bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of the properties of dissociated bovine casein micelles
Authors: Creamer L. K. , Berry Gillian P. 
Published: June 2009

SummaryAlthough casein micelles are disrupted by removal of Ca, individual caseins remain aggregated in sub-micellar casein aggregates or sub-units. These sub-units have been studied by: (1) the use of gel filtration on Sepharose 4B at 6, 20 and 37°C at pH 6·7 and 0·1 ionic strength, (2) ultracentrifugation and (3) electron microscopy. At 37°C the protein composition of the sub-units varied across the gel-filtration peak, with κ-casein being eluted towards the leading edge and the ratio of αs1- to β-casein being almost constant across the peak. Re-chromatography of the protein from the leading edge of this peak gave a new wide peak with the κ-casein again being eluted towards the leading edge. However, αs1-casein was eluted before β-casein in the leading edge of the new peak. Prior treatment of the casein micelles by dispersion with 6 m-urea solution, precipitation with acid or reduction with 2-mercaptoethanol did not alter the gel-filtration pattern. An examination of the purified casein components and their mixtures showed that a 1:1 ratio mixture of αs1- and β-casein had the same peak maximum elution volume as casein micelle sub-units. κ-Casein by itself eluted at the void volume of the gel-filtration column, but after admixture with a sample of small micelles it eluted at the leading edge of the sub-unit peak and was indistinguishable from the κ-casein normally present. These results suggest that the sub-units are in equilibrium with their component caseins and that their size distribution is determined by only those factors (such as protein concentration, pH, temperature and ionic strength) which determine the strength of association between the casein components. The results from electron microscopy and ultracentrifugation support these conclusions.
Autoxidation in milk rich in linoleic acid I. An objective method for measuring autoxidation and evaluating antioxidants
Authors: Sidhu G. S. , Brown M. A. , Johnson A. R. 
Published: June 2009

SummaryAutoxidation was studied in milk obtained from cows fed on formaldehyde-treated casein-safflower oil supplement. The fat of this milk contained high levels of linoleic acid. A rapid disappearance of dissolved oxygen (DO), measured by using an oxygen electrode, from milk samples stored at 0°C in tubes without headspace, coincided with the development of oxidized flavours detected organoleptically. A correlation coefficient of 0·9 with 69 degrees of freedom (P < 0·001) was obtained between the amount of DO disappearing and the taste panel scores for oxidized flavours.Butylated hydroxyanisole, sesamol, nordihydroguaiaretic acid, ethoxyquin, or butylated hydroxyanisole with propylgallate or tocopherols, when added in emulsified form to the milk at the rate of 10–15 mg/l milk, checked the development of oxidized flavours and the rapid disappearance of DO. Other antioxidants tested were either ineffective or imparted off-flavours to milk.Samples of mare's milk neither developed oxidized flavours nor showed rapid disappearance of DO over a test period of 8 d.The oxygen electrode provides a convenient and sensitive method for studying autoxidation and evaluating antioxidants in milk.
Dephosphorylation of bovine casein by milk alkaline phosphatase
Authors: Lorient D. , Linden G. 
Published: June 2009

SummaryThe pH of optimum activity of alkaline phosphatase from cow's milk depended on the substrate, being 10·1 for p-nitrophenylphosphate, 8·6 for phosphoserine, 8·0 for phosvitin and 6·8 for casein. Individual casein components were dephosphorylated more rapidly than mixtures of αs- and β-caseins or of αs-, β- and κ-caseins and micellar casein. Mixtures of 2 components involving κ-casein were more readily dephosphorylated than αs- and β-casein mixtures. At pH 6·8, lactose, whey proteins and phosphate ions had an inhibitory effect. β-Lactoglobulin had an inhibitory effect only when the pH of the reaction was lower than the optimum pH value of the enzyme. Mg2+ and Zn2+ were not inhibitory. The optimum conditions for dephosphorylation of casein are described.
Contribution of rennet and starter proteases to proteolysis in Cheddar cheese
Authors: O'Keeffe R. B. , Fox P. F. , Daly C. 
Published: June 2009

