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The Chaplin E peptide is a surface-active agent that can adsorb to the air/water interface and form interfacial films that display distinct interfacial properties as a function of pH. The ~2 nm thick homogeneous Chaplin E film formed under acidic conditions contains ordered structures that give a high dilatational elasticity. In contrast, the heterogeneous film formed under basic conditions contained fibrils resulting in a rough ~17 nm thick film with predominantly viscoelastic properties, probably due to the reduced intermolecular interactions. These fibrils were also susceptible to breakage, fragmenting into shorter fibrils, which gave a greater elasticity. The fibrils also lead to a greater shear viscosity compared to the ordered structures aligned within the Chaplin E film at pH 3.0. A higher stability was observed for the foam formed by the Chaplin E compared to the foam formed by β-lactoglobulin, consistent with the greater rheological properties observed for the Chaplin E film at the interface. Our findings suggest that Chaplin E has potential to provide long time stability to dispersions in food, consumer goods or pharmaceutical applications, forming films with greater rheological properties and at least similar thickness to those formed by other surface-active proteins such as β-casein and β-lactoglobulin.

Honey is a biologically active material functioning antibacterial, anti-inflammation and immune responses that enhance wellbeing. This research aims to record and rationalise the structural properties of honey as part of a convenient delivery system in the presence of gelatin that provides the structuring matrix. In doing so, we employ dynamic oscillation in-shear, micro and modulated DSC, WAXD, FTIR and ESEM. A wide range of solids was employed from 10% (w/w) gelatin to mixtures with up to 75% (w/w) honey. Increasing addition of co-solute created thermally stable gelatin networks, which at high levels of total solids undergo a glass transition. This allows deconvolution of the total heat flow into the reversing and non-reversing thermograms. In addition, mechanical spectra can be treated by the combined free volume/reaction rate theory to predict the molecular dynamics of the gelatin-honey system. Molecular interactions between the two components and the relative contribution of honey to the crystalline or amorphous part of the binary preparation are elucidated guiding future applications for orally and topically treated ailments.

The purpose of this research is to investigate swellable genipin-crosslinked gelatin matrices for the controlled delivery of water soluble vitamins (ascorbic acid). The following methods were utilized to describe the physicochemical properties of the system: micro differential scanning calorimetry and small deformation dynamic oscillation in shear. Hydrogel microstructural properties were reported in terms of the average molecular weight between crosslinks and network mesh size. Degree of crosslinking in gels with concentration of genipin crosslinker from 0 to 2.8% (w/w) was measured using ninhydrin assay and UV-vis spectroscopy. Swelling of the gel matrix in aqueous solvent was followed and colorimetric methods were used to measure the diffusion kinetics of ascorbic acid from the gel to the surrounding aqueous phase. Results after treatment of swelling data with improved Fickian theory found matrix swelling was limited by the relaxation of polymer chains. Significance of results lies in the derivation of apparent diffusion coefficients for the transport of water molecules and bioactive compound at 85% and 98% crosslinking that relates the kinetics of bioactive compound release to mesh size of the polymeric network. Thus, there is strong evidence that modulation of the extent of crosslinking impacts on hydrogel morphological characteristics and structural properties, with resulting control of bioactive compound release. Outcomes may be implemented in targeted delivery of bioactive compounds, including vitamins, within the human body, for improved bioavailability.

Delivery of techno- and bio-functionality in all-natural processed foods is an area of steadily increasing fundamental and technological interest. One of the main aspects in this field is based on the diffusion of natural bioactive compounds that have been incorporated in high-solid biopolymers matrices. Organoleptic considerations dictate that the delivery vehicles are characterised by a highly amorphous fraction in the biopolymer network. Molecular diffusion in the amorphous state is a complex process associated with the effect of the glass transition temperature (Tg) on the mobility of low molecular-weight bioactives. This work will review the molecular dynamics of high-solid biopolymer systems, and model food preparations in the presence of co-solute, in relation to the diffusion kinetics of natural bioactive compounds. Literature indicates that the metastable properties of condensed biopolymer networks traversing the rubber-to-glass transition region affect significantly the diffusion kinetics of bioactive compounds. These have been modelled using concepts from the classical and improved diffusion theory to unveil a relationship between apparent diffusion coefficient of bioactives and free volume characteristics of the condensed biopolymer network. Further work is required in added value foods, sourcing inspiration from the “sophisticated pharmaceutical research”, to develop food systems that control transport phenomena for targeted release from a specific dosage form.

A fundamental study was carried out to evaluate patterns of vitamin B6 release from genipin crosslinked gelatin in aqueous media at ambient temperature. Up to ninety percent crosslinking was achieved, with FTIR and WAXD data arguing for partial replacement of the triple helix with a covalent pattern of bonding between protein and crosslinker. Formation of a “composite network” yielded increasing compressive stress-at-failure values followed by a decrease as a function of genipin addition, with the yield strain decreasing continuously. Electron microscopy images showed a reduction in the size of the hydrogel pores with a higher degree of crosslinking. Experimental evidence was supported by the Flory-Rehner theory that predicted a lower swelling ratio and reduced molecular weight between adjacent crosslinks with genipin addition. Furthermore, Peppas-Sahlin equation was used to rationalise the interplay between network morphology and diffusion of bioactive compound over prolonged timeframes of release testing.

