Decrease In Gel Strength Research Articles

Effect of Dry Heating on Physicochemical Properties of Pregelatinized Rice Starch

Japonica and indica rice starches (10% w/w) were pregelatinized in a boiling water bath for 5 or 10 min and subsequently heat‐treated in a dry state for 0, 1, 2, or 3 h at 130°C to examine the effects of dry heating on pasting viscosity, paste clarity, thermal properties, X‐ray diffraction pattern, and gel strength of pregelatinized starches. Heat treatment obviously changed the physicochemical properties of pregelatinized rice starch. The pregelatinized rice starches had higher peak viscosity and final viscosity than the corresponding native rice starches. Heat treatment of pregelatinized rice starch for 1 h increased the peak viscosity, but treatment for 2 or 3 h decreased the peak viscosity compared with the unheated pregelatinized rice starch. The indica rice starch exhibited more substantial changes in pasting viscosity than did japonica rice starch during heat treatment. The melting enthalpy of the endothermic peak occurred at 90–110°C, and the intensity of the X‐ray diffraction peak at 20° was increased by dry heating, possibly owing to the enhanced amylose‐lipid complexes. The dry heat treatment of pregelatinized starch caused an increase in paste clarity and a decrease in gel strength.

Degradable thermosensitive injectable hydrogels with two-phase composite structure from aqueous solutions of poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene-1,3-dioxepane)—poly(ethylene glycol) triblock copolymers and biopolymers

Novel degradable thermosensitive injectable hydrogels with two-phase composite structure and improved mechanical strength were prepared by adding sodium alginate or dextran to the aqueous solution of a hydrolytically degradable ABA triblock copolymer with poly(ethylene glycol) middle block and poly(N-isopropylacrylamide) containing in-chain ester groups as side blocks. The two-phase structure, demonstrated by SEM measurements, resulted as a consequence of the triblock copolymer-biopolymer incompatibility. The biopolymer addition decreased the gelation temperature (T gel) and strongly improved the viscoelastic properties of the resulted hydrogel, whose behavior at 37 °C turned from liquid-like to a gel-like one. The composite hydrogels displayed low gelation time and high stability (i.e., no sign of syneresis after 42 days) at 37 °C. They partially degraded in PBS at 37 °C as a consequence of the hydrolysis of the in-chain ester groups of the thermosensitive blocks, leading to a progressive increase of T gel and decrease of gel strength. The ability of the composite hydrogels to control the release rate of drugs was tested in PBS at 37 °C by employing 5-flurouracil (5FU) and chlorambucil (CLB) as model drugs with different hydrophilicity. 5FU displayed a pretty fast release rate, unlike CLB whose release rate was much slower, no effect of the biopolymer nature being noticed. During the drug release experiments, the hydrogels showed a moderate mechanical stability, although higher than in the absence of the biopolymer, and also progressively dissolved within 12–17 days because of the hydrogel erosion phenomenon, probably accelerated by the partial degradation of the triblock copolymer.

Физические свойства инкапсулированных форм биологически активных веществ в процессе ферментативного гидролиза in vitro

This work deals with evaluation of possibility of encapsulated form of essential fatty acids development and their behavior during the enzymatic hydrolysis. Studies on the degree of swelling show that all capsules are reduced in size in “artificial stomach” due to the protonation of the free carboxylate groups of plant biopolymer used as the wall material, while capsules in the conditions of “artificial gut” showed swelling (? 40%). Observations showed that changes in the size of capsules containing 20 and 40% of essential fatty acids were similar. It has been revealed that increasing of the content of fatty acids leads to a decrease in gel strength and, consequently, a decrease in Young’s modulus. During the intestinal phase, Young’s modulus of the encapsulated form was not statistically different due to swelling and fragmentation of the polymer network. The data obtained allow considering the designed capsules as a protective material to prevent oxidation of essential fatty acids and their controlled delivery.

