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1.
In this study, factors influencing the disruption and aggregation of casein micelles during high-pressure (HP) treatment at 250 MPa for 40 min were studied in situ in serum protein-free casein micelle suspensions. In control milk, light transmission increased with treatment time for approximately 15 min, after which a progressive partial reversal of the HP-induced increase in light transmission occurred, indicating initial HP-induced disruption of casein micelles, followed by reformation of casein aggregates from micellar fragments. The extent of HP-induced micellar disruption was negatively correlated with the concentration of casein micelles, milk pH, and levels of added ethanol, calcium chloride, or sodium chloride and positively correlated with the level of added sodium phosphate. The reformation of casein aggregates during prolonged HP treatment did not occur when HP-induced disruption of casein micelles was limited (<60%) or very extensive (>95%) and was promoted by a low initial milk pH or added sodium phosphate, sodium chloride, or ethanol. On the basis of these findings, a mechanism for HP-induced disruption of casein micelles and subsequent aggregation of micellar fragments is proposed, in which the main element appears to be HP-induced solubilization of micellar calcium phosphate. 相似文献
2.
Ausar SF Bianco ID Castagna LF Alasino RV Narambuena CF Leiva EP Beltramo DM 《Journal of agricultural and food chemistry》2005,53(23):9031-9038
The cationic hydroxyethylcellulose Polyquaternium 10 (PQ10) was found to produce a dose-dependent destabilization of casein micelles from whole or skim milk without affecting the stability of most of the whey proteins. The anionic phosphate residues on caseins were not determinant in the observed interaction since the destabilization was also observed with dephosphorylated caseins to the same extent. However, the precipitation process was completely inhibited by rising NaCl concentration, indicating an important role of electrostatic interactions. Furthermore, the addition of 150 mM NaCl solubilized preformed PQ10-casein complexes, rendering a stable casein suspension without a disruption of the internal micellar structure as determined by dynamic light scattering. This casein preparation was found to contain most of the Ca2+ and only 10% of the lactose originally present in milk and remained as a stable suspension for at least 4 months at 4 degrees C. The final concentration of PQ10 determined both the size of the casein-polymer aggregates and the amount of milkfat that coprecipitates. The presence of PQ10 in the aggregates did not inhibit the activity of rennet or gastrointestinal proteases and lipases, nor did it affect the growth of several fermentative bacteria. The cationic cellulose PQ10 may cause a reversible electrostatic precipitation of casein micelles without disrupting their internal structure. The reversibility of the interaction described opens the possibility of using this cationic polysaccharide to concentrate and resuspend casein micelles from whole or skim milk in the production of new fiber-enriched lactose-reduced calcium-caseinate dairy products. 相似文献
3.
Anema SG 《Journal of agricultural and food chemistry》2007,55(9):3635-3642
Reconstituted skim milk at pH from 6.5 to 7.1 was unheated, preheated (68 degrees C/20 min), or heated at 90 degrees C for 20-30 min. On preheating, the size of the casein micelles decreased by about 5-20 nm, with a greater effect at higher pH. The casein micelle size of the heated milk at pH 6.5 increased by about 30 nm when compared to that of the unheated or preheated milk. As the pH was increased before heating, the particle size gradually decreased so that, at pH 7.1, the size was markedly smaller than that for the unheated milk and slightly smaller than that for the preheated milk. High levels (about 85%) of denatured whey protein associated with the casein micelles at pH 6.5, and this level decreased as the pH increased so that, at pH 7.1, low levels (about 15%) were associated with the micelles. Low levels of alphaS-casein and beta-casein were found in the serum regardless of the heat treatment or the pH of the milk. At pH 6.5, low levels (about 10%) of kappa-casein were also found in the milk serum. In the unheated milk, the level of serum kappa-casein increased slightly with increasing pH; in the heated samples, the level of serum kappa-casein increased markedly and linearly with increasing pH so that, at pH 7.1, about 70% of the kappa-casein was in the serum phase. The results of this study indicate that the pH dependence of the levels of serum phase kappa-casein may be responsible for the change in distribution of the whey proteins between the colloidal and serum phases. This is the first report to demonstrate significant levels of dissociation of kappa-casein from the micelles at pH between 6.5 and 6.7, although this dissociation phenomenon is well known on heating milk at high temperatures at pH above 6.7. 相似文献
4.