Crosslinking of hydroxypropyl methyl cellulose (HPMC) and acrylic acid (AAc) was carried out at various compositions to develop a high-solid matrix with variable glass transition properties. The matrix was synthesized by the copolymerisation of two monomers, AAc and N,N′-methylenebisacrylamide (MBA) and their grafting onto HMPC. Potassium persulfate (K2S2O8) was used to initiate the free radical polymerization reaction and tetramethylethylenediamine (TEMED) to accelerate radical polymerisation. Structural properties of the network were investigated with Fourier transform infrared spectroscopy (FTIR), Xray diffraction (XRD), modulated differential scanning calorimetry (MDSC), small-deformation dynamic oscillation in-shear, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show the formation of a cohesive macromolecular entity that is highly amorphous. There is a considerable manipulation of the rheological and calorimetric glass transition temperatures as a function of the amount of added acrylic acid, which is followed upon heating by an extensive rubbery plateau. Complementary TGA work demonstrates that the initial composition of all the HPMC-AAc networks is maintained up to 200 °C, an outcome that bodes well for applications of targeted bioactive compound delivery.

High-solid chitosan matrices were prepared to investigate the effect of their swelling on structural relaxation and glass transition. Degree of crosslinking in genipin-crosslinked chitosan networks was measured with a ninhydrin assay and a suitable crosslinker concentration was determined for gels used in swelling and thermomechanical analysis. Fourier transform infrared spectroscopy and wide angle X-ray diffraction examined the intermolecular interactions, crystallinity and amorphicity of the biopolymer networks. Swelling characteristics following immersion in water included approximate equilibrium values of the average molecular weight between crosslinks and network mesh size, e.g. 902 g mol−1 and 110 nm for the preparation with an initial solids content of 60% (w/w) after 80 min of swelling, which were quantified with the modified Flory-Rehner theory. Thermal glass transition temperature was observed in the condensed crosslinked networks (≥ 70% w/w total solids) during differential scanning calorimetry experiments. Time-temperature superposition of rheological measurements, obtained with dynamic oscillation in-shear, generated a master curve describing the viscoelastic behaviour of the system, moving through the rubbery, glass transition region and glassy state. Combined analysis using the modified Arrhenius and William-Landel-Ferry theories determined mechanical glass transition temperatures in the range of −68 to −8 °C for the crosslinked biopolymer at intermediate-solid concentrations (40 to 60% w/w solids). An understanding of the effect of swelling on molecular network characteristics was achieved, which is crucial for greater control in the design of systems for the targeted delivery of bioactive compounds.

Vitamin entrapment in matrices made of natural polymers and its controlled release has application to a variety of added value foods and nutraceuticals. This communication utilises data from published literature on the molecular transport of vitamin B6 from condensed matrices of genipin-crosslinked gelatin, bovine serum albumin and whey protein isolate to develop a mechanistic model that accounts for moving boundary conditions. In doing so, it utilises the apparent diffusion coefficient of the micronutrient, the molecular weight of the uncrosslinked polymer chain and the average molecular weight between neighbouring crosslinks. The derived mathematical expression for swellable matrices in an aqueous environment can follow the progression of diffusivity with degree of crosslinking in the polymeric excipients. Model fitting provides a minimisation parameter, which is interpreted in terms of the extent of coupling between solute diffusion and matrix structural relaxation. Parallel predictions of polymer network mesh and critical molecular weight between crosslinks indicate that values of normalised size well above one are required for anomalous (non-Fickian) release due to obstructed diffusion.

Changes in the structural properties of hydrogels made with gelatin and bovine serum albumin mixtures were recorded following exposure to high pressure at 300 MPa for 15 min at 10 and 80 °C. Dynamic oscillation, SEM, FTIR and blending law modelling were utilised to rationalise results. Pressurization at the low temperature end yielded continuous gelatin networks supporting discontinuous BSA inclusions, whereas an inverted dispersion was formed at the high temperature end with the continuous BSA network suspending the discontinuous gelatin inclusions. Lewis and Nielsen equations followed the mechanical properties of the composites thus arguing that solvent partition between the two phases was always in favour of the polymer forming the continuous network. As far as we are aware, this is the first attempt to elucidate the solvent partition in pressurised hydrogel composites using blending law theory. Outcomes were contrasted with earlier work where binary mixtures were subjected only to thermal treatment.

Functionalized halloysite nanotubes were prepared by surface activation of halloysite (Hal) with sodium hydroxide and deposition of zinc oxide nanoparticles (ZnONP). The surface charge of Hal was changed from 0.18 ± 0.6 mV to −35.2 ± 2.8 mV after alkali treatment. The functionalized Hal (AT-Hal/ZnONP) was incorporated into alginate biopolymer as a reinforcing filler with different concentration of AT-Hal/ZnONP (1, 3, 5, and 7 wt% of alginate). Alginate films with AT-Hal/ZnONP exhibited a significant increase in the mechanical, water vapor barrier, and UV light barrier properties. The thermal stability of composite films has not changed after AT-Hal/ZnONP incorporation. The AT-Hal/ZnONP incorporated alginate films demonstrated strong antibacterial activity against food-borne pathogenic bacteria, Escherichia coli and Listeria monocytogenes. The nanocomposite film with 7 wt% of AT-Hal/ZnONP exhibited complete sterilization of E. coli and L. monocytogenes after 3 and 9 h of treatment, respectively.

Metastable properties of biopolymer networks affect significantly the diffusion kinetics of bioactive compounds. That was shown to be the case in high solid samples of protein and polysaccharide supporting a homogeneous distribution of polyunsaturated fatty acids. Thermomechanical behaviour of these matrices was characterised in relation to their glass transition temperature ( T g ). A free volume theory of diffusion was considered to treat transport phenomena of fatty acids within glassy polymers. It was found that at T > T g the effective diffusion coefficient of microconstituent transport would increase in accordance with the free volume of the polymer matrix. Fitting experimental diffusivity data in glassy polymers to a free volume based theory generates a two-parameter equation that calculates the extent of molecular interaction between macromolecule and microconstituent. Gradual substitution of polymer with small-molecule co-solute, glucose syrup in this case, induces a plasticising effect that profoundly affects the level of interaction, hence the diffusion of fatty acids in the condensed biomaterial.

