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This paper systematically compared the effects of heteroaggregation, layer-by-layer and directly mixing techniques on the physical properties of emulsions through mechanical rheology, microrheology, LUMisizer stability analyzer, Cryo-scanning electron microscopy (Cryo-SEM) and in vitro simulated gastrointestinal model. The shear rheology results showed that the viscosity of emulsions stabilized with whey protein isolate (WPI) and flaxseed gum (FG) by different techniques was in the order of heteroaggregated emulsion > layer-by-layer emulsion > directly mixing emulsion. Furthermore, it confirmed that the heteroaggregated emulsion had a best stability and the interface moving speed was the slowest compared with those of layer-by-layer and directly mixing emulsions. Cryo-SEM microstructure results showed that the three dimensional network structure of heteroaggregate was the main reason for maintaining high stability and shear rheological properties. Microrheological properties results indicated that heteroaggregated emulsion was sensitive to the shearing force due to the liquid behavior. While, the structures of WPI-FG emulsions prepared by layer-by-layer and directly mixing were not destroyed after shearing due to their high elasticity and solid behaviors. It was found that the order of released FFA content at the beginning of 30 min was directly mixing emulsion > layer-by-layer emulsion > heteroaggregated emulsion, but the released free fatty acid of heteroaggregated emulsion was the most in the end, which indicated that heteroaggregated emulsion had a certain controlled release effect. The study could be helpful for choosing proper technique to gain good emulsion delivery system.

The impact of oil content on the stability, shear rheology, microrheology and microstructure of heteroaggregated emulsions with 40% whey protein isolate (WPI)-coated droplets and 60% flaxseed gum (FG)-coated droplets at pH 3.0 was studied. The mean particle size, zeta-potential, physical stability, the mean square displacement (MSD), solid liquid balance (SLB), viscosity and Cryo-SEM microstructure of the heteroaggregated emulsions as a function of oil contents ranging from 10% to 30% were measured. It was found that the physical stability and viscosity of the heteroaggregated emulsion was decreased with increasing oil content. MSD curves showed that the particle motion of heteroaggregated emulsions with increasing oil contents was obviously accelerated at a shorter decorrelation time, which indicated that elastic behavior would be dominated with higher oil content (20% & 30%). Cryo-SEM microstructure proved that the specific three-dimensional network of the heteroaggregated emulsion could be formed at low oil content (10% & 15%) by the strong electrostatic and steric interactions between droplets and free WPI and FG. It proved that heteroaggregates formed by WPI-coated droplets and FG-coated droplets may be useful for creating specific food structures that lead to desirable viscosity at low fat content.

In this study, the interaction of ovalbumin with lutein dipalmitate and the effect of ovalbumin on marigold lutein esters extracts were investigated. Lutein dipalmitate quenched the fluorescence of ovalbumin by static quenching. Binding and thermodynamic parameters proved that lutein dipalmitate bound to ovalbumin spontaneously by van der Waals force and hydrogen bond, and the complex stoichiometry was 1:1. Through three-dimensional fluorescence spectroscopy, Fourier transform infrared spectroscopy and circular dichroism experiments, the conformation of ovalbumin was unfolded, and alteration in the ovalbumin secondary structure induced by lutein dipalmitate was observed. The results of transmission electron microscopy and particle size revealed that there were spherical and nano-sized aggregates in the ovalbumin-lutein dipalmitate system, indicating the lutein dipalmitate not only could bind to ovalbumin at molecular level, but also promote the aggregation of ovalbumin. Additionally, the addition of ovalbumin had a positive effect on the stability of marigold lutein esters extracts.

