Isoelectric Point Of pH Research Articles

Effect of pH on Stability of Oil-in-Water Emulsions Stabilized by Pectin-Zein Complexes

The purpose of this study was to investigate the influence of pH on properties and stability of oil-in-water emulsions using pectin as an emulsifier and zein as an auxillary emulsifier. Primary emulsions were prepared by mixing rice bran oil with anionic polysaccharide, pectin, at pH 4 or 7. Zein solution was then added in order to prepare secondary emulsions. Final concentration of secondary emulsions was 20% (w/w) rice bran oil, 2% (w/w) pectin and 0.5% (w/w) zein. The results demonstrated that emulsions prepared at pH 4 were smaller in size, higher viscosity, and more stable after stability test than those prepared at pH 7. Light microscopic images showed that, at pH 7, emulsion droplets were aggregated. At pH 7, both pectin and zein represented as negative charge and no complex was formed, leading to the less stable emulsions. Below the isoelectric point (pH 5.5) of zein, i.e. at pH 4, zein molecules represented as positive charge and pectin represented as negative charge, resulting in a light cross-linking polymer network. It is possible that a low concentration of zein helps to stabilize the emulsions by improving the rigidity of coated layer on oil droplets, thus reducing the depletion flocculation to occur. The stabilizing effect in presence of zein, at pH 4, is attributed to a pectinzein complex formation at the interface.

Studies on the viability of Saccharomyces boulardii within microcapsules in relation to the thermomechanical properties of whey protein

Present work investigates the effectiveness of using whey protein isolate as an encapsulant for a biotherapeutic agent (Saccharomyces boulardii) under varying concentrations of protein and CaCl2. Viability of S. boulardii within the matrix of whey protein is highly dependent on the physicochemical properties of the protein network, and its response to various environmental stress factors including processing temperature, moisture content and change in pH. Our interest is to optimise the spray drying conditions of whey protein isolate, through observations from differential scanning calorimetry and small deformation dynamic oscillation on shear, in relation to the denaturation and subsequent aggregation of the globular molecules. It is evident from this work that protein concentration is directly proportional to the strength of the network, but inversely proportional to the denaturation temperature. Increasing concentrations of calcium chloride have a direct influence on electrostatic repulsion between protein molecules thus creating a better protein structure. Development of a cohesive network was used as a basis of manipulating the viability of S. boulardii under given conditions of spray drying. Analysis on spray dried powders suggests that whey protein preparations at the isoelectric point (pH ∼5) and with CaCl2 additions of 50–100 mM act as an efficient encapsulant providing high viability of S. boulardii.

Dispersion Stability and Electrokinetic Properties of Intrinsic Plutonium Colloids: Implications for Subsurface Transport

Subsurface transport of plutonium (Pu) may be facilitated by the formation of intrinsic Pu colloids. While this colloid-facilitated transport is largely governed by the electrokinetic properties and dispersion stability (resistance to aggregation) of the colloids, reported experimental data is scarce. Here, we quantify the dependence of ζ-potential of intrinsic Pu(IV) colloids on pH and their aggregation rate on ionic strength. Results indicate an isoelectric point of pH 8.6 and a critical coagulation concentration of 0.1 M of 1:1 electrolyte at pH 11.4. The ζ-potential/pH dependence of the Pu(IV) colloids is similar to that of goethite and hematite colloids. Colloid interaction energy calculations using these values reveal an effective Hamaker constant of the intrinsic Pu(IV) colloids in water of 1.85 × 10(-19) J, corresponding to a relative permittivity of 6.21 and refractive index of 2.33, in agreement with first principles calculations. This relatively high Hamaker constant combined with the positive charge of Pu(IV) colloids under typical groundwater aquifer conditions led to two contradicting hypotheses: (a) the Pu(IV) colloids will exhibit significant aggregation and deposition, leading to a negligible subsurface transport or (b) the Pu(IV) colloids will associate with the relatively stable native groundwater colloids, leading to a considerable subsurface transport. Packed column transport experiments supported the second hypothesis.

