Aggregation Of Oil Droplets Research Articles

Insight into interfacial adsorption behavior of high-density lipoprotein hydrolysates regulated by carboxymethyl dextrin and in vitro digestibility of curcumin loaded high internal phase emulsions

The interaction between high-density lipoprotein hydrolysate hydrolyzed by trypsin (EHT) and carboxymethyl dextrin (CMD) at pH 7.0, and in vitro digestibility of high internal phase emulsions (HIPEs) were studied. The particle size of EHT/CMD mixtures increased from 207.2 nm to 1229.6 nm with increase of the ratio of EHT to CMD from 8:1 to 1:2. The proportion of EHT adsorbed on the surface increased from 60.83 % to 80.81 %, forming thicker interfacial layer, exhibiting higher resistance to centrifugation and ionic strength. And more uniform proton density distribution and shorter relaxation time (T2) were charactered in HIPEs formed by mixtures. Rheological analysis further proved that CMD could lead to high viscosity, high elasticity, excellent oscillation performance of HIPEs. The spatial and electrostatic repulsion forces reduced the aggregation of oil droplets and promoted the formation of more mixed micelles, improving the bioaccessibility of curcumin. These findings provided theoretical strategies for lipid-soluble nutrients delivery systems.

Ultrasound-assisted preparation of lactoferrin-EGCG conjugates and their application in forming and stabilizing algae oil emulsions

The aim of this study was to prepare lactoferrin-epigallocatechin-3-gallate (LF–EGCG) conjugates and to determine their ability to protect emulsified algal oil against aggregation and oxidation. LF–EGCG conjugates were formed using an ultrasound-assisted alkaline treatment. The ultrasonic treatment significantly improved the grafting efficiency of LF and EGCG and shortened the reaction time from 24 h to 40 min. Fourier transform infrared spectroscopy and circular dichroism spectroscopy analyses showed that the covalent/non-covalent complexes could be formed between LF and EGCG, with the CO and CN groups playing an important role. The formation of the conjugates reduced the α-helix content and increased the random coil content of the LF. Moreover, the antioxidant activity of LF was significantly enhanced after conjugation with EGCG. LF–EGCG conjugates as emulsifiers were better at inhibiting oil droplet aggregation and oxidation than LF alone. This study demonstrates that ultrasound-assisted formation of protein–polyphenol conjugates can enhance the functional properties of the proteins, thereby extending their application as functional ingredients in nutritionally fortified foods.

Molecular Dynamics Simulation for the Demulsification of O/W Emulsion under Pulsed Electric Field.

A bidirectional pulsed electric field (BPEF) method is considered a simple and novel technique to demulsify O/W emulsions. In this paper, molecular dynamics simulation was used to investigate the transformation and aggregation behavior of oil droplets in O/W emulsion under BPEF. Then, the effect of surfactant (sodium dodecyl sulfate, SDS) on the demulsification of O/W emulsion was investigated. The simulation results showed that the oil droplets transformed and moved along the direction of the electric field. SDS molecules can shorten the aggregation time of oil droplets in O/W emulsion. The electrostatic potential distribution on the surface of the oil droplet, the elongation length of the oil droplets, and the mean square displacement (MSD) of SDS and asphaltene molecules under an electric field were calculated to explain the aggregation of oil droplets under the simulated pulsed electric field. The simulation also showed that the two oil droplets with opposite charges have no obvious effect on the aggregation of the oil droplets. However, van der Waals interactions between oil droplets was the main factor in the aggregation.

Preparation and Evaluation of Undaria pinnatifida Nanocellulose in Fabricating Pickering Emulsions for Protection of Astaxanthin.

