Decreased Gel Strength Research Articles

Interaction of polysaccharides on gel characteristics and protein microstructure of threadfin bream surimi gel

SummaryPolysaccharide is widely used to improve gel characteristics of surimi gel. The impacts of the polysaccharides tamarind kernel powder (TKP) and tapioca starch (TS) at concentrations of 0%, 2.5% and 5% by weight were investigated on protein conformation [Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM)] and textural characteristics (rheological property, gel strength, solubility, SH contents) of threadfin bream surimi gel. Higher G′ and G″ values were observed in surimi paste added with TKP. Hydrogen bonding increased at higher concentrations of polysaccharides. Addition of TS increased hydrophobic interaction and promoted alteration of the α‐helix to the β‐sheet in the gel structure, while adding TKP to surimi gel had the opposite effect. FTIR images indicated that higher concentrations of polysaccharides resulted in abundant specific polysaccharide functional groups. Microstructures of surimi gel with TKP exhibited an irregular network, with large voids leading to decreased gel strength, while addition of TS increased network density, promoting higher gel strength.

Optimizing the formation of myosin/high-density lipoprotein composite gels: PH-dependent effects on heat-induced aggregation

This study investigated impact of high-density lipoprotein (HDL) on thermal aggregation and gelling behavior of myosin in relation to varied pHs. Results revealed that HDL modified myosin structure before and after heating, with distinct effects observed at varied pH. Under pH 5.0, both myosin and HDL-MS exhibited larger aggregates and altered microstructure; at pH 7.0 and 9.0, HDL inhibited myosin aggregation, resulting in enhanced solubility, reduced turbidity and particle size. Comparative analysis of surface hydrophobicity, free sulfhydryl groups and secondary structure highlighted distinct thermal aggregation behavior between MS and HDL-MS, with the latter showing inhibitory effects under neutral or alkaline conditions. Gelation behavior was enhanced at pH 7.0 with maximum strength, hardness, water-holding capacity and rheological properties. Under acidic pH, excessive protein aggregation resulted in increased whiteness and rough microstructure with granular aggregates. Under alkaline pH, gel network structure was weaker, possibly due to higher thermal stability of protein molecules. Scanning electron microscopy revealed expanded HDL protein particles at pH 7.0, accounting for decreased gel strength and altered rheological properties compared with myosin gel. Overall, the results indicated a positive role of HDL at varied pH in regulating thermal aggregation of myosin and further impacting heat-induced gel characteristics.

Effect of egg white protein-insoluble soybean fiber interactions on the formation and structural characteristics of low-oil emulsion gels

Emulsion gels with low oil content have attracted increasing interests, and insoluble soybean fibers (ISFs) have been proven to be the potential natural emulsifying stabilizers for emulsion gels. In this work, the structure and characteristics of low-oil emulsion gels stabilized by egg white protein (EWP) and ISF were investigated via tuning interactions between EWP-ISF below, near, or above the isoelectric point (pI) of EWP. EWP was adsorbed onto ISF matrix via electrostatic attraction and hydrogen bonding as EWP-ISF ratio changed from 1:0 to 1:2 below the pI (pH 3.2), resulting in a 3.52 mg/mL decrease in soluble EWP content. EWP-ISF synergistically adsorbed onto the oil-water interface, and the droplets were incorporated into gel matrix via hydrophobic interaction, improving the water-binding capacity and gel structure. The addition of ISF could still improve the gel structure at pH 4.5 despite the weakened interactions of EWP-ISF. However, the competitive adsorption occurred above the pI (pH 7.0), with more ISFs participating in interfacial stabilization; simultaneously the interactions between droplet-gel matrix were weakened, resulting in a decreased gel strength. Overall, ISF improved structural properties of low-oil emulsion gels, which exhibited a higher water-binding capacity and gel strength (14.9 g) at pH 3.2 and EWP-ISF ratio of 1:2.

Impacts of agar gum and fucoidan on gel properties of surimi products without phosphate.

