Chemical imaging of protein hydrogels undergoing alkaline dissolution by CARS microscopy.

Hydrogels swell, shrink and degrade depending on the solution they are in contact which, strongly affecting their performance. The minimum information needed to validate many published simulations would be the spatial quantification of the solute material with time. In this study we develop a simple methodology to quantify the protein content in heat induced protein hydrogels using a commercial Coherent anti-Stokes Raman Spectroscopy (CARS) microscope.

Micromechanical Characterization of Hydrogels Undergoing Swelling and Dissolution at Alkaline pH.

The swelling of polyelectrolyte hydrogels usually depends on the pH, and if the pH is high enough degradation can occur. A microindentation device was developed to dynamically test these processes in whey protein isolate hydrogels at alkaline pH 7⁻14. At low alkaline pH the shear modulus decreases during swelling, consistent with rubber elasticity theory, yet when chemical degradation occurs at pH ≥ 11.

Fluorescence lifetime of Rhodamine B in aqueous solutions of polysaccharides and proteins as a function of viscosity and temperature.

Rhodamine B (RhB) is a well known dye extensively used in thermometric studies, either considering the decrease in the fluorescence intensity or the lifetime (τ) with temperature. Lifetime measurements are preferred over intensity ones as they are more robust. In order to expand microscopy thermometry to complex food fluids, the effect of solutes on the τ of RhB was studied using fluorescence lifetime imaging microscopy (FLIM) in a two-photon microscope.

Effect of N-Ethylmaleimide as a Blocker of Disulfide Crosslinks Formation on the Alkali-Cold Gelation of Whey Proteins.

N-ethylmaleimide (NEM) was used to verify that no new disulfide crosslinks were formed during the fascinating rheology of the alkali cold-gelation of whey proteins, which show Sol-Gel-Sol transitions with time at pH > 11.5. These dynamic transitions involve the formation and subsequent destruction of non-covalent interactions between soluble whey aggregates.

Swelling of whey and egg white protein hydrogels with stranded and particulate microstructures.

Swelling of protein hydrogels in alkaline conditions strongly depends on the gel microstructure. Stranded transparent gels swell as predicted using a modified Flory-Rehner model with the net protein charge. Particulate opaque gels swell very differently, with a sudden increase at a narrow pH range.

The effect of pre-adsorption of OVA or WPC on subsequent OVA or WPC fouling on heated stainless steel surface.

Fouling on the heat exchanger surface during food processing has been researched extensively due to its great importance in energy efficiency, product quality and food safety. The nature of heat exchanger surface has an effect on the initial deposition behavior and deposit removal behavior to some degree. Protein adsorption on surface is considered to be the initial stage in fouling.

Mechanical double layer model for Saccharomyces cerevisiae cell wall.

The elastic modulus of the Baker's yeast (Saccharomyces cerevisiae) cell wall reported in studies using atomic force microscopy (AFM) is two orders of magnitude lower than that obtained using whole cell compression by micromanipulation. Using finite element modelling, it is shown that Hertz-Sneddon analysis cannot be applied to AFM indentation data for single layer core-shell structures. In addition, the Reissner solution for shallow homogeneous spheres is not appropriate for thick walls such as those of yeast cells.

Determination of the shell permeability of microcapsules with a core of oil-based active ingredient.

An experimental and theoretical methodology is proposed to calculate the permeability of microcapsules that contain a core of oil-based active ingredient. Theoretical analysis is performed considering the polydispersity of the measurable capsule size, which allows the estimation of the permeability polydispersity via three different methods. The models proposed were applied in order to determine the permeability of melamine-formaldehyde microcapsules with hexyl salicylate as core oil.

Mechanical characterization of microspheres - capsules, cells and beads: a review.

Microspheres, including microcapsules and cells or beads, are widely used to produce many functional products. Information about their mechanical properties is essential to understanding their performance during manufacturing, processing and end-use applications. The mechanical characterization of microspheres requires applying a mechanical load onto single microspheres and measuring the corresponding deformation, and theoretical modelling of the force-deformation relationship, which allows the determination of mechanical property parameters of the materials such as the elastic modulus, yield stress or failure stress/strain.

Alkali cold gelation of whey proteins. Part II: Protein concentration.

The effect of the whey protein isolate (WPI) concentration on the sol-gel-sol transition in alkali cold gelation was investigated at pH 11.6-13 using oscillatory rheometry. The elastic modulus increases quickly with time to reach a local maximum (G'max), followed by a degelation step where the modulus decreases to a minimum value (G'min).

Alkali cold gelation of whey proteins. Part I: sol-gel-sol(-gel) transitions.

The cold gelation of preheated whey protein isolate (WPI) solutions at alkaline conditions (pH>10) has been studied to better understand the effect of NaOH in the formation and destruction of whey protein aggregates and gels. Oscillatory rheology has been used to follow the gelation process, resulting in novel and different gelation profiles with the gelation pH. At low alkaline pH, typical sol-gel transitions are observed, as in many other biopolymers.

The pH threshold in the dissolution of beta-lactoglobulin gels and aggregates in alkali.

The existence of a practical minimum pH for the dissolution of heat-induced whey gels in alkaline solutions has been studied using beta-lactoglobulin (betaLg) as a model protein. A sharp transition in solubility was observed between pH 11 and 12; this transition shifts to higher pHs for gels formed at higher temperatures and for longer gelling times. The breakdown reactions of heat-induced aggregates in alkali were monitored with size exclusion chromatography.

Swelling and dissolution of beta-lactoglobulin gels in alkali.

It is well documented in the literature that during the dissolution of whey protein gels in alkali, the gels swell to a great extent. However, the relevance of the swelling step in the dissolution process of the protein gel remains unknown. In the present article we present a systematic study on the swelling of beta-lactoglobulin gels at different alkaline pH and ionic strengths.

Effect of gel structure on the dissolution of heat-induced beta-lactoglobulin gels in alkali.

The dissolution of heat-induced beta-lactoglobulin (betaLg) gels in alkaline solution plays an important role in the cleaning-in-place of fouled dairy and other food plants. The dissolution behavior is strongly influenced by the conditions under which the gel is formed. At low alkaline pH values (<13), the dissolution rate constant kg' decreases with longer gelation time and higher temperature.