Effect of whey protein agglomeration on spray dried microcapsules containing Saccharomyces boulardii

This work investigates the effect of whey protein agglomeration on the survivability of Saccharomyces boulardii within spray dried microcapsules. It attempts to go beyond phenomenological observations by establishing a relationship between physicochemical characteristics of the polymeric matrix and its effect on probiotic endurance upon spray drying. It is well known that this type of thermal shock has lethal consequences on the yeast cells. To avoid such undesirable outcome, we take advantage of the early agglomeration phenomenon observed for whey protein by adjusting the pH value of preparations close to isoelectric point (pH 4–5). During the subsequent process of spray drying, development of whey protein agglomerates induces formation of an early crust, and the protein in this molten globular state creates a cohesive network encapsulating the yeast cells. It appears that the early crust formation at a given sample pH and temperature regime during spray drying benefits the survivability of S. boulardii within microcapsules.

Effect of polyelectrolytes and polyelectrolyte mixtures on the electrokinetic potential of dispersed particles. 2. Electrokinetic potential of silica particles in electrolyte, polyelectrolyte and polyelectrolyte mixtures solutions

The effect pH, ionic strength (KCl concentration), weakly and medium charged anionic and cationic polyelectrolytes (PEs) as well as their binary mixtures on the electrokinetic potential of silica particles as a function of the polyelectrolyte/mixture dose, its composition, charge density (CD) of the PE, and way of adding the polymers to the suspension has been studied. It has been shown that addition of increasing amount of anionic PEs increases the absolute value of the negative zeta-potential of particles at pH > pH isoelectric point (IEP = 2.5); this increase is stronger the charge density of the polyelectrolyte is higher. Adsorption of cationic polyelectrolytes at these pH values gives a significant decrease in the negative ζ-potential and overcharging the particles; changes in the ζ-potential are more pronounced for PE samples with higher CD. In mixtures of cationic and anionic PE at pH > pHIEP, the ζ-potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of PEs, the mixture composition and the sequence of addition of the mixture components. Unexpectedly, the ζ-potential of silica at pH = 2.1, i.e. < pHIEP, turned out to be positive in the presence of both anionic PE and cationic + anionic PE mixtures. This is explained by formation (and adsorption onto positively charged silica surface) of pseudo-cationic PEs from anionic ones due to transfer of protons from the solution to the amino-group of the anionic polymer. Considerations about the role of coulombic and non-coulombic forces in the mechanism of PE adsorption are presented.

Impact of the virus purification protocol on aggregation and electrokinetics of MS2 phages and corresponding virus-like particles

Previous experimental and theoretical studies have established that electrokinetic and aggregation properties of soft MS2 phages are not only governed by the physico-chemical features of their proteinaceous outer surface but are also significantly impacted by those of their inner RNA component (Dika et al. Appl. Environ. Microbiol., 2011, 14, 4939-4948). These conclusions contradict the recent findings of Nguyen et al. (Soft Matter, 2011, 7, 10449-10456) who reported identical electrokinetic and aggregation characteristics for MS2 and corresponding virus like particles (VLPs) that lack the internal RNA component. We demonstrate here that this contradiction originates from the different purification methods adopted prior to measurements. More generally, we show that stability and electrohydrodynamics of viruses differ according to purification by (i) dialysis, (ii) isopycnic centrifugation in the cesium chloride gradient, and (iii) precipitation using polyethylene glycol (PEG). Methods (i) and (iii) lead to aggregation of MS2 phages at pH ≤ 4 and pH ≤ 6 in 1-100 mM NaNO3 solutions, respectively, while under such conditions aggregation is not observed for MS2 and VLP suspensions prepared according to (ii). In addition, VLPs prepared following methods (i) and (iii) aggregate only at the isoelectric point (pH ~ 3-4) in 1 mM NaNO3 solution. Electrophoretic mobility data of stable MS2 and VLP particles were further examined using a recent formalism for electrokinetics of soft multilayered colloids. The analysis qualitatively shows how the purification protocol may affect either the outer particle surface properties and/or the inner particle content. Finally, the non-DLVO aggregation behavior of MS2 and VLPs purified via the above protocols is discussed in terms of the possible change in corresponding interparticular interactions.

