Oscillatory Rheological Measurements Research Articles

Ileal mucus viscoelastic properties differ in Crohn’s disease

Crohn’s disease (CD) is an inflammatory bowel disease (IBD) that can affect any part of the gastrointestinal tract, frequently involving the terminal ileum. While colonic mucus alterations in CD patients have been described, terminal ileal mucus and its mechanobiological properties have been neglected. Our study is the first of its kind to decipher the viscoelastic and network properties of ileal mucus.With that aim, oscillatory rheological shear measurements based on an airway mucus protocol that was thoroughly validated for ileal mucus were performed. Our pilot study analyzed terminal ileum mucus from controls (n=14) and CD patients (n=14). Mucus network structure was visualized by scanning electron microscopy (SEM).Interestingly, a statistically significant increase in viscoelasticity as well as a decrease in mesh size was observed in ileal mucus from CD patients compared to controls. Furthermore, rheological data were analyzed in relation to study participants’ clinical characteristics, revealing a noteworthy trend between non-smokers and smokers.In conclusion, this study provides the first data on the viscoelastic properties and structure of human ileal mucus in the healthy state and in Crohn’s disease, demonstrating significant alterations between groups and highlighting the need for further research on mucus and its effect on the underlying epithelial barrier.

Self-assembly and hydrogelation of a potential bioactive peptide derived from quinoa proteins

In this work the identification of peptides derived from quinoa proteins which could potentially self-assemble, and form hydrogels was carried out with TANGO, a statistical mechanical based algorithm that predicts β-aggregate propensity of peptides. Peptides with the highest aggregate propensity were subjected to gelling screening experiments from which the most promising bioactive peptide with sequence KIVLDSDDPLFGGF was selected. The self-assembling and hydrogelation properties of the C-terminal amidated peptide (KIVLDSDDPLFGGF-NH2) were studied. The effect of concentration, pH, and temperature on the secondary structure of the peptide were probed by circular dichroism (CD), while its nanostructure was studied by transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). Results revealed the existence of random coil, α-helix, twisted β-sheet, and well-defined β-sheet secondary structures, with a range of nanostructures including elongated fibrils and bundles, whose proportion was dependant on the peptide concentration, pH, or temperature. The self-assembly of the peptide is demonstrated to follow established models of amyloid formation, which describe the unfolded peptide transiting from an α-helix-containing intermediate into β-sheet-rich protofibrils. The self-assembly is promoted at high concentrations, elevated temperatures, and pH values close to the peptide isoelectric point, and presumably mediated by hydrogen bond, hydrophobic and electrostatic interactions, and π-π interactions (from the F residue). At 15 mg/mL and pH 3.5, the peptide self-assembled and formed a self-supporting hydrogel exhibiting viscoelastic behaviour with G' (1 Hz) ~2300 Pa as determined by oscillatory rheology measurements. The study describes a straightforward method to monitor the self-assembly of plant protein derived peptides; further studies are needed to demonstrate the potential application of the formed hydrogels in food and biomedicine.

Nanocomposite Hydrogels with Self-Assembling Peptide-Functionalized Carbon Nanostructures.

Carbon nanostructures (CNSs) are attractive components to attain nanocomposites, yet their hydrophobic nature and strong tendency to aggregate often limit their use in aqueous conditions and negatively impact their properties. In this work, carbon nanohorns (CNHs), multi-walled carbon nanotubes (CNTs), and graphene (G) are first oxidized, and then reacted to covalently anchor the self-assembling tripeptide L-Leu-D-Phe-D-Phe to improve their dispersibility in phosphate buffer, and favor the formation of hydrogels formed by the self-organizing L-Leu-D-Phe-D-Phe present in solution. The obtained nanocomposites are then characterized by transmission electron microscopy (TEM), oscillatory rheology, and conductivity measurements to gain useful insights as to the key factors that determine self-healing ability for the future design of this type of nanocomposites.

