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Producción Científica, The physical modification of rice flour by heat-moisture treatment assisted by microwave radiation and its effect on the rheological and pasting properties of gluten-free doughs and the physical quality of their resulting bread was investigated. Two levels of flour initial moisture content, 20% (MW-20%) and 30% (MW-30%) and two levels of its addition (30% and 50%) to the dough were evaluated to assess the potential of the physical treatment to modify dough viscoelasticity and bread-making ability. MW-30% treated rice flour showed the most notable results. It provided enhanced dough viscoelasticity vs the control (100% native rice flour), increasing the dough G1′ modulus up to 69% and 135% for the treated flour additions of 30% and 50% of MW-30% respectively. The treated flour increased the resistance of doughs to deformation and enhanced their elastic behavior and recovery capacity up to 170% when compared to the control dough. The major effects on pasting parameters were also obtained for the doughs formulated with MW-30% flour at the maximum substitution level (50%). It delayed the pasting temperature, decreased the peak, trough and final viscosities with respect to the control dough. Both MW-treated rice flours (MW-20% and MW-30%) led to bread with higher-specific volume, softer crumb and delayed staling. The MW assisted heat moisture treatment of rice flour seems to be a valuable procedure to improve the viscoelastic behavior and bread-making performance of gluten-free doughs., Ministerio de Economía y Competitividad and the European Regional Development Fund (FEDER) - AGL2015-63849-C2-2-R, Junta de Castilla y León and FEDER - VA072P17, European Commission for the Individual Fellowship Grant - 706102–BreadForAll

The effect of Basil Seed Gum (BSG) on native and pre-gelatinized corn starch and flour gels was evaluated. With this purpose, the hydration, pasting, rheological, textural and microstructural properties of the mixed gels were analyzed. Xanthan was used as a comparison, as it presents comparable high zero shear viscosity to BSG. The presence of BSG led to greater water binding capacity and greater water absorption index of the starch and flours compared to the free-gum systems. In general BSG substantially increased the peak and final viscosities of the pastes, also leading to a raise in the viscoelasticity (G’ and G”) and hardness of the final gels, native or treated (pregelatinized starch and extruded flour). A more opened microstructure—compared to a homogeneous and dense matrix of the control native starch gels— with strands and a spider-like network of BSG across the pockets was detected. On the other hand, xanthan showed the opposite effect, decreasing the peak and final viscosities of the native systems, delaying the gelatinization process, and also leading to weaker gels of reduced viscoelasticity with opened honeycomb-like microstructures. However, for pregelatinized flour and starch the effect of xanthan was minimal., Spanish Ministry of Economy and Competitiveness (Project AGL2014-52928-C2-2-R) and the European Regional Development Fund (FEDER)

Limited fractionation of yellow pea yielded functional protein fractions with higher gelling capacity. Pea protein concentrates were obtained by dispersing flour at unadjusted pH (~6.7) and at pH 8. An additional isoelectric precipitation step resulted in a protein-rich isolate and a protein-poor supernatant. Aqueous solutions of these pea fractions (up to 15 wt %) were heated from 20 to 95 and subsequently cooled to 20 °C, and their viscoelastic response was characterized by small and large amplitude oscillatory shear measurements (SAOS and LAOS, respectively). SAOS rheology showed that the limited fractionated protein concentrates formed significantly firmer gels per mass of protein after cooling, than the more extensively fractionated protein isolate, with elastic moduli of G’~103 Pa and G’~102 Pa, respectively. LAOS rheology showed an overall strain softening behaviour for all pea fractions and a transition from elastic to viscous behaviour at smaller strain for the protein isolate. Confocal and electron microscopic images were consistent with those observations, and revealed a more homogeneous network for the limited fractionated samples, and a more heterogenous network for the protein isolate. A number of experiments showed that there are different processing and compositional factors affecting gelling capacity. These are isoelectric precipitation, amount of sugars upon lyophilization and differences in ash content. Furthermore, differences in pre-aggregated state, as found in earlier research, may be partially responsible for the different gelling behaviour. In conclusion, we explain how fractionation affects pea proteins and found that limited fractionation yields pea proteins that form stronger gels.

