Decrease In Gel Strength Research Articles

Changes in the structural, aggregation behavior and gel properties of pork myofibrillar protein induced by theaflavins

This study explores the effect of different theaflavins (TFs) concentrations (0, 100, 300, 600 and 900 mg/L) on the structure, aggregation behavior and gelation properties of pork myofibrillar protein (MP). The protein structure and aggregation behavior were characterized by free sulfhydryl groups, surface hydrophobicity, fluorescence emission spectra, particle size and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The gel properties of samples were characterized by gel strength, cooking loss, microstructure and gel supernatant SDS-PAGE. The results showed a significant decrease in free thiol content with increasing TFs concentration, suggesting thiol-quinone covalent interaction between TFs and thiol group of MP. Intrinsic fluorescence spectroscopy confirmed a static quenching between TFs and MP. And TFs reduced the particle size of MP suspension and caused no protein aggregation bond in SDS-PAGE. For gel properties, TFs caused a decrease of gel strength from 96.77 g to 21.91 g and an increase in cooking loss from 40.34 % to 71.15 %. The bond of protein aggregates in gel supernatants SDS-PAGE revealed that some protein aggregates formed by disulfide bonding were not involve in gel formation with TFs addition. In conclusion, TFs cause thiol loss of MP and impaired MP gelling ability by interfering with disulfide bond formation during gelation.

Influence of the thermal shrinkage-induced volume contraction on the yielding behavior of waxy oil

The present article investigates the effect of thermal shrinkage on the yielding behavior of waxy oil gel. The paper compares constant gap and constant normal force measurement protocols to examine the effect of measurement protocol on the rheological behavior of thermoreversible gel. The findings of this study reveal that the extent of stress overshoot and yield stress in a constant shear-rate start-up flow shows a lower magnitude in a constant gap protocol compared to a constant normal force protocol. The decrease in gel strength in the former protocol is mainly attributed to the formation of voids. These voids cause localized fractures within the crystal network. In contrast, in the constant normal force measurement protocol, gel contraction is compensated by utilizing a variable gap setting. Variable gaps compensate for the lower specific volume of the gel after crystallization, minimizing void formation and subsequent rupture of the crystal network. Hence, the gel network formed using the constant normal force protocol is more homogeneous, eliminating the uncertainties in yield stress measurement. Finally, the effect of thermal history, wax content, and aging period on the yield stress values highlights notable findings. Contrary to the conventionally accepted results, the aging period is found to impact the yield stress negatively, and a nonmonotonic relationship between the cooling rate and yield stress is noticed under the constant gap protocol. Thus, the results obtained under the constant normal force protocol are more reliable and can help in developing a fundamental understanding of the yielding behavior.

Towards higher-quality low salt surimi gels: Significance of the combinatorial effects of chickpea protein with transglutaminase on their micro-structures

The textural properties of low-salt hybrid gel made from silver carp (Hypophthalmichthys molitrix) and chickpea protein (CPP) with or without external transglutaminase (TGase) were investigated. A decrease in gel strength (P﹤0.01), hardness (P﹤0.01), storage modulus (G′) and loss modulus (G″) of the hybrid gel containing CPP appeared regardless of the addition of TGase. Furthermore, the addition of CPP combining with TGase significantly induced a significantly higher resilience (from 43.5% to 50.3%), cohesiveness (from 0.72 to 0.79), proportion of immobilized water (from 95.7% to 97.4%), number of pores (from 3181 to 4868) and apparent porosity (from 30.55% to 40.26%) than those of the group containing TGase alone, which indicated the combining effect of CPP and TGase on the textural properties. The SDS-PAGE profiles showed that the covalent complex between CPP and myofibrillar proteins was not observed. During the gelation of myofibrillar protein filaments, CPP wrapped the fibres shown by the microstructure morphology and increased the friction between fibres, leading to an increase in relaxation time. TGase promoted this effect and induced the formation of a denser microstructure. The present study provided a feasible approach for the preparation of high-quality low salt surimi products with more favorable texture and acceptability.