Can wormlike micelle stiffness be estimated from zero‐shear viscosity? Experimental investigation with a model system and specific salt interactions

AbstractThe microstructure of wormlike micelles (WLM) directly affects the rheological properties of their solutions. Investigating the structure–property relationships of WLM has long been a popular topic for researchers who have developed theoretical and empirical models to describe their viscoelastic behavior. All these models rely on a collection of characteristic “length” parameters that are often difficult to estimate using relatively simple rheological tests. In particular, the micelle stiffness, as described by the persistence length, can be difficult to measure experimentally, while being very impactful on the bulk rheology of WLM solutions. Here, an array of inorganic salts (NaCl, LiCl, MgCl2, NaBr, NaI, and Na2SO4) have been used to induce wormlike micelle formation in an aqueous solution of the surfactant sodium lauryl ether sulfate. Ion dissociation/association with the surfactant head groups and the hydrogen bond network of the water alters the effective stiffness of the micelles, allowing for an estimation of the stiffness using three different methods: (1) small angle neutron scattering (SANS) measurements, (2) oscillatory rheological measurements, and (3) steady rheological measurements with a thermodynamic packing parameter model. Each of these methods are then compared and shown to be consistent with each other for the micelle solutions tested. The consistency of the results across all the measurements suggests that the approach used in this study, which estimates micelle parameters using steady shear rheology and a thermodynamic model, could provide a simpler and more accessible method for estimating micelle parameters in a wide range of surfactant systems.

Random vibration of sandwich beam with a shear thickening fluid core

The dynamic performances of a sandwich beam with a shear thickening fluid (STF) core subjected to a random excitation are investigated. First, the STF is prepared and a new constitutive model is proposed based on the oscillatory rheological measurements. Next, a flexural vibration model of the sandwich beam with an STF core under random load is developed, and a parametric study is carried out. It is found that the response frequencies and damping ratios for the first three modes of the beam increase with the standard deviation of the external random excitation. The sandwich beam with STF provides better damping for larger broadband excitation. Additionally, the beam with an STF core will produce a response both inside and outside the load frequency domain. Furthermore, an optimal thickness ratio for the structure that maximizes the damping ratio of the structure is identified. It is important to note that this optimal thickness ratio of the structure varies with the order of vibration modes. This research provides valuable insights into the design of structures using STF and also contributes to the development of dynamic constitutive models for STF.

Polyglycerol‐modified polyvinyl alcohol with improved stability during thermoplastic processing

AbstractPolyvinyl alcohol (PVA), which can be synthesized via a non‐petroleum route, is a multi‐hydroxyl polymer with good comprehensive properties and environmental friendliness. However, poor thermal processability impedes its development. Herein, polyglycerol (PGL) was firstly adopted to substitute parts of glycerin as one of the plasticizers to prepare modified PVA with greater thermal stability. FTIR spectra revealed the strong hydrogen‐bonding interaction between PGL and PVA which would be destroyed during heating, indicating that PGL was suitable for plasticizing PVA. The introduction of PGL weakened the volatilization of plasticizer as T5% of modified PVA was remarkably improved from 174.7°C to 245.8°C with the addition of 20 wt% PGL. The effects of PGL content on the crystallization behaviors, melting characteristics, dynamic rheological behaviors, and mechanical properties of PVA were investigated. It revealed that the substitution of PGL for glycerin did not influence the final crystalline structure and crystallinity of PVA, but shortened the crystallization time, improved the tensile strength and decreased the melt index owing to the entanglement between PVA and PGL molecules. Dynamic oscillatory rheological measurement showed that the lowest complex viscosity was obtained when 10 wt% PGL was incorporated, which is beneficial for practical processing and film forming. Under proper processing conditions, the production and application of this hot‐blown PVA film were realized at an experimental scale. This work sheds light on the exploitation of new plasticizers with high plasticizing efficiency and thermal stability during processing of PVA.