Extraction and Characterization of Refined K-carrageenan of Red Algae [Kappaphycus Alvarezii (Doty ex P.C. Silva, 1996)] Originated from Karimun Jawa Islands

The properties of refined κ-carrageenan (RC) extracted from red algae originated from Karimun Jawa Island has never been studied. The objective of this research was determining the effect of KCl on characteristic of refined κ-carrageenan extracted from the red algae [Kappaphycus alvarezii (Doty ex P.C. Silva, 1996)]. The result indicated that higher KCl concentration resulted in the increase of the carrageenan yield, ash and sulphate content, and the decrease of gel strength, moisture and acid-insoluble ash content. The carrageenan viscosity demontrated a fluctuated value due to KCl concentration. This study suggested extraction process by using 2.5% KCl solution. The carrageenan yield was 34.3% and the result demonstrated the carrageenan properties as follow: 8.20 cP viscosity, 94.45g · cm–2 gel strength, 6.3% moisture content, 59.4% ash content, 1.78% acid-insoluble ash, and 7.75% sulphate content. The absrbance peak at 849 cm–1 detected from infrared spectrscopy indicated D-galactose-4-sulphate which is related with κ-carrageenan.

A comparison of endogenous and microbial proteolytic activities during fast fermentation of silver carp inoculated with Lactobacillus plantarum

The study was aimed to investigate different roles of endogenous and Lactobacillus plantarum proteases during fast fermentation of silver carp. The results show that endogenous proteases could degrade both sarcoplasmic and myofibrillar proteins. In contrast, L. plantarum had low proteinase activities and could only hydrolyze sarcoplasmic peptides. This indicates that gel properties could be mainly affected by endogenous proteolysis while microbial proteolysis contributed to the production of smaller peptides and free amino acids which may be related to flavor and taste. Texture and free amino acid analyses verified these hypotheses. It shows that endogenous lysosomal proteases were the major contributors for the decrease of gel strength while L. plantarum proteolytic activities could lead to the increase of aspartic acid, glutamic acid, and alanine, which may result in umami and sweet taste; and also lead to a rise in some amino acids which were volatile compounds precursors.

Effect of ethanolic extract of coconut husk on gel properties of gelatin from swim bladder of yellowfin tuna

The impacts of ethanolic extract from coconut husk (EECH) rich in tannic acid at different levels (0.25, 0.5, 0.75, 1, 2, 3 and 5 mg g−1 dry gelatin) on gel properties of gelatin from yellowfin tuna swim bladder were investigated. Gel strength of gelatin increased when EECH concentrations increased up to 0.5 mg g−1 (p < 0.05). Nevertheless, the gradual decrease in gel strength was found with increasing EECH levels. When EECH at different levels was incorporated, no marked changes in protein patterns determined by SDS-PAGE were observed, suggesting that most of bondings were hydrogen bond or other weak bonds. Gel matrix with uniformity and larger strands were observed with gels added with 0.5 EECH mg g−1. Gelling and melting temperatures were also increased when EECH at a level of 0.5 mg g−1 was incorporated. The color of all gelatin gels slightly increased with increasing concentrations of EECH. Therefore, ethanolic extract from coconut husk at an appropriate level could act as a natural gel enhancer of gelatin.

Novel Gel with Controllable Strength for In-Depth Conformance Control: Bulk Gelation Performance and Propagation Properties in Porous Media

Polymer gel has been widely used to control excessive water production in mature oilfields. However, in view of reservoir conditions characterized by serious heterogeneous thick oil layers, high strength and in-depth propagation are required of polymer gel to achieve good treatment efficiency. Based on the concept of in-depth conformance control, a novel gel with controllable strength composed of polymer, resorcinol/hexamethylenetetramine (HMTA), acetic acid and gel strength modifier was developed. The effects of component concentrations on bulk gelation properties were investigated. The microstructures of conventional gel and novel gel at different aging time were studied by scanning electron microscopy (SEM), which can provide insight into the mechanism of controllable gel strength. Moreover, sandpack flow experiments were carried out on sandpacks (Φ2.5 × 100 cm) with multi-point pressure taps to investigate whether the novel gel can propagate in porous media. Compared with the conventional gel, SEM results showed that the three-dimensional network structure of novel gel was weakened more seriously, resulting in the decrease of gel strength. Due to decreased gel strength at different aging time, the novel gel can propagate in porous media to achieve in-depth conformance control.