Ausar SF Bianco ID Castagna LF Alasino RV Beltramo DM 《Journal of agricultural and food chemistry》2003,51(15):4417-4423
When whole or skim milk was incubated with the cationic acrylate polymer Eudragit E100, a biphasic effect on the stability of casein micelles was observed. A precipitation phase was observed at low polymer/casein ratios. Strikingly, a solubilization phase of the aggregates was observed when the ratios of polymer/casein were increased. Purified alpha(s)-, beta-, and kappa-caseins or dephosphorylated caseins were equally precipitated and resolubilized by the cationic polymer, indicating no special selectivity for a particular protein or phosphate residue for these events. An increase in the size of the aggregates as the optimum precipitating amount of Eudragit E100 was reached suggests a crossbridging of the micelles by the polymer. The inhibition of the precipitation phase by high ionic strength indicates that electrostatic interactions play a critical role in complex formation. Furthermore, a dramatic reduction in size of the protein colloidal particles upon solubilization of the aggregates was observed by dynamic light scattering, indicating a dissociation of the micellar structure. Taken together, the results indicate that at low concentration Eudragit E100 may act as a precipitant of casein micelles, mainly by ionic interaction and at high concentration as an amphipathic agent, solubilizing casein micelles with a disruption of their internal structure. 相似文献
5.
Skim milk was adjusted to pH values between 6.5 and 6.7 and heated (80, 90, and 100 degrees C) for up to 60 min. Changes in casein micelle size, level of whey protein denaturation, and level of whey protein association with the micelles were monitored for each milk sample. Changes in casein micelle size were markedly affected by the pH at heating. At low pH (6.5-6.55), the casein micelle size increased markedly during the early stages of heating, and the size plateaued on prolonged heating. The maximum increase in size was approximately 30-35 nm. In contrast, at high pH (6.7), much smaller changes in size were observed on heating and the maximum increase in size was only approximately 10 nm. An intermediate behavior was observed at pH values between these two extremes. The rate of denaturation of the major whey proteins, alpha-lactalbumin and beta-lactoglobulin, was essentially unaffected by the pH at heating for the small pH changes involved in this study, and the changes in casein micelle size were poorly related to the level of whey protein denaturation. In contrast, the level of denatured whey proteins associating with the micelles was markedly dependent on the pH at heating, with high levels of association at pH 6.5-6.55 and low levels of association at pH 6.7. Changes in casein micelle size were related to the levels of denatured whey proteins that were associated with the casein micelles, although there was a small deviation from linearity at low levels of association (<15%). Further studies on reconstituted and fresh milk samples at smaller pH steps confirmed that the association of whey proteins with the casein micelles was markedly affected by the pH at heating. These results indicate that the changes in casein micelle size induced by the heat treatment of skim milk were a consequence of the whey proteins associating with the casein micelles and that the level of association was markedly influenced by small pH changes of the milk. It was not possible to determine whether the association itself influenced the casein micelle size or whether parallel reactions involving micellar aggregation caused the increase in micelle size as whey protein association progressed. 相似文献
6.
The rennet-induced coagulation of bovine milk at 10 degrees C was investigated. The rate of change of absorbance at 600 nm was higher in milk renneted at 30 degrees C than that at 10 degrees C. The amount of casein sedimented on centrifuging skim milk at 5000g for 1 h at 10 degrees C increased with time after renneting. The viscosity of milk at 10 degrees C at low shear rates did not change significantly until 10 h after rennet addition, but it increased markedly after 20 h. Smaller particles in milk at 10 degrees C disappeared slowly over 36 h after rennet addition and aggregated into larger particles. These results suggested that casein micelles in milk aggregate at low temperatures. Reasons for the slow aggregation of milk renneted at 10 degrees C were investigated by inhibiting chymosin activity by pepstatin A. It is likely that beta-casein, or its hydrolysis, plays a role in aggregation of rennet-altered casein micelles at low temperatures. 相似文献
7.
Anema SG Lee SK Lowe EK Klostermeyer H 《Journal of agricultural and food chemistry》2004,52(2):337-343
Reconstituted skim milk was adjusted to pH values between 6.5 and 7.1 and heated (90 degrees C) for up to 30 min. The skim milk samples were then readjusted to pH 6.7. Acid gels prepared from heated milk had markedly higher G ' values, a reduced gelation time, and an increased gelation pH than those prepared from unheated milk. An increased pH at heating decreased the gelation time, increased the gelation pH, and increased the final G ' of acid set gels prepared from the heated milk samples. There were only small differences in the level of whey protein denaturation in the samples at different pH values, and these differences could not account for the differences in the G ' of the acid gels. The levels of denatured whey protein associated with the casein micelles decreased and the levels of soluble denatured whey proteins increased as the pH at heating was increased. The results indicated that the soluble denatured whey proteins had a greater effect on the final G ' of the acid gels than the denatured whey proteins associated with the casein micelles. 相似文献
8.
