Gel Hardness Research Articles

Improvement in texture and color of soy protein isolate gel containing capsorubin and carotenoid emulsions following microwave heating.

The effects of microwave heating on the properties and pigment release of soybean protein isolate (SPI) emulsion gel and hydrogel were investigated. The properties of the samples were analyzed by rheology and texture. The results showed that the hardness of the emulsion gel was lower than that of the hydrogel, but the cohesiveness was the opposite. The hydrogen bonding and electrostatic interaction between SPI and soybean soluble polysaccharide (SSPS) enhanced the thermal stability of the gel, and the enthalpy values were the lowest. In addition, a chroma meter was used to assess the slow-release effect of pigment, with results indicating that the emulsion gel was more red and yellow than the hydrogel; the values of a* and b* were reduced with the extension of heating time, indicating that the emulsion had a good protective effect on carotenoids and capsorubin, which was helpful to the application of the pigment in food.

Gel properties and in vitro digestion of sea bass (Lateolabrax japonicus) myofibrillar protein – Lipid composite gels: Focus on lipid type and content

The effects of lipid type and content on gel and digestion properties of myofibrillar proteins (MPs) were studied. The MPs sol was combined with three types of lipid (peanut oil, sunflower oil, and lard) with different contents (0.5–2%) to obtain composite gels. As for whiteness, no differ was observed in composite gels without or with lipid addition. The water holding capacity and hardness of composite gels with lipid addition increased. Moreover, fourier transform infrared spectra (FTIR) demonstrated composite gels with 1% emulsion addition exhibited the highest β-sheet content. The confocal laser scanning microscope (CLSM) revealed that networks of composite gels with 1% emulsion addition possessed more densely compared to control group. During the in vitro digestion, high performance liquid chromatography (HPLC) results showed the peptide (>10 kDa) contents of composite gels with lipid addition were lower than that of control group under the simulated gastric phase. Moreover, the 2–5 kDa polypeptide content of composite gels with lipid addition was higher than that in observed in control group under intestinal phase. The results illustrated the gel and in vitro digestion mechanism of composite gels with lipid addition, which can be valuable for the fabrication of functional surimi products.

Effect of feruloylated arabinoxylan on the retrogradation and digestibility properties of pea starch during short-term refrigeration: Dependence of polysaccharide structure and bound ferulic acid content

In this study, arabinoxylans (AX) with various molecular weights (Mw) and bound ferulic acid (FA) contents were prepared to compare their effects on the gelatinization, short-term retrogradation and digestive properties of pea starch (PeS). The results indicated that all AX samples could obviously impede the pasting process of PeS and inhibit the short-term retrogradation of PeS-based gels during refrigeration by hindering the rearrangement and double helical associations of amylose. More precisely, AXs with low Mw and the highest FA content (H-FAX) exhibited the strongest intervention ability on PeS compared with the other samples. According to the Fourier transform infrared spectroscopy and X-ray diffraction results, it might be due to the unique role of bound FA as a noncovalent cross-linking agent, which enhanced the association between AX and starch molecules through extra hydrogen bonding interactions and entanglement behaviour. On these bases, H-FAX clearly improved the hardness, chewiness, moisture content, and sensory acceptance of PeS-base gels (pea jelly), and could also regulate its starch composition during short-term refrigeration to delay starch digestion. Overall, AXs with appropriate structural features might obviously improve the quality and storage stability of PeS-based foods.

Development of non-linear prediction model for starch blending

Starch blending is a common method for achieving ‘clean label’ with altered properties. However, blending is typically non-additive, making it challenging to predict property changes after mixing. Therefore, this study not only investigated the physicochemical properties of blended starch but also predicted them from individual starches. Six starch samples (rice, corn, potato, tapioca, mungbean, waxy rice) were selected and assessed for individual intrinsic properties (granule size, amylose content, crystallinity, amylopectin chain length). Starch binary blends were then prepared from six starch samples at different blending ratios (100:0, 75:25, 50:50, 25:75, 0:100). Non-additive behaviors were shown in pasting stability, gel storage modulus, and hardness. Notably, the gel storage modulus exceeded expectations, increasing by 140.5% in rice-potato (50:50) and 116.2% in potato-tapioca (50:50) blends. The study also revealed strong correlations among starch properties, suggesting the potential to predict physical properties (e.g., gel hardness, storage modulus) based on intrinsic properties. Developed non-linear models based on the data accurately predicted properties beyond the test set, with a high coefficient of determination (R2 ≒ 0.9). As a result, the models proposed in this study successfully predict physical properties of blended starch, benefiting the food industry interested in clean label starch production and application.