SummaryProteolysis in aseptic, chemically acidified (GDL) cheese and in starter cheese made under controlled bacteriological conditions (i.e. free of non-starter micro-organisms) was measured by gel electrophoresis, the formation of pH 4·6- and 12% TCA-soluble N, gel filtration and the liberation of free amino acids. The results show that rennet was mainly responsible for the level of proteolysis detected by gel electrophoresis, pH 4·6-soluble N and gel filtration i.e. large, medium and small peptides. However, rennet alone was capable of producing only a limited range of free amino acids; only methionine, histidine, glycine, serine and glutamic acid were produced at quantifiable levels (> 0·2 μmoles/g) in GDL cheese; it is suggested that free amino acids in Cheddar cheese are mainly the result of microbial peptidase activity. The levels of free amino acids in the starter cheese were considerably lower than values reported for commercial Cheddar.
Effect of feeding fat to dairy cows receiving a fat-deficient basal diet: I. Milk yield and composition
Authors: Banks W. , Clapperton J. L. , Ferrie Morag E. , Wilson Agnes G. 
Published: June 2009

SummaryThe effects of supplementing a basal diet, in which the low level of fatty acids limited milk production, with soya oil, a palm oil/palmitic acid mixture and tallow, on the yield of milk and of its constituents, and on the composition of the milk, are reported. The yields of milk and milk fat were greatly increased by all the oil-supplemented diets; the mean daily yield of solids-not-fat (SNF) was also increased, but supplementation with soya oil caused the yield of crude protein (CP) to decrease, whereas the other fat-rich concentrate mixtures gave the same mean yield of protein as did the low-fat, control diet. All 3 oil-supplemented diets lowered the proportion of CP in the milk, but the SNF content was unchanged by any treatment. Dietary soya oil tended to lower the proportion of fat in the milk, whilst the palm oil/palmitic acid mixture raised it, with the tallow exerting no effect. The results are discussed in relation to previous work in which these dietary oils have been used, but in which the intake of fatty acids from the control diets did not limit milk production to the extent reported here.
Heat stability of forewarmed milks: influence of κ-casein, serum proteins and divalent cations
Authors: Morrissey P. A. , O'Mahony F. 
Published: June 2009

SummaryAddition of isolated κ-casein to milk reduced the destabilizing influence of forewarming, while the addition of isolated β-lactoglobulin (β-lg) to the κ-casein-enriched systems resulted in a loss in stability on forewarming. This effect was ascribed mainly to a β-lg:κ-casein interaction. Some individual milks were unaffected by forewarming while others were markedly destabilized by the same treatment. Addition of Ca2++ Mg2+and interchanging of milk sera by dialysis influenced stability.It is concluded that milks which are destabilized by forewarming generally give a type A response (minimum in the pH–heat stability curves) and that preheat-stable milks generally give a type B curve (no minimum).
The influence of dietary protein intake on milk production and blood composition of high-yielding dairy cows
Authors: Treacher R. J. , Little W. , Collis K. A. , Stark A. J. 
Published: June 2009

SummaryCows were fed either 75 or 100% of the recommended intake levels for protein and 100% of recommended energy levels (Agricultural Research Council, 1965) from 8 weeks pre-calving until 14 weeks post calving. From 14 weeks post calving and to the end of lactation all the cows received 100% of the recommended protein and energy intakes.The mean of the 305-d milk yields of the 2 groups was not significantly different and although cows on the lower protein intake produced less lactose during the first 14 weeks of lactation there was no significant difference in total lactose, fat, protein or total solids production between the groups. In both groups blood packed-cell volume, red cell count and haemoglobin decreased during the first 10 weeks of lactation and then began to increase in the high-protein group. The cows receiving the low-protein diet showed a similar increase only when they received the high-protein ration from 14 weeks post calving. The mean interval from calving to conception was 27·5 weeks in the high-protein group and 20 weeks in the low-protein group.It is concluded that feeding 75% of protein requirements to dairy cows during the first 14 weeks of lactation does not reduce milk yield or quality significantly and probably has no adverse effect on fertility.
The heat stability of milk and concentrated milk containing added aldehydes and sugars
Authors: Holt C. , Muir D. D. , Sweetsur A. W. M. 
Published: June 2009