We investigated the gelation characteristics of aiyu jelly derived from the polymeric extract obtained by washing the seeds of Ficus Pumila var. Awkeotsang. The main gel component is low methoxyl pectin, which forms crosslinks with divalent ions that bind the exuded polysaccharide chains. Unlike many fruit pectins used in jam and jellies that require heating, additional sugars, and acidic conditions to gel, the aiyu exudate gels at room temperature with just the addition of water. In this study, the time-resolved dynamics of the gelation process and the evolution of the viscoelastic relaxation spectrum with frequency and gel age are obtained via Optimally Windowed Chirp rheometry (OWCh), conventional time-sweep rheometry, and cryo-scanning electron microscope (cryo-SEM) microstructural characterization. During gelation, we observed distinctive frequency-dependent inflection points in both the time-evolving storage and loss moduli which occur nearly simultaneously in time. Close inspection of high resolution cryo-SEM images taken at different times during the gelation process showed that the gels initially form nano-fiber networks with mesh sizes on the order of tens of microns and the stiffer mature gels observed at longer times develop sub-micron mesh sizes. These observations suggest a progressive transformation between microstructures may accompany the progressive growth in the elasticity of the aiyu gels and the local inflection points in the viscoelastic moduli. We also developed a multi-species reaction kinetics model for calcium – pectin binding in aiyu gelation. By including methylesterase enzymatic conversion of pectin binding sites, combined with calcium binding and the slower formation of consecutively-bound junction zones, the distinctive inflection points in the viscoelastic moduli are captured by the kinetic gelation model. By combining rheological measurements, microstructural observations, and reaction kinetics modeling, this study not only characterizes a unique water-soluble natural extract that gels at room temperature with no additives or thermomechanical processing, it also demonstrates that the aiyu polysaccharide system is a safe and controllable model for gelation systems in which binding site activation is concurrently coupled to crosslink formation.

In the present paper the effect of pH and salts on microstructural and viscoelastic properties of lemon peel acid insoluble fiber residue (AR) suspensions upon mild and intense shearing was investigated. To this aim, AR suspensions were adjusted to a pH of 2.5 (as is), 4.5, 5.5, 7 or 10 prior to or after high pressure homogenization (HPH) at 20 MPa (high shearing), with or without blending (low shearing). Furthermore, the effect of salts was investigated by addition of NaCl or CaCl2 to the AR suspensions upon blending and HPH. Microstructural characterization of the AR suspensions, was performed through microscopic visualization and determination of the particle size distribution by laser diffraction, whereas viscoelastic properties were determined by rheological analysis.Regardless of the pH conditions, blending prior to HPH was essential to obtain optimally functionalized AR suspensions. Furthermore, the effect of the sequence of blending and pH adjustment was negligible, whereas pH adjustment played a crucial role prior to HPH. In particular, increasing the pH above its intrinsic condition (pH 2.5) assisted the functionalization of AR suspensions by HPH, improving its viscoelastic properties. Contrarily, high salt concentrations negatively influenced the functionalization of AR suspensions. This effect of pH and salts was attributed to changes in electrostatic forces between AR fibers due to the presence of negative charged residual pectin polymers, favoring fiber separation (upon HPH) and increasing its hydration potential. On the other hand, high salt concentrations will shield AR fiber charges, thereby reducing the viscoelastic properties of the fiber suspensions. ispartof: Food Hydrocolloids vol:82 pages:144-154 status: published