Understanding ion-ion and ion-urea interactions in mixtures of urea and choline oxyanions salts

Rotational and oscillatory rheology, Raman, and infrared spectroscopy were used to examine the anion effect on the structure of deep eutectic solvents (DES) by contrasting reline (the 1:2 mixture of choline chloride and urea, [Chol]Cl:U) with other mixtures at the same composition based on oxyanion salts of different acceptor and donor characteristics for hydrogen bonding (choline acetate, [Chol][Ac], and choline dihydrogen phosphate, [Chol][DHP]). Oscillatory rheological measurements of [Chol][DHP] suggest the presence of hydrogen-bonded [DHP] chains that can be broken and recombined. Far-infrared spectra also show that [Chol][DHP] has stiffer dynamics when compared to the other two mixtures under investigation. The high-frequency range of the vibrational spectra provides further proof of differences in the hydrogen bond strengths across the systems under study. The fingerprint region of the vibrational spectra provides information about [Chol] and urea conformations in the presence of different anions in the liquid phase.

Cerebrosides lipids and their physical effect on multiple sclerosis membranes.

The myelin sheath is a critical component of the central nervous system (CNS) and peripheral nervous system (PNS). It is a multilamellar membrane consisting of a coiled bilayer that acts as an electrical insulator for nerve impulses traveling along axons between nerve cells. Compared to other membranes in the body, the myelin sheath contains a large lipid fraction in the range of 75-80% of the dry mass, compared to about 50% in other membranes, consisting of many different lipids. The lipids in the myelin sheath play a critical role in membrane stability and compaction. While previous investigations have used model lipid bilayers and monolayers to study their interactions with important proteins including myelin basic protein (MBP) and proteolipid protein (PLP), our understanding of the role of lipid composition on membrane formation thermodynamics and rheology, particularly the effects produced by lipid cerebrosides (Hydroxylated cerebrosides, Non Hydroxylated cerebrosides and Cerebroside sulfatide). In this presentation we study the formation and interfacial dilatational rheology of lipid monolayers. We use a Langmuir trough for both surface pressure versus area isotherms and oscillating area interfacial rheology measurements, all performed at approximately body temperature (37°C). From isotherm data, we calculate differences in the Gibbs free energy of mixing between the four monolayers to show differences in intermolecular interactions and miscibility. These results are used to support observations in interfacial rheology results, where. We also analyze the nonlinear rheological behavior of the monolayers, for example observing in general film softening during compression and expansion. These first oscillatory interfacial rheology measurements of model myelin monolayers, coupled with the thermodynamic analysis of film formation, improve our understanding of the lipid the film properties, and provide clues to how the changes in lipid composition may lead to demyelination.

Soybean oleosome-based oleogelsviapolymer-bridging based structuring. Mechanical properties at large deformations

Oleosomes have emerged in the last decade as a multipurpose oil-in-water emulsion suitable for engineering new lipids materials. The need to increase alternative and sustainable methods to modulate the rheological properties of emulsions has been the leading research interest in the oleogelation field. Soybean oleosomes are evaluated as building blocks for creating oleogels in combination with sodium alginate or ι-carrageenan as the structuring elements. Polymer bridging provides a route to produce compact soft, malleable gels by exploiting attractive electrostatic interactions between negatively charged polysaccharides and oleosome surfaces. We investigated the viscoelastic properties of concentrated polymer bridged gels by oscillatory rheological measurements. The rheological characteristics are governed predominantly by the type of polysaccharide and by the ratio between polysaccharide and oleosome content. One yielding step at low strains indicates the breaking of polysaccharide bridging bonds and was visible in all samples. A two-step yielding process, where the second step corresponds to the cage-breaking process, was present at polysaccharide/oleosome ratios where optimum bridging occurs for alginate and carrageenan, 0.005 g/g, 0.01 g/g, respectively. Nonetheless, the bumps corresponding to the second yielding point were more prominent in alginate gels than in carrageenan gels due to the greater bridging ability of alginate. Identifying these rheological hallmarks could provide new ideas towards the improved design of plant-based fatty food products,e.g., cream cheeses and vegan sausages surrogates.