The gelation of oil using ethyl cellulose.

The characterization of the thermo-gelation mechanism and properties of ethyl cellulose/canola oil oleogels was performed using rheology and thermal analysis. Thermal analysis detected no evidence for thermal transitions contributed to secondary conformational changes, suggesting a gelation mechanism that does not involve secondary ordered structure formation. Rheological analysis demonstrated a relationship between the polymer molecular weight and the final gel strength, the cross-over behavior as well as the gel point temperature. Increasing polymer molecular weight led to an increase in final gel strength, the modulus at cross-over, and the gel point temperature. Cooling/heating rates affect gel modulus only for the low molecular weight samples. A decrease in gel strength with increasing cooling rate was detected. The cross-over temperature was not affected by the cooling/heating rates. Cooling rate also affected the gelation setting time where slow cooling rates produced a stable gel faster.

Protein–Peptide Interaction: Study of Heat-Induced Aggregation and Gelation of β-Lactoglobulin in the Presence of Two Peptides from Its Own Hydrolysate

Two peptides, [f135-158] and [f135-162]-SH, were used to study the binding of the peptides to native β-lactolobulin, as well as the subsequent effects on aggregation and gelation of β-lactoglobulin. The binding of the peptide [f135-158] to β-lactoglobulin at room temperature was confirmed by SELDI-TOF-MS. It was further illustrated by increased turbidity of mixed solutions of peptide and protein (at pH 7), indicating association of proteins and peptides in larger complexes. At pH below the isoelectric point of the protein, the presence of peptides did not lead to an increased turbidity, showing the absence of complexation. The protein-peptide complexes formed at pH 7 were found to dissociate directly upon heating. After prolonged heating, extensive aggregation was observed, whereas no aggregation was seen for the pure protein or pure peptide solutions. The presence of the free sulfhydryl group in [f135-162]-SH resulted in a 10 times increase in the amount of aggregation of β-lactoglobulin upon heating, illustrating the additional effect of the free sulfhydryl group. Subsequent studies on the gel strength of heat-induced gels also showed a clear difference between these two peptides. The replacement of additional β-lactoglobulin by [f135-158] resulted in a decrease in gel strength, whereas replacement by peptide [f135-162]-SH increased gel strength.

Effects of starches on the textural, rheological, and color properties of surimi–beef gels with microbial tranglutaminase

In order to evaluate effects of starches (corn starch, potato starch, and tapioca starch) on the characteristics of surimi–beef gels with microbial transglutaminase, the cooking loss, gel strength, color and rheological properties of samples were investigated. Results demonstrated that starches gave negative effects on the cooking loss of surimi–beef gels. The gel with corn starch had the highest cooking loss while that with tapioca starch showed the lowest value. The gel with potato starch obtained the highest gel strength. During the sol–gel transitions, surimi–beef complexes with 3% corn starch exhibited the highest storage modulus value, while that with 3% tapioca starch had the lowest one. The addition of starch caused the increase of L* values of surimi–beef gels. Results showed that the excessive amount of starch resulted in the decrease in gel strength of surimi–beef gels.