Specific volume and crumb hardness, cohesiveness and porosity of gluten-free breads (GFBs) are still far from consumers’ expectations. Since additives are increasingly avoided by the consumers, a quality improvement of GFBs through the optimization of the starch source may provide important benefits. In this study, the effect of five different A-to B-type wheat starch ratios (100A-0B, 75A-25B, 50A-50B, 25A-75B, 0A-100B) on the quality of GFBs was investigated. The increase of the proportion of B-type granules (small ones) augmented the packing degree and uniformity of the continuous phase (starch-hydrocolloid matrix) as well as the Pickering effect (B-type granules being adsorbed onto the air-liquid interface), improving air bubble stabilization. In addition, 0A-100B dough displayed a more delayed crumb settling due to the higher pasting temperatures of B-type granules. Furthermore, the increase of the proportion of B-type granules also increased the apparent viscosity and viscoelastic moduli of doughs, which noticeable diminished bread expansion in 0A-100B sample. Interestingly, 75A-25B and 25A-75B doughs resulted in GFBs with the highest specific volume and crumb cohesiveness and lower crumb hardness, the former with open grain structure (fewer cells with larger size) and the latter with close grain structure (more cells with smaller size). For the first time, it is shown that a specific A-to B-type wheat starch ratio enables: 1) the simultaneous optimization of dough viscosity and Pickering stabilization to attain GFBs with improved physical quality and; 2) the modification of crumb porosity while maintaining specific volume and crumb texture.

Bacterial cellulose (BC) has several current and potential future uses in the food industry because of its ability to form hydrogels with distinctive properties. The texture of BC hydrogels is determined by both the cellulose fibre network and the internal dispersed water. In this study, mechanical properties of hydrated BC synthesised by six different strains of Komagataeibacter genus were investigated with regards to their extensibility, compressive strength, relaxation ability, viscoelasticity and poroelasticity. The stress/strain at failure and Young's modulus were assessed by uniaxial tensile testing. The compressive strength, relaxation ability and viscoelasticity were measured via a series of compression and small amplitude oscillatory shear steps. A poroelastic constitutive modelling simulation was used to investigate the mechanical effects of water movement. The morphology of the BC fibril network under compression was observed via scanning electron microscopy. Results showed that the mechanics of BC were highly dependent on the cellulose concentration, as well as the morphology of the fibril network. BC synthesised by ATCC 53524 was the most concentrated (0.71 wt%), and exhibited high tensile properties, stiffness and storage moduli; whereas comparatively low mechanical properties were noted for BC produced by ATCC 700178 and ATCC 10245, which contained the lowest cellulose concentration (0.18 wt%). Small deformation responses (normal stress, G′) scaled with cellulose concentration for all samples, whereas larger deformation responses (Young's modulus, poroelasticity) depended on both cellulose concentration and additional factors, presumably related to network morphology. Increasing concentration and compressive coalescence of fibres in the integrated BC network reduced both the relaxation of the normal stress and the movement of water. This research aids the selection of bacterial strains to modulate the texture and mechanical properties of hydrated BC-based food systems.

Whey-plant protein-based emulsions had high physicochemical stability. Whey and plant protein blend-based interfaces were viscoelastic while casein-based interfaces were relatively viscous. Whey-plant and plant-plant protein blends behaved synergistically leading to enhanced emulsion stability. Sodium caseinate-plant protein-based emulsions were physically unstable.

Partially denatured whey protein products (PDWPC's) can be classified based on the viscoelastic properties of their solutions. Strain sweeps show that PDWPC-A and –B and microparticulated WPC (MPWPC) with compact, spherical aggregated particles exhibit a strong strain overshoot. PDWPC-C and –D, on the other hand, which have open, elongated porous particles show a weak strain overshoot. The concentration dependence of the elastic modulus G′ in the linear viscoelastic region has a biphasic power law dependence with concentration for all protein products studied, except for WPC where G′ is independent of protein concentration. Frequency sweeps suggest that MPWC solutions form a strong physical gel at all concentrations above 14% (w/w). PDWPC-A and –B form weak gels over the same concentration range. PDWPC-C and –D also form weak gels at 14% protein (w/w) but strong physical gels at higher concentrations. The frequency dependence of G′ and G″ for all aggregated proteins show a power law dependence indicating fractal type structures. For all solutions above a critical concentration, the fractal dimensions span the range 1.6–2.3, indicating a range of gel network structures from open and diffuse to compact and dense. Adherence to the empirical Cox-Merz rule was observed in PDWPC-A, -C and –D at concentrations of 14 and 16% (w/w) protein, suggesting liquid-like behaviour. At higher protein concentrations the deviations from the Cox-Merz rule suggest more pronounced elasticity in the structure. For PDWPC-B, the behaviour is complex, with deviation from the Cox-Merz rule at low frequencies/shear rates, but correspondence at higher frequencies/shear rates at all concentrations. This indicates a frequency-dependent change from liquid-like behaviour over long timescale deformations, to a solid-like behaviour at short timescale deformations. MPWPC solutions of all concentrations do not follow the Cox-Merz rule, suggesting solid-like behaviour. The PDWPCs exhibit a complex rheological behaviour which suggests they could be versatile thickening, texturizing and fat replacement ingredients that will offer food manufacturers greater control over the texture of formulated fluid foods.