Recent studies have shown that controlled heteroaggregation of oppositely charged lipid droplets can be used to control the rheological properties of emulsion. The effect of unadsorbed emulsifier on the microstructure and rheological properties of heteroaggregate of emulsion is not clear. Therefore, the influence of unadsorbed emulsifiers (whey protein isolate-WPI & Flaxseed gum-FG) on the microstructure and rheological properties of heteroaggregate of 40% WPI-coated droplets and 60% FG-coated droplets was studied. WPI-stabilized emulsions and FG-stabilized emulsions were centrifuged to separate the aqueous phase from the oil droplets to prepare the washed emulsions, separately. Emulsions containing mixtures of droplets with washed and unwashed WPI-emulsion and FG-emulsion were prepared, respectively. Droplet size, zeta-potential, transmission-physical stability, rheological behavior, and Cryo-SEM microstructure of the heteroaggregates were measured as a function of unwashed and washed WPI & FG emulsion. It was found that the presence of unadsorbed WPI in the aqueous phase of mixed emulsion adsorbed onto the FG-coated droplets, meanwhile, the unadsorbed FG could bind WPI-droplet and FG-droplet-WPI together forming a special three-dimensional network. Rheological properties indicated that free WPI and FG played dominated roles in the heteroaggregation of mixed emulsions. The shearing viscosity of the heteroaggregates formed by washed WPI-droplets and FG-droplets was significantly decreased compared with the unwashed mixed emulsion. Microrheological analysis showed that heteroaggregate of mixed emulsion became liquid behavior after washing compared to the solid behavior of unwashed emulsion. It indicated that unadsorbed WPI and FG dominated the physical property through a specific network structure. This study proved the effect of the continuous phase on the rheological properties of heteroaggregates and provided theoretical basis for the development of reduced-fat food.

It was reported that the controlled heteroaggregation of oppositely charged lactoferrin (LF)-lutein droplets and whey protein isolate (WPI)-DHA droplets enhanced the physicochemical properties of emulsions. The effect of the unadsorbed proteins on the physicochemical properties of the heteroaggregates of emulsions has not been clear. Therefore, the effects of unadsorbed proteins on the physicochemical stability of heteroaggregates of LF-lutein droplets and WPI-DHA droplets were investigated. The particle size, zeta-potential, transmission-physical stability, microstructure were observed by confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscopy (cryo-SEM) and the chemical stability (lutein degradation and DHA oxidation) of the unwashed and washed heteroaggregates were measured. The results showed that compared with unwashed emulsions, the particle sizes and instability indexes of WPI-DHA emulsions, heteroaggregated LF-lutein/WPI-DHA emulsions and LF-lutein emulsions changed after washing. The instability index of washed-1 heteroaggregated LF-lutein/WPI-DHA emulsion was 10.5 times greater compared with the unwashed samples. The microstructure images showed that the washed single and heteroaggregated emulsions resulted in creaming. The unadsorbed proteins had a great protective effect on the physical stability of the emulsions, especially for the heteroaggregated LF-lutein/WPI-DHA emulsion. The degradation rate of lutein, lipid hydroperoxides and thiobarbituric acid reactive substance (TBARS) values of DHA in washed single and heteroaggregated emulsions were higher than those of the unwashed samples. This proved that the unadsorbed proteins dominated the physicochemical stabilities of heteroaggregates. This laid the foundation for the study of a delivery system of functional component heteroaggregates.

Bovine serum albumin (BSA) is a natural protein commonly used to prepare nanoparticle to encapsulate food ingredients. The interaction between lutein dipalmitate and BSA was investigated using fluorescence, UV–vis absorption, circular dichroism (CD) spectroscopies and molecular docking. The fluorescence quenching study suggested the quenching process of BSA by lutein dipalmitate was static, which was consistent with the results of UV–vis absorption. The binding parameters proved that the binding stoichiometry between BSA and lutein dipalmitate was 1:1. Molecular docking revealed that lutein dipalmitate bound to site I on BSA, which was confirmed by site competitive experiments. Moreover, thermodynamic study and molecular docking suggested lutein dipalmitate spontaneously bound to BSA by hydrogen bond, van der Waals force, and hydrophobic interaction. The synchronous and three-dimensional fluorescence showed that the microenvironment of Tyr and Trp was changed and the protein skeleton got loosened in the presence of lutein dipalmitate. According to CD, a decrease in α-helix content of BSA was observed upon the addition of lutein dipalmitate.