Detecting Early-Stage Cohesion Due to Calcium Silicate Hydration with Rheology and Surface Force Apparatus.

Extremely robust cohesion triggered by calcium silicate hydrate (C-S-H) precipitation during cement hardening makes concrete one of the most commonly used man-made materials. Here, in this proof-of-concept study, we seek an additional nanoscale understanding of early-stage cohesive forces acting between hydrating model tricalcium silicate (C3S) surfaces by combining rheological and surface force measurements. We first used time-resolved small oscillatory rheology measurements (SAOSs) to characterize the early-stage evolution of the cohesive properties of a C3S paste and a C-S-H gel. SAOS revealed the reactive and viscoelastic nature of C3S pastes, in contrast with the nonreactive but still viscoelastic nature of the C-S-H gel, which proves a temporal variation in the cohesion during microstructural physicochemical rearrangements in the C3S paste. We further prepared thin films of C3S by plasma laser deposition (PLD) and demonstrated that these films are suitable for force measurements in the surface force apparatus (SFA). We measured surface forces acting between two thin C3S films exposed to water and subsequent in situ calcium silicate hydrate precipitation. With the SFA and SFA-coupled interferometric measurements, we resolved that C3S surface reprecipitation in water was associated with both increasing film thickness and progressively stronger adhesion (pull-off force). The lasting adhesion developing between the growing surfaces depended on the applied load, pull-off rate, and time in contact. These properties indicated the viscoelastic character of the soft, gel-like reprecipitated layer, pointing to the formation of C-S-H. Our findings confirm the strong cohesive properties of hydrated calcium silicate surfaces that, based on our preliminary SFA measurements, are attributed to sharp changes in the surface microstructure. In contact with water, the brittle and rough C3S surfaces with little contact area weather into soft, gel-like C-S-H nanoparticles with a much larger surface area available for forming direct contacts between interacting surfaces.

A multifunctional ultra-thin acoustic membrane with self-healing properties for adaptive low-frequency noise control

This paper proposes a novel multifunctional ultra-thin membrane based on a Polyborosiloxane-based gel with stimuli-responsive sound absorption and sound transmission loss (STL) and characterised by excellent self-healing properties. This adaptive behaviour is the result of a dynamically activated phase transition in the membrane’s polymeric network which is given by the interaction with the travelling sound pressure wave. The presence and the extent of such phase transition in the material was investigated via oscillatory rheological measurements showing the possibility to control the dynamic response by modifying the Boron content within the polymer. Acoustic analyses conducted at different stimuli responses showed high and dynamic absorption (95%) at the absorption coefficient peaks and an adaptive shift to lower frequencies while sound amplitudes were increased. An average STL up to 27 dB in the frequency range between 500 to 1000 Hz was observed and an increased STL above 2 dB was measured as the excitation amplitude was increased. Results demonstrated that the new membrane can be used to develop deep subwavelength absorbers with unique properties (1/54 wavelength in absorption and 1/618 in STL) able to tune their performance in response to an external stimulus while autonomously regaining their properties in case of damage thanks to their self-healing ability.

The impact of thermomechanical and chemical treatment of waste Brewers’ spent grain and soil biodegradation of sustainable Mater-Bi-Based biocomposites