采用广义回归神经网络建立酪蛋白乳化性与疏水性关系 总被引：2，自引：1，他引：1
为了研究琥珀酰化修饰后酪蛋白乳化性与疏水性关系,该文以琥珀酰化牦牛乳酪蛋白为研究对象,分析了不同酰化程度酪蛋白乳化性及疏水性变化趋势,采用广义回归神经网络建立了牦牛乳酰化酪蛋白乳化性与疏水性关系模型。结果显示,琥珀酰化牦牛乳酪蛋白乳化性和疏水性均与酰化程度、pH值有关,pH值为5以上,随着酰化程度的增加,酪蛋白乳化活性增大;等电点附近,酪蛋白乳化活性较差,等电点之后乳化活性迅速增大。pH值介于2-6时,所有酪蛋白乳化稳定性较强,pH值介于6-11之间时,酪蛋白乳化稳定性差异较小,pH值为12时乳化稳定性有所增加。酪蛋白内荧光与1-苯胺基萘-8-磺酸(1-aniline napthalene-8-sulfonic acid,ANS)外源荧光最大荧光强度和最大发射波长随酰化程度及pH值变化表现出较为复杂的关系。通过广义回归神经网络(generalized-regression-neu-network,GRNN)建立了牦牛乳酪蛋白疏水性参数、pH值、酰化程度与乳化性关系,网络模型对乳化性的预测相对误差小于10%,预测结果良好。研究结果为酪蛋白乳化性研究提供了参考依据。 相似文献
9.
O'Connell JE Kelly AL Fox PF de Kruif KG 《Journal of agricultural and food chemistry》2001,49(9):4424-4428
An explanation as to how casein micelles dissociate when heated in the presence of ethanol is presented. Dissociation of casein micelles in milk-ethanol mixtures was studied using (1)H NMR, and the effects of addition of CaCl(2), NaCl, or EDTA or alteration of milk pH on this dissociation were studied. It is proposed that at low temperatures, ethanol reduces the solvent quality of milk serum, but above a critical temperature (approximately 30 degrees C in a 35% ethanol solution), ethanol enhances solvent quality and dissociates the casein micelles. Ethanol reduced protein hydrophobicity and increased the pK(a) value of phosphoserine, effects that are likely to be significant in the dissociating effect of ethanol at elevated temperatures. 相似文献
10.
Li CP Salvador AS Ibrahim HR Sugimoto Y Aoki T 《Journal of agricultural and food chemistry》2003,51(23):6808-6815
Food proteins were phosphorylated by heating in a dry state in the presence of phosphate. When casein, whey protein isolate (WPI), and egg white proteins (EWP), which were lyophilized from their solutions in a phosphate buffer, were dry-heated at various temperatures and pH levels for 1-5 days, EWP was more highly phosphorylated than casein and WPI. Phosphorylation of EWP was promoted with a decrease of pH from 7.0 to 3.0 when the incubation temperature was raised from 55 to 100 degrees C. The phosphorus content of EWP increased from 0.08 to 0.64% by dry-heating at pH 3.0 and 85 degrees C for 5 days in the presence of phosphate. The electrophoretic mobility of EWP increased with an increase in the phosphorylation level. The heat-induced polymerization of EWP by dry-heating was not affected by the presence of phosphate. Although the solubility of EWP decreased by dry-heating at pH 3.0-5.5, the phosphorylation depressed the insolubilization at low pH. The phosphate bonds in phosphorylated EWP (P-EWP) were stable at pH 2.0-10.0 and were more acid-labile and base-stable than phosphoesters of egg riboflavin-binding protein (RfBP). (31)P NMR spectral data suggested that besides phosphoesters, phosphodiester and polyphosphate bonds were introduced in P-EWP. Heat stability of EWP was improved, and calcium phosphate-solubilizing ability of EWP was enhanced by phosphorylation. 相似文献
11.
12.