Microstructure & rheology of mixed colloidal dispersions: Influence of pH-induced droplet aggregation on starch granule–fat droplet mixtures

The creation of high quality reduced-fat food products is challenging because the removal of fat adversely affects quality attributes, such as appearance, texture, and flavor. This study investigated the impact of pH-induced droplet aggregation on the properties of model food systems consisting of fat droplets and starch granules. Oil-in-water emulsions (2wt.% oil) containing whey-protein coated lipid droplets aggregated extensively when heated (90°C, 5min) at pH values around their isoelectric point (pH 5) but not at lower (pH 3.5) or higher (pH 7) values, which was attributed to changes in electrostatic repulsion. The physicochemical properties of mixed lipid droplet–starch dispersions (2wt.% oil, 4wt.% starch) prepared under similar conditions (pH 3.5, 5, and 7; 90°C for 5min) were also measured. At pH 5, extensive lipid droplet aggregation was observed in mixed systems, which led to a large increase in their yield stress and apparent viscosity when compared to mixed systems at pH 3.5 and 7. These results show that the rheological properties of mixed fat droplet–starch granule suspensions can be modulated by controlling the electrostatic interactions between the fat droplets so as to change their flocculation state. This study has important implications for fabricating high quality reduced-fat products with desirable sensory attributes.

Molecular cloning and analysis of residues associated with iron binding of Spodoptera litura transferrin

We isolated transferrin cDNA from tobacco cutworm (Spodoptera litura) and refer to it as SlTf (Spodoptera litura transferrin). The 2,237-bp SlTf cDNA encoded 685 amino acids, with a predicted Mw of 76.3 kDa and an isoelectric point of pH 7.97. The amino acid sequence of the SlTf protein had 11–81% similarity with those of other reported animal transferrins, showing the highest similarity with another Lepidopteran insect, the silkworm (Bombyx mori), and the lowest similarity with atlantic cod (Gadus morhua) serum transferrin. Phylogenetic tree analysis showed that SlTf was close to transferrins of B. mori and M. sexta. By urea-polyacrylamide gel electrophoresis, four different iron-bound forms (apo-, C-terminal monoferric, N-terminal monoferric and diferric) were found from both SlTf and human transferrin, suggesting the C-lobe iron-binding motif of SlTf possesses the iron-biding activity, although its amino acid sequence is not well conserved compare to that of vertebrate transferrins. Accordingly, we suggest that the amino acid residues of iron-binding sites in SlTf are different from those of human serum transferrin, however the iron-binding capacity is conserved in both the C-lobe and the N-lobe of SlTf.

Influence of pressure on filtration of aqueous alumina suspensions

The dispersibility of colloidal alumina particles (median size 310 nm) was related to the surface potential, the solid concentration in a suspension and the pressure applied to the particles. The consolidation behavior of colloidal alumina particles with an isoelectric point pH 8.7 was examined using a developed pressure filtration apparatus at 1–10 MPa of applied pressure. The height of 7 or 20 vol% alumina suspensions at pH 3.0, 7.8 and 9.0 as a function of filtration time was fitted by a filtration model developed for a flocculated suspension rather than a traditional filtration model for a dispersed suspension. An increased pressure, a decrease of particle concentration and a porous microstructure of colloidal cake reduced the consolidation time of alumina suspension. The wet alumina compacts were significantly compressed during filtration but relaxed after the release of the applied pressure. However, the packing density of alumina compact after calcination at 700 °C was almost independent of the filtration pressure and controlled by the structure of network of alumina particles in a solution.

