首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 62 毫秒
1.
The influence of sucrose on the flocculation stability of hydrocarbon oil-in-water emulsions stabilized by a globular protein was examined using laser diffraction. Salt (150 mM NaCl) and sucrose (0-40 wt %) were added to n-hexadecane oil-in-water emulsions stabilized by beta-lactoglobulin (beta-Lg, pH 7.0) either before or after isothermal heat treatment (30-95 degrees C for 20 min). When salt was added to emulsions before heat treatment, appreciable droplet flocculation was observed below the thermal denaturation temperature of the adsorbed beta-Lg (T(m) approximately 70 degrees C), and more extensive flocculation was observed above T(m). On the other hand, when salt was added to emulsions after heat treatment, appreciable droplet flocculation still occurred below T(m), but little flocculation was observed above T(m). Addition of sucrose to the emulsions increased T(m) and either promoted or suppressed droplet flocculation depending on whether it was added before or after heat treatment. These results are interpreted in terms of the influence of sucrose on protein conformational stability, protein-protein interactions, and the physiochemical properties of aqueous solutions. This study has important implications for the formulation and production of protein stabilized oil-in-water emulsions.  相似文献   

2.
Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion containing anionic lecithin-coated droplets was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (5 wt % corn oil, 1 wt % lecithin, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic lecithin-chitosan-coated droplets was formed by diluting the primary emulsion with an aqueous chitosan solution (1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0.036 wt % chitosan). The stabilities of the primary and secondary emulsions with the same oil concentration to thermal processing, freeze-thaw cycling, high calcium chloride concentrations, and lipid oxidation were determined. The results showed that the secondary emulsions had better stability to droplet aggregation during thermal processing (30-90 degrees C for 30 min), freeze-thaw cycling (-10 degrees C for 22 h/30 degrees C for 2 h), and high calcium chloride contents (相似文献   

3.
In this study fish oil was incorporated into commercial homogenized milk using different homogenization temperatures and pressures. The main aim was to understand the significance of homogenization temperature and pressure on the oxidative stability of the resulting milks. Increasing homogenization temperature from 50 to 72 degrees C decreased droplet size only slightly, whereas a pressure increase from 5 to 22.5 MPa decreased droplet size significantly. Surprisingly, emulsions having small droplets, and therefore large interfacial area, were less oxidized than emulsions having bigger droplets. Emulsions with similar droplet size distributions, but resulting from different homogenization conditions, had significantly different oxidative stabilities, indicating that properties of significance to oxidation other than droplet size itself were affected by the different treatments. In general, homogenization at 72 degrees C appeared to induce protective effects against oxidation as compared to homogenization at 50 degrees C. The results thus indicated that the actual composition of the oil-water interface is more important than total surface area itself.  相似文献   

4.
The ability of two protein fractions extracted from cod to form and stabilize oil-in-water emulsions was examined: a high salt extracted fraction (HSE protein) and a pH 3 acid extracted fraction (AE protein). Both fractions consisted of a complex mixture of different proteins, with the predominant one being myosin (200 kDa). The two protein fractions were used to prepare 5 wt % corn oil-in-water emulsions at ambient temperature (pH 3.0, 10 mM citrate-imidazole buffer). Emulsions with relatively small mean droplet diameters (d(3,2) < 1 microm) and good creaming stability (> 9 days) could be produced at protein concentrations > or =0.2 wt % for both fractions. The isoelectric point of droplets stabilized by both protein fractions was pH approximately 5. The emulsions were stable to droplet flocculation and creaming at relatively low pH (< or =4) and NaCl concentrations (< or =150 mM) when stored at room temperature. In the absence of salt, the emulsions were also stable to thermal treatment (30-90 degrees C for 30 min), but in the presence of 100 mM NaCl droplet flocculation and creaming were observed in some of the emulsions, particularly those stabilized by the AE fraction. The results suggest that protein fractions extracted from cod can be used as emulsifiers to form and stabilize food emulsions.  相似文献   