The impact of flaxseed gum (FG) on the microrheological properties and physicochemical stability of whey protein isolate (WPI) stabilized β-carotene emulsions at pH 3.0 was studied. A layer-by-layer electrostatic deposition method was used to prepare multilayered β-carotene emulsions with interfacial membranes consisting of WPI and FG. The microrheological behavior of the multilayered β-carotene emulsions was measured through the diffusive wave spectroscopy technique. WPI alone and WPI-FG (concentration of FG = 0.1, 0.2, 0.3 wt%) stabilized β-carotene emulsions were purely viscous giving a mean square displacement that scaled linearly with decorrelation time (τ). The presence of 0.01, 0.02, and 0.05 wt% FG in the WPI-stabilized emulsions caused them to exhibit viscoelastic properties. Meanwhile, the increase in τ reflected the increase in the length scale of connectivity in the emulsions until a "cluster" was formed and the droplets were not free to move due to droplet-network interaction. The apparent increase in the macroscopic viscosity and elasticity index and decrease in the solid lipid balance and fluidity index of emulsions with lower concentrations (0.01, 0.02, 0.05 wt%) of FG indicated that the bridging flocculation of FG had a much more appreciable influence on the microrheological properties than depletion flocculation (higher concentrations, 0.1, 0.2, 0.3 wt%). Droplet size, zeta-potential, and transmission profiles using the centrifugal sedimentation technique and β-carotene degradation during storage were also characterized. With the addition of FG, the zeta-potential of WPI coated β-carotene droplets decreased from positive to negative, and an increase in the apparent droplet size was also noted. LUMISizer analysis exhibited an improvement in physical stability with the addition of 0.1 wt% FG. FG also helped to chemically stabilize the WPI emulsions against β-carotene degradation mainly by slowing down the mobility of the droplets.

The influence of calcium-induced droplet heteroaggregation on the formation and physicochemical stability of mixed lutein and DHA emulsions was studied. Heteroaggregation was induced by mixing oppositely charged lactoferrin (LF)-coated lutein and whey protein isolate (WPI)-coated DHA emulsions with different CaCl2 concentrations at pH 6.0. The droplet size, zeta-potential, transmission-physical stability and microstructure behavior (CLSM and Cryo-SEM) of single-protein emulsions and mixed emulsions were measured as a function of different CaCl2 concentrations. Lutein degradation and DHA oxidation by measurement of lipid hydroperoxides and thiobarbituric acid reactive substances were determined during storage. The physical stability of the mixed emulsions could be modulated by controlling CaCl2 concentrations. Microstructure behavior indicated that a mixed emulsion with 30 mM CaCl2 promoted more droplets to form a special three-dimensional network and microcluster structures. The chemical stability of the mixed lutein and DHA emulsions was obviously enhanced by the addition of 30 mM CaCl2. The decreased surface areas of the DHA and lutein droplets and the physical barrier of the network of heteroaggregates against transition metals and free radicals could mainly explain the improvement in chemical stability. Calcium-induced droplet aggregation may be useful for creating specific food structures that lead to desirable physicochemical properties of multiple functional components.