Phosphate is widely used in surimi products to improve the gel properties. However, excess addition of phosphate occurs, which can harm the consumer's health. This study aimed to evaluate the effects of agar gum and fucoidan on maintaining the gel properties of surimi products instead of phosphate. Interestingly, our results showed that 0.125% of agar gum and fucoidan to replace phosphate could enhance water-holding capacity and maintain gel strength and textual properties of surimi products well. Especially at frozen storage for 1year, 0.125% of agar gum reduced the expressible moisture content of surimi products by around 10% (p < .05). Sensory evaluation showed that 0.125% of agar gum and fucoidan instead of phosphate can improve tissue and fondness of surimi products in refrigerated storage for 24 h but not in frozen storage for 1year. The addition of agar gum and fucoidan at a high concentration >0.50% increased the WHC, but significantly decreased gel strength and springiness of surimi products (p < .05). Particularly, 1.00% of agar gum and fucoidan reduced gel strength by around 20% (p < .05). It might be due to the destruction of the gel network structure of surimi protein following the excess addition of these polysaccharides. It can be concluded that 0.125% of agar gum and fucoidan can replace phosphate to develop high-quality surimi products, and excessive addition of them have negative effects.

Effect of high-pressure treatment on the heat-induced emulsion gelation of rabbit myosin

The effects of high-pressure treatment (100–200 MPa) on the emulsion and gelation properties of rabbit myosin were investigated. When the myosin treatment pressure was increased from 0.1 (control) to 150 MPa, the proportion of α-helix significantly decreased, those of β-sheet and β-turn significantly increased, and the absolute enthalpy value significantly increased (P < 0.05). Myosin emulsion exhibited increased storage modulus and loss modulus, increased gel strength, decreased centrifugal loss and a dense, compact network of emulsion gel when the myosin treatment pressure was increased from 0.1 to 150 MPa. When the treatment pressure was increased to 200 MPa, the emulsion showed decreased storage modulus and loss modulus, decreased gel strength, increased centrifugal loss, and a less compact network with large cavities and globular aggregates. Therefore, moderate pressure treatment (150 MPa) modified the myosin emulsion structure and improved the thermal, rheological and gelation properties of the myosin emulsion, while higher-pressure treatment (200 MPa) weakened the thermal, rheological and gelation properties of the emulsion.

Influence of gel-strength and magnesium doping on the organization of calcite/hydrogel mesocrystal composites

Calcite growing in biomimetic hydrogel environments incorporates the gel during its growth. The amount of occluded gel within the composite is mainly determined by the interaction between gel strength and crystallization pressure, with the latter being directly related to supersaturation and growth rate. In previous work we established a direct correlation between increased amounts of occluded gel with misorientations in the growing calcite crystals or aggregates. The presence of Mg2+ in the growth environment adds complexity to the internal structuring of the mineral. In this contribution we examine the effects of Mg2+ on the mechanical parameters of gelatin hydrogel and silica hydrogel by mechanical shear stress tests, we determine characteristics of the gel fabric occluded in the calcite using selective etching techniques and high-resolution field emission scanning electron microscope (FE-SEM) imaging, and we use electron backscatter diffraction (EBSD) to study co-orientation or misorientation in the calcite crystals or aggregates. We show that two independent mechanisms are responsible for the complex impact of Mg2+ in the growth medium on the calcite/gel composites. First, addition of 0.1 M Mg2+ reduces the yield-strength of the gels by about 50%. While gelatin gel shows continuous strain hardening in a similar way for Mg-bearing and Mg-free systems, the silica-gel weakens after reaching an ultimate shear strength, where the strain associated with the maximum in strength shifts by 350% to higher values. The decreased gel strength in the Mg-bearing systems leads to decreased amounts of occluded gel. Second, incorporation of Mg2+ in the growing calcite (i) increases its solubility and thus decreases crystallization pressure, and (ii) introduces small angle grain boundaries due to misfit strains which lead to “split growth”, i.e. misoriented subunits of the calcite or – ultimately – spherulitic growth. Our study further clearly shows that Mg not only influences the organization of the mineral component within the aggregate but also the fabric of the occluded gel matrix. The fabrics of the occluded gel change from compact gel membranes to finely dispersed networks with increasing Mg and, correspondingly, decreased crystallization pressure via increasing solubility as more Mg incorporates into calcite structure. This circumstance initiates the large variety of calcite crystal co- and misorientation patterns and hierarchical assemblies that we find in the investigated composites.