5.
The purpose of this study was to create water-in-oil (W/O) and water-in-oil-in-water (W/O/W) emulsions containing gelled internal water droplets. Twenty weight percent W/O emulsions stabilized by a nonionic surfactant (6.4 wt % polyglycerol polyricinoleate, PGPR) were prepared that contained either 0 or 15 wt % whey protein isolate (WPI) in the aqueous phase, with the WPI-containing emulsions being either unheated or heated (80 degrees C for 20 min) to gel the protein. Optical microscopy and sedimentation tests did not indicate any significant changes in droplet characteristics of the W/O emulsions depending on WPI content (0 or 15%), shearing (0-7 min at constant shear), thermal processing (30-90 degrees C for 30 min), or storage at room temperature (up to 3 weeks). W/O/W emulsions were produced by homogenizing the W/O emulsions with an aqueous Tween 20 solution using either a membrane homogenizer (MH) or a high-pressure valve homogenizer (HPVH). For the MH the mean oil droplet size decreased with increasing number of passes, whereas for the HPVH it decreased with increasing number of passes and increasing homogenization pressure. The HPVH produced smaller droplets than the MH, but the MH produced a narrower particle size distribution. All W/O/W emulsions had a high retention of water droplets (>95%) within the larger oil droplets after homogenization. This study shows that W/O/W emulsions containing oil droplets with gelled water droplets inside can be produced by using MH or HPVH.  相似文献   

6.
The interactions of proteins during the heat treatment of whey-protein-isolate (WPI)-based oil-in-water emulsions with and without added hydroxylated lecithin were studied by examining the changes in droplet size distribution and the quantity and type of adsorbed and unadsorbed proteins. Heat treatment at 90 degrees C of WPI emulsions resulted in an increase in total adsorbed protein; unadsorbed beta-lactoglobulin (beta-lg) was the main protein interacting with the adsorbed proteins during the first 10 min of heating, but after this time, unadsorbed alpha-lactalbumin (alpha-la) also associated with the adsorbed protein. In emulsions containing hydroxylated lecithin, the increase in total adsorbed protein during heat treatment was much lower and the unadsorbed beta-lg did not appear to interact with the adsorbed proteins during heating. However, the behavior of alpha-la during heat treatment of these emulsions was similar to that observed in the emulsions containing no hydroxylated lecithin. In the presence of NaCl, the particle size of the emulsion droplets and the quantities of adsorbed protein increased markedly during heating. Emulsions containing hydroxylated lecithin were less sensitive to the addition of NaCl. These results suggest that the binding of hydroxylated lecithin to unfolded monomers or intermediate products of beta-lg reduces the extent of heat-induced aggregation of beta-lg and consequently decreases the interactions between unadsorbed beta-lg and adsorbed protein. This was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of heated whey protein and hydroxylated lecithin solutions.  相似文献   

7.
The influence of chelating agents (disodium ethylenediaminetetraacetate (EDTA) and sodium citrate) on the physicochemical properties of whey protein isolate (WPI)-stabilized oil-in-water emulsions containing calcium chloride was determined. The calcium-binding characteristics of EDTA and citrate at 30 degrees C were characterized in aqueous solutions (20 mM Tris buffer, pH 7.0) by isothermal titration calorimetry (ITC). EDTA and citrate both bound calcium ions in a 1:1 ratio, but EDTA had a much higher binding constant. Oil-in-water emulsions (pH 7.0) were prepared containing 6.94% (w/v) soybean oil, 0.35% (w/v) WPI, 0.02% (w/v) sodium azide, 20 mM Tris buffer, 10 mM CaCl(2), and 0-40 mM chelating agent. The particle size, apparent viscosity, creaming stability, free calcium concentration, and particle surface potential of the emulsions were measured. The chelating agents reduced or prevented droplet aggregation in the emulsions. When they were present above a certain concentration (>3.5 mM EDTA or >5 mM citrate), droplet aggregation was prevented. The reduction of aggregation was indicated by decreases in particle size, shear-thinning behavior, apparent viscosity, and creaming. Emulsions containing chelating agents had lower free calcium concentrations and more negatively charged droplets, indicating that the chelating agents improved emulsion stability by binding calcium ions. EDTA could be used at lower concentrations than citrate because of its higher calcium ion binding constant.  相似文献   