Background: Ultrasound treatment has been shown to be an effective technique for improving the activity of immobilized enzymes. However, its mechanism is unclear.; Results: The effect of ultrasonic pretreated chitosan-sodium alginate (CHI-ALG) on the enzymatic activity of papain was investigated via a single factor (temperature, time, frequency, power) experiment. The maximum relative enzyme activity of papain was observed when it was mixed with ultrasound pretreated CHI-ALG at 135 kHz, 0.25 W cm-2 and 50 °C for 20 min, during which the relative activity increased by 72.14% compared to untreated CHI-ALG. Viscosity analysis of papain mixed with CHI-ALG pretreated and untreated with ultrasound revealed that stronger association interactions between the polymers were formed compared to the untreated sample. Fluorescence and circular dichroism spectra indicated that the ultrasonic pretreatment of CHI-ALG increased the number of tryptophan on the papain surface and also increased the content of α-helix by 6.97% and decreased the content of β-sheet by 3.45% compared to the untreated solution.; Conclusion: The results of the present study indicate that papain combined with CHI-ALG pretreated with the appropriate ultrasound could be effective technique for improving the activity of immobilized enzymes as a result of changes in its structure and intermolecular interactions. It is important to extend the application of CHI-ALG gel in the immobilized enzyme industry. © 2016 Society of Chemical Industry.; © 2016 Society of Chemical Industry.

The impact of chitosan (CTS) on the physicochemical stability, microrheological property and microstructure of whey protein isolate (WPI)-flaxseed gum (FG) stabilized lutein emulsions at pH 3.0 was studied. A layer-by-layer electrostatic deposition method was used to prepare multilayered lutein emulsions. Droplet size, zeta-potential, instability index, microstructure and microrheological behavior of lutein emulsions were measured. The influences of interfacial layer, metal chelator and free radical scavenger on the chemical stability of lutein emulsions were also investigated. It was found that multilayer emulsions had better physical stability showing the pronounced effect of 1wt% CTS. The mean square displacement analysis demonstrated that CTS led to increases of macroscopic viscosity and elasticity index for WPI-FG stabilized lutein emulsions due to CTS embedding in the network. CTS also helped to chemically stabilize the lutein emulsions against degradation. The combination of interfacial membrane and prooxidative metal chelator or free radical scavenger was an effective method to control lutein degradation.

In this study, the effect of heteroaggregation (HA) on the physicochemical stability and the formation of volatile substances of DHA emulsions was investigated. HA-DHA emulsions were produced by combination of lactoferrin (LF)-DHA and soy protein isolate (SPI)-DHA emulsions at pH 6.0. Zeta-potentials, droplet sizes, stability, and microstructures were measured as a function of different ratios of LF-DHA to SPI-DHA droplets. DHA oxidation of single and HA emulsions was determined through measurements of lipid hydroperoxides, thiobarbituric acid reactive substances, and the formation of volatile substances. LF-DHA to SPI-DHA droplets ratios of 5:5, 4:6, and 3:7 formed stable emulsions. The lowest zeta-potential, biggest droplet size, and optimum physical stability of heteroaggregated emulsion occurred at a 5:5 of LF-DHA to SPI-DHA droplet ratio. Microstructure behavior indicated that the HA emulsions (LF-DHA droplets/SPI-DHA droplets = 5:5) formed specific three-dimensional uniform networks. The formation of thiobarbituric acid reactive substances, lipid hydroperoxides, and volatile compounds including hexanal and ( E, E)-2,4-heptadienal decreased in HA compared to single emulsions. The results indicated that the physicochemical stability of DHA emulsions was enhanced and that the formation of volatile substances was inhibited by HA. It thus demonstrated the utilization of HA to improve the stability of bioactive compounds in emulsions.