We prepared alginate capsules with a wide range of fish oil loading in order to develop a delivery device that targets a specific part of the human digestive system. In-vitro studies demonstrated that alginate capsules can hold up to ∼15% (w/w) oil leading to a controlled diffusion process under simulated gastrointestinal conditions. Assessment of large deformation properties shows that the polysaccharide networks are firm in the model gastric phase but weaken in intestinal conditions. The amount of encapsulated oil remains stable during the gastric stage but it is released at the intestinal phase. Observations of release rates were treated with classic theory of diffusion revealing that changes in mechanical properties govern transport phenomena of fish oil in the encapsulated matrix. A partial differential equation was solved successfully to monitor the entirety of fish oil release unveiling apparent diffusion coefficients that vary five orders of magnitude between gastric and intestinal stages.

This study deals with the distribution of added calcium ions and their effect on the phase behaviour of hydrogels made of bovine serum albumin and gelatin. Structural properties of single and mixed systems were identified using small-deformation dynamic oscillation in shear, microdifferential scanning calorimetry and scanning electron microscopy. The experimental procedure was designed to encourage formation of micro phase-separated materials, where i) a continuous gelatin matrix supported liquid BSA inclusions, ii) an inverted dispersion of gelled BSA was interspersed by liquid gelatin inclusions and iii) a rigid BSA phase supported softer filler particles of gelatin. The Lewis-Nielsen equations and a series of models developed by Takayanagi were adapted for predicting the phase behaviour of BSA/gelatin mixtures in the presence of added calcium chloride. As far as we are aware, this is the first attempt to model the partition of added counterions between polymeric phases in binary hydrogels based on classic blending law analysis.

Structural relaxation of a delivery vehicle has been identified in the literature as a limiting parameter for the controlled diffusion of a bioactive compound. To further examine the kinetics of controlled release, this study designed a system of homogeneously dispersed linoleic acid in a high-solid whey protein matrix. Amorphous glucose-syrup liquid was added systematically up to about 48% (w/w), with the total solids level in the formulation being kept constant at 80% (w/w), and experimental observations were obtained over a broad timeframe and temperature range. Structural and physicochemical properties of the blend were monitored using dynamic oscillation in-shear, WAXD, FTIR and confocal laser scanning microscopy. A specific chromogenic reaction with UV–vis spectroscopy was employed to follow the release of linoleic acid under perfect sink conditions. Variation in the amount of glucose syrup, as the co-solute, within the high-solid whey protein network affected profoundly the values of the mechanical glass transition temperature. That was reflected in the kinetics of fatty acid diffusion from the glass transition region of our composite materials. Transport phenomena were quantified via the concept of effective diffusion coefficient, which increases with higher levels of glucose syrup leading to structural relaxation of the delivery vehicle.

Diffusion coefficients are utilised to provide a realistic approach in the quantification of mass transport phenomena, which are important for the delivery of bioactivity from high-solid biopolymer systems. Following this mechanistic consideration, we employ spray drying to produce microcapsules of waxy maize starch that suspend homogeneously tocopheryl acetate. An array of physicochemical techniques including dynamic oscillation in-shear or compression mode, microDSC, WAXD, FTIR, scanning electron or optical microscopy, and UV-vis assays were utilised to relate structural properties of the macromolecular network to diffusivity of the bioactive compound. A modified version of the free-volume theory designed to address molecular diffusion was evaluated over a wide temperature range. Predictive capabilities were facilitated by proposing a mathematical relationship between diffusion coefficient of tocopheryl acetate and fractional free volume of waxy maize starch. Moreover, the theoretical approach is able to accurately describe the extent of cooperativity in the vitamin-biopolymer interaction that determines transport kinetics.

This study optimises a protocol for the estimation of α-amylase activity in a condensed starch matrix in the vicinity of the glass transition region. Enzymatic activity on the vitrified starch system was compared with that of a reference substrate, maltodextrin. The activity was assayed as the rate of release of reducing sugar using a dinitrosalicylic acid procedure. The condensed carbohydrate matrices served the dual purpose of acting as a substrate as well as producing a pronounced effect on the ability to enzymatic hydrolysis. Activation energies were estimated throughout the glass transition region of condensed carbohydrate preparations based on the concept of the spectroscopic shift factor. Results were used to demonstrate a considerable moderation by the mechanical glass transition temperature, beyond the expected linear effect of the temperature dependence, on the reaction rate of starch hydrolysis by α-amylase in comparison with the low-molecular weight chain of maltodextrin.

This study examined the release of vitamin B6 from a hydrogel made of whey protein isolate (WPI). Work was carried out at ambient temperature without preheating the whey protein. Native-state macromolecules were crosslinked with a nontoxic compound, genipin. Experimentation included a ninhydrin assay with UV–vis absorbance, FTIR, 13C NMR, compression testing, SEM imaging, WPI matrix swelling and vitamin release protocols. It was confirmed that geninin crosslinked effectively the protein chains whose network strength was reinforced with increasing crosslinker concentrations. The modified Flory-Rehner theory predicted the molecular weight between crosslinks, network mesh size and crosslinking density in the swollen WPI gels as a function of added crosslinker. Transport patterns of vitamin B6 through the polymeric matrix were monitored over prolonged periods of observation. These were examined with the generalised Fick’s equation and the Peppas-Sahlin equation to unveil the interplay between diffusion and relaxation dynamics in the anomalous transport of the bioactive compound.