8.
The objective of this study was to investigate the influence of globular protein interfacial cross-linking on the in vitro digestibility of emulsified lipids by pancreatic lipase. 3% (wt/wt) corn oil-in-water emulsions stabilized by either lecithin or beta-lactoglobulin were prepared (pH 7). A portion of the beta-lactoglobulin stabilized emulsions was subjected to a heat treatment known to cross-link the adsorbed globular proteins (85 degrees C, 20 min). Pancreatic lipase and bile extract were then added to each emulsion at 37 degrees C (pH 7) and the evolution of the particle charge, particle size, appearance and free fatty acids released were measured over a period of 2 h. The rate and extent of lipid digestion did not differ greatly between lecithin and beta-lactoglobulin stabilized emulsions, nor did it differ greatly for unheated (BLG-U) or heated (BLG-H) beta-lactoglobulin stabilized emulsions. For example, the initial rate of lipid digestion was found to be 3.1, 3.4, and 2.3 mM fatty acids s(-1) m(-2) of lipid surface for droplets stabilized by BLG-U, BLG-H, and lecithin, respectively. Pancreatic lipase was able to adsorb to the droplet surfaces and access the emulsified lipids, regardless of the initial interfacial composition and the fact that some of the original emulsifier appeared to remain at the oil-water interface during digestion. These results help to explain why the human body is so efficient at digesting dietary triacylglycerols.  相似文献   

9.
Protein fractions were isolated from coconut: coconut skim milk protein isolate (CSPI) and coconut skim milk protein concentrate (CSPC). The ability of these proteins to form and stabilize oil-in-water emulsions was compared with that of whey protein isolate (WPI). The solubility of the proteins in CSPI, CSPC, and WPI was determined in aqueous solutions containing 0, 100, and 200 mM NaCl from pH 3 to 8. In the absence of salt, the minimum protein solubility occurred between pH 4 and 5 for CSPI and CSPC and around pH 5 for WPI. In the presence of salt (100 and 200 mM NaCl), all proteins had a higher solubility than in distilled water. Corn oil-in-water emulsions (10 wt %) with relatively small droplet diameters (d32 approximately 0.46, 1.0, and 0.5 mum for CSPI, CSPC, and WPI, respectively) could be produced using 0.2 wt % protein fraction. Emulsions were prepared with different pH values (3-8), salt concentrations (0-500 mM NaCl), and thermal treatments (30-90 degrees C for 30 min), and the mean particle diameter, particle size distribution, zeta-potential, and creaming stability were measured. Considerable droplet flocculation occurred in the emulsions near the isoelectric point of the proteins: CSPI, pH approximately 4.0; CSPC, pH approximately 4.5; WPI, pH approximately 4.8. Emulsions with monomodal particle size distributions, small mean droplet diameters, and good creaming stability could be produced at pH 7 for CSPI and WPI, whereas CSPC produced bimodal distributions. The CSPI and WPI emulsions remained relatively stable to droplet aggregation and creaming at NaCl concentrations of < or =50 and < or =100 mM, respectively. In the absence salt, the CSPI and WPI emulsions were also stable to thermal treatments at < or =80 and < or =90 degrees C for 30 min, respectively. These results suggest that CSPI may be suitable for use as an emulsifier in the food industry.  相似文献   