Potential relation between starch granule-associated proteins and retrogradation properties of buckwheat starch

To elucidate the effect of starch granule-associated proteins (SGAPs) on retrogradation properties of buckwheat starch, the retrogradation properties of Tartary buckwheat starch (TBS) and common buckwheat starch (CBS) before and after removal of SGAPs were systematically investigated, with wheat starch (WS) as reference. A significant decrease in gel strength of starches and density of starch aggregates were observed after removing SGAPs. The results were in line with the changes in retrogradation enthalpy of starches and short-range ordered structure of starch aggregates. After removing SGAPs, the retrogradation enthalpy of TBS decreased from 4.16 J/g to 3.74 J/g, CBS decreased from 4.05 J/g to 3.35 J/g and WS decreased from 3.27 J/g to 2.81 J/g, respectively. Taken together the results of LF-NMR, FTIR and rheological analysis, it can be concluded that SGAPs could promote the hydrogen bond interactions between starch molecules by competitively binding with water molecules, enhancing the rearrangement of starch molecules and forming a more ordered structure. Overall, the study suggested that the presence of SGAPs could enhanced the interaction between starch molecules chains, thus accelerated the retrogradation process. The research results provide more information about SGAPs in buckwheat starch and support further study for manipulation of starch properties.

Preparation, physicochemical characterization and swelling properties of composite hydrogel microparticles based on gelatin and pectins with different structure

Composite hydrogel microparticles based on pectins with different structures (callus culture pectin (SVC) and apple pectin (AU)) and gelatin were developed. Hydrogel microparticles were formed by the ionotropic gelation and electrostatic interaction of COO− groups of pectin and NH3+ groups of gelatin, which was confirmed by FTIR spectroscopy. The addition of gelatin to pectin-based gel formulations resulted in a decrease in gel strength, whereas increasing gelatin concentration enhanced this effect. The microparticle gel strength increased in proportion to the increase in the pectin concentration. The DSC and TGA analyzes showed that pectin-gelatin gels had the higher thermal stability than individual pectins. The gel strength, Ca2+ content and thermal stability of the microparticles based on gelatin and SVC pectin with a lower degree of methylesterification (DM) (14.8 %) were higher compared to that of microparticles based on gelatin and AU pectin with a higher DM (40 %). An increase in the SVC concentration, Ca2+ content and gel strength of SVC-gelatin microparticles led to a decrease in the swelling degree in simulated gastrointestinal fluids. The addition of 0.5 % gelatin to gels based on AU pectin resulted in increased stability of the microparticles in gastrointestinal fluids, while the microparticles from AU without gelatin were destroyed.

Structural, physicochemical and digestive properties of rice starch modified by preheating and pullulanase treatments

The structural, physicochemical and digestive properties of rice starch modified by the combination of different temperature (60, 70, 80, 90 and 100 °C) preheating and pullulanase (PUL60, PUL70, PUL80, PUL90 and PUL100) treatments were investigated. The PUL60 treatment mainly modified the surface layer of starch granules, which increased the amylose content and damaged some ordered structures, resulting in slight decreases of gel strength and estimated glycemic index (eGI). With the increase of preheating temperature, PUL could act on more enzymatic sites to release a large amount of linear chains, reduce the ordered degree, and transform the A-type crystalline structure into B-type. The low molecule interaction strength between linear chains weakened the gel network structure, and some stable crystal structures formed by longer chains resisted the enzyme digestion. The gel strength and eGI value of PUL70 starch decreased significantly, and the properties of PUL80–100 starches tended to be stable, showing a further significant decrease of gel strength and a slight reduction of eGI value. Therefore, the preheating treatments at 60, 70 and 80 °C were suitable for the PUL modification of rice starch to obtain strong, medium and weak gel strength respectively, and the digestibility decreased with increasing preheating temperature.

Effect of Protein-Glutaminase on Calcium Sulphate-Induced Gels of SPI with Different Thermal Treatments.

The effects of protein-glutaminase (PG) on calcium sulphate (CaSO4)-induced gels of soy protein isolate (SPI) with different heat treatment levels were investigated. The time-dependent degree of deamidation showed that the mild denaturation of the protein favored the deamidation. The particle size distribution showed that the heat treatment increased the SPI particle size, and the particle size distribution of the SPI shifted to the right or increased the proportion of the large particle size component as the degree of deamidation increased for each sample. Rheological analysis showed that the deamidation substantially pushed up the gel temperature and decreased the value of G'. The gel strength and water-holding capacity showed that the higher the amount of enzyme added, the more significant the decrease in gel strength, while the gel water-holding capacity increased. In summary, the deamidation of PG and heat treatment can affect the gel properties of SPI synergistically.