Producción Científica, The addition of bioactive β-glucan to gluten-free breads is of special interest to people suffering from celiac disease. Most of the studies found in literature involve cereal (1 → 3)(1 → 4)-β-glucan, while those from yeast and fungi are still nearly unexplored. This study focuses on the effect of fortifying gluten-free rice-based doughs and breads with (1 → 3)(1 → 6)-β-glucan concentrates derived from yeasts –soluble (SBG) and insoluble (IBG)– and fungi (Pleurotus Ostreatus) (FBG). SBG-enriched doughs were less firm and exhibited lower resistance to deformation than doughs with FBG or IBG. In contrast, FBG- and IBG-enriched doughs increased their resistance to deformation as the concentration increased. Doughs with a firmer consistency as determined by a forward extrusion test (FBG- and IBG-enriched doughs) corresponded to those with larger dynamic moduli and lower frequency dependence, lower elastic deformation and higher viscosity at steady state. The physical quality of breads was significantly improved by addition of all types of (1→3)(1→6)-β-glucan at optimized dough hydration. They caused an increase in the specific volume of the breads, a reduction in their hardness and longer shelf-life. Sensory evaluation also demonstrated an improvement in bread organoleptic attributes when SBG was added., Ministerio de Economía, Industria y Competitividad - FEDER (Proyects AGL2012-35088 and AGL2015-63849-C2-2-R), Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA072P17)

To understand the role of hydrocolloids' viscosity in developing gluten-free (GF) bread, a range of hydroxypropylmethylcellulose (HPMC) with similar backbone and percentage of methoxyl and hydroxypropoxyl residues was selected in order to vary the viscosity (100 mPa.s, 4000 mPa.s, 15,000 mPa.s) while keeping the main chemical structure. Viscosity of HPMC was used as quantitative independent factor in a multilevel factorial model along with HPMC level (1%, 2%, 3%) and hydration level (90%, 100%, 110%). The model results in 27 formulation based on rice flour. A Mixolab system was uses to analyse the rheological parameters of the GF batters during mixing, cooking and cooling stage. In addition, GF breads were characterised for their quality parameters. Analytical data were fitted to multiple regression equations in order to estimate the dependence of the collected parameters on the quantitative independent factors. Results confirmed the importance of hydration level in determining the viscoelastic behaviour of the GF batter and influencing the rheology characteristics of bread. Moreover, it was possible to underline the role of the HPMC viscosity along with the level of HPMC, both to control the batter consistency and some desirable textural features of GF bread such as crumb hardness, cohesiveness and resilience. Finally, some analytical parameters were used as quality indicators in desirability index calculation, which would represent a GF breads with optimum quality obtained by the inclusion of a 2.2% of HPMC 15000 cP with hydration level to 110%., Financial support of the Spanish Ministry of Economy and Competitiveness (Project AGL2014-52928-C2-1-R) and the European Regional Development Fund (FEDER).