The formation and physicochemical stability of mixed functional components (lutein & DHA) emulsions through heteroaggregation were studied. It was formed by controlled heteroaggregation of oppositely charged lutein and DHA droplets coated by cationic lactoferrin (LF) and anionic whey protein isolate (WPI), respectively. Heteroaggregation was induced by mixing the oppositely charged LF-lutein and WPI-DHA emulsions together at pH 6.0. Droplet size, zeta-potential, transmission-physical stability, microrheological behavior and microstructure of the heteroaggregates formed were measured as a function of LF-lutein to WPI-DHA droplet ratio. Lutein degradation and DHA oxidation by measurement of lipid hydroperoxides and thiobarbituric acid reactive substances were determined. Upon mixing the two types of bioactive compounds droplets together, it was found that the largest aggregates and highest physical stability occurred at a droplet ratio of 40% LF-lutein droplets to 60% WPI-DHA droplets. Heteroaggregates formation altered the microrheological properties of the mixed emulsions mainly by the special network structure of the droplets. When LF-coated lutein droplets ratios were more than 30% and less than 60%, the mixed emulsions exhibited distinct decreases in the Mean Square Displacement, which indicated that their limited scope of Brownian motion and stable structure. Mixed emulsions with LF-lutein/WPI-DHA droplets ratio of 4:6 exhibited Macroscopic Viscosity Index with 13 times and Elasticity Index with 3 times of magnitudes higher than the individual emulsions from which they were prepared. Compared with the WPI-DHA emulsion or LF-lutein emulsion, the oxidative stability of the heteroaggregate of LF-lutein/WPI-DHA emulsions was improved. Heteroaggregates formed by oppositely charged bioactive compounds droplets may be useful for creating specific food structures that lead to desirable physicochemical properties, such as microrheological property, physical and chemical stabilities.

The influence of whey protein isolate (WPI)-beet pectin conjugates formed by dry-heating on the oxidative stability of β-carotene in O/W emulsions was studied. It was mainly focused on the influence of pH, metal chelator, free radical scavenger and interfacial characteristics on the degradation of β-carotene in the emulsion stabilised by conjugate. The conjugate increased the oxidative stability of β-carotene in the emulsion as compared to their unconjugated mixture at pH 7.0. The desferoxamine retarded β-carotene degradation at pH 4.0 more effectively than pH 7.0 and more effectively in the emulsion with the conjugate than the unconjugated mixture (p

The addition order of mixed layers of protein and polysaccharide on oil-water interface has been shown to influence physical stability of the emulsion, but little is known about how it impacts chemical stability. Therefore, this study investigated differences in the chemical stability of oil-in-water (O/W) emulsions containing β-carotene droplets coated by whey protein isolate (WPI)-beet pectin through direct preformed mixture (mixed emulsion) and consecutive layer-after-layer (bilayer emulsion) at pH 4.0 and 7.0. The results clearly indicated that both forms of β-carotene emulsions exhibited nearly identical degradation profiles during storage at 55°C. The stability of β-carotene in O/W emulsions could be significantly improved by the addition of iron chelator desferroxamine for both mixed and bilayer emulsions at pH 4.0, but not at pH 7.0. The addition of α-tocopherol could also significantly inhibit the β-carotene degradation for both emulsions at pH 4.0 and 7.0. However, the difference of the improved...

The aim of the present study was to investigate the impact of whey protein isolate (WPI)-beet pectin conjugation on the physical and chemical properties of oil-in-water emulsions incorporating β-carotene within the oil droplets. Covalent coupling of WPI to beet pectin was achieved by dry heating of WPI-beet pectin mixtures of different weight ratios at 80, 90, 100 °C and 79% relative humidity for incubation times ranging from 1 to 9 h. It was confirmed by SDS-polyacrylamide gel electrophoresis that WPI covalently linked to beet pectin. The physical and chemical stability of β-carotene emulsions was characterized by droplet size and distribution, transmission profiles using novel centrifugal sedimentation technique, microstructure and β-carotene degradation during the storage. Compared with those stabilized by WPI alone and unheated WPI-beet pectin mixtures, β-carotene emulsions stabilized by WPI-beet pectin conjugates had much smaller droplet sizes, more homogenous droplet size distribution, less change in centrifugal transmission profiles and obviously improved freeze–thaw stability, indicating a very substantial improvement in the physical stability. Rheological analysis exhibited that emulsions stabilized by WPI-beet pectin conjugates changed from a shear thinning to more like Newtonian liquid compared those with WPI alone and unheated WPI-beet pectin mixtures. Degradation of β-carotene in emulsion during storage was more obviously retarded by WPI-beet pectin conjugate than WPI and unheated WPI-beet pectin mixture, probably due to a thicker and denser interfacial layer in emulsion droplets. These results implied that protein–polysaccharide conjugates were able to improve the physical stability of β-carotene emulsion and inhibit the deterioration of β-carotene in oil-in-water emulsions.