Pickering emulsions stabilized from natural sources are often used to load unstable bio-active ingredients, such as astaxanthin (AXT), to improve their functionality. In this study, AXT-loaded Pickering emulsions were successfully prepared by 2,2,6,6-tetramethy-1-piperidine oxide (TEMPO)-oxidized cellulose nanofibers (TOCNFs) from Undaria pinnatifida. The morphology analysis showed that TOCNFs had a high aspect ratio and dispersibility, which could effectively prevent the aggregation of oil droplets. The stable emulsion was obtained after exploring the influence of different factors (ultrasonic intensity, TOCNFs concentration, pH, and ionic strength). As expected, AXT-loaded Pickering emulsions showed good stability at 50 °C and 14 days of storage. The results of simulated in vitro digestion showed that the emulsions exhibited higher release of free fatty acids (FFAs) and bioaccessibility of AXT than those in sunflower oil. Hence, our work brought new insights into the preparation of Pickering emulsions and their applications in protection and sustained, controlled release of AXT.

Improving emulsifying properties of carboxylated microcrystalline cellulose by calcium bridging to hydrophobic peptides

This study aimed to improve the emulsifying properties of microcrystalline cellulose by carboxylating (CC) and bridging to hydrophobic oat globule peptides (HP) via Ca2+ (CC-Ca-HP). FTIR and XRD spectra analysis proved the successful attachment of HP to CC through a salt bridge. The Ca2+-bridging significantly changed the particle characteristics of CC-Ca-HP, including particle size, ζ-potential, and wettability. The Ca2+-bridged composite CC-Ca-HP demonstrated remarkable emulsifying stability compared with the nonbridged blend (CC–HP). Further analysis of the steady flow characteristics and dynamic viscoelastic properties revealed a network structure formed in the CC-Ca-HP emulsion. Moreover, the CC-Ca-HP emulsion showed a marked release of free fatty acids, increased bioaccessibility of zeaxanthin in the simulated gastrointestinal digestion, and less oil oxidation under the accelerated oxidation condition, indicating that the stable structure of CC-Ca-HP imparted by Ca2+-bridging prevented the aggregation of oil droplets as collision occurred under the harsh gastric conditions.

Formation of Antioxidant Multilayered Coatings for the Prevention of Lipid and Protein Oxidation in Oil-in-Water Emulsions: Lycium barbarum Polysaccharides and Whey Proteins.

The impact of Lycium barbarum polysaccharides (LBPs) on the physical and chemical stability of oil-in-water emulsions coated by a whey protein isolate (WPI) was investigated. At pH 3.0, the anionic LBP (0.2-0.6 wt %) molecules were electrostatically deposited onto the cationic surfaces of the WPI-coated oil droplets, leading to the formation of stable multilayered emulsions containing WPI-/LBP-coated oil droplets. However, increasing the LBP concentration to 0.8 wt % led to oil droplet aggregation, which was attributed to charge neutralization, bridging flocculation, and/or depletion flocculation. For subsequent experiments, a low (0.2%) and an intermediate (0.6%) LBP dose was used to prepare the secondary emulsions, and then their physical and oxidative stability was studied during 8 days of storage at 37 °C. The presence of the multilayer WPI/LBP coatings around the oil droplets inhibited lipid oxidation (reduced levels of lipid hydroperoxides and 2-thiobarbituric acid-reactive substances), as well as protein oxidation (reduced levels of carbonyl formation, sulfhydryl consumption, molecular weight modifications, intrinsic fluorescence loss, and Schiff-base fluorescence gain). The antioxidant effects of the multilayer coatings were greater at the higher LBP concentration. These results suggest that LBP, a natural plant-based polysaccharide isolated from a traditional Chinese medicine, can be used to improve the quality of emulsion-based foods. However, the level used should be optimized to ensure good physical and oxidative stability of the emulsions.

