Decrease In Zeta Potential Research Articles

Insight on Exogenous Calcium/Magnesium in Weakening Pyrite Floatability with Prolonged Pre-Oxidation: Localized and Concomitant Secondary Minerals and Their Depression Characteristics

In this study, we investigated the localized and concomitant precipitation of calcium (Ca)/magnesium (Mg)-bearing species and iron oxides/oxyhydroxides, and their depression characteristics to the pyrite floatability in flotation process at pH 9 and pH 10.5 with prolonged pre-oxidation. Contrary to the depression characteristics at pH 9, the incipient (within aeration times of 30 min) depression of pyrite floatability in Ca/Mg-bearing solutions was more obvious at pH 10.5, while the subsequent decline was only slightly when the pre-oxidation time was expanded to 120 min and 360 min. The competitive adsorption among Ca/Mg-bearing species and potassium amyl xanthate (PAX, C6H11OS2K, collector) at specific sites onto the pyrite surface was demonstrated by the regularly decreased zeta potential of the pyrite surface pretreated in Ca/Mg-bearing solutions. Further scanning electron microscopy-energy dispersive spectrometry demonstrated the concomitant secondary Ca/Mg/Fe-bearing precipitates on the pyrite surface. X-Ray photoelectron spectroscopy suggested strong reprecipitation of iron oxides/oxyhydroxides on the pyrite surface via acid–base complexation among Ca/Mg hydroxy species and iron hydroxy species. Incipient occupation efficiency of specific reaction sites by Ca/Mg-bearing species, which were mainly controlled by the metastable distribution of Ca/Mg hydroxy species and their electrostatic affinity with pyrite surface, was the crucial factor that influenced the competitive adsorption of xanthate and pyrite floatability. More obvious incipient depression at pH 10.5 rather than at pH 9 contributed to more effective Ca/Mg-bearing species and their higher affinity to pyrite surface at pH 10.5. The localized and concomitant precipitation of secondary Ca/Mg/Fe-bearing species leads to a slightly increased hydrophilic coverage upon the pyrite surface, thus a slowly decreased pyrite floatability with increasing pre-oxidation time.

Size-dependent visible-light-enhanced Cr(VI) bioreduction by hematite nanoparticles

Light irradiation would affect the electron transfer between dissimilatory metal-reducing bacteria (DMRB) and semiconducting minerals, which may impose a great influence on the biogeochemistry cycle of heavy metals. However, the size effect of semiconducting minerals on the its electron transfer with DMRB and microbial Cr(VI) reduction under visible light irradiation is little known. Herein, the Cr(VI) reduction by Shewanella oneidensis MR-1 (MR-1) was investigated in the presence of hematite nanoparticles with average diameters of 10 nm and 50 nm in dark and under visible light irradiation. It is found that hematite nanoparticles adhered onto MR-1 cells to form the composites, leading to the decrease in surface sites and Zeta potential. Hematite mediated-Cr(VI) bioreduction rate under visible light irradiation was 0.342 h−1, which is 3.4 folds enhancement compared with that in dark and 4.4 folds compared with the MR-1 alone under visible light irradiation. Decreasing nanoparticle size of hematite from 50 nm to 10 nm promoted the Cr(VI) reduction under visible light irradiation but impeded it in dark. It was deduced that the bioelectrons from MR-1 could promote the separation of photoelectron-hole pairs of light-irradiated hematite, which consequently enhanced the Cr(VI) bioreduction by MR-1-hematite composites. Moreover, mutant strains experiments demonstrated the vital role of c-cytochrome for the conducting network actively established by MR-1 with hematite nanoparticles. Those findings expand the understanding of the electron transfer pathway for enhancing Cr(VI) reduction by hematite-MR-1 composites, and the impact of particle size on the interaction between semiconducting mineral and electroactive bacteria under light irradiation.

Phage display-derived immunorecognition elements LSPR nanobiosensor for peptide hormone glycine-extended gastrin 17 detection.