Modifications of the bacterial reverse mutation test reveals mutagenicity of TiO2 nanoparticles and byproducts from a sunscreen TiO2-based nanocomposite

The bacterial reverse mutation test, recommended by the Organization for Economic Co-operation and Development (OECD) to determine genotoxicity of chemical compounds, has been recently used by several authors to investigate nanoparticles. Surprisingly, test results have been negative, whereas in vitro mammalian cell tests often give positive genotoxic responses. In the present study, we used the fluctuation test procedure with the Salmonella typhimurium strains TA97a, TA98, TA100 and TA102 to determine the mutagenic potential of TiO2 nanoparticles (NP-TiO2) and showed that, when it is used conventionally, this test is not suitable for nanoparticle genotoxicity assessment. Indeed, the medium used during exposure prevents electrostatic interactions between bacterial cells and nanoparticles, leading to false-negative responses. We showed that a simple pre-exposure of bacteria to NP-TiO2 in a low ionic strength solution (NaCl 10mM) at a pH below the nanoparticle isoelectric points (pH 5.5) can strongly improve the accuracy of the test. Thus, based on these improvements, we have demonstrated the genotoxicity of the engineered NP-TiO2 tested and a NP-TiO2 byproduct from a sunscreen nanocomposite. It was also shown that strain TA102 is more sensitive than the other strains, suggesting an oxidative stress-mediated mechanism of genotoxicity.

Water-Soluble Pendant Copolymers Bearing Proline and Permethylated β-Cyclodextrin: pH-Dependent Catalytic Nanoreactors

To achieve efficient proline-based catalysis in water, proline has been supported in the past to porous and hydrophobic solid resins leading to heterogeneous systems. These solid resins provide a hydrophobic environment to the active centers, mimicking what happens in natural enzymes. However, a more realistic mimetic approach would be to carry out the aldol reaction in a homogeneous way, maintaining the hydrophobic environment, using for example properly designed noncross-linked polymer carriers. In this work, we report the synthesis and aqueous catalytic evaluation of a linear copolymer bearing both pendant proline and permethylated β-cyclodextrin (β-CD) groups. It was designed on the basis that the presence of the hydrophobic cavity of the β-CD could bring aromatic substrates into close proximity to the surrounding catalytic proline residues through host–guest interactions. The compound is water-soluble and catalyzes aldol reactions in this medium without the need for any extra organic solvent. We employed a model reaction between cylohexanone and p-nitrobenzaldehyde, and we observed a decrease of the reaction rate when a competing aromatic compound, known to form a strong inclusion complex with β-CD, was added. The copolymeric catalyst showed a pH-dependent behavior. At pH 7, the copolymer is found in solution as extended single chains with negative charge, catalyzing the reaction in a fast and nonstereoselective mode. At the isoelectric point (pH 3.8) where the positive and negative charges of the zwitterionic proline are canceled by forming charge complexes, the copolymer forms multichain hydrophobic nanoaggregates most probably stabilized by the permethylated β-CD. Although the reaction inside these “nanoreactors” is slower, it exhibits high stereoselectivity. It is proposed that the observed stereoselectivity is caused by the exclusion of water from the core of these homogeneous entities.

Influence of Inorganic Ions on Aggregation and Adsorption Behaviors of Human Adenovirus

In this study, we investigated the influence of inorganic ions on the aggregation and deposition (adsorption) behavior of human adenovirus (HAdV). Experiments were conducted to determine the surface charge and size of HAdV and viral adsorption capacity of sand in different salt conditions. The interfacial potential energy was calculated using extended Derjaguin and Landau, Verwey and Overbeek (XDLVO) and steric hindrance theories to interpret the experimental results. Results showed that different compositions of inorganic ions have minimal effect on varying the iso-electric point pH (pH(iep)) of HAdV (ranging from 3.5 to 4.0). Divalent cations neutralized/shielded virus surface charge much more effectively than monovalent cations at pH above pH(iep). Consequently, at neutral pH the presence of divalent cations enhanced the aggregation of HAdV as well as its adsorption to sand. Aggregation and adsorption behaviors generally agreed with XDLVO theory; however, in the case of minimal electrostatic repulsion, steric force by virus' fibers can increase the energy barrier and distance of secondary minimum, resulting in limited aggregation and deposition. Overall, our results indicated that subsurface water with low hardness residing in sandy soils may have a higher potential of being contaminated by HAdV.