Effect of pH and Calcium on the Techno Functional Properties of Different Pulse Flours, Pastes, and Gels

AbstractIn this study, our objective was to show the effects of pH and calcium on the techno functional properties of four pulse flours (chickpea, lentil, red lentil, and white bean) and the rheological properties of their pastes and gels. Five conditions were considered: a natural condition and four modifications (pH 3 and pH 5; with or without calcium addition). All measured properties varied with the type, condition, and the interaction among them. All flours exhibited high foaming capacity (44.3 − 78.8%) and emulsifying capacity (46.6 − 49.9%). The white bean flour showed a high water holding capacity (1.6 – 2.0 g/g), and the red lentil, lentil, and chickpea formed strong gels and high viscosity pastes. For the four pulses, the water holding capacity and foaming capacity of the flours and the viscosity of the pastes were improved by decreasing the pH (at 3 or 5) plus the addition of calcium. The hardness, elasticity, and resistance of gels obtained from pulse flours (except for white bean) were high when using natural conditions. Lowering pH resulted in a reduction of these parameters.

Tea polyphenol-mediated network proteins modulate the NaOH-heat induced egg white protein gelling properties

The crosslinked network aggregation of proteins regulates the formation and property maintenance of gels. In this study, we analyzed the influence of tea polyphenol (TP)-mediated network proteins on the formation and gel properties of NaOH-thermally induced egg white gels (EWGs). The free sulfhydryl content decreased slowly from 13.12 μmol/g pro to 10.89 μmol/g pro with the addition of TP and reduced the degradation of ovalbumin as a network protein during the formation of EWGs. With increased TP and NaOH concentrations, the surface hydrophobicity and absolute value of ζ-potentials of EWG improved obviously. The mechanical test results revealed that an increase in the NaOH concentration weakened the textural properties of EWG, while adding TP increased the gel strength from 161.38 g to 195.89 g, but the rupture strength decreased from 2144.6 g to 471.59 g. Rheological results demonstrated that EWG with TPs exhibited enhanced rigidity, an increased proportion of covalent bonds, and a more compact gel network structure than EWG without TPs. The stress relaxation results were fitted using the five-element Maxwell model, which revealed that an increase in the NaOH concentration decreased gel hardness and viscosity, whereas an increase in the TP concentration enhanced gel hardness. The increase in the NaOH and TP concentrations significantly increased the surface hydrophobicity of EWGs and promoted the rise of intermolecular forces and disulfide bond interactions. Heat modification further denatured and crosslinked the non-alkalized EW proteins, resulting in a compact protein gel network structure and improved gelation characteristics.

Characterization of a low-methoxyl pectin extracted from red radish (Raphanus sativus L.) pomace and its gelation induced by NaCl

There is an increasing demand for obtaining pectin from new sources. Red radish (Raphanus sativus L.) pomace pectin extracted by alkali was low-methoxyl pectin with esterification degree of 10.17 %, galacturonic acid content of 69.71 % (wt), and average molar weight of 78.59 kDa. The pectin primarily consisted of rhamnogalacturonan I and homogalacturonan domains. The predominant monosaccharides of the pectin were galacturonic acid (46.32 mol%), arabinose (16.03 mol%), galactose (10.46 mol%), and rhamnose (10.28 mol%), respectively. The red radish pomace pectin solution exhibited a shear-thinning behavior. NaCl could induce gelation of red radish pomace pectin, and the gel properties of red radish pomace pectin were considerably affected by the NaCl concentration. As the NaCl concentration (0.25–0.50 mol/L) increased, the rate of gelation accelerated, and the time to gelation point appeared earlier. There was an optimal NaCl concentration (0.50 mol/L) for the pectin to form a gel with the greatest solid-like properties, gel hardness (33.84 g) and water-holding capacity (62.41 %). Gelation force analysis indicated gel formation mainly caused by electrostatic shielding effect of Na+ and hydrogen bonding. This research could facilitate the applications of the red radish pomace pectin in the realm of edible hydrocolloids.