SummaryThe addition of simple aldehydes brought about large increases in the heat stability of both skim-milk and concentrated skim-milk over a comparatively wide milk–pH range. The coagulation time–pH minima of type A milks were completely removed by aldehyde treatment. Some sugars, which react readily as aldehydes on heating, were also shown to stabilize concentrated milk to prolonged heat treatment at 120 °C.
The effect of supplementation of the diet of lactating Jersey cows with varying levels of acetic acid
Authors: Johnson C. Lewis , Kitchen David I. 
Published: June 2009

SummaryTwO Latin-square experiments using lactating Jersey cows have been made to determine the response to 4 levels of acetic acid given as a supplement to diets fed at Woodman's Standards. The response in milk yield and composition to daily supplementary infusions of acetic acid is curvilinear, the point of inflexion occurring between the levels of 450 and 600 ml acetic acid/d. The direction of responses to the 150-ml level of infusion varied between the experiments. At the 600-ml level of addition the non-significant increases in milk fat, protein and lactose yield led to a significant increase in solids corrected milk yield. The effects of acetic acid infusion on the composition of the milk fat were determined.
Natural variations in the average size of bovine casein micelles: III. Studies on colostrum by electron by microscopy and light scattering
Authors: Brooker Brian E. , Holt Carl 
Published: June 2009

SummaryBovine casein micelles in pre- and post-partum colostrum have been characterized by both electron microscopy and light scattering. Attempts have been made to relate the changes in average micelle size to the partitioning of Ca and inorganic orthophosphate betwen the colloidal and aqueous phases. Pre-partum colostrum, and to a decreasing extent post-partum colostrum, contain casein micelles several microns in diameter. These giant micelles often contain closed cavities suggesting that they are formed by aggregation of particles comparable in size to normal casein micelles. Electron microscopy of mammary gland alveoli from nearterm pregnant heifers shows clear differences in average size between micelles immediately before and after secretion from Golgi vesicles. It appears that micelles aggregate in the alveolar lumen, possibly as a result of continuing co-precipitation of casein with Ca phosphate.
Intermicellar relationships in rennet-treated separated milk: II. Process of gel assembly
Authors: Green Margaret L. , Hobbs David G. , Morant Steven V. , Hill Valerie A. 
Published: June 2009

SummaryThe aggregation of casein micelles in milk by the action of rennet, examined by electron microscopy and viscometry, was correlated with visually-observed coagulation. The spatial relationships between micelles were quantified from measurements made on micrographs. Aggregation did not start until about 60% of the rennet-clotting time, when the enzymic action was almost complete. The micelles tended to form chains which then linked into a loose network. This became more extensive with time as the average size of the aggregates increased. By the clotting time, most micelles were in contact with another and a network was beginning to form. Initially, micelles probably linked by bridges. These then appeared to contract, bringing the particles into contact and eventually causing partial fusion.
Peptide hydrolases ofLactobacillus casei: isolation and general properties of various peptidase activities
Authors: Soda Morsi El , Desmazeaud Michel J. , Bergère J.-L. 
Published: June 2009

SummaryDiscovery of an endopeptidase by gel chromatography and separation of 3 exopeptidases (a dipeptidase, an aminopeptidase and a specific carboxypeptidase) fromLactobacillus caseiNCDO 151 by affinity chromatography is described. The 3 exopeptidases were strongly inhibited by the metal chelators EDTA and 1,10-phenanthroline but were reactivated with Co2+and Mn2+. The pH optima for aminopeptidase, dipeptidase and carboxypeptidase activities were 6·5, 7·6 and 7·2, respectively. Maximum activity was obtained at 45 °C for the aminopeptidase, at 30 °C for the dipeptidase and at 40 °C for the carboxypeptidase.The substrate specificities of the 3 enzymes were also studied. The properties of these 3 enzymes are compared with those of other bacteria.
Proteolysis in Cheddar cheese: role of coagulant and starter bacteria
Authors: O'Keeffe Arthur M. , Fox Patrick F. , Daly Charles 
Published: June 2009