The current study intended to evaluate two types of biorecognition element (BRE), namely recombinant antibody fragments and M13 bacteriophage-displayed antibody fragments, where protein L and electrostatic interactions were used to respectively conjugated antibodies and bacteriophages on AuNPs. The functionalization process was examined by DLS to monitor the changes in the size and zeta potential. The formation of the BRE-G17-Gly immunological complexes was manifested by aggregation (confirmed by FE-SEM) and color change from red to dark blue visible to the naked eye. Local refractive index variations of functionalized AuNPs were monitored by a UV - vis spectrophotometer, showing increasing size and decreasing zeta potential in all stages. The calibration plot was developed in the concentration range 1-5µg/mL and the limit of detection (LOD) was 1µg/mL. The LSRP nanobiosensor in combination with the phage-based BRE was an affordable and simple approach, as it was able to eliminate the time-consuming and costly step of extracting antibodies. Contrary to the traditional immunoassays, this method does not require additional amplification, e.g., enzymatic, to read the result. The proposed LSPR nanobiosensor model can be adapted to detect a wide range of pathogens, viruses, and biomarkers in the shortest possible time.

Improving sedimentation and lipid production of microalgae in the photobioreactor using saline wastewater

Saline wastewater was used in this study to culture freshwater microalgae Chlorella pyrenoidosa in sequencing batch photobioreactor to improve the sedimentation and lipid production of algal cells. Influent salinity of 0.5% or above effectively promoted the sedimentation of microalgae in the settling stage of photobioreactor, and greatly reduced the algal biomass in effluent. The mechanism of the saline wastewater in improving the sedimentation of microalgae included decreasing zeta potential, increasing cell particle size and promoting extracellular polymeric substances synthesis, which varied with influent salinity. Saline wastewater also promoted the lipid accumulation in microalgae. Lipid content of microalgae increased with increasing influent salinity. However, the growth of microalgae was greatly inhibited at the influent salinity of 2.0% and 3.0%. Therefore, the PBR with influent salinity of 1.0% achieved the highest productivity of microalgae lipid. The saturation of fatty acids of microalgae gradually increased with increasing influent salinity.

Development of alendronate niosomal delivery system for gastrointestinal permeability improvement

In this study, the influences of surfactant types, the molar ratio of surfactant and cholesterol, and the molar ratio of drug load and total lipids on the size, zeta potential and drug entrapment efficiency of niosomes were statistically evaluated using a central composite design. Alendronic acid, a bisphosphonate compound was used to study. Stability, in vitro drug release and gastrointestinal permeability improvement of alendronate niosomal dispersion were also studied. The results showed that surfactant types, molar ratios of surfactant to cholesterol and molar ratios of drug load to total lipids had a significant effect on particle size, zeta potential and drug entrapment efficiency of niosomes (P < 0.05). The obtained niosomes were of a unilamellar spherical shape with negative zeta potential values. The niosomes prepared from Span 60 were larger and more entrapment efficient than those prepared from Span 20. In addition, the decrease of molar ratios of Spans and cholesterol resulted in the increase of zeta potential. The particle size and drug entrapment efficiency decrease when the molar ratio of Spans and cholesterol was decreased. Moreover, increase of drug load and total lipid molar ratio resulted in the decrease of zeta potential. However, particle size and drug entrapment efficiency could be increased with increasing molar ratio of drug loading and total lipid. Niosomes prepared from Span 60 showed a slower release rate than those prepared from Span 20. In the stability study, when stored at 4 °C for 90 days, only niosomes prepared from Span 20 have no significant change in particle size, zeta potential and the percentage of drug entrapment. The permeation of alendronate niosomes across Caco-2 cells monolayer showed that the average apparent permeability of alendronic acid from the niosomal dispersion prepared from Span 20 and Span 60 were significantly greater than that of the drug solution. This study revealed that niosomal dispersion can improve the oral bioavailability of alendronic acid.