High-internal-phase pickering emulsions stabilized by ultrasound-induced nanocellulose hydrogels

The present work applied nanocellulose hydrogels for the first time to stabilize high internal phase emulsions (HIPEs, oil-in-water) with a 75% oil phase. Nanocellulose hydrogels are easily fabricated by ultrasonic treatments based on the physical entanglement between slender nanocelluloses. This ultrasound-induced hydrogel had reversible gelation properties. Small-angle X-ray scattering measurements revealed that ultrasonic treatments reduced the interfibrillar distance of hydrogels from 86.81 to 6.05 nm with increasing ultrasonic time from 10 to 90 min. Hydrogels with small interfibrillar distances showed the stronger gel strength. The influence of the hydrogel/water ratio (ranging from 2:8–8:2, w/w) in the aqueous phase on the formation and stability of HIPEs was investigated. Stable HIPEs could be prepared using hydrogel ratios ranging from 3 to 7. Nevertheless, the gel behavior of HIPEs depended on the hydrogel ratio level. HIPEs with strong gel strength showed the better physical and storage stability. The stabilization mechanism was clearly exhibited by the three-dimensional image from confocal laser scanning microscopy (CLSM): gaps between oil droplets were fully filled with the continuous network structure which was re-formed by dispersed hydrogels due to its reversible gelation property. This continuous network structure effectively solidified the surrounding oil droplets, preventing oil droplet aggregation and coalescence. The findings could extend the applications of unmodified nanocellulose in emulsion formulations in the food and pharmaceutical fields.

Enhanced oil droplet aggregation and demulsification by increasing electric field in electrocoagulation

Electrocoagulation (EC) is an efficient technology for removing oil-in-water (O/W) emulsions. However, the role of the electric field in EC for demulsification remains unclear and an obstacle for improving reactor design and operation. Herein, demulsification and oil removal performance by EC under different electric field conditions were investigated. Increasing the EC electric field intensity was beneficial for oil removal, and tandem EC had a higher electric field intensity than parallel EC under the same current density. When the current density was 0.67 mA cm−2, the chemical oxygen demand (COD) removal rates of tandem EC and parallel EC were 1 136.47 and 745.99 g COD kWh−1, respectively. Oil droplets were polarized by the electric field, and then aligned and aggregated parallel to the direction of the electric field. Increasing electric field intensity accelerated the aggregation of oil droplets, as verified by physical fluid simulation. Furthermore, results showed a higher Al3+ dosage and larger electric field intensity in EC with increasing current density, which was conducive to oil droplet demulsification. These findings provide insight into and a theoretical basis for improving oil removal by EC processes.

Improving freeze–thaw stability of soy protein isolate-glucosamine emulsion by transglutaminase glycosylation

This paper studies the improvement of freeze–thaw stability of emulsions by incorporating glucosamine into soy protein isolate (SPI) by using transglutaminase. The occurrence of enzymatic glycosylated SPI reaction is confirmed by SDS-PAGE. Through the measurement of creaming index and oiling off, we find that both soy protein isolate-enzymatic without glucosamine (SPI-E) and glycosylated SPI by transglutaminase (SPI-G) can effectively improve the freeze–thaw stability of emulsions. The analysis of particle size, degree of flocculation and coalescence indicates that macromolecular aggregates were formed because transglutaminase enzyme promoted glycosylation and also promoted the cross-linking of protein and protein or the internal cross-linking of protein. Therefore, the particle size of the SPI-G emulsion before freezing and thawing is larger than that of the SPI emulsion. After freeze–thaw cycles, it can be seen that although the particle size of SPI-G is increasing, it is significantly smaller than that of SPI emulsion after freeze–thaw. According to the optical microscope, it can be seen that the SPI emulsion has obvious aggregation of oil droplets after freeze–thawing, and SPI-G effectively improves oil droplet aggregation.

Stability Issues, Probable Approaches for Stabilization and Associated Patents in the Pharmaceutical Field for Oleosome, A Novel Carrier for Drug Delivery.

Oleosomes are oil-containing micro-carriers of natural origin that are comprised of special oleosin proteins embedded with a monolayer of phospholipids having a triacylglycerol core. Due to their unique structure and non-toxicity in the biological system, these oil carriers are becoming very eye-catching for formulation development in the field of pharmacy. Consequently, oleosome offers emoliency, occlusivity, self-emulsification, anti-oxidant, and film-forming properties, which leads to controlled and sustained release of encapsulated bio-actives. It is also feasible to load oil-soluble ingredients, such as fragrance, vitamins (retinol), and lipophilic drug moieties inside the core. Being a natural carrier, it shows some stability issues (leakage of oil from the core, oxidation of the loaded oil, aggregation of oil droplets), which are controllable. In this review, we have focused on the various stability issues, the techniques (coating, surface modification, solvents) and how to overcome those problems, and how to load any lipophilic drug into the oil core, and we have also linked patent research works in the field of formulation development.

