Whistler Center for Carbohydrate Research

West Lafayette, IN, United States

Whistler Center for Carbohydrate Research

West Lafayette, IN, United States

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Cheng C.J.,Purdue University | Cheng C.J.,Whistler Center for Carbohydrate Research | Jones O.G.,Purdue University | Jones O.G.,Whistler Center for Carbohydrate Research
Food Hydrocolloids | Year: 2017

Zein nanoparticles (ZNPs) suspended in water were produced by the antisolvent precipitation method and combined with ι-carrageenan (ι-CGN) suspended in sodium phosphate buffer in order to evaluate the ability of the negatively-charged ι-CGN to stabilize ZNPs against flocculation and gravitational separation. Physical stability of 0.01% ZNP (w/v) dispersions with 0%–0.02% ι-CGN (w/v) was observed during storage at 4 °C and during centrifugation. Colloidal properties of the particles during storage, such as hydrodynamic radius, turbidity, and ζ-potential were characterized at pH values above pH 5. At pH 5, ZNPs were present as small aggregates with an average hydrodynamic radius of approximately 500 nm, and at higher pH values these aggregated further so that the average size was greater than 1000 nm. Addition of sufficient ι-CGN to achieve a ZNP:ι-CGN weight ratio less than or equal to 10:1 prevented aggregation in the pH range of 5.25–6.75 and limited aggregation at pH 7.0 (average particle radius of 200–400 nm). Enhanced stability was attributed to the adhesion of ι-CGN to the nanoparticle surface, as the ZNPs surface charge became significantly negative with introduction of ι-CGN. These particles remained stable for up to 30 days with significantly lower turbidity and greater resistance to gravitational separation when compared to ZNPs alone. Characterization of ZNPs with an atomic force microscope showed that the particles possessed a nearly spherical geometry with a Young's modulus of ∼100 MPa, neither of which was significantly altered after addition of interactive ι-CGN. © 2017 Elsevier Ltd

Murphy R.W.,Purdue University | Murphy R.W.,Whistler Center for Carbohydrate Research | Farkas B.E.,Purdue University | Jones O.G.,Purdue University | Jones O.G.,Whistler Center for Carbohydrate Research
Journal of Colloid and Interface Science | Year: 2016

Hypothesis: Microgel particles formed from the whey protein β-lactoglobulin are able to stabilize emulsion and foam interfaces, yet their interfacial properties have not been fully characterized. Smaller microgels are expected to adsorb to and deform at the interface more rapidly, facilitating the development of highly elastic interfaces. Methods: Microgels were produced by thermal treatment under controlled pH conditions. Dynamic surface pressure and dilatational interfacial rheometry measurements were performed on heptane-water droplets to examine microgel interfacial adsorption and behavior. Langmuir compression and atomic force microscopy were used to examine the changes in microgel and monolayer characteristics during adsorption and equilibration. Findings: Microgel interfacial adsorption was influenced by bulk concentration and particle size, with smaller particles adsorbing faster. Microgel-stabilized interfaces were dominantly elastic, and elasticity increased more rapidly when smaller microgels were employed as stabilizers. Interfacial compression increased surface pressure but not elasticity, possibly due to mechanical disruption of inter-particle interactions. Monolayer images showed the presence of small aggregates, suggesting that microgel structure can be disrupted at low interfacial loadings. The ability of β-lactoglobulin microgels to form highly elastic interfacial layers may enable improvements in the colloidal stability of food, pharmaceutical and cosmetic products in addition to applications in controlled release and flavor delivery systems. © 2015 Elsevier Inc.

Eren N.M.,Purdue University | Eren N.M.,Whistler Center for Carbohydrate Research | Jones O.G.,Whistler Center for Carbohydrate Research | Jones O.G.,Purdue University | And 2 more authors.
Rheologica Acta | Year: 2015

A rheological phenomenon associated to the adsorption of a soluble protein in the surface of silica nanoparticles is reported along the mechanisms that could explain it. Rheological behavior and structural relaxation of hydrophilic fumed silica suspensions in the absence and presence of α-lactalbumin were studied at pH values 2, 4, and 6 using rheological tests and dynamic light scattering (DLS). The addition of α-lactalbumin caused an increase in viscosity and elasticity of the samples at pHs 2 and 4, whereas an opposite effect was observed at pH 6. Structural relaxation of the nanoparticles forming the suspensions slowed down upon protein addition at pHs 2 and 4 but did not change significantly at pH 6. Changes in rheological properties and structural relaxation were attributed to electrostatic interactions induced by the changes in the silica surface charges at the different pH studied; also by perturbation of the short-range interactions (pH 2), protein bridging (pH 4) and better dispersion of particles (pH 6). © 2015, Springer-Verlag Berlin Heidelberg.

Eren N.M.,Purdue University | Eren N.M.,Whistler Center for Carbohydrate Research | Santos P.H.S.,Purdue University | Santos P.H.S.,Whistler Center for Carbohydrate Research | And 2 more authors.
Carbohydrate Polymers | Year: 2015

Xanthan gum solutions were treated with high-pressure homogenization (HPH) in order to provide alternative treatments to enzymatic and chemical modification of this carbohydrate. Rheological properties of the treated and control samples were investigated in detail to gain an understanding of functional consequences of physical modification. The molecular structural properties were investigated via Size exclusion chromatography (SEC) coupled with Multi-angle laser light scattering (MALLS) and Circular dichroism (CD). Structured network of xanthan gum solutions was lost gradually depending on the severity of the HPH treatment as evidenced by the observed changes in the viscosity and viscoelasticity of the treated solutions. Reduction in molecular weight and a significant increase in polydispersity of the polymer were the expected causes of these rheological changes. Observed increase in hydrodynamic volume upon HPH treatment was not surprising and attributed to the loss of structured networks. Changes in the rheological and structural characteristics of biopolymer were irreversible and significant recovery was not detected over a period of 11 weeks. © 2015 Elsevier Ltd.

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