Preparation of thermo-reversible eugenol-loaded emulgel for refrigerated meat preservation

The spoilage and weight loss of meat products during storage always results in numerous problems for their commercialization and economic value. An edible thermo-reversible emulgel was prepared in this study, and its application in the preservation of meat products was investigated. The microstructure of the emulgel in liquid and solid forms was characterized. The decreased gel strength of the emulgel compared to the gelatin gel was likely due to the presence of the surfactant. The interaction between eugenol (Eu) and gelatin was mainly due to hydrophobic interactions and was weakened at 4 °C. The results of the physicochemical and antibacterial experiments for the meat products showed that the emulgel effectively controlled the release of Eu on the meat surface; thus, it could significantly inhibit the growth of microorganisms and weight loss in meat, which prolonged the shelf-life of meat for more than 3 days. The transparent emulgel can be easily removed from meat by soaking in warm water (∼40 °C), and it is a promising application for improving the safety and quality of meat products.

Effects of salts on the freeze-thaw stability, gel strength and rheological properties of potato starch.

The objective of this study was to evaluate the effects of different salts (NaF, NaCl, NaBr, NaI, K2SO4, KCl, KNO3, KSCN, LiCl) on freeze-thaw stability, gel strength and rheological properties of potato starch. Addition of the structure-making (salting-out) ions, such as F- and SO42-, decreased freeze-thaw stability and increased gel strength, maximal storage modulus (G') and maximal loss modulus (G″) of potato starch, due to a stronger three-dimensional network by promoting the starch retrogradation and inhibiting starch gelatinization. Shear stress versus shear rate of all samples at 25°C was well fitted to the simple power-law model with high determination coefficients (R2=0.9863-0.9990). Flow behavior index (n), consistency index (K) and apparent viscosities increased with adding salting-out ions. However, the structure-breaking (salting-in) ions had reverse effects on freeze-thaw stability, gel strength and rheological characteristics of potato starch. The addition of structure-breaking ions, such as Br-, NO3-, I-, SCN-, Na+ and Li+, decreased gel strength, G' and G″ values and increased freeze-thaw stability. Salts could significantly influence on the retrogradation of potato starch, generally following the ion order: F->SO42->Cl->Br->NO3->I->SCN- for anions and K+>Na+>Li+ for cations, consistent with the Hofmeister series.

Effect of salt, rice bran oil and malva nut gum on chemical, physical and physico – Chemical properties of beef salt – Soluble protein and its application in low fat salami

The effect of salt, malva nut gum (MNG) and rice bran oil (RBO) on pH, water holding capacity (WHC) and rheological properties of beef salt soluble protein (BSSP) was studied. BSSP, which possessed protein 6.8%, was extracted with saline buffer. The MNG, which was extracted with water and precipitated with 95% ethanol, had dark brown color (L*, b* and a* at 36.1, 11.6 and 7.0, respectively), 50% yield, 75.1% carbohydrates, 15.5% moisture, 4.7% ash, 4.7% protein and water activity at 0.344. The effect of MNG (0.2, 0.4 and 0.6%) and NaCl (2, 3 and 4%) on BSSP gel strength was studied. The rheological properties of all treated samples revealed the property as a gel-like material with a network formed by a loosely-ordered structure with the consistency of viscoelastic gel. The increase of MNG resulted in higher WHC and storage modulus at all salt concentrations. The addition of 3% NaCl and 0.6% MNG into BSSP gel provided the gel with highest storage modulus, imparted the strongest gel. This treatment was selected and subjected to mix with RBO at 5, 10, 15 and 20%. The addition of RBO decreased gel strength. BSSP gel with 10% RBO had greatest gel strength and WHC. This condition was found appropriate for designing a low fat salami. The developed salami possessed higher titratable acidity and thiobarbituric acid number, and lower hardness and chewiness than basic formulation, while liking scores in all characteristics and overall liking score of those two formula were not significantly different (p > 0.05).