It has been suggested that microcrystalline cellulose (MCC) can be used in biodegradable films to improve techno-functionality by providing bulk and enhancing mechanical strength. This study aimed to investigate the effect of MCC addition on the structural properties of potato starch films. Samples were prepared by hot pressing at 120 °C for 7 min to produce systems that covered a broad range of moisture content and relative humidity. Complimentary experimental techniques, including thermomechanical analysis, FTIR, wide-angle X-ray diffraction and SEM, were employed to examine the micro- and macromolecular characteristics in these mixtures. Both moisture content and the presence of MCC have a plasticising effect on the composites yielding a reduction in its glass transition temperature. It appears that there is no specific and nontrivial interaction between potato starch and MCC, an outcome which indicates that the cellulose fibres act as inert filler in the polymeric composite.

The effect of calcium chloride on the structural properties of condensed potato starch undergoing a thermally induced glass transition has been studied using dynamic mechanical analysis and modulated differential scanning calorimetry. Extensive starch gelatinisation was obtained by hot pressing at 120°C for 7 min producing materials that covered a range of moisture contents from 3.7% w/w (11% relative humidity) to 18.8% w/w (75% relative humidity). FTIR, ESEM and WAXD were also performed in order to elucidate the manner by which salt addition affects the molecular interactions and morphology of condensed starch. Experimental protocol ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of calcium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Highly reactive calcium ions form a direct interaction with starch to alter considerably its structural properties via an anti-plasticizing effect, as compared to the polymer-water matrix.

The structural behaviour of soy glycinin systems following application of industrially relevant high hydrostatic pressure (600 MPa for 15 min at ambient temperature) was investigated throughout the experimental range up to 80% (w/w) solids content, and results were compared to conventional thermal treatment. Using small-deformation dynamic oscillation in shear, modulated differential scanning calorimetry, infrared spectroscopy and X-ray scattering, it was demonstrated that soy glycinin with twelve disulphide linkages displays extensive unfolding at low to intermediate solid levels (30–60%, w/w). In contrast, it largely maintains native conformation at 70 and 80% (w/w) solids showing about 20% denaturation, as compared to the thermal transition of native counterparts. Experimental data from infrared spectroscopy also argue for retention of the native conformation in condensed soy glycinin systems comprising mainly beta sheets in the secondary structure. At subzero temperatures, condensed glycinin at atmospheric and pressurised conditions undergoes vitrification phenomena recording experimental glass transition temperatures. Experimental data were successfully modelled using theoretical frameworks for mechanical studies on amorphous synthetic polymers.

The relative mobility of ascorbic acid incorporated in a condensed matrix of high-methoxy pectin (HMP) and polydextrose is reported. Physicochemical and structural characterisation of the high-solid systems utilised modulated differential scanning calorimetry, small deformation dynamic oscillation in shear, scanning electron microscopy, Fourier transform infrared spectroscopy and wide angle X-ray diffraction. Theoretical modeling of the thermomechanical measurements demonstrated that the mechanism of free volume governs stress relaxation phenomena of the polymeric system through the process of vitrification yielding the mechanical glass transition temperature. Combination of UV-vis spectrophotometry and a vitamin-dye binding method was employed to follow for 60 min the diffusion process of ascorbic acid from the concentrated HMP/polydextrose matrix to the absolute ethanol phase throughout the temperature range of −30 to 20 °C. A relatively low estimate of activation energy for the diffusion of vitamin C reflects its freedom of mobility and high free volume, as compared to the relaxation of the polymeric system that exhibits strong temperature dependence in the glass transition region. Utilisation of the concept of diffusion coefficient sheds further light into the relationship between free volume of the polymeric system and diffusional mobility of the micronutrient.

This work explores the process of alginate molecule crosslinking to form cohesive gels that were induced by the addition of calcium ions at various stoichiometric equivalents. Polysaccharide gels were used as a delivery vehicle for the study of transport phenomena of entrapped caffeine as the bioactive compound. Initial physicochemical characterisation through FTIR and WAXD of the alginate matrix showed successful inclusion of caffeine in the bulk system. Rheological analysis in the form of dynamic oscillation in-shear highlighted issues of developing network integrity and its eventual collapse with increasing levels of the crosslinker. Swelling in neutral solvent (water molecules) yielded information on the molecular features of the gel, as determined by the Flory-Rehner theoretical framework. Analysis of molecular transport with modified Fickian diffusion equations showed anomalous behaviour and a sustained release of caffeine. Overall, alteration in mesh size and diffusion parameters can be ascribed to the microstructural changes controlled by calcium crosslinking and the formation of junction zones in the alginate network.

The work provides insights into the effect of pH on the changing microstructural characteristics of swollen BSA networks and the concomitant release profiles of an entrapped bioactive compound. In doing so, a delivery vehicle was developed at ambient temperature with the native BSA molecule and genipin, a natural crosslinker. Ninhydrin assay, FTIR, X-ray, SEM and texture profile analysis documented successful crosslinking that resulted in matrices with distinct morphology and mechanical properties. Water infusion was monitored, which allowed estimation, with the modified Flory-Rehner theory, of microstructural parameters of the swollen network, including the polymer molecular weight between crosslinks and mesh size. Transportation of entrapped vitamin B6 from crosslinked BSA networks was followed over long periods of observation in release media of acidic, neutral and alkaline conditions. Utilisation of diffusion theory predicted the apparent diffusion coefficient and diffusion exponent for the release of the bioactive compound, which was correlated to the morphological characteristics of the crosslinked protein network via the change in pH.