Influence of solvent polarity of ethonal/water binary solvent on the structural, emulsifying, interfacial rheology properties of gliadin nanoparticles

Gliadin nanoparticles (GNPs) is a promising material for stabilizing Pickering emulsions. The present work aimed to investigate the effect of solvent polarity of ethonal/water binary solvent on the structure and emulsifying property of GNPs and provide reference information for the potential application of GNPs in alcoholic food system. The structural, emulsifying and interfacial rheology properties of GNPs in aqueous phases with different polarity (EN(T):1.00–0.94) were evaluated. The solvent polarity was regulated by changing the ethanol concentration in aqueous phase. Results showed that the emulsifying activity of GNPs significantly improved as the EN(T) decreased from 1.00 to 0.96, and then decreased as the EN(T) further decreased from 0.96 to 0.94 for the rising particle size. Meanwhile, the decrease of solvent polarity improved the diffusion rate, viscoelastic modulus (E) and the interparticle interaction of GNPs. The possible mechanism was investigated by discussing the relationship among the structural, emulsifying and interfacial rheology properties of GNPs. It was found that the decrease of solvent polarity triggered the increase of hydrophobic groups distributed on the particle surface, and then resulted in the decrease of zeta potential and the increase of surface hydrophobicity of GNPs, which benefited the diffusion/adsorption of particles and the formation of viscoelastic protein layers for lower electrostatic repulsion, moderate surface wettability and stronger hydrophobic interaction. The results also suggested that GNPs might be a natural and economical material for low-degree alcohol emulsion food.

Upgrade of low rank coal by using emulsified asphalt and its application for preparation of coal water slurry with high concentration

The hydrophilic surface and developed pore structure restricted the application of abundant low rank coals (LRC) for the preparation of coal water slurry (CWS) with high concentration. In this work, emulsified asphalt was applied as an effective and low cost modifier to modify coal surface and improve the slurry making performance of LRC. The successful modification was verified by various technologies, such as chemical titration, X-ray photoelectron spectroscopy (XPS) and Zeta potential measurements. The results revealed that the oxygen containing groups located at LRC surface were covered by emulsified asphalt, which further caused the decrease of Zeta potential. The influence of modification on wettability of coal was also evaluated by contact angle and moisture re-adsorption. It showed that the hydrophobicity of LRC significantly increased, which is accompanied with the reduction of inherent moisture. Besides, the results of nitrogen adsorption and scanning electron microscope (SEM) verified that the hydrophobic layer formed by emulsified asphalt blocked the pores of LRC. The modified LRC also exhibited better adsorption ability to the widely used anionic dispersant naphthalene sulfonate formaldehyde condensate (NSF) than that of raw coal (RC) and microwave dehydration coal (MDC). Anyhow, modified LRC possessed the characteristics as high rank coal. Afterwards, modified coal was applied to prepare CWS. The results showed that CWS prepared by modified LRC exhibited superior slurry making performance as compared to RC and MDC. The surface modification reduced the inherent moisture and promoted the adsorption of dispersant, which increased the free water amount and enhanced electrostatic repulsion and steric hindrance among coal particles. Accordingly, the maximum concentration for CWS increased, and the static stability enhanced.

Effect of acid on the hydrophysical properties of red clay

With the exception of the engineering properties of kaolinite, bentonite, silt and sand, little attention has been paid to how the hydrophysical properties of red clay vary with the pH value, even though acid contamination of red clay occurs widely. The purpose of this paper is to investigate the laws and mechanisms for the hydrophysical properties of red clay treated with dilute hydrochloric acid. Tests were performed on a natural red clay from South China to determine how hydrochloric acid influences the hydraulic conductivity, expansibility and shrinkage. The test data are of the mineral composition, main metal oxide and zeta potential of the red clay before and after being soaked in various acidic solutions with pH values of 3.0, 4.0, 5.0 and 6.5. The results show that the consistency decreased with the pH value for decreasing zeta potential. In addition, the hydraulic conductivity first decreased and then increased, but the expansibility and contractility behaved in the opposite manner as the pH value of the solution decreased. These phenomena depend on the decrease in the zeta potential, the water amount entering the montmorillonite crystal cells and the formation of open voids.