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.

Apple pomace powder as natural food ingredient in bakery jams

The aim of the present study was to investigate whether apple pomace powder produced by a simple drying method is suitable for replacing pectin in bakery jam products. Rheological properties of bakery jams were tested by oscillatory tests using amplitude sweep method. Apple pomace addition decreased gel strength and stability of bakery jams, while 12-month storage increased the gel strength of samples. Based on our results, dried apple pomace powder seems to be suitable to replace pectin up to 40% without changing rheological properties of bakery jams.

Effect of incorporating prebiotics in coating materials for the microencapsulation of Sacharomyces boulardii

The objective of this study was to microencapsulate Saccharomyces boulardii using the emulsion technique. To microencapsulate the yeast, alginate sodium blended with inulin and mucilage from Opuntiaficus-indica was used as a coating material. The textural properties of the gels formed by the encapsulating materials and the in vitro viability of the yeast strain in the simulated conditions were studied. Textural profile analyses of the gels revealed differences (p < 0.05) in hardness because alginate produced stronger gels, whereas the incorporation of other hydrocolloids with alginate decreased gel strength and resulted in a more uniform, cohesive gel matrix. When alginate was blended with mucilage and inulin, encapsulated yeast presented higher counts and more viable cells, as compared to free yeast following 30 days of storage at 4°C. Encapsulated and free yeast had 76.1% and 63.3%, respectively, of cell viability after 35 days of storage.

Gelation properties of salt-extracted pea protein isolate induced by heat treatment: Effect of heating and cooling rate

Gel network formation of a salt-extracted pea protein isolate was studied using dynamic rheological measurements. The gelling point was dependent on heating rate and was unaffected by cooling rate. When both the heating and cooling rates were increased (from 0.5 to 4 °C/min) final G′ value decreased, indicative of decreased gel strength. During the heating phase, the storage modulus and loss modulus fluctuated below 1 Pa at almost constant values with the storage modulus smaller than the loss modulus until the gelling point was reached. The rate of cooling has a greater impact on the development of storage modulus than that of heating. Compared to the gel strength of commercial pea protein isolate (PPIc) and soy protein isolate (SPIc) at the same protein concentration, salt-extracted pea protein isolate (PPIs) was much stronger than PPIc but weaker than SPIc. Careful control of the heating and cooling rates enable maximum gel strength for heat-induced pea protein gel, thus enhancing utilisation of pea protein as an additive in meat food industry.

Compression of gellan gels. Part I: effect of salts

SummaryGellan gels, in the presence of potassium and calcium ions and their mixtures, were tested using large deformation compression experiments. Characterisation was based on stress and strain at failure along with Young’s modulus. Samples prior to compression were refrigerated at 5 °C for 1, 2 and 24 h. In the case of potassium, the strongest gel was obtained for a cation concentration of 80 mm. Increasing concentrations of calcium resulted in decreased gel strength. Brittleness values for potassium and calcium gels fluctuated around ∼0.5 and ∼0.3 respectively. The strength for both, potassium and calcium, gels did not increase significantly over time. For each cation, Young’s modulus and stress at failure showed the same variation. In the case of mixtures, strength was determined by calcium as its progressive replacement by potassium was actually similar to reducing its concentration. Potassium determined the remaining properties.

