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Abstract
SummaryThree enzymes were assessed as rennet substitutes for cheese-making. The bovine and chicken pepsins used were relatively crude extracts of bovine stomach mucosa and chicken proventriculae respectively; the swine pepsin was a partially purified commercial product. The ratios of milk-clotting activity to general proteolytic activity were high for rennet and bovine pepsin and low for swine and chicken pepsins. Both bovine mucosa and chicken stomach gave low milk-clotting activities compared with calf stomach. For all the enzymes the chemical reactions causing milk clotting appeared to be the same. The milk-clotting activity showed a decrease with increase in substrate pH for all the enzymes, although they were all still active at pH 6·81.Duplicate cheeses were made from each of the swine, bovine and chicken pepsins, with rennet as a standard in each trial. The cheese-making process was similar with each enzyme, but differences appeared during ripening. The chicken-pepsin cheeses had poor body and weak Cheddar-cheese flavour, with many and intense off-flavours. The cheeses made with bovine and swine pepsins were only slightly inferior in quality and intensity of Cheddar-cheese flavour to the rennet cheeses. From a simulated cheese-making experiment it was concluded that 30–40 % of the added rennet, bovine pepsin and chicken pepsin was probably inactivated during the cheese-making process and that most or all of the swine pepsin was lost. These results provide an explanation for the variations observed in cheese ripening.It was concluded that chicken pepsin would not prove a suitable rennet substitute for making Cheddar cheese because of the quality of the cheese produced, and that bovine pepsin would not prove suitable because of the cost of preparing a suitable extract. Swine pepsin would appear to be suitable if the ripening time were to be lengthened or if another enzyme were to be added to assist ripening; it is cheaper than rennet and other rennet substitutes.
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The interaction of bovine milk caseins with the detergent sodium dodecyl sulphate. I. The relationship between the composition and the size of the protein–detergent aggregate. J DAIRY RES 2009. [DOI: 10.1017/s0022029900013303] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SummaryStudy of the dissociation of high-molecular-weight aggregates of preparations of αs1-, β-, κ-, and para-κ-casein by the detergent, sodium dodecyl sulphate (SDS), showed that there are differences in the aggregation properties of the individual caseins. Binding of detergent led first to the dissociation of casein aggregates and then to further interaction with the casein molecules. The amounts of detergent required to give the minimum sized protein-detergent aggregate when expressed as mg/mg casein were similar for κ-, para-κ- and αs1-casein but much less for β-casein. However, expressed as mole/mole the requirement for κ- and αs1-casein was similar but was twice that found for para-κ- and β-casein. The maximum amount of SDS bound was about twice that required for complete dissociation of the aggregates for κ-, para-κ- and αs1-casein but was 13 times greater for β-casein.Complete dissociation of κ-casein aggregates by SDS alone was not possible due to the presence of aggregates formed by disulphide linkages. These aggregates, which consisted of 3±1 protein molecules, accounted for about one-third of the κ-casein in the preparations examined.
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4
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Abstract
Summaryα-Lactalbumin and SDS in addition to β-lactoglobulin introduced pH sensitivity to the heat stability–pH curve of serum protein free casein micelles particularly by increasing stability in the pH range 6·4–6·7. Bovine serum albumin, ovalbumin and lysozyme caused marked destabilization of milk and casein micelle suspensions throughout the pH range 6·4–7·4. Tetramethyl ammonium bromide caused destabilization of milk at pH values > 7·0, but had no effect in the region of maximum stability while the non-ionic detergents Triton X-100 and Tween 80 had no effect on heat stability.
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5
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Abstract
SummaryA method has been developed for quantitative determination of para-κ-casein, involving spectrophotometric scanning of stained protein bands following polyacrylamide gel electrophoresis. The rate of hydrolysis of κ-casein in skim-milk at pH 6·6 and 30 °C was compared with that in EDTA-treated skim-milk under the same conditions. This showed that at the visually observed clotting time, at least 90% of the total κ-casein in milk had been hydrolysed. The time course of the reaction was consistent with all the κ-casein molecules being hydrolysed with the same efficiency. The results strongly suggest that essentially all of the κ-casein in milk is equally accessible to rennet action. This is consistent with the casein micelle being porous, or having all the κ-casein on the surface.