10.
共轭亚油酸水包油型乳液的物理化学稳定性   总被引:2,自引:1,他引:1  
共轭亚油酸(conjugated linoleic acid, CLA)是一种具有多重生理功效的不饱和脂肪酸,其氧化稳定性较差,对光、热、氧气很不稳定。以亲水胶体为乳化剂制备CLA的水包油(O/W)型乳液可改善其氧化稳定性,扩大其在食品中的应用。该研究采用改性阿拉伯胶EM2为乳化剂、2种不同黏度的CLA为油相,通过测定乳液颗粒的粒径和粒径分布以及乳液在40℃贮存过程中的过氧化值和茴香胺值,研究了CLA的水包油(O/W)型乳液的物理化学稳定性。结果表明,高质量分数的EM2有利于形成粒径更小且分布均一的乳液颗粒。乳液的氧化稳定性很大程度上依赖于其物理稳定性。对于黏度较小的CLA,在各测试EM2质量分数下,CLA乳液具有较好的物理稳定性,且随着EM2质量分数的增大,乳液氧化稳定性提高。对于黏度较大的CLA,EM2质量分数为5%时,乳液具有较好的物理化学稳定性;增大EM2的质量分数,其稳定性下降。该研究可为今后研究基于乳液技术的功能性因子保护和增效提供参考,有利于CLA在食品行业中的推广应用。  相似文献   

11.
Oil-in-water emulsions allow the preparation of lipophilic compounds such as carotenoids in the liquid form. Here, the effect of a combination of some emulsifiers, such as two whey protein isolates (BiPro and BioZate), sucrose laurate (L-1695), and polyoxyethylene-20-sorbitan-monolaurate (Tween 20), on the stability of lycopene and astaxanthin in emulsions, droplet size, and cellular uptake of these carotenoids has been investigated. The degradation of lycopene was slightly more pronounced than that of astaxanthin in all emulsions. The concentration of lycopene and astaxanthin decreased by about 30% and 20%, respectively, in all emulsions after 3 weeks of storage in the dark at 4 degrees C. The kind of emulsifiers or their combinations have played an important role in the cellular uptake by the colon carcinoma cells line HT-29 and Caco-2.  相似文献   

12.
The potential of utilizing interfacial complexes, formed through the electrostatic interactions of proteins and polysaccharides at oil-water interfaces, to stabilize model beverage cloud emulsions has been examined. These interfacial complexes were formed by mixing charged polysaccharides with oil-in-water emulsions containing oppositely charged protein-coated oil droplets. Model beverage emulsions were prepared that consisted of 0.1 wt % corn oil droplets coated by beta-lactoglobulin (beta-Lg), beta-Lg/alginate, beta-Lg/iota-carrageenan, or beta-Lg/gum arabic interfacial layers (pH 3 or 4). Stable emulsions were formed when the polysaccharide concentration was sufficient to saturate the protein-coated droplets. The emulsions were subjected to variations in pH (from 3 to 7), ionic strength (from 0 to 250 mM NaCl), and thermal processing (from 30 or 90 degrees C), and the influence on their stability was determined. The emulsions containing alginate and carrageenan had the best stability to ionic strength and thermal processing. This study shows that the controlled formation of protein-polysaccharide complexes at droplet surfaces may be used to produce stable beverage emulsions, which may have important implications for industrial applications.  相似文献   

13.
Oil-in-water emulsions (4 wt % soy oil) containing 4 wt % whey protein hydrolysate (WPH) (27% degree of hydrolysis) and different levels of calcium, magnesium, or potassium chloride were prepared in a two-stage homogenizer. Other emulsions containing 4 wt % WPH but including 0.35 wt % hydroxylated lecithin and different levels of the above minerals were similarly prepared. The formation and stability of these emulsions were determined by measuring oil droplet size distributions using laser light scattering and by confocal scanning laser microscopy and a gravity creaming test. Both lecithin-free and lecithin-containing emulsions showed no change in droplet size distributions with increasing concentration of potassium in the range 0-37.5 mM. In contrast, the diameter of emulsion droplets increased with increasing calcium or magnesium concentration >12.5 mM. Emulsions containing hydroxylated lecithin were more sensitive to the addition of calcium or magnesium than the lecithin-free emulsions. Storage of emulsions at 20 degrees C for 24 h further increased the diameter of droplets and resulted in extensive creaming in emulsions containing >25 mM calcium or magnesium. It appears that both flocculation and coalescence processes were involved in the destabilization of emulsions induced by the addition of divalent cations.  相似文献   