The influence of high hydrostatic pressure (HHP) on the emulsifying properties of whey protein isolate (WPI) and chitosan mixtures in sunflower oil-in-water emulsion has been investigated at pH 4.0. WPI and chitosan mixtures at various ratios were treated at pressure levels in the range of 0–600 MPa for 10–30 min. The emulsifying properties of the mixtures were analyzed by dynamic light scattering and a centrifugal sedimentation technique. HHP treatments of the mixtures resulted in improvement in their emulsifying properties, with the emulsions formed showing more than threefold reductions in droplet size, much more homogeneous droplet distribution, and better creaming stability. The higher the treatment pressure was, the smaller the droplet size and more stable the emulsions were, with those prepared with the mixtures treated at 600 MPa showing no noticeable creaming after 30 days of storage at ambient temperature. The ratio of WPI to chitosan and treatment time also affected the emulsification stability of the mixtures, with a WPI to chitosan ratio of 1:4 (w/w) and treatment time of 20 min found to be the optimum conditions. These results showed that HHP could be a useful method for enhancing the emulsifying properties of protein–polysaccharide mixtures.

In this paper, the effect of supercritical carbon dioxide (SC-CO2) treatment on the structure and conformation of whey protein isolate (WPI) were investigated. The WPI solution treated with SC-CO2 at 20 MPa and 30–60 °C for 1 h showed that its turbidity and particle size were increased. The effect of SC-CO2 treatment at 60 °C on the fluorescence intensity of WPI was elevated indicating partial denaturation of its fractions and exposure of more hydrophobic regions. The secondary structure change of SC-CO2 treated WPI revealed a decrease in the α-helix content, hydrogen bonds and an increase in the amount of β-sheet. A high shift of endothermic peak after SC-CO2 treatment was observed by the thermal analysis of WPI. These results confirmed that the structure and conformation of protein were modified with SC-CO2 treatment. Industrial relevance There is a strong interest in the food industry in studying the modifying protein functionality to produce higher quality products. Supercritical carbon dioxide (SC-CO2) treatment described as green method has raised interests in its application for polymer modification. SC-CO2 is a unique processing method offering many advantages over conventional thermal processing methods, including the ability to retain the quality of food, which may be lost during conventional thermal processing. This work explores the SC-CO2 effect on the structural and conformational modification of protein which would be extremely helpful in understanding the improving of the protein functionalities such as, emulsifying and rheological properties in order to produce higher quality food products.

This study examines the impact of Maillard-type conjugates formed between whey protein isolate (WPI) and the nonionic polysaccharide dextran by dry heating at 80°C for 2 hours (conjugate 1) and at 60°C for 5 days (conjugate 2) on the freeze-thaw stability of oil-in-water emulsions. Emulsions stabilized with WPI, WPI-dextran mixture, conjugates 1 and 2, were prepared using microfluidizer, respectively, and then subjected to from one to three freeze-thaw cycles (−18°C for 22 hours, +40°C for 2 hours). The emulsion stability to freeze-thaw processing was assessed by zeta potential, average particle size, polydispersity index (PDI) and backscattering profile by a recently developed optical analyzer (Turbiscan). Results demonstrated that WPI-dextran conjugates brought about a remarkable improvement in freeze-thaw stabilizing properties when compared with WPI or WPI-dextran mixture which can be attributed to the enhancement of repulsive steric forces between the oil droplets as a result of dextran overlapping t...