Due to the massive plastic pollution, development of sustainable and biodegradable polymer materials is crucial to reduce environmental burdens and support climate neutrality. Application of lignocellulosic wastes as fillers for polymer composites was broadly reported, but analysis of biodegradation behavior of resulting biocomposites was rarely examined. Herein, sustainable Mater-Bi-based biocomposites filled with thermomechanically- and chemically-modified brewers’ spent grain (BSG) were prepared and subjected to 12-week soil burial test simulating their biodegradation in natural environment. BSG stabilizing effect on polymer matrix affected by the content of melanoidins and antioxidant phytochemicals, along with the impact of diisocyanate applied to strengthen the interfacial adhesion. Biocomposites showed 25–35 wt% mass loss over 12 weeks resulting from swelling of BSG filler and sample microcracking, which increased surface roughness by 247–448 %. The degree of decomposition was partially reduced by BSG modifications pointing to the stabilizing effect of melanoidins and phytochemicals, and enhanced interfacial adhesion. Soil burial-induced structural changes enhanced biocomposites’ thermal stability determined by thermogravimetric analysis shifting decomposition onset by 14.4–32.0 °C due to the biodegradation of lower molecular weight starch macromolecules confirmed by differential scanning calorimetry. For unfilled Mater-Bi, it caused an average 32 % reduction in complex viscosity and storage modulus captured by oscillatory rheological measurements. Nonetheless, the inverse effect was noted for biocomposites where modulus increased even by one order of magnitude due to the swelling of BSG particles and amorphous phase decomposition. Presented results indicate that BSG promotes soil degradation of Mater-Bi and its rate can be engineered by biofiller treatment elaboration.

Research on viscoelastic properties of SLG-LHSB system: Effects of pH and concentration on micelles in the system

The pH and the state of SLG in aqueous solution are strongly connected. When the pH was below 5.5, it would be transformed into N-lauroyl glutamic acid (LGA) with limited solubility; when the pH was between 5.5 and 6.5, SLG was the major component in the system; and when the pH was above 6.5, disodium lauroyl glutamate predominated (DLG). Because SLG and lauramidopropyl hydroxy sulfobetaine (LHSB, also known as lauramidopropyl hydroxy Sultaine) can combine to generate mixed micelles that can solubilize insoluble materials, the compound system outperformed the single system in terms of dissolving. The viscosity of the SLG and LHSB compound system changed dramatically with pH, corresponding to the change in SLG components with pH. The viscoelastic properties of the composite system were investigated by using steady-state and oscillatory shear sweep rheological measurements. The zero-shear viscosity (η0) had a strong dependence on the concentration of the compound system. The compound system began to form worm-like micelles at 0.05 mol/L. When the system concentration hit 0.35 mol/L, the worm-like micelles began to break, and their length reduced while their quantity rose. (Cryogenic-transmission electron microscopy (Cryo-TEM) confirmed the formation of worm-like micelles. The system demonstrated benign features and outstanding foaming performance in the foam performance and irritation tests.

An optimized protocol for assessment of sputum macrorheology in health and muco-obstructive lung disease

Background: Airway mucus provides important protective functions in health and abnormal viscoelasticity is a hallmark of muco-obstructive lung diseases such as cystic fibrosis (CF). However, previous studies of sputum macrorheology from healthy individuals and patients with CF using different experimental protocols yielded in part discrepant results and data on a systematic assessment across measurement settings and conditions remain limited. Objectives: The aim of this study was to develop an optimized and reliable protocol for standardized macrorheological measurements of airway mucus model systems and native human sputum from healthy individuals and patients with muco-obstructive lung disease. Methods: Oscillatory rheological shear measurements were performed using bovine submaxillary mucin (BSM) at different concentrations (2% and 10% solids) and sputum samples from healthy controls (n = 10) and patients with CF (n = 10). Viscoelastic properties were determined by amplitude and frequency sweeps at 25°C and 37°C with or without solvent trap using a cone-plate geometry. Results: Under saturated atmosphere, we did not observe any temperature-dependent differences in 2% and 10% BSM macrorheology, whereas in the absence of evaporation control 10% BSM demonstrated a significantly higher viscoelasticity at 37°C. Similarly, during the measurements without evaporation control at 37°C we observed a substantial increase in the storage modulus G′ and the loss modulus G″ of the highly viscoelastic CF sputum but not in the healthy sputum. Conclusion: Our data show systematically higher viscoelasticity of CF compared to healthy sputum at 25°C and 37°C. For measurements at the higher temperature using a solvent trap to prevent evaporation is essential for macrorheological analysis of mucus model systems and native human sputum. Another interesting finding is that the viscoelastic properties are not much sensitive to the applied experimental deformation and yield robust results despite their delicate consistency. The optimized protocol resulting from this work will facilitate standardized quantitative assessment of abnormalities in viscoelastic properties of airway mucus and response to muco-active therapies in patients with CF and other muco-obstructive lung diseases.