The composition of artificial casein micelles (ACM) prepared at constant concentration of caseins, calcium (Ca), and phosphate (P(i)) in media with different citrate (Cit) concentrations was studied. The incorporation of the different mineral and protein components to the ACM was conditioned by the Cit concentration. In our working condition, the ACM size remained almost constant for Cit concentration ranging from 7 to 10 mM. This behavior could be indicating that the action of Cit essentially consists of a regulation of the Ca activity. The molar ratio at which Ca and P(i) were incorporated to the ACM varied for different Cit concentrations. At decreasing pH, the Ca/P(i) molar ratios for the remanent ions in the ACM were dependent on the Cit concentration. These observations could be related to a certain kind of competition between Cit, micellar calcium phosphate (MCP), and other groups able to bind Ca in the ACM. 相似文献
13.
Guyomarc'h F Queguiner C Law AJ Horne DS Dalgleish DG 《Journal of agricultural and food chemistry》2003,51(26):7743-7750
Gel formation was monitored by low amplitude rheometry during acidification at 40 degrees C with 1.5% glucono-delta-lactone in combined milk systems containing soluble and/or micelle-bound heat-induced (95 degrees C/10 min) aggregates of denatured whey proteins and kappa-casein and in heated dairy mixes with varying micellar casein/whey protein ratio (CN/WP). Both soluble and micelle-bound aggregates increased gelation pH and gel strength. Micelle-bound aggregates seemed to modify the micelle surface so that micelles were destabilized at a pH of 5.1 (instead of 4.7), while soluble aggregates precipitated at their calculated pI of approximately 5.3, and initiated an early gelation by interacting with the micelles. Decreasing the CN/WP ratio produced larger aggregates with higher whey protein: kappa-casein ratio, which gave more elastic gels. The specific effects of the micellar and soluble aggregates on gel strength are discussed with respect to their relative proportions in the heated milk. 相似文献
14.
The influence of pH, calcium ion activity, protein, and enzyme purification on the kinetics of heat inactivation of the extracellular proteinase from Pseudomonas fluorescens 22F was studied in the temperature range 80-120 degrees C. At pH 5.5-8.6 the rate of inactivation increased slightly with increasing pH values. The pH dependence of inactivation suggests that the inactivation mechanism is mainly through deamidation. Calcium ion activity had no influence on the kinetics of heat inactivation of the proteinase. Addition of 1.8% sodium caseinate to the enzyme solution slightly decreased the heat stability of the proteinase, possibly because part of the inactivation of the proteinase is caused by aggregation to casein. Purification of the proteinase did not change the rate of thermal inactivation. 相似文献
15.
Anema SG 《Journal of agricultural and food chemistry》2000,48(9):4168-4175
The kinetics of beta-lactoglobulin (beta-LG) denaturation in reconstituted skim milk samples of various concentrations (9.6-38.4% total solids) over a wide temperature range (75-100 degrees C) was studied. The thermal denaturation of beta-LG had a reaction order of 1.5 at all milk solids concentrations and at all temperatures. The rate of denaturation of beta-LG was markedly dependent on the milk solids concentration and the heating temperature. At 75 degrees C, the thermal denaturation of beta-LG was retarded at higher milk solids concentrations. However, this retardation was less pronounced at higher temperatures so that a similar rate of denaturation was observed at all milk solids concentrations at 100 degrees C. From an examination of the level of disulfide-aggregated beta-LG, it was evident that most, but not all, of the denatured beta-LG was involved in disulfide-aggregated complexes, either with other denatured whey proteins or with the casein micelles. As with beta-LG denaturation, the rate of disulfide aggregation of beta-LG was markedly dependent on the milk solids concentration. 相似文献
16.
R D Keenan D J Young C M Tier A D Jones J Underdown 《Journal of agricultural and food chemistry》2001,49(7):3394-3402
The pressure-induced gelation of concentrated skimmed milk and milk-sugar mixtures was studied to discover the main components responsible for gelation. The major protein component responsible for gelation is micellar casein. Gelation occurs at similar pressures to casein micelle disintegration in dilute milk, and both can be prevented by inclusion of excess calcium chloride. Transmission electron micrographs show that the protein network is formed from particles with diameters approximately an order of magnitude smaller than those of intact casein micelles. Gelation occurs on decompression and is found to be baroreversible. Concentrations of sugar up to 30% reduce the critical concentration of casein required for gelation, but higher sugar concentrations inhibit gelation. A mechanism of gelation based on the aggregation of casein submicelles formed by pressure-induced disintegration of casein micelles is proposed. Observations on the effect of sucrose on gelation are discussed in terms of the influence of sugars on the solvent quality in aqueous casein systems. 相似文献
17.