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6
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Abstract
SummaryThe temperature-dependent dissociation of β-casein from the casein micelles of milk and from the soluble casein complexes of colloidal phosphate-free (CPF) milk was investigated by high-speed centrifugation and gel-filtration. The percentage of the total casein in supernatants prepared by high-speed centrifugation of mid-lactation milks increased from approximately 6 to 15% on cooling the milks from 30 to 5 °C; β-casein accounted for about 46% of this increase, while αs-and κ-casein constituted 30 and 23%, respectively. On gel-filtration both of skim-milk and CPF milk on Sepharose 2B at 0, 2, 5, 10 and 25 °C, maximum amounts of free β-casein (c. 60% of total) were obtained at 5 °C. The remainder of the β-casein appeared to be more strongly bound to the αs- and κ-casein and may be involved in the internal cohesion of casein micelles. The free β-casein of both milk preparations appeared to be in equilibrium with the bound β-casein. On Sephadex G-200 columns at 5 °C, approximately 5 and 60% of the β-casein of skim-milk and CPF milk, respectively, was eluted in the free form in the expected position for a globular protein of molecular weight about 200000. At low temperatures, particularly at 5 °C, colloidal phosphate appeared to play an integrating role in the association of over half the total β-casein with the other casein components of native micelles. However, when the equilibrium between micellar and free β-casein was disturbed by gel-filtration on Sepharose 2B, the presence of colloidal phosphate did not prevent the release of most of the β-casein from casein micelles. Some problems encountered in the use of densitometry for the estimation of individual caseins on electropherograms are described.
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7
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The preparation and assessment of a suitableMucor pusillusLindt proteinase–swine pepsin mixture for Cheddar cheese-making. J DAIRY RES 2009. [DOI: 10.1017/s0022029900015338] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SummaryA simple test procedure was used to predict the most suitable mixture of Noury rennet (Mucor pusillusLindt proteinase) and swine pepsin for Cheddar cheesemaking. Duplicate cheeses were made with 6 Noury rennet–swine pepsin mixtures and with each enzyme alone, with calf rennet as the control. There were slight differences in the course of the cheese-making process and in the yields of the cheeses. Sensory evaluation showed that the most acceptable cheeses were those made by coagulant mixtures closely similar to the predicted mixture and these were as acceptable as cheeses made with calf rennet. The survival rates of different groups of bacteria were similar in all cheeses. There were differences in the products of proteolysis in the various cheeses throughout ripening, particularly with respect to products derived from αs1-casein. The Noury rennet was characterized for the proportion of milk clotting activity associated with each of 4 components and its stability in solution was determined.
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8
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Simple methods for the purification of crude κ-casein and β-casein by treatment with calcium phosphate gel. J DAIRY RES 2009. [DOI: 10.1017/s0022029900012851] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SummaryBatch methods applicable on a large scale are described for the purification of crude κ- and βκ-Casein, dissolved in urea-containing buffer, was freed from αs- and β-caseins by treatment with calcium phosphate gel and recovered in about 60% yield. β-Casein was freed from most impurities by adsorption on to calcium phosphate gel at pH 7·8 in the presence of urea and elution with 6 M-urea–N-NH4OH at 4°C. The recovery was about 50%.