Microfluidization and high pressure valve homogenization were applied to prepare β-carotene nanoemulsions, and the mathematical relationship between homogenization pressures and emulsion temperatures, homogenization pressures/cycles, and droplet sizes, were established. Emulsions through Microfluidizer had lower temperature and much smaller droplet sizes, compared with those through high pressure valve homogenizer. Four emulsifiers were compared for their capacities to stabilize nanoemulsions. The two large molecule emulsifiers, octenyl succinate starch (OSA) and whey protein isolate (WPI), were less effective for the formation of nanoemulsions with smaller droplets than the two small molecule emulsifiers, polyoxyethylene sorbitan monolaurate (Tween 20, TW) and decaglycerol monolaurate (DML). The nanoemulsion containing WPI was the most stable, while the one containing DML was the least stable. During storage, significant degradation of β-carotene occurred in all nanoemulsions, especially in the DML stabi...

The aim of the study was to investigate the impact of sodium alginate (ALG) pretreated by ultrasound on the enzyme activity, structure, conformation and molecular weight and distribution of papain. ALG solutions were pretreated with ultrasound at varying power (0.05, 0.15, 0.25, 0.35, 0.45 W/cm 2 ), 135 kHz, 50 °C for 20 min. The maximum relative activity of papain increased by 10.53% when mixed with ALG pretreated by ultrasound at 0.25 W/cm 2 , compared with the untreated ALG. The influence of ultrasound pretreated ALG on the conformation and secondary structure of papain were assessed by fluorescence spectroscopy and circular dichroism spectroscopy. The fluorescence spectra revealed that ultrasound pretreated ALG increased the number of tryptophan on papain surface, especially at 0.25 W/cm 2 . It indicated that ultrasound pretreatment induced molecular unfolding, causing the exposure of more hydrophobic groups and regions from inside to the outside of the papain molecules. Furthermore, ultrasound pretreated ALG resulted in minor changes in the secondary structure of the papain. The content of α-helix was slightly increased after ultrasound pretreatment and no significant change was observed at different ultrasound powers. ALG pretreated by ultrasound enhanced the stability of the secondary structure of papain, especially at 0.25 W/cm 2 . The free sulfhydryl (SH) content of papain was slightly increased and then decreased with the increase of ultrasonic power. The maximum content of free SH was observed at 0.25 W/cm 2 , under which the content of the free SH increased by 6.36% compared with the untreated ALG. Dynamic light scattering showed that the effect of ultrasound treatment was mainly the homogenization of the ALG particles in the mixed dispersion. The gel permeation chromatography coupled with the multi-angle laser light scattering photometer analysis showed that the molecular weight ( M w ) of papain/ALG was decreased and then increased with the ultrasonic pretreatment. Results demonstrated that the activity of immobilized papain improved by ultrasonic pretreatment was mainly caused by the variation of the conformation of papain and the effect of interactions between papain and ALG. This study is important to explain the intermolecular interactions of biopolymers and the mechanism of enzyme immobilization treated by ultrasound in improving the enzymatic activity. As expected, ALG pretreated by appropriate ultrasound is promising as a bioactive compound carrier in the field of immobilized enzyme.

The impact of a whey protein isolate (WPI)–beet pectin (BP) conjugate (formed by dry-heating) on the physical properties and digestibilities of β-carotene and carrier oil in oil-in-water emulsions was studied when they passed through a model gastrointestinal system. β-Carotene emulsions were stabilized by WPI, unconjugated and conjugated WPI–BP, separately. The emulsions were then passed through an in vitro digestion model and the mean droplet size, droplet distribution, zeta-potential, free fatty acids and β-carotene released were measured. The stability to droplet flocculation and coalescence during digestion was increased for the WPI–BP conjugate stabilized emulsion. Addition of BP onto the WPI stabilized emulsions could inhibit the releases of carrier oil (MCT) and β-carotene. The releases of free fatty acids and β-carotene did not differ greatly between the unconjugated and conjugated WPI–BP stabilized emulsions. These results have important implications for protein–polysaccharide stabilized emulsions and conjugates used for the protection and delivery of bioactive compounds.