Ethanol-dependent heat-induced dissociation of casein micelles 总被引：1，自引：0，他引：1
O'Connell JE Kelly AL Auty MA Fox PF de Kruif KG 《Journal of agricultural and food chemistry》2001,49(9):4420-4423
The dissociation of casein micelles when heated to approximately 65 degrees C in the presence of ethanol [1:1 mixture (v/v) of milk and 65% (w/w) aqueous ethanol] was investigated using L* values and transmission measurements. Mixtures of milk and ethanol became transparent on heating, which suggests dissociation of casein micelles. Results of experiments using confocal laser scanning microscopy, light scattering (static and dynamic), and dialysis to examine the changes of milk during heating in the presence of ethanol supported the assertion that such treatments result in dissociation of casein micelles, as did studies of model beta-casein micellar systems. 相似文献
18.
Portnaya I Cogan U Livney YD Ramon O Shimoni K Rosenberg M Danino D 《Journal of agricultural and food chemistry》2006,54(15):5555-5561
The association behavior, critical micellization concentration (CMC), and enthalpy of demicellization (DeltaHdemic) of bovine beta-casein were studied, for the first time by isothermal titration calorimetry, in a pH 7.0 phosphate buffer with 0.1 ionic strength and in pure water. In the buffer solutions, the CMC decreased asymptotically from 0.15 to 0.006 mM as the temperature was raised from 16 to 45 degrees C. DeltaHdemic decreased with increasing temperature between 16 and 28 degrees C but increased from 28 to 45 degrees C. Thermodynamic analysis below 30 degrees C is consistent with the Kegeles shell model, which suggests a stepwise association process. At higher temperatures, this model exhibits limitations, and the micellization becomes much more cooperative. The CMC values in water, measured between 17 and 28 degrees C, decreased with increasing temperature and, expectedly, were higher than those found in the buffer solutions. beta-Casein micelles were visualized and characterized, for the first time in their hydrated state, using advanced digital-imaging cryogenic transmission electron microscopy. The images revealed small, oblate micelles, about approximately 13 nm in diameter. The micelles shape and dimensions remained nearly constant in the temperature range of 24-35 degrees C. 相似文献
19.
Dupont D Johansson A Marchin S Rolet-Repecaud O Marchesseau S Leonil J 《Journal of agricultural and food chemistry》2011,59(15):8375-8384
Several theoretical models of the casein micelle structure have been proposed in the past, but the exact organization of the four individual caseins (α(s1), α(s2), β, and κ) within this supramolecular structure remains unknown. The present study aims at determining the topography of the casein micelle surface by following the interaction between 44 monoclonal antibodies specific for different epitopes of α(s1)-, α(s2)-, β-, and κ-casein and the casein micelle in real time and no labeling using a surface plasmon resonance (SPR)-based biosensor. Although the four individual caseins were found to be accessible for antibody binding, data confirmed that the C-terminal extremity of κ-casein was highly accessible and located at the periphery of the structure. When casein micelles were submitted to proteolysis, the C-terminal extremity of κ-casein was rapidly hydrolyzed. Disintegration of the micellar structure resulted in an increased access for antibodies to hydrophobic areas of α(s1)- and α(s2)-casein. 相似文献
20.
Heated (20-100 °C/0-30 min) skim milks (pH 6.5-7.1) were diluted in buffer (pH 7.0). Rennet was added, and the particle size with time was measured. For all samples, the size initially decreased (lag phase) and then increased (aggregation phase). Milks heated at ≤60 °C had short lag phases and rapid aggregation phases regardless of pH. Milks heated at >60 °C at pH 6.5 had long lag phases and slow aggregation phases. As the pH increased, the lag phase shortened and the aggregation phase accelerated. The aggregation time was correlated with the level of whey protein associated with the casein micelles and with the level of κ-casein dissociated from the micelles. Heated milks formed weak gels when renneted. It is proposed that the milks heated at low pH have whey proteins associated with the casein micelles and that these denatured whey proteins stabilize the micelles to aggregation by rennet and therefore inhibit gelation. In the milks heated at higher pH, the whey proteins associate with κ-casein in the serum and, on rennet treatment, the κ-casein-depleted micelles and the serum-phase whey protein/κ-casein complexes aggregate; however, the denatured whey proteins stabilize the aggregates so that gelation is still inhibited. 相似文献