Synthesis and properties of maleic anhydride-modified agar with reversibly controlled gel strength

Agar is modified by chemical methods to improve its functional properties and meet the increasing demand of the market. Some of the functional properties of agar are improved after chemical modification, while other properties are reduced, especially gel strength. This study aimed to comprehensively improve the functional properties of agar through acylation and crosslinking by reacting with maleic anhydride. 13C NMR indicated the maleylation reaction was preferred at the C2 hydroxyl group of D-galactose, and the crosslinking reactions occurred at the C2 and C6 hydroxyl groups of D-galactose in different agar chains. Interestingly, the maleylated agar monoester had higher gel transparency (1.5%, w/v) of up to 76% than the native agar (58%). However, it showed a significant decrease in gel strength from 783 g/cm2 to 403 g/cm2, while crosslinking endowed agar with higher gel strength (845 g/cm2) and gel transparency (78.4%). The high transparency of the modified agar plate made colony observation and colony counting easy. Maleylation of agar further enhanced the freeze–thaw stability of agar gel (24.8%, 7th freeze–thaw cycles). Overall, the maleylated agar possessed superior functional properties, and it could be used as food, bacteriological, and biotechnological agar.

A green extraction method for gelatin and its molecular mechanism

In this work, a green extraction method of gelatin was proposed to replace traditional acid and alkali treatment by microwave-rapid freezing-thawing coupling method. The mechanism of rapid gelatinization of fish skin collagen induced by microwave-rapid freezing-thawing coupling was examined systematically. The results showed that the dense structure of fish skin collagen fibers became loose, the collagen molecular on the surface was gelatinized and degraded gradually, then more internal collagen molecular without gelatinization were exposed with the increase of microwave pre-treatment time (0–60 min), resulting in an increase of gelatin yield (5.32%–19.94%) and a decrease of the gel strength (675.17–419.6 g). With the increase of freezing-thawing cycles (0–3), the gelatinized collagen fibers structure was further loosened and the balance of hydrogen bond was destroyed seriously due to the rapid formation and melting of ice crystals, thus leading to the dissolution and degradation of subunit components. This also resulted in an increases of gelatin yield (13.91%–19.01%) and a decrease of gel strength (580.01–413.33 g). Ultimately, the gelatin yield and gel strength were 17.01% and 591.50 g respectively under optimal conditions (microwave pre-treatment 15 min, one freezing-thawing cycle). This study could provide theoretical basis and guiding significance for the production of gelatin in a green way.

Effects of the Mixture of Xylooligosaccharides and Egg White Protein on the Physicochemical Properties, Conformation, and Gel-Forming Ability of Culter alburnus Myofibrillar Protein during Multiple Freeze-Thaw Cycles.

This study focuses on the effect of the mixture (XO/EW) of xylooligosaccharides (XO) and egg white protein (EW) on the physicochemical properties, conformation, and gel-forming ability of Culter alburnus myofibrillar proteins (MP) during multiple freeze–thaw (FT) cycles. In our methodology, MP samples added with EW, XO, or XO/EW mixture (1%, v/v) are prepared, and after multiple FT cycles, the XO or XO/EW-treated samples show significant (p < 0.05) inhibition on the decrease of sulfhydryl content and the increase of carbonyl content of MP. Compared with EW, XO or XO/EW could delay the increase of surface hydrophobicity and the decline of secondary and tertiary structural properties of MP, indicating that XO or XO/EW could more effectively increase the stability of MP conformation. Meanwhile, XO/EW could more effectively reduce the decrease of gel strength and gel water holding capacity, and the increase in the T2 relaxation time of MP gel, confirming that XO/EW could substantially improve the MP gel-forming ability. Analysis of intermolecular interaction force proves that, compared with EW, XO/EW could reduce the content decrease of ionic and hydrogen bonds in MP gel. Overall, XO/EW could improve the stability of MP functional properties over multiple FT cycles. This study provides a new perspective for the potential commercial application of EW as a low-calorie cryoprotectant in aquatic products.