Construction of carboxymethyl konjac glucomannan/chitosan complex nanogels as potential delivery vehicles for curcumin

Construction of nanoscale delivery systems from natural food biopolymer complexes have attracted increasing interests in the fields of food industries. In this study, novel carboxymethyl konjac glucomannan/ chitosan (CMKGM/CS) nanogels with and without 1-ethyl-3-(3-dimethylaminopropyl) /N-hydroxysuccinimide) (EDC/NHS)-initiated crosslinking were prepared. The physicochemical and structural properties of the CMKGM/CS nanogels and their potential to be a delivery vehicle for curcumin were investigated. Compared to original uncrosslinked nanogels, crosslinking did not alter particle size and morphology but decreased zeta potential of nanogels. Fourier transform infrared spectrum confirmed that the amide linkage was formed between CMKGM and CS, which obviously enhanced the stability of crosslinked nanogels under gastrointestinal conditions. Furthermore, the crosslinked nanogels not only had higher encapsulation efficiency of curcumin but also better sustained release behavior under simulated gastrointestinal conditions. These findings suggested that the crosslinked CMKGM/CS nanogels might be a promising delivery system for nutrients.

Phenothiazinium Photosensitizers Associated with Silver Nanoparticles in Enhancement of Antimicrobial Photodynamic Therapy.

Antimicrobial photodynamic therapy (APDT) and silver nanoparticles (AgNPs) are known as promising alternatives for the control of microorganisms. This study aims to evaluate the antifungal activity of APDT, particularly by using the association of low concentrations of phenothiazinium photosensitizers (PS) methylene blue (MB), new methylene blue N (NMBN), and new methylene blue N Zinc (NMBN-Zn) in association with biosynthesized AgNPs. The AgNPs were characterized by UV-Vis spectrophotometry, transmission electron microscopy, and the dynamic light scattering method. The minimum inhibitory concentration of compounds in APDT against Candida albicans and Fusarium keratoplasticum was obtained and the Fractional Inhibitory Concentration Index determined the antifungal effect. The toxicity of compounds and associations in APDT were evaluated in Galleria mellonella. The AgNPs presented a surface plasmon band peak at 420 nm, hydrodynamic diameter of 86.72 nm, and zeta potential of −28.6 mV. AgNPs-PS showed a wider and displaced plasmon band peak due to PS ligands on the surface and decreased zeta potential. AgNPs-NMBN and AgNPs-NMBN-Zn associations presented synergistic effect in APDT with 15 J cm−2 against both fungi and did not show toxicity to G. mellonella. Hence, the enhancement of antifungal activity with low concentrations of compounds and absence of toxicity makes APDT with AgNPs-PS a promising therapeutic alternative for fungal infections.

Development of Highly Efficient, Glassy Carbon Foam Supported, Palladium Catalysts for Hydrogenation of Nitrobenzene.

Glassy carbon foam (GCF) catalyst supports were synthesized from waste polyurethane elastomers by impregnating them in sucrose solution followed by pyrolysis and activation (AC) using N2 and CO2 gas. The palladium nanoparticles were formed from Pd(NO3)2. The formed palladium nanoparticles are highly dispersive because the mean diameters are 8.0 ± 4.3 (Pd/GCF), 7.6 ± 4.2 (Pd/GCF-AC1) and 4.4 ± 1.6 nm (Pd/GCF-AC2). Oxidative post-treatment by CO2 of the supports resulted in the formation of hydroxyl groups on the GCF surfaces, leading to a decrease in zeta potential. The decreased zeta potential increased the wettability of the GCF supports. This, and the interactions between –OH groups and Pd ions, decreased the particle size of palladium. The catalysts were tested in the hydrogenation of nitrobenzene. The non-treated, glassy-carbon-supported catalyst (Pd/GCF) resulted in a 99.2% aniline yield at 293 K and 50 bar hydrogen pressure, but the reaction was slightly slower than other catalysts. The catalysts on the post-treated (activated) supports showed higher catalytic activity and the rate of hydrogenation was higher. The maximum attained aniline selectivities were 99.0% (Pd/GCF-AC1) at 293 K and 98.0% (Pd/GCF-AC2) at 323 K.