Gelation properties of salt-extracted pea protein induced by heat treatment

Gelation is one of the most important properties of plant proteins. In this paper, a low denaturation salt extraction method was used to extract pea (Pisum sativum L.) protein isolate from commercial pea flour. The gelation properties of this isolate were examined and compared to commercial products. The pea protein isolate followed the three-step process of gelation that is generally accepted for heat-induced gelation of globular proteins. The minimum gelation concentration of salt-extracted pea protein isolate (PPIs) was 5.5% while that of commercial pea protein isolate (PPIc) was 14.5%. The gelling point was in the range of 82–86 °C for 14.5% PPIs, 0.3 M NaCl at natural pH (5.65). With increasing heating rate, the gelling point tended to increase. Higher heating and cooling rates resulted in decreased final G′ (storage modulus) and G″ (loss modulus) values, indicative of decreased gel strength. A higher protein concentration resulted in higher G′ and G″ values and it was found that there was a power law relationship between protein concentration and G′ and G″. Tan delta (δ) values decreased with increasing protein concentration and at concentrations of 5.5% and above, tan δ remained constant which means the critical concentration for gel formation was 5.5%. The values of G′ and G″ for PPIs were greater than those of PPIc, and tan δ of PPIs was smaller, indicative of a stronger gel network. DSC data showed that PPIc had undergone denaturation whereas PPIs had not (ΔH = 15.81 J/g protein). Although rheometer data showed that the final G′ value of commercial soy protein isolate (SPIc) was smaller than that of PPIs, the gel prepared with SPIc was visually stronger than that of PPIs. The rheological data obtained with small amplitude oscillatory testing was not consistent with the actual observations. Overall, the low degree of denaturation of the PPIs resulted in a stronger gel than that of PPIc making the PPIs a more attractive food ingredient.

Comparison of rennet gelation using raw and reconstituted skim milk

The gelation properties of raw skim milk were compared with milk reconstituted from low-heat skim milk powder. Coagulation of reconstituted milk, as monitored by capillary viscometry, was slower than that of raw milk, but increased markedly with increased reconstitution time. This was attributed to re-equilibration of calcium from the micelles to the serum. Freshly reconstituted milk supplemented with calcium confirmed this suggestion. The results emphasise the importance of calcium being present in the serum for coagulation of renneted micelles. Gel strength was also improved by increasing reconstitution time. However, gels made from raw milk were significantly stronger than those made from reconstituted milk, even when supplemented with 3 m m calcium. The decreased gel strength from reconstituted milk was attributed to a general increase in casein micelle size that occurs during powder manufacture and is not reversed upon reconstitution.

Incorporation and stabilization of omega-3 fatty acids in surimi made from cod, Gadus morhua.

Surimi containing omega-3 fatty acids from algal oil was prepared by the addition of oil-in-water emulsions or bulk oil. Emulsion and bulk oil were added separately to surimi to provide approximately 500 mg of omega-3 fatty acids per serving of surimi (85 g). Addition of the emulsion had no effect on surimi gel strength, whereas bulk oil decreased gel strength an average of 31%. All surimi treatments containing algal oil increased in Hunter b values due to the presence of carotenoids in the oil. Among cryoprotectants, sodium tripolyphosphate was the major surimi additive responsible for retarding the formation of lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS). Lipid hydroperoxide and TBARS formation was lower in surimi containing bulk oil compared to surimi with emulsified oil. Both EDTA and lipid soluble antioxidants were able to decrease lipid oxidation in surimi fortified with omega-3 fatty acids. This suggests that surimi containing nutritionally beneficial omega-3 fatty acids could be developed with good oxidative stability and gel strength.

The effect of two cryoprotectant mixtures on frozen surubí surimi

Surimi itself is not a food; it is an intermediate phase of the production of kamaboko(a gel formed by the addition of salt to the surimi and direct heating to 80-90oC) and a series of high-priced shellfish analogs. The protective effect that two cryoprotectant mixtures exerted during freezing and frozen storage of frozen surimi of surubi (Pseudoplatystoma coruscans) on the functional quality of the gels prepared was studied. The selected washing conditions selected to obtain an acceptable functional quality of gels prepared from frozen surimi (25% extracted proteins and of final moisture) using the response surface methodology were wash temperature, 18oC; washing time for each of the three washing cycles, 4.62 min. and water-mince ratio, 3.5:1. Cryoprotectant mixtures used were sucrose/sorbitol (1:1) and maltodextrin/sorbitol (1:1) and they were added (8%) to the washed and drained minced fish before freezing. To evaluate the functionality of the frozen surimi during six months of storage, the penetration test to measure the gel strength was chosen; samples were assessed at 4, 45, 90 and 180 days of frozen storage. Results showed that even with the cryoprotectants freezing decreased gel strength, since it produced a decrease of almost 32% in the strength of the gel prepared with fresh surimi. However, the two cryoprotectant mixtures tested showed very good behaviour throughout frozen storage; specially at 45 and 90 days of storage the surimi gels with the sucrose/sorbitol mixture had a greater resistance than those with maltodextrin/sorbitol.