SummaryCheddar cheese was produced free of non-starter bacteria, acidified with starter or glucono-δ-lactone and containing active coagulant (chymosin or pepsin) or inactivated coagulant (pepsin). The level and type of proteolysis in the experimental cheeses was monitored by protein solubility at pH 4·6 and in 12 % TCA, polyacrylamide gel and high voltage paper electrophoresis, gel filtration and paper chromatography. The results show that the coagulant was primarily responsible for the formation of large peptides while small peptides and free amino acids were produced principally by the starter, possibly from coagulant-produced peptides.
Whey protein denaturation in heated milk and cheese whey
Authors: Hillier Robyn M. , Lyster Richard L. J. 
Published: June 2009

SUMMARYQuantitative polyacrylamide gel electrophoresis has been used to measure residual native whey proteins remaining after heat treatment of skim-milk and cheese whey in a kinetic study. The denaturation of α-lactalbumin (α-la) appeared to be first order, but was probably a second-order reaction displaying pseudo first-order kinetics. The denaturation of both β-lactoglobulin A and B (β-lgA and β-lgB) followed second-order kinetics while that of serum albumin was more complex, and could equally well be described as first or second order. Equations are given relating logk1(in s-1) to temperature for α-la denaturation in skim-milk between 70 and 95 °C and between 100 and 150 °C. Similarly, equations relating logk2(in lg-1s-1) to temperature are given for ²-lgA in skim-milk between 100 and 150 °C, and for ²-lgB between 95 and 150 °C. The relative heat stability of ²-lgA and ²-lgB was found to vary.Below 95 °C ²-lgA appeared slightly more thermostable than ²-lgB in skim-milk, and the same was observed in cheese whey below 100 °C. Above these temperatures ²-lgB appeared more stable than ²-lgA.Denaturation of ²-lgB was only slightly more rapid in skim-milk than in whey at temperatures below 95 °C, but was significantly slower at higher temperatures.
Strains ofStreptococcus lactiswhich contain β-galactosidase
Authors: Farrow John A. E. , Garvie Ellen I. 
Published: June 2009

SUMMARYIn the past the classification of ATCC 7962 as a strain ofStreptococcus lactishas been questioned because it contains β-galactosidase and not β-phosphogalactosidase, and because all extracts do not react with group N antiserum. A comparison was made between ATCC 7962 and known strains ofStr. lactisusing physiological properties, some of the properties of the lactate dehydrogenases and percent guanine plus cytosine in the DNA. ATCC 7962 was distinguished only by its ability to ferment pentoses. The degree of hydribization between the DNA of ATCC 7962 and that of a typical strain ofStr. lactiswas 67 %. ATCC 7962 is an atypical strain ofStr. lactis. The properties of a wild strain ofStr. lactisisolated from radishes in Brunei which contains β-galactosidase and β-phosphogalactosidase, are given also. This strain ferments pentoses.
A genetic and biochemical analysis of a polymorphism of bovine αs2-casein
Authors: Grosclaude François , Joudrier Philippe , Mahé Marie-Françoise 
Published: June 2009

SUMMARYUsing gel electrophoresis a genetic polymorphism of αs2-casein (Cn) was discovered in individual milk samples from 2 bovine breeds of the eastern part of France (Vosgienne and Montbéliarde). The 3 observed phenotypes (Plate 1) are determined by 2 co-dominant alleles at an autosomal locus. The αs2-Cn A variant was the only one known up to now in European breeds (reference variant) and ±s2-Cn D is a new variant, whose bands overlap the β-casein A band at pH 8.6, and migrate faster than αs2-Cn A at pH 3.0.The sequence of the polypeptide chain αs2-Cn D differs from that of αs2-Cn A by the deletion of a very acidic nonapeptide, which includes a cluster of 3 phosphoseryl residues. Due to the characteristics of the reference sequence, this deletion cannot be exactly located but it involves residues 50–58, or 51–59, or 52–60.A genetic analysis shows that locus αs2-Cn is closely linked to the cluster αsl-Cn–β-Cn-K-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.
The formation and structure of some proteose-peptone components
Authors: Andrews Anthony T. 
Published: June 2009