We examined the morphology of a network made with native BSA molecules being crosslinked with genipin at ambient temperature. Ninhydrin assay, FTIR, WAXD, SEM and mechanical tests documented successful crosslinking that enhanced the structural properties of the three dimensional structure. Its hydrophilic nature allows swelling with water absorption, which can be monitored with the modified Flory-Rehner theory to predict the molecular weight between adjacent crosslinks, network mesh size and crosslinking density as a function of crosslinker addition. Characterisation studies were carried out with a view to developing a delivery vehicle for the controlled release of vitamin B6 over a prolonged period of observation. Moving boundaries associated with swelling of the protein matrix resulted in vitamin transport that could be described with the interplay of diffusional and relaxational kinetics via the Peppas-Sahlin equation. Combination of diffusion and swelling equilibrium theories unveils a measurable effect of network characteristics on vitamin B6 release.

The present investigation deals with the structural properties of condensed potato starch-sodium chloride systems undergoing a thermally induced glass transition. Sample preparation included hot pressing at 120°C for 7 min to produce extensive starch gelatinisation. Materials covered a range of moisture contents from 3.6% to 18.8%, which corresponded to relative humidity values of 11% and 75%. Salt addition was up to 6.0% in formulations. Instrumental work was carried out with dynamic mechanical analysis in tension, modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and wide angle X-ray diffraction. Experimental conditions ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of sodium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Sodium ions interact with chemical moieties of the polysaccharide chain to alter considerably structural properties, as compared to the starch-water matrix.

The formation of heat induced whey protein isolate (WPI) and wheat starch (WS) gels in the presence of added calcium chloride (5–192 mM) has been examined. Thermal properties, including the onset temperature of starch gelatinization and protein denaturation, are defined by low amplitude oscillation on shear and modulated temperature differential scanning calorimetry. Upon heating and subsequent cooling, comparison of the storage modulus values bear information on the enhancement of protein aggregation by the electrolyte and the occurrence of phase separation phenomena between the two polymeric constituents in the mixture. Further confirmation of observed trends has been provided by measurements on textural hardness of gels in single cycle compression tests. Porous and aggregated microstructures are identified upon visual examination by environmental scanning electron microscopy. The gels were subjected to in vitro enzymatic hydrolysis and the role of calcium in reducing the extent of starch degradation by α-amylase has been established. It is evident from the results that ionic strength in the form of added calcium ions largely influences gelation kinetics of whey protein leading to significant variability in the hydrolytic potential of α-amylase on wheat starch.

The work prepared high-solid mixtures of whey protein or bovine serum albumin with an amorphous co-solute (glucose syrup) and examined their glass transition behaviour at subzero temperatures. The interest in these condensed matrices was in relation to what extent thermal denaturation and subsequent aggregation of the proteinaceous molecules affects vitrification and, therefore, they were subjected to distinct heating regimes followed by cooling. Small-deformation dynamic oscillation in shear is known to respond to changes in network formation as a function of thermal treatment, albeit published reports thus far focused on low-solid aqueous hydrocolloid samples, and it has been chosen presently to examine the viscoelasticity of their high-solid counterparts. Results were further compared with those from a micromolecular technique, i.e. modulated differential scanning calorimetry. It appears that thermally induced cross-linking is readily recorded in what is known in the literature as the mechanical or network glass transition temperature, whereas the calorimetric Tg is not affected by the extent of polymeric associations in these mixtures. Further, the thermal protocol employed presently results in considerable differences in predictions of the mechanical Tg, which should reflect distinct three dimensional morphologies in these systems of globular protein and co-solute.

The current study evaluates the effect of temperature on α-glucosidase activity, following incorporation of the enzyme into a whey protein matrix through spray drying. Thermomechanical characterization of the matrix was achieved using the techniques of modulated temperature differential scanning calorimetry and small-deformation dynamic mechanical analysis. As the concentration was raised from 75 to 94% (w/w), denaturation of the protein occurred at increasing temperatures. In contrast, denaturation was not observed in calorimetric scans after spray drying. The glass transition temperature (Tg) measured in the dried particles using dynamic mechanical analysis was approximately 40°C. An optimized procedure was developed whereby α-glucosidase and its substrate p-nitrophenyl α-d-glucopyranoside were incorporated into the whey matrix. The effect of temperature on enzymatic catalysis was investigated and, below 40°C, activity was low and relatively independent of temperature. However, the rates of product formation markedly accelerated as temperatures were increased beyond Tg. These novel observations strongly emphasize the pronounced effect of mechanical Tg of the protein matrix on enzymatic activity.

The rheological and structural changes in heat induced pastes and gels of lentil starch and lentil protein composites were investigated at various starch to protein ratios. The starch fraction ( φ s ) in the mixtures was varied from 0 to 1 and the total solid content was maintained at 25% (w/w). Results showed that the gel strength of the composite gels increased exponentially with the increase in lentil starch fraction. The pasting temperature increased and the paste viscosity decreased with the increase in the lentil protein fraction. The high starch composite gels ( φ s > 0.5) showed higher elastic ( G ′) and loss ( G ″) moduli at higher temperature (60 °C) than at lower temperature (10 °C). The high protein composite gels ( φ s ≤ 0.5) showed higher G ′ and G ″ values at lower temperature (10 °C) than at higher temperature (60 °C). Segregation of protein-rich domains was observed in the high starch gels ( φ s > 0.7) whereas low starch composite gels ( φ s ≤ 0.5) appeared more homogeneous. The microstructure of composite gels appeared to be more fragile with larger pore size and thinner wall compared to the microstructure of starch gel. Both non-covalent interactions (hydrophobic and hydrogen bonding) and covalent bonding were found to contribute to the gel structure and firmness of these composite gels. The NaCl concentration increased the paste viscosity and gel firmness of the composite gels up to 0.25 mM above which the magnitudes of these parameters were decreased. Both the paste viscosity and the gel firmness of the composite gels were found to be higher above the isoelectric point of lentil protein and vice versa. From this study, textural properties of the composite gel/paste were found to be strongly affected by the proportion of the starch and protein as well as the extrinsic factors (pH, ionic strength, presence of reducing agents). Therefore, understanding of gelling behaviour of lentil starch and protein in composite gel would be helpful for structure formation of these two biopolymers in mixtures and would help their application in new product development.