Effects of protein concentration, pH, and NaCl concentration on the physicochemical, interfacial, and emulsifying properties of β-conglycinin

The physicochemical characteristics, interfacial, and emulsifying properties of β-conglycinin (7S) at various protein concentrations (c), pH values (pH), and NaCl concentrations (NaCl) were characterized. The increase in c did not change the z-average diameters, solubility, and hydrophobicity but remarkably increased the net charges of 7S. The interfacial properties and emulsifying efficiency of 7S exhibited a dramatic dependence on the increase in c. Thus, the increased electrostatic repulsions facilitating the structural rearrangement and enough protein adsorbing onto the oil droplets' interfaces were the requirements for good emulsifying efficiency. 7S at pH 3 and 8 exhibited smaller z-average diameters, higher net charges, and solubility than that at pH 5, positively affecting their adsorption and the formation of viscoelastic layers. Thus, 7S at pH 3 and 8 showed better emulsifying efficiency. The increased NaCl did not change the z-average diameters, solubility, and hydrophobicity but decreased Zeta potentials of 7S due to electrostatic screening effects. Also, the increased NaCl improved interfacial adsorption kinetics but less viscoelastic interfacial layers of 7S. It suggested that low net charges decreased the electrostatic barrier for adsorption but did not benefit the intermolecular interaction of 7S at the interface. The emulsions aggregation at a high ionic strength indicated a negative effect on emulsifying activity.

Effect of hydrothermal pretreatment on surface physicochemical properties of lignite and its flotation response

Flotation is the common method for fine low rank coal upgrading while it is always inefficient due to the rough surface morphology and rich oxygen-containing functional groups. Hydrothermal pretreatment is widely used in dewatering for low rank coal. The physicochemical properties of coal surface considerably vary following the hydrothermal pretreatment. In this study, hydrothermal pretreatments at different temperatures for different times were applied to enhance lignite flotation. The hydrothermal pretreatment at 200 °C can significantly improve the flotation efficiency, while the temperature raised to 300 °C, the flotation recovery did not increase or even decrease. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Zeta potential, Brunauer–Emmett–Teller, and particle size distribution analysis were conducted to explain the underlying mechanism. The contents of pore and crack on coal surface considerably decreased and more fresh and smooth surfaces exposed following hydrothermal pretreatment, according to SEM analysis. The FTIR spectroscopy and XPS showed that the contents of oxygen-containing functional groups were decreased, while the hydrophobicity of lignite was increased following pretreatment. The decrease of Zeta potential also indicated the decrease of oxygen-containing functional groups and increase of hydrophobicity on coal surface. However, excessive temperature of hydrothermal pretreatment could increase the pore diameter and fine particle fraction, leading to a higher collector consumption and lower bubble–particle collision efficiency. Consequently, the flotation recovery was not improved or even decreased at the hydrothermal pretreatment temperature of 300 °C.

Shelf life extension of apricot fruit by application of nanochitosan emulsion coatings containing pomegranate peel extract

The effect of nanochitosan coating containing pomegranate peel extract (PPE) at concentrations 0.5, 0.75 and 1% (w/v) on postharvest quality of apricot fruit was studied during storage at 4 °C for 30 days. Nanoemulsions showed significant increase in droplet diameter 275–400 nm, decrease in zeta potential −30–23 mV and viscosity 90–76 mPas−1 with increase in PPE concentration. Results confirmed that apricot fruit treated with chitosan and 1% PPE showed significantly reduced decay percentage, weight loss, effectively retained DPPH radical scavenging activity, ascorbic acid, kept titratable acidity and firmness at high level than untreated fruit. Color attributes showed decrease in L*, a* values and significant increase in b* value. Nanochitosan containing 1% PPE significantly inhibited total psychrophilic bacterial count, yeast and mold count during storage. Our results suggest that chitosan coatings enriched with pomegranate peel extract has the potential to preserve the quality and extend shelf life of apricot.

Humic-mineral interactions modulated by pH conditions in bauxite residues – Implications in stable aggregate formation