In this work, the interfacial and bulk properties of oil-in-water emulsions stabilized by glycyrrhizic acid (GA), structurally a saponin and cellulose nanocrystals (CNC) as a co-stabilizer are investigated at different ionic strengths. The influence of GA, CNC, and NaCl concentration on the bulk stabilization of the emulsion as well as on the adsorption behavior and dilatational viscoelasticity at a model oil-water interface are discussed. At the oil-water interface GA adsorbs with appropriate CNC concentration due to salt-induced charge screening, but desorbs from the interface into bulk by excessive increase of the CNC concentration. An interfacial synergistic effect between GA and CNC was found at GA concentrations below interfacial saturation, attributed to the formation of interfacial GA-CNC complexes. In emulsions, the synergistic stabilization concentrations of the compounds are found at higher concentration of 1 wt% GA, 1 wt% CNC, and 20 mM NaCl. FTIR measurements suggest complexation of GA and CNC via hydrogen bonds and intermolecular interactions. The results provide evidence of network formation due to GA-CNC complexes at the interface and aggregation in the continuous phase, which eventually stabilize the emulsion systems.

The fabrication of high-quality low-fat 3D printed foods is strongly dependent on the development of shear-thinning, viscoelastic, and thixotropic ink with a monomodal particle size distribution. In this study, oil was partially or totally replaced with hydrophobically modified biosurfactants (acetylated starch, octenyl succinic anhydride starch, ethyl (hydroxyethyl) cellulose, and dodecenyl succinylated inulin) in a soy protein-based emulsion to produce the desired reduced-fat emulsion gels for potential applications in the 3D printing process. These reduced-fat emulsion gels exhibited pseudoplastic behavior with viscoelastic properties, where viscosity recovery, frequency crossover point, and storage modulus were found to increase with increasing biosurfactants ratio. Higher levels of surface-active biopolymers also yielded inks with lower creep compliance, a smaller droplet size having a more uniform distribution, and possessing improved structural strength and storage stability. Spherical droplets of inks with higher ratios of biosurfactants remained well dispersed. The differences in molecular weight and radius of gyration of biosurfactants accounted for the observed differences in flow behavior and emulsion stability, where inks including dodecenyl succinylated inulin and ethyl (hydroxyethyl) cellulose offered stable structures with strong gel-like properties compared to acetylated and octenyl succinic anhydride starches. All ink networks were also dynamic and recoverable, thus demonstrating the potential of these reduced-fat inks in 3D printing processes.

Four lots of glucomannan (GM) gels (5 g/100 mL w/v): two lots of native GM gels (pH = 6.6; lot N) and two lots of deacetylated GM gels (pH = 11; lot D) were subjected to high hydrostatic pressure (HHP) at 0 (N0 and D0 respectively), and 400 MPa (N400 and D400 respectively). All samples were frozen and stored at −20 °C for two years to analyse the effect of long-term frozen storage on the viscoelastic parameters of pressurized samples according to pH (FN400, FD400) vs unpressurized samples (FN0, FD0), all in comparison with the respective unfrozen unpressurized controls (N0, D0). HHP improved the gel properties of frozen native gels as evidenced by significantly higher stress (σ) and strain (γ) amplitudes in FN400 vs FN0, albeit the effect was attenuated when GM was deacetylated (FD400 vs FD0). From T > 65 °C, HHP produced rubber-like elasticity in native GM gel (N400), and this thermal response was maintained in frozen native gel (FN400). Thermal profiles of deacetylated GM gels suggest that HHP reduced vitrification of physical networks in FD400 vs FD0., Authors wish to thank the Spanish Ministry of Economy and Competitiveness for financial support (AGL2011-24693) and Xunta de Galicia for its financial support under the consolidation and restructuring program of competitive research units.