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.

High hydrostatic pressure was applied on immunoglobulin samples whose molecular, structural and glass transition properties were examined in comparison to thermal effects at atmospheric pressure. Immunoglobulins exhibit pressure stability throughout the experimental concentration range by conserving native conformation, which results in cohesive structure formation observed by small-deformation dynamic oscillation on shear, modulated differential scanning calorimetry and infrared spectroscopy. Application of the combined WLF/free volume theoretical framework demonstrates that pressurised immunoglobulin preparations are able to form glassy systems upon cooling at subzero temperatures. This has been attributed to a reduction in polymeric free volume under pressure and the development of an efficient friction coefficient amongst tightly packed particles that link to form a three-dimensional matrix. Pressure treated assemblies of condensed immunoglobulins demonstrate viscoelastic behaviour matching that of the thermally treated counterparts, but retain bioactivity, which is largely lost with thermal treatment.

The present work deals with the changing network morphology of whey protein isolate (15%, w/w) in the presence of glucose syrup (co-solute) with concentrations ranging from 0% to 65% (w/w) in 10 mM CaCl2 solution, thus producing formulations with a total level of solids of up to 80% (w/w). Denaturation behaviour and aggregation of whey protein systems were investigated using small deformation dynamic oscillation on shear, micro and modulated differential scanning calorimetry, and confocal laser scanning microscopy. A progression in the mechanical strength of protein aggregates was observed resulting from enhanced protein-protein interactions in the presence of glucose syrup. Addition of the co-solute resulted in better thermal stability of protein molecules by shifting the process of denaturation to higher temperature, as observed by calorimetry. Observations are supported by micrographs showing coherent networks with reduced size of whey protein aggregates in the presence of high levels of glucose syrup, as opposed to thick and random clusters for systems of whey protein by itself. Glass transition phenomenon was observed for condensed protein/co-solute systems, which were treated with theoretical concepts adapted from synthetic polymer research to pinpoint the mechanical glass transition temperature.

The effect of varying concentrations of co-solute (polydextrose) on thermomechanical and physicochemical properties of deacylated gellan matrices is presented. Modulated differential scanning calorimetry, micro differential scanning calorimetry, small deformation dynamic oscillation in shear, Fourier transform infrared spectroscopy, wide angle X-ray diffraction and environmental scanning electron microscopy have been used to investigate the structural transformations in aqueous, low-solid and condensed systems. There was a rise in values of storage modulus as the level of co-solute was increased, followed by a significant decline at intermediate concentrations, with high modulus values being regained as more of the co-solute was incorporated. These results confirm the hypothesis of a structural transformation from a highly enthalpic aggregated assembly in the aqueous/low-solid environment to a lightly cross linked polysaccharide network in the high solids regime. Time-temperature superposition (TTS) phenomena observed for amorphous synthetic polymers have been utilised to generate master curves of viscoelasticity, which afforded rationalisation of results on the basis of the free volume theory.

The present investigation deals with the changing network morphology of agarose and high methoxy pectin when mixed with polydextrose as co-solute at concentrations varying up to high level of solids. Thermomechanical analysis and micro-imaging were performed using small deformation dynamic oscillation in shear, modulated differential scanning calorimetry and environment scanning electron microscopy. Fourier transform infrared spectroscopy and wide angle X-ray diffraction were practised to examine the nature of interactions between polymer and co-solute, and the extent of amorphicity of preparations. We observed a decline in the mechanical strength of aqueous agarose preparations upon addition of high levels of polydextrose, which should be attributed to reduced enthalpic content of the coil-to-helix transition of the polysaccharide network. Glass transition phenomena were observed at subzero temperatures in condensed preparations, hence further arguing for the formation of a lightly cross-linked agarose network with changing solvent quality. High levels of co-solute induce formation of weak pectin gels at elevated temperatures (even at 95°C), which with lowering temperature exhibit increasing strength. This results in the formation of rubbery pectin gels at ambient temperature, which upon controlled cooling to subzero temperatures convert to a clear glass earlier than the agarose counterparts.

The structural properties of five ethyl cellulose polymers (EC) in mixture with the non aqueous solvent of propylene glycol dicaprylate (PGD) have been investigated with a view to facilitating topical drug delivery. Total concentration of the polymer varied from 12 to 20% (w/w) and its weight average molecular weight was in the range of 64–223 kDa. Experimental techniques utilised were small-deformation dynamic oscillation in shear, attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR) and wide-angle X-ray diffraction. The nature of the time and temperature dependence on viscoelastic functions of all samples could be treated with the Chambon and Winter criterion allowing determination of the critical gelation temperature in relation to polymer concentration and molecular weight. A further refinement of this school of thought allowed correlation between the viscoelastic relaxation exponent and fractal dimensions in thermally treated EC/PGD matrices. Tangible evidence on the packing arrangements of the ethyl cellulose network and the molecular nature of its interaction with the non aqueous solvent as a function of polymer concentration and molecular weight was provided by X-ray diffraction and infrared studies.