PH-mediated interfacial chemistry and particle interactions in aqueous chlorite dispersions

Interfacial chemistry and particle interactions of polydispersed chlorite clay mineral dispersions as a function of pH, solid content and ageing time have been investigated in the pH range 2–9 at 25°C. Particle zeta potential, reflecting interfacial chemistry indicates a strong pH history and solid loading dependency. Zeta potential trends observed from high to low pH sweep show that an isoelectric points of pH≈2.5 and 5, respectively for dilute (0.05wt.%) and both 8 and 57wt.% suspension. An electrokinetic potential bifurcation is observed upon reverse pH from low (e.g. 2) to high value (e.g. 9), indicative of pH-mediated interfacial chemistry modification. Particle interactions measured through dispersion shear yield stress show a similar pH-history dependency and compliance with DLVO theory. Supernatant analysis suggests that the suspension pH dependent behaviour may be attributed to the leach of Mg(II), Fe(II/III), Al(III) and Si(IV) ions from the chlorite particles at lower pH. Formation and specific adsorption of hydrolysed metal complexes onto particles which occurs at higher pH values manifest in the observed interfacial chemistry and particle interactions. The findings enable us to accurately rationalise the nature of the inter-particle forces underpinning particle network structure and strength as a function of dispersion conditions during aqueous processing of clay-based minerals.

Simultaneous Control of pH and Ionic Strength during Interfacial Rheology of β-Lactoglobulin Fibrils Adsorbed at Liquid/Liquid Interfaces

Proteins can aggregate as amyloid fibrils under denaturing and destabilizing conditions such as low pH (2) and high temperature (90 °C). Fibrils of β-lactoglobulin are surface active and form adsorption layers at fluid-fluid interfaces. In this study, β-lactoglobulin fibrils were adsorbed at the oil-water interface at pH 2. A shear rheometer with a bicone geometry set up was modified to allow subphase exchange without disrupting the interface, enabling the investigation of rheological properties after adsorption of the fibrils, as a function of time, different pH, and ionic strength conditions. It is shown that an increase in pH (2 to 6) leads to an increase of both the interfacial storage and loss moduli. At the isoelectric point (pH 5-6) of β-lactoglobulin fibrils, the maximum storage and loss moduli are reached. Beyond the isoelectric point, by further increasing the pH, a decrease in viscoelastic properties can be observed. Amplitude sweeps at different pH reveal a weak strain overshoot around the isoelectric point. With increasing ionic strength, the moduli increase without a strain overshoot. The method developed in this study allows in situ subphase exchange during interfacial rheological measurements and the investigation of interfacial ordering.

Utilization of interfacial engineering to produce novel emulsion properties: Pre-mixed lactoferrin/β-lactoglobulin protein emulsifiers

The interfacial coatings around lipid droplets can be tailored in a number of ways to alter the functionality of emulsion-based delivery systems. In this study, a “premix” approach was utilized that involved mixing two globular proteins with different isoelectric points prior to emulsion formation: β-lactoglobulin (BLG) and lactoferrin (LF). The influence of environmental stresses (pH, ionic strength and temperature) on the physicochemical properties of the emulsions produced using this approach was examined. Droplets coated by BLG were unstable to aggregation near their isoelectric point (pH≈5), whereas those coated by LF were stable across the whole pH range. The stability of emulsions to pH induced aggregation improved as the ratio of LF-to-BLG in the mixed systems was increased. Lipid droplets coated by either LF or BLG were unstable to aggregation at high salt concentrations (500mM NaCl, pH 6.5), but those stabilized by mixed protein coatings (LF and BLG) were stable, which was attributed to an increase in interfacial thickness and steric repulsion. Droplets coated by BLG were stable to droplet aggregation after thermal treatment (30 to 90°C, 0mM, NaCl pH 7), whereas those coated by LF were highly unstable when heated above their thermal denaturation temperature. The thermal stability of the droplets depended on the amount of LF in the mixed systems. Overall, this study shows that mixtures of LF and BLG are able to modulate the physicochemical properties and stability of protein-coated lipid droplets in oil-in-water emulsions. This study provides useful information for designing emulsion-based delivery systems for use in functional food and beverage products.