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9
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A quantitative gel-filtration method for analysis of the proteinaceous fraction of Cheddar cheese. J DAIRY RES 2009. [DOI: 10.1017/s0022029900019671] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
SummaryMethods are described for the solubilization of the nitrogenous portion of cheese in a dissociating solvent system and separation of the solution into fractions on a Sephadex G-100 column under conditions where the proteins and peptides would be expected to be split into monomeric units. TheE280measurement of the fractions, expressed as a percentage of the total material eluted, followed a reproducible pattern, both with duplicate runs on the same sample and comparative runs on non-identical samples of the same type. With cheese curd, a small peak of undissociated material was obtained at the void volume of the column; this was followed by a main peak and a minor third peak, with a small quantity of material being eluted at larger volumes. A qualitatively similar pattern was obtained with 43-day-old cheese as the sample, but the main peak was smaller, the third peak was larger, and a relatively larger amount of material was eluted at greater volumes. There was only partial separation of the proteins on the column; the main peak contained β- and αs-caseins, their larger breakdown products and some para-κ-casein, and the third peak contained smaller breakdown products of the main casein fractions and para-κ-casein. Although the resolution was considerably inferior to that obtained by gel electrophoresis, the method has the advantage over this and other methods in that it gives a quantitative analysis of the sample based on molecular size. Thus, it is suggested that it may find use in analysing protein breakdown in cheese during ripening.
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10
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The effect of the chemical structure of additives on the coagulation of casein micelle suspensions by rennet. J DAIRY RES 2009. [DOI: 10.1017/s0022029900021257] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SummaryCasein micelles in milk-salts solution adsorbed charged detergents and highly-charged polypeptides strongly, neutral detergents less strongly and low molecular-weight amines weakly. A tetra-amine was adsorbed more strongly than a tri-amine. The extent of adsorption of proteins tended to rise as the molecular weight increased. Glycerol and lactate were adsorbed to a limited extent but dextran and α-ketoglutarate were not adsorbed at all. Proline was partly adsorbed, indicating that hydrophobic binding sites were available, and caused some disruption of the casein micelles. Additives were bound to approximately the same extent by casein micelles and rennet coagula. The proportions adsorbed were constant over at least 10-fold ranges of concentration. Additives which increased the rennet clotting time (RCT) acted by binding Ca2+. Most additives decreased the RCT, the extent increasing with the amount adsorbed and the positive charge on the additive. The greatest reduction in RCT was observed with those additives which had positively-charged and hydrophobic moieties and bound most strongly to casein micelles. Of the additives tested, only sodium dodecyl sulphate affected the enzymic action of rennet. The reduction in RCT may have resulted from the neutralization of the negative charge of the micelles or enhancement of their hydrophobicity, favouring hydrophobic interactions between the particles.
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11
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An examination of the factors affecting the reverse osmosis of milk with special reference to deposit formation. J DAIRY RES 2009. [DOI: 10.1017/s0022029900020227] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SummaryChanges in the dependent variables flow velocity, inlet pressure and temperature affected the rate of concentration of separated milk by reverse osmosis; their values were measured for minimum fouling at the membrane, resulting in maximum rates of concentration. Most of the deposit formed at an early stage of concentration and its extent depended on the operational variables.Electron micrographs showed that the major component of the deposit was casein micelles linked by bridges to form a lattice. Chemical analysis of the deposit confirmed a high casein content and showed that Ca phosphate was precipitated in the deposit throughout concentration. When fat globules and fat globule membrane were present in the feed, they appeared to be caught up in the deposit, but did not affect its initial formation.
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12
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Abstract
SummaryLamb and kid rennets were prepared by extraction of dried abomasa with 6% (w/v) NaCl-2% (w/v) H3BO3 and activation of the proenzymes at pH 2·0. Each gave one zone of precipitation on casein-agar gel diffusion, enabling them to be differentiated from calf rennet and pig pepsin. After agarose gel electrophoresis, the proteinase activity of lamb rennet occurred in chymosin and pepsin bands only, whereas kid rennet contained an additional proteinase of intermediate mobility. Relative to their milk-clotting activities, lamb and kid rennets contained less pepsin and were less proteolytic on both haemoglobin at pH 1·8 and casein at pH 5·3 than calf rennet. The milk-clotting activities of lamb and kid rennets increased less with decrease in pH and were more stable to storage at both the pH value of maximum stability and lower pH values than that of calf rennet. Neither cathepsin activity nor lipolytic activity on milk fat was detected in any of the 3 rennets, but lamb rennet caused slight hydrolysis of tributyrin.