Effect of freezing temperature on molecular structure and functional properties of gelatin extracted by microwave-freezing-thawing coupling method

The effect of different freezing temperature (−20 °C, −40 °C and −80 °C) on the properties (mainly molecular structure and functional properties) of gelatin extracted by microwave-freezing-thawing coupling method were compared systematically. The results showed that as the decrease of freezing temperature (−20 °C ~ −40 °C), the yield and gel strength increased from 11.80% to 14.55% and 753.00 g–825.67 g respectively due to the easier dissolution of subunit components induced by destruction of fish skin structure, while the lower freezing temperature (−80 °C) resulted in decrease of gel strength (734.00 g) due to the easier degradation of subunit components induced by excessive destruction of fish skin structure during the microwave extraction process. The FTIR results confirmed the destruction of the triple helix structure of gelatin at freezing temperature −80 °C, thus decreasing the thermal stability and exposing more hydrophilic amino acids with a reduced surface hydrophobicity (281.72–200.21). At freezing temperature (−40 °C), the gelatin showed the best foaming property and emulsifying properties, attributing to the lower interface tension induced by higher hydrophobicity. This study would provide guiding significance for the industrial production and the regulation of the physicochemical and functional properties of green gelatin.

Quality attributes enhancement of ready-to-eat hairtail fish balls by high-pressure processing

High-pressure processing (HPP) subject to 250 MPa for 5 min or 300, 350 MPa for 3 or 5 min was applied to pre-cooked hairtail (Trichiurus haumela) fish balls for manufacturing ready-to-eat (RTE) surimi products, while effects on quality attributes (microorganism, texture, color, freshness, protein structure, sensory, and water distribution) were investigated. The results indicated that safety and freshness of fish balls treated at 350 MPa for 5 min were significantly improved evidenced by the reduction of total bacterial count (from 726.67 to 7.33 CFU/g) and total volatile basic nitrogen content (from 3.45 to 0.93 mg N/100 g). Additionally, a moderate high-pressure treatment was beneficial for improving textural and sensory properties of hairtail fish balls, including higher springiness, cohesiveness and gel strength. However, a higher pressure (350 MPa) unfolded proteins, and changed the secondary structure of myofibrillar protein, resulting in the decrease of gel strength. Color changes caused by pressurization were within acceptable ranges. Low-field NMR (LF-NMR) results showed a reduction in water mobility and a transfer of immobilized water to bound water for pressure-induced samples. Overall, HPP at 300 MPa for 5 min is suggested for the development of RTE fish balls with favorable quality attributes.

Physicochemical properties and structure of modified potato starch granules and their complex with tea polyphenols

The physicochemical, rheological properties and structure of potato starch and starch-tea polyphenols (TPs) complex modified by enzyme and alcohol was investigated in this study. Cavities on the modified starch granules and morphology change could be investigated by SEM, while significant birefringence observed in complete granules by polarizing light microscope, but disappeared in crashed starch. TPs inhibited the aggregation of amylose and retrogradation of starch-TPs complex, resulting in the decrease of gel strength, and the increase of viscosity and gelatinization stability of starch granules. Fourier transform infrared (FT-IR) spectra showed that intramolecular hydrogen bond could be formed between TPs with modified starch, and the hydrogen bond force formed by starch and TPs was stronger than that between starch molecules. X-ray diffraction (XRD) analysis revealed that three modification methods did not change the crystalline structure of starch, but new diffraction peaks appeared in the four starch-TPs complex, suggesting that the hydrogen bond was incurred by interaction between TPs and amylose to form V-type crystalline. These results demonstrated that the complex formed by TPs and native/modified potato starch could be used in food industrial applications due to the inhibition of starch retrogradation.

Physicochemical, rheological, and micro-structural properties of yogurts produced from mixtures of camel and bovine milks

This study evaluated the influence of supplementing bovine milk with increasing levels of camel milk (0–60%) on different properties of yogurt. Fresh raw camel and bovine milks were heated separately at 85 °C for 5 min and mixed before fermentation with lactic acid bacteria. The decrease in gel strength after camel milk addition caused a decrease in viscosity and related parameters including G', G", stringiness, and syneresis. The Bostwick consistency values increased with increasing proportions of camel milk providing further evidence that the produced yogurts are less viscous and have higher water holding capacity and lower gel contraction during storage. Scanning electron micrographs showed that the addition of camel milk to bovine milk led to larger and less differentiated casein micelles. After fermentation, the pH of all yogurts was 4.5–4.6 and it decreased to 4.3 after 2 weeks of storage suggesting that the soft gels caused by the addition of camel milk is due to the structure and concentration of its proteins rather than limitations related to bacterial growth. The results obtained in this work are of particular interest especially in the understanding of how variation in milk protein composition may affect its gelation properties.