Photometric determination of aqueous cobalt (II), nickel (II), copper (II) and iron (III) with 1-nitroso-2-naphthol-3,6-disulfonic acid disodium salt in gelatin films

Abstract Photometric determination of aqueous Co(II), Cu(II), Ni(II) and Fe(III) was performed using indicator films prepared by immobilization of 1-nitroso-2-naphthol-3,6-disulfonic acid disodium salt (NRS) into hardened photographic film. Immobilization was based on electrostatic interaction of reagent and metal complexes with the gelatin. The isoelectric point pH of hardened gelatin (4.46±0.04) was evaluated by viscometry. Co(II), Fe(III), Ni(II) form 1:3 complexes with NRS in gelatin at pH 2 and Cu(II) forms 1:2 complexes. Their log β′ values were: Co-6.7, Fe-8.6, Cu-8.0, and Ni-6.4. The absorption maxima were: 370nm for NRS, and 430nm, 470nm, 495nm and 720nm for complexes of Co(II), Ni(II), Cu(II) and Fe(III). An algorithm for their simultaneous determination using the indicator films was developed. The detection limits were: clim(Co2+) = 0.45×10−5 M, clim(Fe3+) = 0.50×10−5 M, clim(Cu2+) = 0.67×10−5 M, clim(Ni2+) = 0.75×10−5 M,; and their sum clim(ΣMn+) = 0.82×10−5 M.

Facile modification of polypropylene hollow fiber microfiltration membranes for nanofiltration

Modification of polypropylene (PP) hollow fiber microfiltration membranes for nanofiltration through dip-coating sodium carboxymethyl cellulose (CMCNa) skin layer followed by cross-linking with AlCl3 was investigated in this study. Modification parameters were studied to optimize the membrane performance and the obtained modified membranes were characterized in terms of surface and permeation properties. It was found that the surface property and solute separation capability of the PP hollow fiber membrane were significantly improved by coating CMCNa surface layer, and the optimized modified membrane took on a composite structure with a hydrophilic selective skin layer having an isoelectric point of pH 3.7. The composite layer was negatively charged at neutral pH and was relatively looser in acidic pH compared with that in basic or neutral. Permeation tests revealed that the desired modified membrane possessed a molecular weight cut-off (MWCO) of 760Da and a high pure water permeability of 10.8l/m2hbar, and exhibited rejections to salts following the order of MgCl2<CaCl2<MgSO4<NaCl<KCl<Na2SO4 at neutral pH. Additionally, the modified membrane could efficiently remove anionic dyes from saline aqueous with good long-term performance stability. Retentions to Congo red and Methyl blue were 99.8% and 99.6%, respectively, under neutral pH and 3.0bar.

Formation of electrostatic complexes involving mixtures of lentil protein isolates and gum Arabic polysaccharides