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13
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Abstract
SummaryThree cationic materials markedly reduced the rennet clotting time of casein micelle suspensions, the efficacy of each being primarily dependent on the charge and the amount absorbed by the micelles. The reduction in coagulation time was unaffected by components of the milk serum other than salts. No enzymic action by lysozyme on casein micelles was detected. All materials acted by the same mechanism, increasing the affinity of rennet for the micelles and accelerating the aggregation phase. Coagulation did not occur until a minimum amount of κ-casein had been hydrolysed to para-κ-casein. All additives increased the proportion of added rennet retained by the casein in the coagulum. The results indicated that coagulation occurs by specific interactions between micelles modified by rennet.
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Comparison of the rates of proteolysis during ripening of Cheddar cheeses made with calf rennet and swine pepsin as coagulants. J DAIRY RES 2009. [DOI: 10.1017/s0022029900019683] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
SummaryThe rates of proteolysis during ripening were followed in cheeses made with either calf rennet or swine pepsin and either starter or δ-gluconic acid lactone (GAL) as a replacement for the starter. A gel-filtration column technique and starch-gel electrophoresis were used for analysis, and bacterial counts were made on all samples. Proteolysis was faster in cheeses made using GAL than in those made using starter and also slightly faster in GAL cheeses made with swine pepsin than in those made with rennet. Further, it was considerably slower in starter-containing cheeses made with swine pepsin than in those made with rennet. It is suggested that these differences were due to the much greater rate of development of acidity in cheeses made with GAL than in those made with starter, which resulted in more of the coagulant being incorporated into the curd in an active state. The rate of proteolysis in starter-containing cheeses appeared to follow a characteristic course, being initially slow, then markedly increasing with a later slow decline. It is suggested that the increase in the rate of proteolysis was due to an increase in the total activity of bacterial proteinases released by lysis of the bacteria. Indications were obtained that the coagulants and bacterial proteinases catalysed broadly similar patterns of protein breakdown in cheese, and that medium-sized peptides (mol. wt 9000–14000) were formed as definite intermediates in the process. The results also showed that rennet and swine pepsin remained active for at least 7 months in GAL cheeses, that rennet contributed significantly to proteolysis in starter-containing cheeses, and that swine pepsin was at least extensively inactivated and possibly completely inactivated during cheese-making with starter.
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15
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Abstract
SummaryTwo possible hypotheses for the mechanism of milk clotting were tested. The results obtained constituted strong evidence against one and suggested that the second is improbable. Milk was separated into a 5-fold-concentrated casein micelle suspension and milk serum. Pre-renneting of the serum did not reduce the rate of clotting on subsequent addition to the micelle suspension whether or not the conditions were such that the para-κ-casein became extensively aggregated. Washing of casein micelles up to 3 times with milk dialysate at 23°C extracted very little casein from the micelles and did not increase the clotting time of micelles resuspended to about the same concentration as in milk. The results appear to constitute decisive evidence against the hypothesis of milk clotting proposed by Parry & Carroll (1969). S-carboxymethyl-κ-casein, S-carboxymethyl-κ-casein containing 2·5 dimethylaminonaphthalene sulphonyl residues per mole, and rennin-treated dimethylaminonaphthalene sulphonated-S-carboxymethyl-κ-casein all bound Ca to the same extent at 30°C and pH 6·5, over the range 0·5–15·3 mM-CaCl2. This adds support to existing evidence that milk clotting does not involve formation of Ca bridges between casein micelles.