14.
Emulsions were made with sunflower protein isolate (SI), helianthinin, and sunflower albumins (SFAs). Emulsion formation and stabilization were studied as a function of pH and ionic strength and after heat treatment of the proteins. The emulsions were characterized with respect to average droplet size, surface excess, and the occurrence of coalescence and/or droplet aggregation. Sunflower proteins were shown to form stable emulsions, with the exception of SFAs at neutral and alkaline pH values. Droplet aggregation occurred in emulsions made with SI, helianthinin, and SFAs. Droplet aggregation and subsequent coalescence of emulsions made with SFAs could be prevented at pH 3. Calcium was found to cause droplet aggregation of emulsions made with helianthinin, at neutral and alkaline pH values. Treatments that increase conformational flexibility of the protein molecule improved the emulsion properties of sunflower proteins.  相似文献   

15.
The properties of whey protein isolate (WPI) stabilized oil-in-water (O/W) nanoemulsions (d(43) ≈ 66 nm; 0.5% oil, 0.9% WPI) and emulsions (d(43) ≈ 325 nm; 0.5% oil, 0.045% WPI) were compared. Emulsions were prepared by high-pressure homogenization, while nanoemulsions were prepared by high-pressure homogenization and solvent (ethyl acetate) evaporation. The effects of pH, ionic strength (0-500 mM NaCl), thermal treatment (30-90 °C), and freezing/thawing on the stability and properties of the nanoemulsions and emulsions were compared. In general, nanoemulsions had better stability to droplet aggregation and creaming than emulsions. The nanoemulsions were unstable to droplet flocculation near the isoelectric point of WPI but remained stable at higher or lower pH values. In addition, the nanoemulsions were stable to salt addition, thermal treatment, and freezing/thawing (pH 7). Lipid oxidation was faster in nanoemulsions than emulsions, which was attributed to the increased surface area. Lipase digestibility of lipids was slower in nanoemulsions than emulsions, which was attributed to changes in interfacial structure and protein content. These results have important consequences for the design and utilization of food-grade nanoemulsions.  相似文献   

16.
The influence of pH and iota-carrageenan concentration on the properties of beta-lactoglobulin (beta-Lg)-stabilized oil-in-water emulsions was investigated by measuring the particle charge, particle size distribution, and creaming stability. Emulsions containing droplets stabilized by beta-Lg were produced by homogenization, and then, iota-carrageenan was added. At pH 3, the droplet charge did not change for iota-carrageenan concentrations 相似文献   

17.
High-pressure treatment represents a potential method to stabilize microbiologically agricultural raw materials that are sensitive to heat treatments. Low-density lipoproteins (LDL), the main contributors to the exceptional emulsifying properties of yolk, are particularly sensitive to heat treatment. In this study, high-pressure treatments have been performed on LDL, and their impact on LDL physicochemical and emulsifying properties has been assessed. LDL dispersions at two pH levels (pH 3 and 8) were treated at different pressure levels: 200, 400, and 600 MPa at 20 degrees C. LDL dispersion characteristics (solubility, aggregation, and protein denaturation) and LDL emulsifying properties (o/w 30:70 emulsions: droplet size, flocculation, and protein adsorption) of nontreated and high-pressure treated dispersions were compared. Solubility is not altered by high-pressure treatment whatever the pH, whereas aggregation and protein denaturation are drastically enhanced, in particular at pH 8. The effects of these modifications on LDL emulsifying properties are mainly a diminution of the flocculation (depletion and bridging) at this same pH. Finally, it seems that high-pressure treatment combined with an alkaline pH decreases droplet flocculation of LDL dispersions.  相似文献   