Formation of electrostatic complexes involving a mixture of lentil protein isolates (LPI) and gum Arabic (GA) as a function of pH (1.50–8.00) and biopolymer mixing ratio (1:4–10:1 LPI:GA) were investigated by turbidimetric analyses during an acid titration. The nature of interactions was also studied in the presence of destabilizing agents (e.g., 100mM urea and NaCl), at an elevated temperature (60°C), and as a function of lentil processing (e.g., hulled vs. dehulled). Complex formation followed two pH-dependent structure forming events associated with the formation of soluble and insoluble complexes. For the 1:1 LPI:GA ratio, soluble and insoluble complexes formed at pH 5.87 and 3.62, respectively, with maximum formation occurring at pH 3.50. The addition of GA also resulted in a shift from of LPI's isoelectric point (pH 4.70) to a lower pH (3.17) as chains complexed to the surface of the protein, as measured by electrophoretic mobility versus pH. As the biopolymer mixing ratios increased, critical pHs shifted towards higher pH until reaching the 1:1 mixing ratio, afterwards becoming relatively ratio independent. Complex formation was found to be primarily driven by electrostatic attractive forces with secondary stabilization by hydrogen bonding. Hydrophobic interactions were thought to play a role in the stabilization of LPI–LPI aggregates as part of the formed complexes, rather than in its formation. Removal of the hull resulted in an isolate product with higher surface hydrophobicity than that with the hull. Complex formation shifted slightly to higher pH within the mixture containing isolates derived from dehulled lentil than with, thought to be associated with the higher surface hydrophobicity on the surface. Knowledge of mechanisms driving complex formation within LPI:GA mixtures could lead to improved utilization as food and/or biomaterial ingredients.

Stability of and attachment to lettuce by a culturable porcine sapovirus surrogate for human caliciviruses.

Human noroviruses (HuNoVs) are the leading cause of food-borne illness, accounting for 58% of U.S. cases. Because HuNoVs are unculturable, surrogates are needed to investigate transmission routes and evaluate disinfection methods. However, the current surrogates, feline calicivirus (FCV) and murine NoV (MNV), are less tolerant than HuNoVs to acid and chlorine, respectively. Porcine sapovirus (SaV) is the only culturable enteropathogenic calicivirus. In this study, the resistance of SaV to physicochemical treatments was compared to that of HuNoVs (by reverse transcription-PCR), FCV, and MNV (by infectivity assays). Sapovirus and HuNoV (viral RNA) showed similar resistances to heat (56°C) and to different concentrations of chlorine. However, SaV was more resistant than HuNoVs to ethanol treatment (60% and 70%). Like HuNoVs, SaV was stable at pH 3.0 to 8.0, with a <1.0 log(10) 50% tissue culture infective dose (TCID(50)) reduction at pH 3.0 compared to the value for pH 4.0 to 8.0. SaV and MNV showed similar resistances, and both were more resistant than FCV to heat inactivation (56°C). FCV was more resistant than MNV and SaV to ethanol, and all three viruses showed similar resistances to treatment with low concentrations of chlorine for 1 min. Those results indicate that SaV is a promising surrogate for HuNoVs. Next, we used SaV as a surrogate to examine virus attachment to lettuce at different pHs. Sapovirus attached to lettuce leaves significantly at its capsid isoelectric point (pH 5.0), and the attached viral particles remained infectious on lettuce after 1 week of storage at 4°C. The culturable SaV is a good surrogate for studying HuNoV contamination and transmission in leafy greens and potential disinfectants.

Protein Adsorption on Citrate Modified Magnetic Nanoparticles

Magnetic iron oxide nanoparticles were prepared by chemical co-precipitation method and then modified with sodium citrate. These iron oxide nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), and vibrating sample magnetometer (VSM). BSA was adsorbed on these citrate modified nanoparticles using two types of buffers (acetate buffer, pH 4.0, 4.7 and phosphate buffer, pH 7.4). The results showed that the maximum adsorption of BSA was 83 mg/g at its isoelectric point (pH 4.7). Fourier-transform infrared spectroscopy (FTIR) was used to confirm the attachment of citrate groups and BSA on the prepared magnetic nanoparticles. BSA was desorbed from nanoparticles under alkaline conditions, which was confirmed by SDS-PAGE electrophoresis, UV-vis and fluorescence spectra. The desorbed BSA showed small changes in its structure. The adsorption results indicated that BSA adsorption on citrate modified iron oxide nanoparticles occurred mainly by electrostatic mechanism.