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Lefebvre-Cases E, La Fuente BTD, Cuq J. Effect of SDS on Casein Micelles: SDS-Induced Milk Gel Formation. J Food Sci 2006. [DOI: 10.1111/j.1365-2621.2001.tb15578.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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18
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Influence of chemical agents on interactions in dairy products: Effect of SDS on casein micelles. Colloids Surf B Biointerfaces 1998. [DOI: 10.1016/s0927-7765(98)00054-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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19
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Creamer LK, Richardson T. Anomalous behavior of bovine alpha s1- and beta-caseins on gel electrophoresis in sodium dodecyl sulfate buffers. Arch Biochem Biophys 1984; 234:476-86. [PMID: 6497382 DOI: 10.1016/0003-9861(84)90295-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Electrophoresis in the presence of sodium dodecyl sulfate (SDS) provides a relatively simple means of determining molecular weights of proteins. This technique relies on the validity of a correlation between some function of Mr and the mobility of the protein through the gel matrix. However, bovine caseins (especially alpha s1-casein) have lower mobilities than expected on the basis of their known Mr. The binding of SDS to both alpha s1-casein (Mr 23,600) and beta-casein (Mr 24,000) reached a maximum at the slightly low value of 1.3 g SDS/g protein. Gel-filtration chromatography showed, however, that the alpha s1-casein:SDS complex was larger than the beta-casein:SDS complex at pH 6.8 or 7.0, but that they were similar in size at pH 2.9 or 3.0. Circular dichroism spectra indicated that the low helical structure content of both alpha s1- and beta-casein increased with the addition of SDS and/or decreasing the pH to 1.5. 13C NMR results showed that SDS bound to alpha s1- and beta-casein in the same way as it did to bovine serum albumin. Either esterification or dephosphorylation followed by amidation of alpha s1-casein increased its mobility in SDS-gel electrophoresis, but neither modification affected beta-casein mobility. These and other results indicate that the low electrophoretic velocity of alpha s1-casein in SDS-gel electrophoresis results from its unexpectedly large hydrodynamic size. This is caused by localized high negative charges on certain segments of alpha s1-casein, which would induce a considerable amount of inter- and intrasegmental electrostatic repulsion, leading to an expanded or extended structure for portions of the alpha s1-casein molecule in the presence of SDS. It is clear that the conformation, and hence the equivalent radius, of an SDS:protein complex is determined by the sequence of amino acids in the protein and that, a priori, it cannot be anticipated that the electrophoretic mobility of such a complex will bear more than a casual relationship to the Mr of the protein.
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20
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Blackwell JH, McKercher PD, Kosikowski FV, Carmichael LE, Gorewit RC. Physicochemical transformation of milk components and release of foot-and-mouth disease virus. J DAIRY RES 1983; 50:17-25. [PMID: 6302144 DOI: 10.1017/s0022029900032489] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Possible mechanisms for protective roles of milk components on foot-and-mouth disease virus present in the milk of infected cows were examined. Light scattering bands collected from Ficoll-sucrose gradient fractions of skim-milk contained membrane-limited structures but these were non-infectious for bovine kidney cells. Infectivity titres in buttermilk higher than those of the original cream or butter suggested association of virus with milk fat globules. Increased infectivity titres in skim-milk after treatment with SDS suggested release of virus particles from dissociated casein micelle subunits. Chelating agents, de-emulsifying agents and trypsin, which alter the structure of the individual milk components casein, lipid and milk fat globule membrane were without effect on infectivity titres.
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21
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Creamer LK. A study of the effect of sodium dodecyl sulfate on bovine beta-casein self-association. Arch Biochem Biophys 1980; 199:172-8. [PMID: 7356328 DOI: 10.1016/0003-9861(80)90270-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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22
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23
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24
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Barratt MD, Rayner L. Lysolecithin-casein interactions. I. Nuclear magnetic resonance and spin label studies. BIOCHIMICA ET BIOPHYSICA ACTA 1972; 255:974-80. [PMID: 4336420 DOI: 10.1016/0005-2736(72)90407-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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25
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Nakahori C, Nakai S. Fractionation of Caseins Directly from Skimmilk by Gel Chromatography. 1. Elution with Sodium Dodecysulfate. J Dairy Sci 1972. [DOI: 10.3168/jds.s0022-0302(72)85426-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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26
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27
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Nagasawa T, Kiyosawa I, Kuwahara K. Human casein. II. Isolation of human beta-casein fraction and human beta-casein B. J Dairy Sci 1970; 53:136-45. [PMID: 5413654 DOI: 10.3168/jds.s0022-0302(70)86170-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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