Forsyth Isabel A. , Buttle Hugh L. , Gurr Michael I. , Dils Raymond R.
Published: June 2009

The whey proteins α-lactalbumin and βMactoglobulin have been investigated as potential markers of mammary development in sows by measuring their concentrations in plasma. The whey proteins were isolated from porcine milk by gel filtration, ion-exchange and hydrophobic interaction chromatography, characterized by several criteria and used to raise antibodies. Specific radioimmuno-assays were set up for porcine α-lactalbumin and β-lactoglobulin and validated for use in porcine blood and milk. Plasma levels of the whey proteins were measured in sows that were pregnant, suckling litters post partum, weaned abruptly at birth or were pregnant but mastectomized. Both whey proteins showed similar patterns in plasma post partum, falling from a maximum 1 d after parturition to values < 0·02% those in milk by day 4–5 post partum in suckling sows and showing a transient peak associated with early involution before declining to very low concentrations in non-suckling sows. α-Lactalbumin was first detected in the last week prepartum, rising markedly in the 3 d before parturition, correlated with rising prolactin (r= 0·986) and falling progesterone (r= –0·998). β-Lactoglobulin rose much earlier from 5 weeks prepartum, at the time when lobulo-alveolar mammary development is occurring, and correlated (r= 0·929) with oestradiol-17β. In mastectomized sows, concentrations of whey proteins in plasma were reduced by 90% or more when compared with intact animals, though following a similar pattern. This study shows that whey protein concentrations in plasma vary with physiological state and reflect aspects of the development of the mammary gland. The very different profiles for α-lactalbumin and β lactoglobulin prepartum indicate that they are differently controlled.