The aim of the work was to analyze the effects of rapeseed protein isolate on the rheological and thermal properties of gluten-free dough, prepared on the basis of corn and potato starches. Starch mix was replaced with rapeseed protein isolate at levels from 6 to 15%. Rheological and thermal properties of such samples were compared with the control dough. Basing on the results it was observed, that the analyzed dough samples behave as weak gels, and the values of storage G′ and loss G″ moduli significantly depend on angular frequency. The presence of rapeseed protein isolate caused a significant drop in the values of G′ and G″ which was accompanied by the increase of phase shift tangent. Additionally, such addition caused an increase of instantaneous and viscoelastic compliance in the system and a decrease of zero shear viscosity in comparison to the control sample. The samples were characterized by non-newtonian shear-thinning flow, and the application of rapeseed protein resulted in a drop of apparent viscosity under applied shear. Partial replacement of starch with rapeseed protein isolate caused a decrease of dough viscosity during pasting. No significant changes in freezable water could be observed due to the application of rapeseed protein isolate, and the values varied between 0.342 and 0.357 g/g. The thermograms obtained for individual samples revealed the presence of two peaks corresponding to the starch sources present in the system.

To obtain bread with a high loaf volume and homogeneous crumb, gas cells require sufficient stability until the discontinuous gas structure of dough is transformed into the continuous structure of bread. At the end of fermentation, dough gas cells are supposedly regionally separated by two air-water (A-W) interfaces and a liquid film. ‘Dough liquor’ (DL) or ‘batter liquor’ (BL), i.e. the supernatant after ultracentrifugation of dough and batter, respectively, is a model system for the fluid in these films. We report here on drainage dynamics of free-standing thin films (TFs) prepared from wheat and rye DLs and oat BL after applying a driving pressure of either 50 or 200 Pa at bulk concentrations lower than and equal to (‘native’) those in the respective supernatants obtained by ultracentrifugation. At lowered bulk concentrations, wheat and rye DL TFs were surrounded by planar and dimpled A-W interfaces, respectively, both of which were composed of weakly viscoelastic mixed protein-lipid films. In contrast, lipids stabilized dimpled oat BL TFs by migrating along their A-W interfaces and thus by generating Marangoni stresses. Liquid drainage and subsequent film rupture occurred rapidly in these TFs. At native bulk concentrations, TFs generally drained much slower and they were even found to be stable at small thicknesses (

The structural relaxation properties of high-solid gelling polysaccharides, gelatin and whey protein with small-molecule co-solutes have been reviewed focusing on the glass transition region and glassy state of the mechanical master curve. Compliance with the principle of thermorheological simplicity is established allowing horizontal superposition of viscoelastic functions in the form of small-deformation stress relaxation or dynamic oscillation modulus. Numerical calculations via the Tikhonov regularization yield smooth stress relaxation spectra over a broad timescale that encompasses the isothermal process of vitrification in these systems. Next, the molecular coupling theory addressed the polymer chain dynamics of the local segmental motions that determine the glass transition temperature (Tg) of condensed matrices. Thus a more complete picture of the physics of intermolecular interactions in the short-time region of the glass dispersion has emerged. It allows estimation of the relaxation time for local segmental motions at Tg, and the extent of cooperativity between adjacent chemical moieties governing kinetics of viscoelastic relaxation in hydrocolloid based systems at the glass transition region.

We use the framework of fractional calculus to quantify the linear viscoelastic properties of full-fat, low-fat, and zero-fat, semi-hard cheeses over a range of temperatures and water/protein ratios. These fractional constitutive models correctly predict the time-dependence and interrelation of the firmness, springiness, and rubberiness of these emulsion-filled hydrocolloidal gels. Our equations for the firmness F, springiness S, and rubberiness R, also correctly predict the effect of changing the magnitude or time-scale of the stress loading on the material even in the case of irreversible flow events, when cheese progressively transitions from a solid to a liquid. Finally we show how our FSR-equations can be used in a texture engineering context; they provide rational guidance to product reformulation studies and allow for extrapolation of a firmness measurement to practical situations in which the gel is subjected to prolonged creep loading. Keywords Rational reformulation Food gels Structure-texture engineering Constitutive model Fractional calculus Scott Blair