Atomization characteristics of impinging jets of gel material containing nanoparticles

We have investigated the spray and atomization behavior of 0.35% C934 Carbopol gels with or without 15 wt.% SUS304 nanoparticles of 100 nm using a doublet like-on-like impinging jet system (orifice diameter of 0.7 mm, impingement angle 2 θ of 90°) and compared with the spray behavior of water. The spray patterns of gel materials were qualitatively different from those of water and could be divided into four types: open rim and no shedding drop; rimless sheet with ray shaped shedding; sheet with ligament separation; fully developed. The sheet sizes of water and the pure Carbopol gel increased with the increase in jet velocity, but the sheet size of the Carbopol gel containing SUS particles did not change with the increase in velocity. The aspect ratio ( L max/ W max) of the sheet was constant at 2.1 for water and 1.7 for two gel materials. Due to the high viscosity of gel materials, the amplification of sinusoidal waves was mitigated and the spreading angle was smaller when compared with water. The breakup length of the pure Carbopol gel was longer than that of water. However the breakup length of the Carbopol gel containing SUS particles was remarkably shorter than that of the pure Carbopol gel due to the increase in impact energy by the heavy particles as well as the decrease in gel strength by the addition of nanoparticles. The drop Sauter mean diameter (SMD) decreased with the increase in jet velocity, and it converged to an asymptotic value. The asymptotically convergent drop SMD of water was about 100 μm while that of Carbopol gels was 75–77 μm. The elasticity of gels appears to reduce the asymptotic drop size.

Mixtures of whey protein microgels and soluble aggregates as building blocks to control rheology and structure of acid induced cold-set gels

Whey proteins (WP) today offer an extremely high potential for innovative development of functional and nutritious food products. Acid cold-set gels present an interesting approach of gelation at low temperature upon acidification of preformed whey protein (WP) aggregates. In the present work, we aimed to demonstrate how structure and rheological properties of acid gels can be controlled by combining two types of WP aggregates with different structural and chemical properties. Whey protein microgels (WPM) and soluble aggregates (WPSA) were generated upon heating WP isolate in specific pH conditions and temperature, leading to Z-average hydrodynamic diameters close to 270 nm for WPM and 100 nm for WPSA. Mixtures of WPM and WPSA were prepared at different weight ratios ranging from 100% WPM to 100% WPSA. The total protein concentration was set to 4 or 8%wt. Acidification was performed at 40 °C by addition of 1%wt glucono-δ-lactone (GDL). Gelation was followed using turbidimetry and small deformation rheology as function of pH. Microstructures of the gel were investigated at different length scales using various microscopy techniques (CLSM, SEM, AFM). When the WPM/WPSA ratio decreased, the pH of gelation and the gel strength increased because of the different structure and chemical reactivity of the two types of WP aggregates. The final pH had a strong impact on the structure of the gels. When final pH decreased below pH 4.3, a structure change was suggested by turbidimetry measurements. This resulted in a non self-supporting gel or in a decrease of gel strength. For pH above 4.3, self supporting gel were obtained. The rheological properties of the gel could therefore be modulated depending on the properties of the building blocks used (WPM versus WPSA). Interestingly, the gel microstructures observed for WPM/WPSA mixtures or WPM were comparable to those of acidified skimmed milk gels ranging from coarse structures with clumps of aggregates or to homogeneous fine networks (WPSA only) that have been described for WP gels obtained upon direct heating at various pH.

Original article: Gel properties of red tilapia surimi: effects of setting condition, fish freshness and frozen storage

SummaryThis study aimed to determine effects of setting condition, fish freshness and storage time of frozen surimi on properties of red tilapia surimi gel. To investigate the effect of setting condition, a combination of eight setting temperatures (35–70 °C) and four setting times (30–120 min) was used. Maximum breaking force, deformation and gel strength were obtained after the gel had been set at 40 °C for 90 or 120 min. Setting at 65 °C resulted in the lowest obtained gel strength, because of proteolytic degradation of myosin heavy chain. Increasing storage time of raw fish material in ice caused a significant decrease in gel strength of the resultant surimi gel (P &lt; 0.05). Gels produced from surimi kept in frozen storage for up to 9 months also exhibited reduced gel strength, with a concomitant increase in the expressible drip, with increasing storage time (P &lt; 0.05).