Anomalous rheological aging of a model thermoreversible colloidal gel following a thermal quench.

We investigate the aging behavior in a well-studied model system comprised of a colloidal suspension of thermoreversible adhesive hard spheres (AHS) but thermally quenched below the gel transition to much larger depths than previously studied. The aging behavior in the model AHS system is monitored by small amplitude oscillatory shear rheology measurements conducted while rapidly quenching from the liquid state at 40 °C to a temperature below the gel temperature, and new, anomalous aging behaviors are observed. Shallow quenches lead to monotonic development of the elastic modulus with time, consistent with prior reports for the development of a homogeneous gel [Gordon et al., J. Rheol. 61, 23-34 (2017)]. However, for deeper quenches, a unique and new phenomenon is reported, namely, after an initial rise in the modulus, a reproducible drop in the modulus is observed, followed by a plateau in the modulus value. This drop can be gradual or sudden and the extent of the drop depends on the quench depth. After this drop in the modulus, AHS gel evolves toward a quench-path independent state over the experimental timescale. These effects of the extent of quenching on aging behavior are hypothesized to be a consequence of quenching into different underlying thermodynamic states of colloidal gels and the possible influence of the adhesive glass dynamical arrest for the deepest quenches. The research connects homogeneous gelation with heterogeneous gel formation due to phase separation and shows that the extent of quench can be used as an independent parameter to govern the rheological response of the arrested gel.

Application of small amplitude oscillatory rheology measurements for estimating residual rennet activity in rennet whey

The relationship between (very low) rennet activity (RA) levels and rennet coagulation time (RCT) is non-linear, and its determination is time consuming, with accuracy depending on an objective RCT. Here, RCT was determined by small amplitude oscillatory rheology and the Carlson, Hill and Olson's spiking technique was modified to estimate the unknown residual RA directly from a linear calibration curve of RCT against 1/RA created using the serum phase of the reconstituted skim milk (RSM) utilised for preparation of the rennet whey. The estimated residual RA mL−1 of the rennet whey could be obtained by spiking the rennet whey with a known RA derived from the linear range of the calibration curve. This observation was confirmed by a commonly used reverse-phase high-performance liquid chromatography (RP-HPLC) method. Using this information, a simple general model that estimates RA partitioning based on total volume of whey separated from the curd could be proposed.

Rheological properties of polysaccharides from Pholiota nameko with different temperature extraction: Concentration, pH, temperature, and saltion.

Cold and hot water extracted polysaccharides (CW-PNPs and HW-PNPs) were isolated from Pholiota nameko. The rheological properties of PNPs were investigated by steady shear and oscillatory rheological measurements. The PNPs exhibited typical non-Newtonian and shear-thinning behavior, which are affected by PNP concentration, temperature, pH value, salt ion, and concentration. Specifically, the apparent viscosity of the two PNPs solutions at concentration of 1% (w/w) was shown as HW-PNPs>CW-PNPs. The apparent viscosity of PNPs decreases under acidic and alkaline conditions and when the temperature rises; K+ and Na+ cause the apparent viscosity of CW-PNPs to decrease, while Ca2+ and Al3+ are opposite. The addition of four different salt ions all caused the apparent viscosity of the HW-PNPs to decrease. The results of dynamic rheological experiments show that G' and G″ showed slightly frequency dependency with G' exceeding G″ throughout the accessible range of frequency for CW-PNPs and HW-PNPs.