Mechanical properties of 2D aggregates of oil droplets as model mono-crystals.

We investigate the elastic and yielding properties of two dimensional defect-free mono-crystals made of highly monodisperse droplets. Crystals are compressed between two parallel boundaries of which one acts as a force sensor. As the available space between boundaries is reduced, the crystal goes through successive row-reduction transitions. For small compression forces, the crystal responds elastically until a critical force is reached and the assembly fractures in a single catastrophic global event. Correspondingly there is a peak in the force measurement associated with each row-reduction. The elastic properties of ideal mono-crystal samples are fully captured by a simple analytical model consisting of an assembly of individual capillary springs. The yielding properties of the crystal are captured with a minimal bond breaking model.

Physicochemical and emulsifying properties of orange fibers stabilized oil-in-water emulsions

The present work aimed to evaluate the physical and techno-functional property and microstructure of freeze-dried orange pulp and peel powders modified by high-pressure homogenization (HPH) treatment, and their emulsifying properties of oil-in-water emulsions treated with HPH. For orange pulp and peel powders, HPH pre-treatment was found to significantly reduce bulk density and increase the water and oil holding capacity (P < 0.05) of orange pulp and peel powders, and the particles appeared to have flake-like shape. When orange-pulp and peel dispersions were subjected to HPH treatment, all samples showed significant decreases in particle size and increases in ζ-potential (P < 0.05), and could maintain higher stability with extended storage time. Furthermore, Confocal Laser Scanning Microscopy (CLSM) also revealed that emulsion destabilization occurred with increased storage time due to oil-droplet aggregation and coalescence. The results indicated that emulsion stability was improved by HPH treatments, probably due to a steric or electrostatic repulsion against flocculation or coalescence of oil droplets, and orange fibers, particularly orange pulp are suitable feedstock as natural emulsifiers.

Whole soybean milk produced by a novel industry-scale micofluidizer system without soaking and filtering

Whole soybean milk (WSM) was prepared by an innovatively created industry-scale microfluidizer system (ISMS). Results showed WSM prepared by ISMS (WSMM) at 60, 90 and 120 MPa kept stable spontaneously for 21 days at 4 °C, while the one prepared by traditional method (WSMT) stratified on day 14. The aggregation of oil droplets and proteins during storage caused the increase of particle sizes of WSMT, while WSMM showed little change in the form and distribution of oil droplets and proteins, as well as particle sizes. The smaller size, looser microstructure of dietary fiber and higher viscosity of WSMM also contributed to the stability of WSMM. WSMM prepared at 90 and 120 MPa exhibited higher isoflavone contents (0.92 and 1.03 mg/g) than those of WSMT (0.89 mg/g). This research suggested that the ISMS was feasible in producing the WSM with superior stability and nutrition.

Effect of ultrasonic treatment on rheological and emulsifying properties of sugar beet pectin.

The effects of ultrasonic treatment on rheological and emulsifying properties of sugar beet pectin were studied. Results indicated that intrinsic viscosity ([η]) and viscosity average molecular weight ([M v]) decreased with the increased time from 0 to 30 min but increased when the duration prolonged to 45 min. The change of apparent viscosity with shear rate of all pectin solutions could be well described by Sisko model (R 2 ≥ .996) and the infinite‐rate viscosity (η ∞) and the consistency coefficient (k s) values decreased after ultrasonic treatment. Ultrasonic treatment could have an effect on dynamic moduli and activation energy of sugar beet pectin solutions. Particle size of pectin emulsions decreased and absolute zeta potential increased with increased time from 0 to 20 min. Excessive ultrasonic duration (30 and 45 min) could result in the aggregation of oil droplets in pectin emulsion and decrease in emulsifying stability. It could be concluded that ultrasonic treatment could affect the rheological and emulsifying properties of sugar beet pectin. The results have important implications for understanding the ultrasonic modification of sugar beet pectin.