BACKGROUND: The granules of amaranth starch are very small compared with starches from other sources. In the current work, amaranth starches with different amylose contents were treated with hydrochloric acid as a function of time in order to study the effect of acid treatments on starches. Differential scanning calorimetry and dynamic oscillation in shear were employed to analyse the thermal and rheological properties of acid-modified amaranth starch. RESULTS: Results showed that gelatinisation temperatures and enthalpy change of gelatinisation (Delta H) decreased steeply initially, and had a slight increase with further treatment up to 12 h then decreased, an outcome that reflected distinct resistance to acid with various amylose contents. Rheological parameters of storage and loss moduli during heating, cooling and frequency sweep of modified starches reflected the differential scanning calorimetry results by decreasing in value as the time of acid hydrolysis increased. CONCLUSION: With amylose content increase, the effects of acid hydrolysis on gelatinisation temperatures became less pronounced. Nevertheless, prolonged acid hydrolysis decreased the storage and loss moduli, with the starch pastes becoming more liquid-like.

The structural properties and morphology of mixed gels made of aqueous preparations of agarose and whey protein were modified by changing thermal treatment and pH. The conformationally dissimilar polymers phase separated and this process was followed by small-deformation dynamic oscillation in shear, differential scanning calorimetry and environmental scanning electron microscopy. Experimental protocol encourages formation of a range of two-phase systems from continuous agarose matrices perforated by liquid-like whey protein inclusions to phase inverted preparations where a soft protein matrix suspends hard agarose-filler particles. These distinct morphologies have widely different mechanical moduli, which were followed by adapting a theoretical analysis (isostress–isostrain and Lewis–Nielsen blending laws) from the literature in synthetic block polymers and polyblends. Based on this framework of thought, reasonable predictions of the elastic moduli in the composite gels were made that led to patterns of solvent partition between the two polymeric networks. It was shown that proteins, in mixture with polysaccharide, exhibit favorable relative affinity (P-factor) for water molecules at a pH above their isoelectric point. This is an unexpected outcome that adds to the central finding of a single P value for the distribution of solvent between the continuous matrix and discontinuous inclusions of binary gels. It was thus proposed that phase continuity and solvent distribution in agarose/whey protein systems are under kinetic control that can be heavily governed by pH changes in the aqueous environment.

The structural properties of ethyl cellulose and propylene glycol dicaprylate mixtures were investigated with a view to facilitating use of the system as excepient for topical drug delivery. The working protocol included small-deformation dynamic oscillation in combination with the principle of time–temperature superposition, micro and modulated differential scanning calorimetry, wide-angle X-ray diffraction patterns, infrared spectroscopy, and optical profile analysis in the form of gel particle roughness. In contrast to thermoreversible gelation upon heating of aqueous ethyl cellulose solutions reported widely in the literature, replacing water with propylene glycol dicaprylate and mixing with the polymer yields gels that revert to the solution state with increasing temperature. Time effects were also probed; the continuous increase in viscoelasticity of preparations as a function of time of observation at ambient temperature was accompanied by structural disintegration of the polymeric particles. This was rationalized by proposing that specific polymer–solvent interactions result with aging in particle erosion and the release of polymeric strands that are able to form a three-dimensional structure. It was thus documented that the time–temperature equivalence was active in the system producing a rubbery state in the master curve of viscoelasticity, which extends from ambient to subzero temperatures and should facilitate pharmaceutical applications.

In an effort to draw attention to the subject of structure/function relationships in high-solid biopolymer mixtures, this investigation produces binary composites of agarose with gelatin and systematically increases the amount of glucose syrup, which is the co-solute in this system. Experimental work was carried out using small-deformation dynamic oscillation on shear and modulated differential scanning calorimetry. Agarose/gelatin mixtures in an aqueous low-solid environment form non-interactive bicontinuous networks. Addition of glucose syrup to the polymeric blend prevents the formation of stable double helices in the environment. Gelatin, on the other hand, better withstands the co-solute-induced change in solvent quality. At subzero temperatures, materials go through the rubber-to-glass transition whose DSC glass transition temperature (Tg) is governed by the total level of solids in the system. Estimation of the mechanical Tg acquires physical significance by utilising the theory of free volume, as modelled by the Williams, Landel and Ferry (WLF) equation. The single value of Tg estimated by this approach argues in accordance with experimental observations for the predominance of the gelatin network in the high-solid mixture.

This study indicates that controlled depolymerization of plant (PC) and bacterial (BC) celluloses can be achieved by employing suitable ultrasonication settings. Size exclusion chromatography results indicate that reduction in the molecular weight of the two polymers was accompanied by a parallel drop in the polydispersity index of PC and an unexpected increase in the said index of BC. X-ray diffraction patterns of the fractionated materials were found to be Cellulose II crystals whereas experimentation on microcrystalline cellulose unveiled the Cellulose I conformation. The crystallinity index revealed no obvious changes in PC as a function of the time of sonication whereas a major increase in the crystalline component was encountered for BC. Furthermore, thermal degradation using TGA and FTIR spectra suggest that the processes of dissolution and regeneration in cuprammonium hydroxide of PC and BC followed by ultrasonication do not affect the chemical fingerprints via oxidative reactions of the cellulosic materials.