Viscosity-modified diet through thickeners is used as a strategy to circumvent swallowing problems by oropharyngeal dysphagia patients. Most commercial products present xanthan and starch in their formulations, but flaxseed gum (FG) is a potential thickener for liquid food that provides additional health benefits. FG was mixed either with modified starch (MS) and/or xanthan gum (XG), varying biopolymersâ concentration according to a central composite rotational design in which rheological and colour properties in water were the evaluated responses. All formulations showed a shear time-independent and shear-thinning behaviour, mainly influenced by XG and MS concentrations. In oscillatory measurements, the formulations presented a prevailing elastic character attributed to MS and mainly to XG, which despite the lower concentration in which it was incorporated, exerted a similar influence on this rheological property. However, the increase of FG concentration was the most significant factor influencing viscosity, but also favoured an increase of both viscoelastic moduli mainly G'. Analysis of the microstructure disclosed different network structures as a result of biopolymers interactions, which was related to rheological behaviour giving insights to design new thickeners for dysphagia management. In addition, the amount of glucose released after in vitro digestion was evaluated and compared to a commercial MS-based thickener. Interestingly, the commercial formulation showed a glucose release significantly higher than the proposed FG/MS/XG-based formulations. These results open the opportunity to tailor the rheological characteristics of food systems by adding and combining natural ingredients, improving technological and nutritional properties., Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (Finance code 001); São Paulo Research Foundation - FAPESP (Process numbers 2016/05448–8; 2011/51707–1; EMU 2009/54137–1; 2007/58017–5; 2006/03263–9; 2004/08517–3) and by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Process 307168/2016–6). Okuro and Santos thanks São Paulo Research Foundation (FAPESP) (Grant numbers 2018/20308–3 and 2017/18109–0), info:eu-repo/semantics/publishedVersion

The differences in viscoelastic properties of gluten from two very different wheat flours, a weak soft flour dough and a strong semolina dough, primarily caused by their gliadin and glutenin content including gliadin to glutenin ratio were studied. The doughs were subjected to oscillatory time sweep tests at small and large amplitudes as well as small and large frequencies. The gluten subunits (LMW, HMW glutenins and gliadins) tagged with specific fluorescent quantum dots with a distint excitation wavelength were imaged with confocal laser scanning microscopy and their distribution and interactions were measured. The quantitative imaging data was converted into networking data that included lacunarity, network area, and number of network junctions. This networking data was correlated with rheology. The two different dough systems showed different oscillatory behavior during time sweeps. The critical role of LMW glutenins in keeping the structural integrity of semolina doughs was demonstrated by a direct correlation between the non-linear elastic component ‘e3/e1’ of the dough and protein network parameters of LMW glutenins. It was also shown that gliadins and HMW glutenins co-localize and associate throughout rheological deformations of the dough. The disruption of the three gluten subunits are responsible for rheological breakdown of soft wheat flour dough, with gliadins influencing the breakdown of the network at higher amplitude deformations. This research presents a new method to analyze the microstructure of wheat doughs and new understanding of how the network structure of the dough subunits contribute and are correlated with fundamental rheological tests.

Chestnut starch ( Castanea sativa Mill) gels from two cultivars, Longal and Lada, showed different mechanical and rheological properties, being dependent on aging temperature. Gels were more elastic at 5 °C evidenced by the higher intensity of relaxation spectra showing a slower relaxation process. Shape of the relaxation spectra was almost insensitive to aging temperature suggesting a similar interaction at the two temperatures. Lada gels had the lowest equilibrium modulus indicating a more fragile gel in the presence of shear disturbances. Under uniaxial compression Longal gels were the most deformable before fracture and yield higher apparent Young modulus showing also a higher firmness. Both starches contained a similar amylose content but amylose leached from Longal presented a higher molecular weight being this the determinant factor for explaining the differences in viscosity, gel firmness and cold past viscosity. Longal starch presented lower gelatinization temperature range, higher peak height index, amylopectin molecular weight and degree of external organization of starch granules suggesting a more rigid swollen starch granules that contribute to the reinforcement of Longal gels. Longal amylopectin structural features such as higher abundance of short chains might explain the higher breakdown during pasting and lower gelatinization temperature. Lada higher gelatinization temperature range is in line with a higher diversity of cluster with different double helix stabilities that can be due to the heterogeneity of the side chains involved in the double helixes. Results indicate that granule properties play an important role during gelation of chestnut starch and impact on their rheological and mechanical properties.