Bauxite residue exhibiting high sodicity, nutrient deficiency, and poor structure, has a very slow effect on natural vegetation. However, it presents some eco-friendly indicators through substrate improvement, which is the basis for bauxite residue to show pedogenesis and vegetation restoration. To test the effectiveness of acid organic materials toward promoting transformation into a soil-like material, bauxite residue was amended with nitrohumic acid to improve the physical and chemical properties. The pH, total alkalinity, and exchangeable sodium percentage of the treated bauxite residues decreased from 10.2, 2.7 cmol/kg, and 20.6% to 8.0, 0.4 cmol/kg, and 5.1%, respectively, whilst organic matter, available N and P increased from 1.3%, 6.7 mg/kg, and 0.8 mg/kg to 7.2%, 69.7 mg/kg, and 2.4 mg/kg, respectively. The results obtained from excitation-emission matrix spectroscopy also indicate that the nitrohumic acid treated residues have a higher fulvic acid content and present a significant amount of humified material and soil maturation. The high alkalinity of bauxite residue promotes the release of hydroxyl and phenolic hydroxyl groups from fulvic acid to combine with cations. Nitrohumic acid neutralization lowered the IEP and PZC to pH 7.83 and 7.79, and made its surface charge properties closer to the soil; the decreased zeta potential of residues resulted in the particles dispersed state tend to aggregate. And as a result, the number of 0.05–0.25 mm and > 0.25 mm aggregates in the treated bauxite residues significantly increased, the sheet-like fine particles adhere to the surface of the large particles resulted in an accumulation and a layer structure formed. Amount of Ca and Fe in the aggregates as an inorganic binder combined with organic to promote the formation of micro-aggregates; whereas the content of Na and Si, which act as a “dispersant” and “filler” decreased.

Hybrid oil-in-water emulsions applying wax(lecithin)-based structured oils: Tailoring interface properties

This study addressed the impact of fruit wax(lecithin)-based oleogels as dispersed phase in formation and stability of oil-in-water emulsions. These hybrid emulsions were prepared above the melting point of the oleogels, using Tween 80 (T80) or whey protein isolate (WPI) as emulsifiers. Both mono- and mixed-component oleogels comprised of fruit wax (FW) or FW + lecithin (FWLEC), respectively, were studied as lipid phases. After hot-homogenization, emulsions were submitted to quiescent cooling and stored over 14 days at 5 or 25 °C, in such temperatures supposed to assist or hinder oleogelation, respectively. Time course promoted a slight decrease in zeta potential only for WPI-stabilized emulsions and particle size distribution was shifted to larger size values, but showing a lesser extent to those stored at 5 °C. The presence of oleogels improved kinetic stability of emulsions compared to liquid oil at both temperatures, disclosing the role of the combined effects of the type of emulsifier and oleogelator(s)-emulsifier interactions. These outcomes are associated with the interfacial activity played by both oleogelators, but mainly lecithin that led to lower values of interfacial tension. In addition FWLEC combined with WPI showed the lowest complex modulus from dilational rheology, which can be related with WPI-LEC complex formation. Overall, results suggest that oleogelators migrated to the O/W interface of dispersed droplets, no longer reflecting oleogel bulk properties and showing a more complex behavior. However, the formation of more complex structures at the interface favored greater stability of the emulsions. Thus, the new perspective of oleogel-inspired fat droplets in hybrid systems can expand the conventional approach of oil structuring to create mixed interfaces tailoring oil-in-water emulsions properties.

The effect of microbial transglutaminase enzyme and Persian gum on the characteristics of traditional kefir drink

The effects of microbial transglutaminase enzyme (m-TG) and Persian Gum (PG) on physicochemical, microbial and sensory properties of kefir were investigated. The addition of m-TG-PG to kefir lead to an increase in pH, particle size and viscosity, while causing a decrease in titratable acidity, syneresis and zeta potential. The lactic acid bacteria decreased about 1–1.5 log units and yeast counts increased about 2 log units during storage, while treated samples lower populations. Fifty-one volatile compositions were isolated and identified with SPME-GC/MS with most of them belonging to acids, alcohols, esters, ketones, and aldehydes, respectively. Alcohol and acid compounds increased, while esters, ketones, and aldehydes decreased during storage. Sensory evaluation results showed a preference for treated samples; although storage time had a negative effect on the all sensory attributes. Use of m-TG with PG could be recommended to improve the quality properties of kefir.