HIGH METHOXYL PECTIN/APPLE PARTICLES COMPOSITE GELS: EFFECT OF PARTICLE SIZE AND PARTICLE CONCENTRATION ON MECHANICAL PROPERTIES AND GEL STRUCTURE

ABSTRACT In order to study the effect of fruit pulp on the structure of fruit jams, they were modeled as composites with a high‐methoxyl pectin (HMP) gel matrix filled with apple particles. The effect of particle concentration (0, 1 and 2 wt%) and particle size (small: &lt;125 µm, and large: 125–850 µm) on a pectin gel (0.5 wt% HMP, 65 wt% glucose, pH 3.0, 0.1 M citrate buffer) were studied. Rheological measurements showed that increasing concentration of small particles produced a significant increase in the elastic modulus of the composite gels. Penetration tests showed that 1 wt% small particles produced a significant decrease of gel strength, rupture strength, adhesiveness and brittleness. Increasing particle size produced a further decrease of these properties (only significant for gel strength). When concentration of small particles was raised to 2 wt%, these parameters (except brittleness) increased back to the control sample (0% particles) values.PRACTICAL APPLICATIONSKnowledge of the effect of fruit particles on the structure of pectin gels would allow controlling the rheological and mechanical properties of fruit jams in terms of the size and concentration of fruit pulp used in their formulation.

Rheological behavior of gel of xanthan with seed galactomannan: Effect of hydroalcoholic–ascorbic acid

The rheological properties of a physically linked hydroalcoholic gel obtained from a binary system consisting of xanthan and of galactomannan from the seeds of Mimosa scabrella (X:GB) with a low Man:Gal ratio of 1.1:1 were compared to those of guar gum (Man:Gal ratio 1.5:1, X:GG). The rheological analysis demonstrated an improvement of strength of X:GB and X:GG hydrogels after dispersion of the polysaccharides in buffer with 1,2-propanediol. The addition of ascorbic acid to these hydrogel formulations resulted in a slight decrease of gel strength. Both hydrogels presented rheological stability over 12 weeks at ambient temperature.

Nonlinear rheological properties and stability of dibenzylidene sorbitol fiber networks in poly(propylene oxide)

Dibenzylidene sorbitol (DBS) is known to gel organic liquids and polymers such as poly(propylene oxide) (PPO) by forming long fibers and fiber networks. Potential applications of these networks depend on their ability to withstand large deformations without significant morphological changes. Therefore, we studied the nonlinear rheological properties of the DBS fiber network in PPO for different DBS concentrations. We found that the concentration dependence of critical deformation (transition from linear to nonlinear viscoelastic region) and gel strength (G′ plateau in the linear region) can be explained on the basis of a model for densely cross-linked fiber gels (MacKintosh et al., Phys Rev Lett 75:4425–4428, 1995). Performing periodic strain sweeps, we found that the decrease in gel strength during the deformation cycles can be ascribed to reversible fiber coarsening. Additionally, start-up experiments showed a strong shear thinning behavior, which is in quantitative agreement with the SGM model (Sollich, Phys Rev E 58:738–759, 1998).

Controlled release of doxorubicin from thermosensitive poly(organophosphazene) hydrogels

Thermosensitive poly(organophosphazenes) bearing hydrophobic isoleucine ethyl esters group and hydrophilic α-amino-ω-methoxy-poly(ethylene glycol) of the molecular weight 550 along with hydrolysis-sensitive glycyl lactate ethyl esters have been synthesized for sustained delivery of anticancer drug. The aqueous solution of poly(organophosphazenes) containing doxorubicin, that represents chemotherapeutic agent for cancer treatment, was transformed into hydrogel with good gel strength at body temperature via hydrophobic interactions. Solubility of hydrophobic doxorubicin in the aqueous poly(organophosphazene) solution was dramatically improved as compared with that in PBS (0.01 M, pH 7.4). The hydrogel property of poly(organophosphazenes) was affected on incorporation of doxorubicin, resulting in increase of gelation temperature and decrease of gel strength. The release of loaded doxorubicin from the polymer hydrogel was significantly sustained over 20 days and the effect of gel strength, polymer concentration and drug concentration on the release rate were observed. The release of doxorubicin from the polymer gels was effectively controlled by the gel strength. As a result of investigating anticancer efficacy using cancer cell line of mouse lymphoblast of P388D1, the efficacy of doxorubicin was observed to be constant over a prolonged period of times for more than 30 days, indicating that the release of doxorubicin was sustained for a long time without any initial burst release, and that the delivery system was an excellent candidate for locally injectable gel–depot system.

