bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of milk protein concentration on the gelling activity of chymosin and bovine pepsin
Authors: Garnot Pascaline , Corre Christian 
Published: June 2009

SummaryTwo stages of gelling by the milk-clotting enzymes chymosin and pepsin were studied at different milk protein concentrations, using milk retentates. In each case, enzymic velocity versus protein concentration described a standard hyperbola. According to the experimental conditions such as pH and type of enzyme, which changed the enzyme concentration used, either the quasi-linear part of the hyperbola was observed, or the velocity hardly increased and tended to a limiting value. Gelling occurred with a lower degree of proteolysis of κ-casein when the protein concentration increased but a minimum proteolysis (1% of total nitrogenous matter content) was required for aggregation to take place. Gelling time varied with the protein concentration, the pH and the enzyme concentration. The final degree of proteolysis of κ-casein was the same whatever the substrate concentration used.
The effect of lα-hydroxycholecalciferol on the concentrations of calcium, magnesium and inorganic phosphate in the plasma of parturient cows
Authors: Wittwer Fernando , Ford Edwin J. H. 
Published: June 2009

Summary135 Cows which were expected to produce a second or subsequent calf within 4–11 d received an intramuscular injection of 500 μg lα-hydroxycholecalciferol (lα-OHD3). In those animals in which the interval between injection and calving was at least 7 d there was, at 7 d after injection of lα-OHD3, a significant increase (P < 0.001) in the blood plasma concentrations of Ca and Pi and a significant reduction (P < 0.05) in that of Mg, compared with those in control animals. Within 24 h of calving there was a significant increase (P < 0.001) in the concentration of Pi but no change in Ca or Mg compared with pre-injection levels, whilst the control animals showed a significant fall (P < 0.001) in the concentration of Ca and a rise in those of Pi (P < 0.001) and Mg (P < 0.05). There was a significant reduction (P < 0.001) in the number of animals with hypocalcaemia (defined as a plasma Ca concentration <1.9 mmol/1) in all animals injected with lα-OHD3; this reduction was particularly marked when the interval between injection and calving was between 1 and 8 d. The previously reported reduction in the incidence of clinical milk fever is considered to be a consequence of the effect of lα-OHD3 on the concentration of Ca in plasma.
Detection of carbonyl sulphide in Cheddar cheese headspace
Authors: Aston John W. , Douglas Keith 
Published: June 2009

SummaryCarbonyl sulphide (COS) was detected in the headspace of Cheddar cheeses in concentrations ranging from 0·01 ng ml-1 to 0.3 ng ml-1. It was also found in the headspace above certain packaging materials and sealing materials used in the analytical procedures. Evidence that COS was produced within the cheese was given by the findings that experimental cheese containing added cysteine had consistently higher COS levels (up to 1·0 ng ml-1) and that COS could be produced chemically from mixtures of cysteine or methionine with riboflavin and ascorbic acid in laboratory trials.
Heat stability of milk: synergic action of urea and carbonyl compounds
Authors: Shalabi Samweul I. , Fox Patrick F. 
Published: June 2009

SUMMARYUrea stabilizes milk to heat only in the presence of a carbonyl compound, such as a reducing sugar. Low molecular weight carbonyl compounds can increase stability in the absence of urea whereas larger molecules, e.g. hexoses and reducing disaccharides, cannot. However, the efficacy of all carbonyl compounds is increased considerably in the presence of urea. Aldehydes and ketones of similar molecular weights appear to be equally effective stabilizers. The optimum concentration of lactose in milk for stability was approximately 1% irrespective of urea concentration within the range 5–20 mM. However, modifying the lactose content of concentrated milks (approximately 8.5% protein) had little effect on heat stability.
Stability of lipoprotein lipase activity in bovine milk
Authors: Anderson Malcolm 
Published: June 2009

SUMMARYThe 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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYExplants 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

SUMMARYThe 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

SUMMARYThe 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

SummaryUsing 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

SummaryAs 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

SummaryBacterial 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

SummaryThe 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

SummaryExperiments 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

SUMMARYTo 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

SUMMARYThe 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

SUMMARYTotal 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

SUMMARYWhey 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

SUMMARYThe 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.