Neutral hydrocolloids promote shear-induced elasticity and gel strength of gelatinized waxy potato starch

Shear forces are important during food processing, food consumption, and food digestion, and often are estimated to evaluate their effects on product quality. However, few studies have been done on shear-induced structure changes of starch/hydrocolloid systems. Our previous work showed that gelatinized waxy potato starch forms a strong viscoelastic gel under the application of long-term low shear at low temperatures, a phenomenon that is not noted in other waxy starches such as rice and corn. In the present study, the rheological properties of gelatinized waxy potato starch in the presence of neutral (guar gum and konjac glucomannan) and anionic hydrocolloids (gum arabic, xanthan gum, sodium alginate, and pectin) were investigated. Results showed that gelatinized starch dispersions containing hydrocolloids with flexible polymer chains (guar gum, konjac glucomannan, sodium alginate, and pectin) or a highly-branched structure (gum arabic) were able to produce gels with a more liquid-like behaviour when compared to gels produced by dispersions containing hydrocolloids with rigid chains (i.e., xanthan gum). Phase separation in starch/xanthan gum system and formation of a 3D-network in the xanthan gum phase may be responsible for the strengthened gel structure resulting in high elasticity. When shearing the gelatinized waxy potato starch/hydrocolloid dispersions at 5 °C for 24 h at 20 s−1, the presence of neutral and highly viscous hydrocolloids drastically increased the gel strength, while anionic and low viscous hydrocolloids decreased it. Such decrease in gel strength was attributed to the electrostatic repulsion between anionic hydrocolloids and the naturally negatively charged phosphorylated chains of waxy potato starch.

The influence of deacetylation degree of konjac glucomannan on rheological and gel properties of konjac glucomannan/κ-carrageenan mixed system

The rheological and textural properties of κ-carrageenan (CAR) and konjac glucomannan (KGM) with definite deacetylation degree (DD) mixed system in the presence of potassium chloride (KCl) were investigated to study the influence of deacetylation degree on KGM, CAR and KCl mixed system. The results revealed that the zero-shear viscosities of the mixed sol system increased firstly and then decreased with the gradual increase of DD. Besides, the sols had the capability of being transformed into irreversible gel by heating them at 80 °C for 30 min and then cooling to room temperature. The DD of KGM did have impacts on the characteristics of the ensuing hydrogels. That is, the mixed gels showed an initial increase and ensuing decrease in gel strength over DD, reaching the maximum with a DD of 21.07%. Overall, by controlling the deacetylation degree of KGM, the gel behaviors of the mixed system can be regulated.

Rheological and microstructural properties of cold-set emulsion gels fabricated from mixed proteins: Whey protein and lactoferrin

Cold-set emulsion gels were fabricated from oil droplets coated by mixed proteins: whey protein and lactoferrin. The impact of protein composition, droplet concentration, pH, and ionic strength on the microstructure, texture, and stability of the cold-set emulsion gels was determined. Protein composition had a major influence on gel strength, with the strongest emulsion gels being formed at an optimized protein composition (0.5 wt% whey protein and 1.5 wt% lactoferrin). The storage modulus of the emulsion gels increased from 149 to 1590 Pa as the droplet concentration increased from 10 to 40 wt%. The gel strength could also be modulated by adjusting pH, with the strongest gels being formed at pH = 6.5, where the net charge on the droplets was neutral. Increasing the ionic strength weakened the electrostatic interactions, which inhibited droplet aggregation and led to a decrease in gel strength. These results may be useful for designing cold-set emulsion gels with rheological properties that can be tailored for specific commercial products.