Effect of ageing time on chemical and rheological evolution in γ-Al 2O 3 slurries for dip-coating

The evolution during ageing time of a suspension of a submicronic γ-Al 2O 3 powder with HNO 3/Al 2O 3 = 2.16 mmol/g and H 2O/Al 2O 3 = 3.2 ml/g has been studied. The physico-chemical and rheological evolution has been followed up to 48 h of ageing. Surface charging and dissolution reactions are fast and proceed with comparable rates in the first 5 h to reach a stable pH 3.5 that corresponds to maximum surface charging and maximum Al 3+. Surface charging is responsible for the formation of the colloidal particles that aggregates to form the physic-type gel phase (weak gel). Gel formation is a slow process and is completed within 20 h of ageing. The suspensions present a non-Newtonian pseudoplastic behaviour; at shear = 10 s −1 viscosities between 0.03 and 0.5 Pa s are measured. Viscosity is strongly time dependent and shows a maximum about 27 h of ageing. This behaviour has been related to the presence of modification of the suspension composition during ageing: viscosity increases due to the increasing amounts of gel, the increasing of gel strength and flocks formation, while the viscosity decreases due to both decrease of gel strength and flocks re-dispersion. Well adherent coating layers characterised by loadings between 1.1–2.2 mg/cm 2 and thickness of 10–20 μm have been obtained upon dip-coating deposition.

Heat-induced modifications in casein dispersions affecting their rennetability

Abstract An alternative method to prevent microbiological problems occurring during cheese manufacture, such as late fermentation by spores from Clostridium tyrobutyricum, is to apply heat treatment of cheese milk. However, thermal inactivation of spore forming bacteria requires high or ultrahigh temperature heat treatment, which simultaneously causes whey protein denaturation and impedes rennet coagulation. A process strategy was designed to remove heat-sensitive whey proteins by diafiltration (microfiltration 0.1 μm) with ultrafiltration permeate. The resulting “whey protein-free” casein dispersion (3% casein, 0.02% whey protein) was heated to temperatures between 100°C and 140°C for up to 600 s before determination of renneting properties. The higher the heat load during thermal treatment the greater is the detected decrease in gel strength in casein dispersions despite the absence of whey proteins. Heat-induced changes in the calcium distribution between the micellar and serum phases were identified as the main factor impairing rennet coagulation. Formal kinetics were applied in order to predict a heating range, in which the casein dispersion shows a high rennetability and guarantees the inactivation of Clostridium tyrobutyricum spores by four log units. The experimental results were confirmed in a pilot-scale plant using UHT-heated “cheese milk” for cheese manufacturing.

Effects of drying on the gel strength and cation mobility of furcellaran

Thermal stability, by means of air drying a furcellaran powder, and its impact on gel strength and cation mobility were studied. Halogen heating in the temperature range 90–115°C for 15 min resulted in loss on drying ( L D, %). These results can be described by polynom L D=−9.583+2.989τ−0.249τ 2+0.00729τ 3+0.1034 t ( R 2=0.9976), indicating a gradual decomposition of carbohydrates. Air-drying induced a decrease in gel strength and the partial removal of potassium, calcium and sodium ions from the matrix. Air drying above 115°C yielded a remarkable destruction of polysaccharides with a total collapse in gelling power.