18.
The disulfide bonds of beta-lactoglobulin (beta-lg) were modified by oxidative sulfitolysis to generate beta-lgSO(3). The native protein (beta-lg) and the modified protein (beta-lgSO(3)) were conjugated to activated polyethylene glycol (PEG) to generate beta-lgPEG and beta-lgSO(3)PEG, respectively. Oil-in-water (o/w) emulsions containing 1% beta-lg or beta-lg conjugates were prepared at pH 2.8, 5.0, and 7.0. Emulsion droplet diameters and zeta potentials were measured. For the same emulsifier, emulsion droplet diameters decreased when emulsion pH increased. Zeta potentials of emulsion droplets increased with pH for beta-lg and beta-lgSO(3). Zeta potentials of beta-lgPEG and beta-lgSO(3)PEG approached zero, suggesting that the protein molecule was covered by PEG chains. Accelerated and 7-day storage stabilities at 21 degrees C of the emulsions were monitored. The emulsifying activity index (EAI) of beta-lgPEG was not significantly different from the EAI of beta-lg. The EAI of beta-lg was enhanced following sulfitolysis of beta-lactoglobulin. The emulsifying activity increased more when the oxidatively modified protein was conjugated to polyethylene glycol. Emulsions made with beta-lgSO(3)PEG were more stable than emulsions made with beta-lg, beta-lgPEG, or beta-lgSO(3) under accelerated stability study and for 7 days at 21 degrees C. The stability of o/w emulsions stabilized with beta-lgSO(3)PEG increased because individual droplets were better protected, against protein bridging or coalescence, by the thick adsorbed protein-PEG layer.  相似文献   

19.
Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion was prepared by homogenizing 5 wt % corn oil with 95 wt % aqueous solution (1 wt % lecithin, 100 mM acetic acid, pH 3.0) using a high-pressure valve homogenizer. This emulsion was diluted with aqueous chitosan solutions to form secondary emulsions with varying compositions: 1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0-0.04 wt % chitosan (pH 3.0). The particle size distribution, particle charge, and creaming stability of the primary and secondary emulsions were measured. The electrical charge on the droplets increased from -49 to +54 mV as the chitosan concentration was increased from 0 to 0.04 wt %, which indicated that chitosan adsorbed to the droplet surfaces. The mean particle diameter of the emulsions increased dramatically and the emulsions became unstable to creaming when the chitosan concentration exceeded 0.008 wt %, which was attributed to charge neutralization and bridging flocculation effects. Sonication, blending, or homogenization could be used to disrupt flocs formed in secondary emulsions containing droplets with high positive charges, leading to the production of emulsions with relatively small particle diameters (approximately 1 microm). These emulsions had good stability to droplet aggregation at low pH (< or =5) and ionic strengths (<500 mM). The interfacial engineering technology utilized in this study could lead to the creation of food emulsions with improved stability to environmental stresses.  相似文献   

20.
Oil-in-water (O/W) emulsions containing small oil droplets (d32 approximately 0.22 microm) stabilized by sodium dodecyl sulfate (SDS)-fish gelatin (FG) membranes were produced by an electrostatic deposition technique. A primary emulsion containing anionic SDS-coated droplets (zeta approximately -40 mV) was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (20 wt % corn oil, 0.46 wt % SDS, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic SDS-FG-coated droplets (zeta approximately +30 mV) was formed by diluting the primary emulsion with an aqueous fish gelatin solution (10 wt % corn oil, 0.23 wt % SDS, 100 mM acetic acid, 2.00 wt % fish gelatin, pH 3.0). The stabilities of primary and secondary emulsions with the same oil concentration to thermal processing, ionic strength, and pH were assessed by measuring particle size distribution, zeta potential, microstructure, destabilized oil, and creaming stability. The droplets in secondary emulsions had good stability to droplet aggregation at holding temperatures from 30 to 90 degrees C for 30 min, [NaCl] < or = 100 mM, and pH values from 3 to 8. This study shows that the ability to generate emulsions containing droplets stabilized by multilayer interfacial membranes comprised of two or more types of emulsifiers, rather than a single interfacial layer comprised of one type of emulsifier, may lead to the development of food products with improved stability to environmental stresses.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号