SUMMARYTwo constituents of the proteose-peptone fraction of bovine milk have been isolated and characterized. Component 5 (PP5) has been shown to represent residues 1–105 and 1–107 of the β-casein amino acid sequence, while component 8-fast (PP8F) corresponds to residues 1–28 of β-casein. Thus, these proteose-peptones represent the N-terminal portions of the β-casein molecule, produced by proteolytic cleavages which form the γ1-, γ2- and γ3-caseins from the C-terminal part. The continuing formation of the total proteose-peptone fraction, PP5, PP8F and the γ-caseins during storage of raw milk at 18 or 37 °C has also been demonstrated
Casein micelles: the colloid-chemical approach
Authors: Payens Theodoor A. J 
Published: June 2009

SUMMARYThe colloidal properties of micellar casein are reviewed. It is shown that the behaviour of intact micelles is much at variance with the predictions from the Schulze–Hardy rule, and that therefore their stability cannot be explained by the principles of the DLVO theory. Towards electrolyte, micelles behave as a protein rather than a lyophobic colloid.Casein is a strong protective colloid. In the micelle, however, it does not completely cover the inorganic constituent which remains sensitive to changes in the ionic environment.The rate theory of the enzyme-induced clotting of casein micelles is summarized. It is shown that the lag phase in the clotting is due to the second order of the coagulation reaction. Flocculation rate constants of micelles have been deduced from clotting times. Their relatively low values can be attributed to an orientational constraint. Practical consequences of the theory with respect to clot structure, gelation of sterilized products and cheese manufacture are discussed.
Properties of artificial casein micelles
Authors: Schmidt Daniël G. 
Published: June 2009

SUMMARYA survey is given of the relationships between various properties of artificial casein micelle systems and their composition with respect to αs1-, β and κ-casein, colloidal phosphate and citrate. Properties investigated were: the amount of colloidal phosphate, the micellar size, and the stability of the micelle towards dialysis, pressure, ethanol and heat.
Utilization of milk proteins as starting materials for other foodstuffs
Authors: Morr Charles V. 
Published: June 2009

SUMMARYThe modern food-processing industry is placing more and more emphasis upon the utilization of protein ingredients to provide specific functional properties to a wide range of formulated foods. Isolated milk protein products represent an important and valuable source of protein ingredients due to their recognized superior nutritional, organoleptic and functional properties. This paper provides up-to-date information on the quantities, production processes, composition, general properties, and specific functional properties of the major milk protein products, e.g. caseinates, co-precipitates, lactalbumin, whey protein concentrates and milk blends. The subject of chemical and enzymic modification to improve certain functional properties of milk proteins is considered briefly.
Observations on the influence of high cell count on lipolysis in bovine milk
Authors: Salih Amer M. A. , Anderson Malcolm 
Published: June 2009

SummaryThe effect that changes in composition which occur in milks possessing high cell counts have on milk lipolysis has been investigated. High cell counts were produced either by intramammary infusion ofEscherichia coliendotoxin orStreptococcus agalactiaeor by addition of washed cells which were isolated from milk obtained from quarters infused with endotoxin. Free fatty acid levels in milk were measured in terms of acid degree value (ADV) either as initial ADV measured immediately after milking or ADV developed after a prescribed incubation period.There was an increase in initial ADV after the infusion either of endotoxin or ofStr. agalactiaerelative to a control quarter. This increase appeared to be associated with changes in cell count, but in absolute terms the influence of cells on ADV became less as cell count increased. Neither type of infusion had any effect on lipoprotein lipase activity. The addition of washed cells to normal milk resulted in an increase in developed ADV, but the increment was not as large as that produced by the addition of 1% blood serum. When cream and skim-milk from endotoxin-treated quarters and control quarters were mixed in different combinations with and without additional cells, developed ADV was higher in those samples containing endotoxin cream and those with added cells. Milk from a quarter treated with endotoxin was diluted with its own skim-milk to produce different cell counts and ADV was determined after various time intervals at 4 and 37 °C. Lipolysis increased with increasing cell count, but a depression in lipolytic rate was noted after incubation for 6 h at 4 °C and 20 min at 37 °C.The proportion of skim-milk lipoprotein lipase activity in milk serum was larger both in milks possessing high cell counts and in normal milk adjusted to between 5 and 20 mM-NaCl by addition of solid NaCl. These levels of NaCl inhibited lipolysis.The possible direct and indirect effects of high cell count on milk lipolysis are discussed.