A pH and mechano-responsive coordination polymeric gel was developed without the use of long chain hydrophobic groups. The hydrogel was synthesised by reacting the aqueous solution of Mg2+ with the basic aqueous solution of N-(7-hydroxyl-4-methyl-8-coumarinyl)-alanine. The gelation is attributed to the self-aggregation of ID coordination polymers to form 3D nanostructures through non-covalent interactions to entrap water molecules. The freeze-dried hydrogel exhibits a fibrillar network structure with a uniform ribbon shape. UV/vis absorption studies illustrate that the hydrogel displays a typical pi-pi* transition. The fluorescence intensity of the hydrogel is enhanced drastically with a longer lifetime upon gel formation. Mechanical analysis including dynamic oscillation on shear, steady shear and creep (retardation-relaxation) testing have been performed to elucidate the supramolecular nature of the 3D assembly. Together with the viscoelastic properties and biocompatibility, the Mg2+ hydrogel may find utility as a novel soft material in biomedical applications. A pH and mechano-responsive coordination polymeric gel was developed without the use of long chain hydrophobic groups. The hydrogel was synthesised by reacting the aqueous solution of Mg2+ with the basic aqueous solution of N-(7-hydroxyl-4-methyl-8-coumarinyl)-alanine. The gelation is attributed to the self-aggregation of ID coordination polymers to form 3D nanostructures through non-covalent interactions to entrap water molecules. The freeze-dried hydrogel exhibits a fibrillar network structure with a uniform ribbon shape. UV/vis absorption studies illustrate that the hydrogel displays a typical I?-I?* transition. The fluorescence intensity of the hydrogel is enhanced drastically with a longer lifetime upon gel formation. Mechanical analysis including dynamic oscillation on shear, steady shear and creep (retardation-relaxation) testing have been performed to elucidate the supramolecular nature of the 3D assembly. Together with the viscoelastic properties and biocompatibility, the Mg2+ hydrogel may find utility as a novel soft material in biomedical applications.

The physical properties of the capsular polysaccharide of Rhizobium Trifolii (CPS) were investigated. Viscosity measurements provided information about the hydrodynamic volume of single coils, the perturbation of solvent flow and the shear-thinning behaviour of concentrated solutions. Changes in chain geometry and the development of an intermolecular network as a function of temperature were monitored using the techniques of optical rotation and dynamic oscillation. Finally, analysis of calorimetric thermograms elucidated the type of interactions between CPS and the bacterial levan. Overall, the Rhizobium polysaccharide was found to form thermally-reversible gels at an extremely low ‘minimum critical gelling concentration’ (co∼ 0.35gl-1). At temperatures above the gel melting point (∼ 48°C), however, the compact polymer coils entangled at comparatively high concentrations (about 60 times higher than co). In the presence of a highly branched levan, the thermal stability of ordered CPS structures increased as a consequence of thermodynamic incompatibility between the two polymers.

The microstructural and mechanical properties of acid-set mixtures of sodium caseinate (2% w/w)/barley β - glucans (2–6% w/w) were studied in an effort to evaluate the effect of these polysaccharides on the texture of fermented dairy products. The phase behavior of the blends was investigated using small deformation dynamic oscillation, differential scanning calorimetry, optical microscopy, and polymer blending-laws analysis. The work aimed to assess the topology of the phase separated mixture, the water holding capacity of its polymeric phases, and the thermal stability of the constituent networks. The mixed network properties were dominated by the protein component at low concentrations of β-glucans (≤3% w/w). In the concentrated regime, the system seems to have a bicontinuous topology governed by the mechanical strength and thermal stability of the β-glucan network structure. Results could assist in optimising the use of sodium caseinate and β-glucans as functional or as bioactive ingredients in acid-set dairy products.

Aqueous and high sugar gels of agarose and κ-carrageenan were prepared to investigate the changing nature of polymeric matrices. Transmission electron microscopy documented a transformation from an aggregated network in the aqueous environment to a lightly cross-linked structure in high solids. The latter possesses an elastic consistency based on the increasing values of yield strain from high- to low-water systems recorded using compression testing. The work provides further confirmation of the increased amorphicity of polysaccharide networks in high solid preparations.

The extension of starch gelatiniaztion to estimate its kinetic parameters in the presence of other ingredients and to apply it on cake baking is discussed. This kinetic model together with mathematical model of heat and moisture transport in cakes is used as a quality control parameter of the baking process. It is stated that the starch gelatinization temperature is greatly influenced by the presence of co-solute. The rise in peak gelatinization temperature increases with increasing temperature of the thermal treatment.

Small deformation dynamic oscillation, large deformation compression and creep testing were carried out to examine the structural properties of agarose in the presence of 50:50 preparations of sucrose and glucose syrup. The content of co-solute varied from 10 to 93% in the mixture. Increasing additions of sugar transform gradually the enthalpic, brittle networks of the polysaccharide to ‘rubbery’ structures of enhanced thermal stability. At saturated levels of solids there is a phase inversion from the gel-like characteristics of the agarose network to the liquid-like response of the continuous phase of co-solute. The latter undergoes vitrification upon cooling thus exhibiting the mechanical glass transition region and the glassy state. Given time, vestigial development and eventual three-dimensional linkage of agarose helices reverts the high viscosity liquids to rubbery gels exhibiting considerable yield strain (140% deformation). The work is compared to sugar/polysaccharide mixtures in the literature with the view to rationalizing underlying molecular processes and defining universal effects.

A high-solid matrix of κ-carrageenan with polydextrose was developed to entrap α-linolenic acid, which is an omega-3 bioactive compound. Physicochemical analysis of this system utilised modulated DSC, dynamic oscillation in shear, ESEM, FTIR and WAX diffraction. The carbohydrate matrix was conditioned through an extensive temperature range to induce changes in molecular morphology and identify the network glass transition temperature. Thermally induced variation in phase morphology was employed to rationalise transportation patterns of the bioactive compound within the high-solid preparation. Thus, experimental observations using UV–vis spectroscopy modelled diffusion kinetics to document the mobility arresting effect of the vitrifying matrix on the micro-constituent. Within the glass transition region, results argue that free volume theory is the molecular process governing structural relaxation. Further, Less Fickian diffusion follows well the rate of molecular transport of α-linolenic acid as a function of time and temperature of observation in the condensed matrix.

Transmission electron microscopy was employed to examine the hypothesis, reached earlier using rheological and thermal analysis, of the changing nature of a polysaccharide network with increasing levels of sugar. Mixtures of deacylated gellan (