Effects of Salinity and pH on the Stability of Clay-Stabilized Oil-in-Water Pickering Emulsions

Summary Most emulsions are thermodynamically unstable and will lose their effectiveness once the emulsion droplets experience creaming or coalescence, which constrains potential further and wide application. Therefore, finding a stable emulsion system is important. In this work, a systematic study was carried out on the use of an oil-in-water (O/W) Pickering emulsion stabilized by sodium (Na)-montmorillonite particles. The particle-size distribution and zeta potential of Na-montmorillonite particle solutions at 0 to 20 wt% sodium chloride (NaCl) and pH of 3.3 to 11 were characterized first. The emulsifying ability of the clay particles and stability of O/W emulsions against creaming and coalescence at a set of salinities and pH were measured to provide suitable salinity and pH range for the emulsions. Results show that the Na-montmorillonite particles can be used as an effective stabilizer for O/W emulsion. Because of the decreased zeta potential, the clay particles are more likely to adsorb on the oil/water interface to form emulsions with smaller droplet size in an acidic and high-salinity environment. At a fixed pH, the emulsion tends to be unstable against creaming at less than a certain critical salinity, which is usually 0.25 wt% NaCl. At the critical salinity, the clay particles form a three-dimensional (3D) clay network to effectively stabilize the emulsion from creaming. This clay network interconnects the emulsion droplets, thus hindering the upward movement of the droplets because of buoyancy. At salinities higher than the critical salinity, the emulsion stability against creaming gradually decreases with salinity because of the compaction of the 3D clay network. At a fixed salinity, the creaming stability also has a similar critical pH, which increases with salinity. In addition, the O/W emulsion droplets are more stable against coalescence under more acidic and saline conditions. This results from denser clay particle adsorption on the droplet surface and a greater restriction on droplet motion and collision by the clay structure. Three 2D diagrams showing clear trend of clay emulsifying ability, long-term emulsion stability against creaming and coalescence at a range of salinity from 0 to 20 wt% NaCl, and at a range of pH from 3.3 to 11 were achieved to provide appropriate emulsions.

Improvement in physical and thermal stability of cloudy ginkgo beverage during autoclave sterilization: Effects of microcrystalline cellulose and gellan gum

This work aimed to apply microcrystalline cellulose (MCC) and gellan gum to improve the physical and thermal stability of cloudy ginkgo beverages. The stability of each beverage samples was characterized in terms of particle size, size distribution, zeta potential, rheological properties, Turbiscan Stability Index (TSI), and changes in backscattered light intensity (△BS). Our results indicate that an irreversible phase separation occurred in the beverage sample, induced by increased particle size, decreased zeta potential, and decreased viscosity during the sterilization process. Although the addition of either MCC or gellan improved beverage stability by decreasing particle size and increasing zeta potential, this improvement was limited; the aggregation and sedimentation of suspended particles still occurred, as revealed by large △BS and TSI changes. Beverage samples added with a mixture of MCC and gellan exhibited different physical and thermal stability values depending on the ratio of MCC to gellan. The addition of MCC (0.3%, w/w) combined with a small amount of gellan (0.05% or 0.08%, w/w) effectively prevented drastic thermal damage and improved physical and thermal beverage stability in comparison to MCC combined with the larger amount of gellan. This study provides some suggestions for the industrial production of cloudy beverages.

Removal of Microcystis aeruginosa and control of algal organic matter by Fe(II)/peroxymonosulfate pre-oxidation enhanced coagulation

Fe(II)/Peroxymonosulfate (PMS) pre-oxidation enhanced coagulation was investigated to remove Microcystis aeruginosa (M. aeruginosa) in this study. When the initial algae cell concentration was 1.0 × 106 cells/mL, the highest removal efficiency of algae cells (94.3%) was achieved with lower chemical dosage (e.g. 20 mg/L PMS and 4.5 mg/L Fe(II)). During the pre-oxidation, the release of K+ and death rate of algae cells were lower, meanwhile, relative intact cellular structure was remained. Sulfate radical (SO4•−) was the predominant radical species to facilitate algae removal by decreasing zeta potential in the Fe(II)/PMS system. The majority of algal organic matter (more than 83% of proteins and 76% of polysaccharides) was eliminated after coagulation and sedimentation, indicating that the potential of disinfection by products (DBPs) formation was decreased. Furthermore, Fe(II)/PMS process was optimized by response surface methodology (RSM) according to central composite design (CCD), the higher removal efficiency of M. aeruginosa with lower reagent cost under optimal conditions were obtained. This study provides a promising method of eliminating M. aeruginosa and controlling algal organic matter effectively in eutrophic water.