Time dependent gelling properties of cuboid alginate gels made by external gelation method: Effects of alginate-CaCl2 solution ratios and pH

This study investigated the gel strength and syneresis of cuboid alginate gels (2 × 2x1.4 cm) using 2% Na-alginate solutions as a function of gelling time, CaCl2 solution concentrations (0.05 M - 0.20 M) and pH (4−11) in an external gelation method. This study also investigated the effects of providing a limited or excess amount of calcium ions needed to completely cross-link the alginate chains by altering the ratio between alginate and CaCl2 solutions. For comparison purpose, the gelling time and syneresis of alginate beads (2.5–3.0 mm in diameter) were also studied. The results showed that an increase in the CaCl2 concentration resulted in a faster gelling time, increased gel strength and higher degree of syneresis. Meanwhile, an increase in pH of the alginate and CaCl2 solutions resulted in the decrease of gel strength and the degree of syneresis. In the presence of excess CaCl2, the gels would reach the same equilibrium degree of syneresis (∼39%) after a certain gelling time, regardless of CaCl2 concentration. It was also observed that the degree of syneresis gradually increased from the start of gelation until a stable point was reached which corresponds to the end of gelation. This trend of syneresis was observed in both cuboid gels and spherical gel beads although stabilisation of syneresis occurred sooner in the gel beads (<2 h) compared to cuboid gels (>5 h). Since the smaller gel beads exhibited syneresis phenomena similar to that of large cuboid gels, it can be inferred that micron size gels may exhibit similar behaviour.

Effects of konjac oligo-glucomannan on the physicochemical properties of frozen surimi from red gurnard (Aspitrigla cuculus)

In this study, the effects of konjac oligo-glucomannan (KOG) on the physicochemical properties of frozen surimi from red gurnard (Aspitrigla cuculus) during frozen storage at −18 °C for 50 days were investigated. An aliquot of 0.5% (w/w) of KOG was added into the surimi and subjected to frozen storage (KOG group), and 8% of a conventional cryoprotectant (4% sorbitol and 4% sucrose, w/w) was used as a positive control (S group). The salt soluble protein content, the Ca2+-ATPase activity, total sulfhydryl (SH) content, gel strength, thiobarbituric acid (TBA) value, and whiteness of frozen surimi were determined. After storage for 50 days at −18 °C, the contents of salt soluble protein of KOG group and S group were 14.81% and 21.27% higher than the control, respectively, and the total SH contents of KOG group and S group were 6.90% and 8.46% higher than the control, respectively, and the gel strengths of KOG group and S group were 10.85% and 11.89% higher than the control, respectively. Although the activities of Ca2+-ATPase of KOG group and S group reached to 0.10 ± 0.02 μmol Pi/mg•min−1 and 0.11 ± 0.01 μmol Pi/mg•min−1 after 50 days, respectively, they are significantly different from the control (0.04 ± 0.02) μmol Pi/mg•min−1, which indicated a strong cryoprotective effect of KOG. KOG exhibited more powerful antioxidant activity with lower TBA values than S group. It can be concluded that the addition of conventional cryoprotectant and KOG can inhibit protein denaturation and reduce the decrease of gel strength, but KOG displayed a stronger antioxidant activity with a small addition amount of only 0.5%, despite having no effect to improve the whiteness. These make KOG a promising cryoprotectant candidate using in frozen surimi industry.

Freeze-dried phosphatidylcholine liposomes encapsulating various antioxidant extracts from natural waste as functional ingredients in surimi gels

Three antioxidant extracts (collagen hydrolysate, pomegranate peel extract, shrimp lipid extract) were encapsulated in soy phosphatidylcholine liposomes with the addition of glycerol. The particle size of the fresh liposomes ranged from 75.7 to 81.0 nm and zeta potential from -64.6 to −88.2 mV. Freeze-drying increased particle size (199–283 nm), and slightly decreased zeta potential. The lyophilized liposomes were incorporated in squid surimi gels at 10.5% concentration. An alternative functional formulation was also prepared by adding 2% of non-encapsulated bioactive extract. The gels were characterized in terms of colour, texture and oxidative stability (TBARS) after processing and also after frozen storage. The incorporation of the freeze-dried liposomes caused a slight decrease in gel strength and contributed to maintaining the stability of the gels during long-term frozen storage. The antioxidant properties of the bioactive extracts, liposomes and in vitro digested surimi gels were determined.