Stability of pH-responsive Pickering emulsion stabilized by carboxymethyl starch/xanthan gum combinations

The objective of this study was to investigate the effect of different pH values (3, 5, 7, 9 and 11) on the stability of Pickering emulsions stabilized by carboxymethyl starch (CMS)/xanthan gum (XG) combinations. The CMS/XG combinations could be used as an effective stabilizer for the preparation of Pickering emulsion. The effects of CMS/XG combinations on oil droplet size, Zeta potential, rheological properties, backscattering profiles, Low-field nuclear magnetic resonance imaging and storage stability of oil-in-water emulsion were evaluated as a function of pH. As pH increased from 3 to 11, the droplet size of the emulsion increased and the absolute value of Zeta potential decreased. Besides, the consistency coefficient of the emulsion was reduced and the pseudoplasticity was weakened. The variation of backscattered light intensity of the emulsion at pH 3 was the smallest. The combination of CMS and XG formed a good network structure and inhibited the phase separation of emulsion. The color distribution of Low-field nuclear magnetic resonance imaging of emulsions at pH 3, 5 and 7 was more uniform and had better storage stability at 25 °C for 9 days. pH affected the aggregation of oil droplets. The Pickering emulsion stabilized by CMS/XG combinations was pH-responsive and could be used as an effective carrier for biologically active substances.

Rearrangement of two dimensional aggregates of droplets under compression: Signatures of the energy landscape from crystal to glass

We study signatures of the energy landscape's evolution through the crystal-to-glass transition by compressing 2D finite aggregates of oil droplets. Droplets of two distinct sizes are used to compose small aggregates in an aqueous environment. Aggregates range from perfectly ordered monodisperse single crystals to disordered bidisperse glasses. The aggregates are compressed between two parallel boundaries, with one acting as a force sensor. The compression force provides a signature of the aggregate composition and gives insight into the energy landscape. In particular, crystals dissipate all the stored energy through single catastrophic fracture events whereas the glassy aggregates break step-by-step. Remarkably, the yielding properties of the 2D aggregates are strongly impacted by even a small amount of disorder.

Characterization of Pickering emulsions stabilized by OSA-modified sweet potato residue cellulose: Effect of degree of substitute and concentration

The aims of the present study were to modify the native sweet potato residue cellulose (NSPRC) with octenyl succinic anhydride (OSA) using DMAc/LiCl reaction system and to evaluate the formation and stability of Pickering emulsion stabilized by this modified cellulose with different degree of substitute (DS) and concentration. The results showed that the molecular structure, crystal character, contact angle and surface texture of OSA-modified sweet potato residue cellulose (OSA-SPRC) were remarkably changed compared to NSPRC. In conclusion, the hydroxyl of the NSPRC was successfully replaced by the carboxyl group of OSA. Moreover, the emulsifying ability and stability of OSA-SPRC were both higher than that of Tween 80 at the same concentration and storage time. Compared with low DS (0.0017 ± 0.0003) OSA-SPRC, the emulsions stabilized by high DS (0.0063 ± 0.0005) OSA-SPRC displayed better creaming index, lower particle size, uniform droplets distribution, higher apparent viscosity, and emulsion stability after storing for 15 d. Similar findings were obtained with the concentration of OSA-SPRC from 0.25% to 1.75%. The improvement in the emulsion properties was likely due to the formation of oil-OSA-SPRC particles network and the saturated adsorption of OSA-SPRC particles at the O/W interface, thereby limiting the aggregation of oil droplets. Overall, the Pickering emulsions stabilized by OSA-SPRC exhibited benign stability against coalescence. The emulsions were found to be responsive to the DS and concentration of OSA-SPRC. This research revealed the formation mechanism of the Pickering emulsion stabilized by OSA-SPRC and its main affecting factors.