Characterization of composite active edible film functionalized through reinforced Pimpinella anisum essential oil

This work aimed to develop biobased composite active edible film of tapioca starch-κ-carrageenan reinforced with Pimpinella anisum essential oil and to evaluate the effect of reinforcement on physico-mechanical, barrier, optical, and antimicrobial properties. Nineteen different components of oil were identified with distinct chromatogram peaks using Gas Chromatography–Mass Spectroscopy. The Minimum Inhibitory Concentration value of essential oil against standard test bacteria ranged between 0.6% and 1%. The dynamic oscillatory rheological measurements of film-forming solution revealed solid-like viscoelastic behavior. Incorporation of oil in the film caused significant (p < 0.05) increase in moisture absorption, b value, total color difference (∆E) haziness, transparency, and significant (p < 0.05) decrease in elongation at break, moisture, whiteness index, and L* value. Antimicrobial functionality by disc diffusion of treated films was found highly significant (p < 0.01). The results of the study provide a promising potential of composite active edible film with enhanced antimicrobial functionality. Novelty impact statement The new-fangled bio composite blend is functionalized with Pimpinella anisum essential oil. The study originally demonstrates the effect of incorporation of P. anisum essential oil on the quality and acceptability of unique bio-composite edible film. The formed composite active edible film can be commercially exploited to provide better quality and safety to various foods with eco-friendly disposal.

Evaluation of the Physical Stability of Starch-Based Hydrogels Produced by High-Pressure Processing (HPP).

Starch-based hydrogels are natural polymeric structures with high potential interest for food, cosmeceutical, and pharmaceutical applications. In this study, the physical stability of starch-based hydrogels produced via high-pressure processing (HPP) was evaluated using conventional and accelerated methods. For this purpose, conventional stability measurements, namely swelling power, water activity, texture, and organoleptic properties, as well as microbiological analysis of rice, corn, wheat, and tapioca starch hydrogels, were determined at different time intervals during storage at 20 °C. Additionally, to assess the stability of these structures, accelerated tests based on temperature sweep tests and oscillatory rheological measurements, as well as temperature cycling tests, were performed. The experimental results demonstrated that the physical stability of starch-based HPP hydrogels was interdependently affected by the microorganisms’ action and starch retrogradation, leading to both organoleptic and texture modifications with marked reductions in swelling stability and firmness. It was concluded that tapioca starch hydrogels showed the lowest stability upon storage due to higher incidence of microbial spoilage. Accelerated tests allowed the good stability of HPP hydrogels to be predicted, evidencing good network strength and the ability to withstand temperature changes. Modifications of the rheological properties of corn, rice, and wheat hydrogels were only observed above 39 °C and at stress values 3 to 10 times higher than those necessary to modify commercial hydrogels. Moreover, structural changes to hydrogels after cycling tests were similar to those observed after 90 days of conventional storage. Data obtained in this work can be utilized to design specific storage conditions and product improvements. Moreover, the accelerated methods used in this study provided useful information, allowing the physical stability of starch-based hydrogels to be predicted.

Pectins with commercial features and gelling ability from peels of Hylocereus spp

Peels of edible fruits from Hylocereus genus have been investigated as possible sources of pectins. In the present study, peels of H. undatus (red peel and white pulp) and H. costaricencis (red peel and red pulp) were extracted using the enzyme preparation Celluclast® (111 μL/g, pH 5, 50 °C for 1.5 h) and conventional acid extraction (boiling 0.1 M nitric acid for 60 min). The monosaccharide composition and the degree of methyl-esterification (DM) were determined by chromatographic and spectroscopic methods. It was possible to obtain pectins with GalA ≥65% from H. undatus and H. costaricencis peels by acid and enzymatic extractions with similar yields. Pectins obtained by acid extraction had higher DM (>50%) and GalA content. The enzymatic extraction resulted in pectins with DM < 50% and higher molar mass. High methoxyl pectins obtained by acid extraction were characterized by NMR analysis. Oscillatory rheological measurements showed they were able to form gel at concentration ≥1% (w/w), 60% sucrose at pH 2.5. Comparing the two species, the pectin obtained from H. undatus peels had longer side chains, higher DM and molar mass than the pectin from H. costaricencis peels. It was demonstrated for the first time that pectins with commercial features can be obtained from peels of H. undatus and H. costaricencis by acid extraction.