Thermosetting gels with modulated gelation temperature for ophthalmic use: the rheological and gamma scintigraphic studies.

For ophthalmic drug delivery, Pluronic F127 solutions have a phase transition temperature too low for them to be instilled into the eye at room temperature. Refrigerator storage is usually required to make administration easier, whereas the potential irritation of cold to the sensitive ocular tissues may result in poor topical bioavailability. The purpose of this study is to develop a thermosetting gel with a suitable phase transition temperature by combining Pluronic analogs and to examine the influence of incorporating mucoadhesive polysaccharide, sodium hyaluronate (HA-Na), on the ocular retention of the gel. Dynamic rheological method and single photon emission computing tomography (SPECT) technique were used to ex/in vivo evaluate the thermosetting gels, respectively. An optimized formulation containing 21% F127 and 10% F68 increased the phase transition temperature by 9 degrees C as evaluated by elasticity modulus compared to that of individual 21% F127 solution. Rheological behaviors of the Pluronic solutions showed that the combined Pluronic formulation was free flowing liquid below 25 degrees C and converted to a firm gel under the physiological condition. Furthermore, this formulation possessed the highest viscosity both before and after tear dilution at 35 degrees C. Gamma scintigraphic data demonstrated that the clearance of the thermosetting gel labeled with 99mTc-DTPA was significantly delayed with respect to the phosphate buffered solution, and at least a threefold increase of the corneal residence time was achieved. However, no further improvement in the ocular retention was observed when adding HA-Na into the thermosetting gel due to the substantially decreased gel strength.

Development of in situ-gelling and mucoadhesive acetaminophen liquid suppository

Conventional suppositories are solid forms which often cause discomfort during insertion. The leakage of suppositories from the rectum also gives uncomfortable feelings to the patients. In addition, when the solid suppositories without mucoadhesivity reach the end of the colon, the drugs can undergo the first-pass effect. To solve these problems, we developed a novel in situ-gelling and mucoadhesive acetaminophen liquid suppository with gelation temperature at 30–36°C and suitable gel strength and bioadhesive force. Poloxamer 407 (P407) or/and poloxamer 188 (P188) were used to confer the temperature-sensitive gelation property. The mixtures of P407 (15%) and P188 (15–20%) existed as a liquid at room temperature, but gelled at 30–36°C. Acetaminophen, the active ingredient of the suppositories, slightly increased gelation temperature, but significantly decreased gel strength and bioadhesive force. To modulate the gel strength and the bioadhesive force of acetaminophen liquid suppositories, bioadhesive polymers such as polyvinylpyrrolidone (PVP), hydroxypropylmethylcellulose (HPMC), hydroxypropylcellulose (HPC), carbopol and polycarbophil were studied. The bioadhesive polymers exerted various impacts on the physicochemical properties of liquid suppositories. The gelation temperature was not significantly affected by PVP, HPMC and HPC, but decreased by carbopol and polycarbophil. Of bioadhesive polymers, carbopol and polycarbophil most significantly enhanced both gel strength and bioadhesive force. The liquid suppositories with carbopol or polycarbophil were inserted into the rectum of rats without difficulty and leakage and retained in the rectum for at least 6 h. These results suggest that in situ-gelling and mucoadhesive liquid suppository for humans can be further developed as a more convenient and effective rectal dosage form.