Effect of Alcohol Additives on the Plate-Out Oil Film in Cold Rolling and Its Molecular Dynamics Simulations

In order to meet the demands of modern rolling technology, improve productivity, and control oil consumption, flexible lubrication control has been more and more important. In this study, a new method to control the plate-out oil film formation has been proposed and clarified by molecular dynamics (MD) simulations. Four alcohol additives are added, namely, propanetriol, 1,2-propanediol, ethylene glycol, and n-propanol; the oil-in-water emulsions display different plate-out behavior with the amount of plate-out film following the order of propanetriol1,2-propanediolethylene glycoln-propanol. The adsorption mechanism, the MD simulation of the flat membrane layer, the mean square displacement (MSD), and the cohesive energy are used to elucidate the relevant mechanism of the additive on the precipitation characteristic. The results show that the capacity of aggregation of oil droplets on the formed film takes the dominant role in the plate-out film formation with different alcohol additives, which is helpful in guiding flexible controllability of plate-out behavior as well as lubrication conditions.

Aggregation of oil droplets and demulsification performance of oil-in-water emulsion in bidirectional pulsed electric field

Electric field driven aggregation of oil droplets in oil-in-water (O/W) emulsion is a novel attempt for enhancing oil-water separation. The chaining and aggregation behavior of oil droplets in O/W emulsion under bidirectional pulsed electric field (BPEF) was studied in this work for the purpose of oil droplets separation from aqueous phase in O/W emulsion for the first time. The BPEF induced oil droplets to aggregate and take shape into three forms of congeries: oil-droplet chain, oil clusters and oil cluster chains. The aggregation effect of oil drops under BPEF voltage, frequency and duty cycle was explored by evaluating the size and formation time of congeries. It was discovered that BPEF voltage could enhance and accelerate oil droplets to aggregate but the aggregation effect was weakened by the increased BPEF frequency. And the best aggregation state of oil droplets under different duty cycles was achieved at BPEF duty cycle 70%. The demulsification performance of O/W emulsion under BPEF was investigated and its variation was consistent with the aggregation regularity and effect of oil drops in BPEF. Therefore, the microcosmic aggregation effect of oil drops in O/W emulsion under BPEF could be used to estimate the demulsification performance and separation effect of O/W emulsion.

Synergetic interfacial adsorption of protein and low-molecular-weight emulsifiers in aerated emulsions

Whipped creams (aerated emulsions) are a complex emulsion-foam system whose oil-stabilizing potential and aeration capacity are determined by the surface activity of proteins and small surfactants. In this study, the interaction between three low-molecular-weight (LMW) emulsifiers [sodium stearoyl lactylate (SSL), phospholipid (PL), and sucrose ester (SE)] with caseinate was investigated to elucidate the mechanism of formation and stability of whipped creams. Competitive adsorption, interfacial tension, droplet aggregation, viscosity, and morphological variations of the emulsions were examined, and aeration capacity, hardness, and microstructure of whipped creams were measured. The combination of surfactants (0.05–1.0% w/w) with caseinate (0.6% w/w) produced concerted effects on the stability of emulsions. Water-soluble surfactant (SE) adsorbed more strongly than oil-soluble surfactants (SSL and PL) onto oil droplets. The lesser protein adsorption in the SE emulsion enabled a strong foaming activity in the subsequent aeration. Protrusions of triacylglycerol crystals and aggregation of oil droplets into an interactive colloidal matrix with considerable hardness and viscosity were prominently observed in SE creams. On the other hand, shear thinning followed by thickening was observed when PL was added to form the caseinate-based emulsion while no foaming was produced, and SSL, known to form α-gel at the interface, produced no stable foam. The improved emulsion stability yet the propensity to coalesce induced by cooperative actions of casein molecules and hydrophilic surfactant played a crucial role in producing aerated emulsions.