Interfacial rheology of interfaces stabilized by food ingredients has been studied extensively within the limits of small and slow deformations, within the linear viscoelastic regime (LVR). However, in practice, products such as foams or emulsions undergo fast and large deformations during food processes such as chewing. emulsifying, or foaming. In this study, we used capillary break-up and droplet formation to observe and quantify large and fast deformations of such interfaces, in the presence of surface viscoelasticity. We studied the inertial thinning of the liquid neck during drop formation using high-speed imaging. We tested solutions of several surface active molecules, including two low molecular weight surfactants (SDS and Tween 20), two milk proteins (β-Lactoglobulin, Bovine Serum Albumin) and the saponin Escin. Escin showed the most significant effect on the shape of the neck and neck thinning dynamics. Interfacial shear rheology measurements indicated that the unusual breakup observation of Escin solutions was related to the high viscoelastic surface shear moduli. These high moduli, and the resulting more symmetric and shorter neck shape observed for the proteins and Escin, are associated with the formation of solid-like interfacial structures. However, the presence of a viscoelastic interface did not affect the inertial thinning regime, which indicates that the solid structures were broken down locally at the area of minimum radius (Rmin), and affected only the shape outside this region. The results of this work therefore, show that interfacial measurements within the LVR are not entirely representative for fast and large deformations well beyond linearity.

In recent years, food-grade Pickering particles have gained considerable interest, because of their ability to form stable emulsions and foams. Such Pickering stabilizers are often produced by aggregation of proteins, which typically results in a mixture of cross-linked particles and unbound proteins (smaller constituents). This study focuses on the possible contribution to the interfacial behaviour of these smaller constituents in whey protein isolate (WPI) bead suspensions, which are produced by cold-gelation of WPI aggregates. To understand the interfacial properties of the total mixture, we have studied the involved structures and interactions hierarchically, from native WPI, to aggregates, and finally gel beads. Air-water interfaces were subjected to large amplitude oscillatory dilatation (LAOD) and shear (LAOS) using a drop tensiometer and a double wall ring geometry. The non-linear responses were analysed using Lissajous plots. The plots of native WPI- and aggregates-stabilized interfaces showed a rheological behaviour of a viscoelastic solid, while bead-stabilized interfaces tended to have a weaker and more fluid-like behaviour. The interfacial microstructure was analysed by imaging Langmuir-Blodgett films of the protein systems using atomic force microscopy (AFM). The native WPI and aggregate films had a highly heterogeneous structure in which the proteins form a dense clustered network. The beads are randomly distributed throughout the film, separated by large areas, where smaller proteinaceous material is present. This smaller and surface-active material present in the bead suspensions plays an important role in interface stabilization, and could also largely influence the macroscopic properties of interface-dominated systems.

The steady shear and extensional rheology of aqueous guar gum solutions was studied for concentrations, C, ranging from 1 g/L to 20 g/L. Extensional rheometry measurements were made using the Cambridge Trimaster filament-stretching device. The steady shear tests indicated a transition between a semi-dilute regime, below 10 g/L, and an entangled regime at higher concentrations. The solutions were shear-thinning and obeyed the unmodified Cox–Merz rule in the dilute regime, but deviated from Cox–Merz and exhibited strongly viscoelastic behaviour at higher concentrations. The surface tension at higher concentration also deviated from the Szyszkowski model, exhibiting behaviour consistent with entanglement. The filament-thinning data did not fit the model for polymer solution behaviour presented by Entov and Hinch (1997) , but gave a good fit to a modified form where time was normalised by the time for filament break-up. This scaling was independent of concentration effects, as reported by Chesterton, Meza, Moggridge, Sadd, and Wilson (2011) for cake batters. The modified model parameters approached asymptotic values for entangled solutions. The estimated apparent extensional viscosity exhibited a peak at unit strain followed by a constant value. The former increased as Cn, where n > 1, while the latter increased linearly with C.