New insights into the interaction between bamboo shoot polysaccharides and lotus root starch during gelatinization, retrogradation, and digestion of starch

In this study, the interaction between bamboo shoot polysaccharides (BSP) and lotus root starch (LS) during gelatinization, retrogradation, and digestion of starch was investigated. The addition of BSP inhibited the gelatinization of LS and decreased the peak viscosity, valley viscosity, and final viscosity. Amylose leaching initially increased and then decreased with the increase in BSP addition. The apparent viscosity and viscoelasticity of LS decreased with the increase in BSP addition. Moreover, 3 % BSP increased the hardness and cohesiveness of LS gel, whereas 6 %–15 % BSP decreased them. In addition, 3 %–6 % BSP promoted the uniform distribution of water molecules in the starch paste, whereas the addition of 12 % and 15 % BSP resulted in the inhomogeneous distribution of the water. The retrogradation degree of LS gel gradually increased with the increase in BSP addition from 3 % to 6 %, whereas 9 %–15 % BSP restricted the short-term and long-term retrogradation of LS. After 12 % BSP was added, the RDS content reduced by 11.6 %, the RS content significantly increased by 75 %, and the digestibility of starch decreased. This work revealed the interaction between BSP and LS during starch gelatinization, retrogradation, and digestion to improve the physicochemical properties and digestive characteristics of LS.

Preparation of egg white powder using electrohydrodynamic drying method and its effect on quality characteristics and functional properties.

This research investigated the effects of spray drying (SD, set at 180°C), freeze-drying (FD, set at -35°C), and electrohydrodynamic drying (EHD) with and without the foam-mat method on egg white. The configuration used in EHD was a wire-to-plate type at room temperature. The results showed no significant difference in gel hardness and WHC% (P≥0.05). Also, the foam-mat EHD powders resembled the FD powders in microstructure, appearance, flowability, and absorption intensity of the Amide I and II bands. Furthermore, the foam-mat EHD (DC-) powder had the highest protein content (66.1%), enthalpy (-183.06J/g), and foaming capacity (725%) (P<0.05). This finding was proved by FTIR, Raman, and SDS-PAGE tests, which revealed the minor structural changes in proteins (peptide chain structure, Amide I, Amide II, α-helix, and β-sheet). FD powder demonstrated good protein stability in zeta potential and foam stability tests.

Retrogradation inhibition of wheat starch with wheat oligopeptides.

Starch staling greatly reduces the cereal products quality, and the staling retardation becomes a focus in current research. The effect of wheat oligopeptide (WOP) on anti-staling properties of wheat starch (WS) was studied. Rheology property indicated that WOP reduced WS viscosity, showing more liquid-like behavior. WOP improved the water holding capacity, inhibited swelling power, and reduced the hardness of WS gels, which decreased from 1200 gf to 800 gf compared with the control after 30days storage. Meanwhile, the water migration of WS gels were also reduced with WOP incorporation. The relative crystallinity of WS gel with 1% WOP was reduced by 13.3%, and the pore size and the microstructure of gels was improved with WOP. Besides, the short-range order degree reached the lowest value with 1% WOP. In conclusion, this study explained the interaction between WOP and WS, which was beneficial to the application of WOP in WS-based food.

Long-Term Retrogradation Properties and In Vitro Digestibility of Waxy Rice Starch Modified with Pectin.

In recent years, the blending of hydrocolloids and natural starch to improve the properties of natural starch has become a research hotspot. In this study, the effects of pectin (PEC) on the retrogradation properties and in vitro digestibility of waxy rice starch (WRS) were investigated. The results showed that PEC could significantly (p < 0.05) reduce the retrogradation enthalpy and reduce the hardness of WRS gel. X-ray diffraction results indicated that PEC could reduce the relative crystallinity of the composite system, and the higher the PEC content, the lower the relative crystallinity. When the PEC content was 10%, the relative crystallinity of the composite system was only 10.6% after 21 d of cold storage. Fourier transform infrared spectroscopy results proved that the interaction between PEC and WRS was mainly a hydrogen bond interaction. Furthermore, after 21 d of cold storage, the T23 free water signal appeared in the natural WRS paste, while only a small free water signal appeared in the compound system with 2% PEC addition. Moreover, addition of PEC could reduce the starch digestion rate and digestibility. When the content of PEC increased from 0% to 10%, the digestibility decreased from 82.31% to 71.84%. This study provides a theoretical basis for the further application of hydrocolloids in starch-based foods.

Interpreting the “twice gelation” mechanism of a novel egg-based yoghurt through the dynamics of rheology, microstructure, and intermolecular forces

In this paper, we interpreted the “twice gelation” mechanism of egg-based yoghurt through the integrated multidimensional dynamic change analysis of rheology, microstructure, and intermolecular forces. The results showed that during the first gelation stage (i.e., thermal gelation), egg proteins underwent heat denaturation and formed crosslinks, with the main intermolecular forces involved in gel formation being disulfide bonds (∼84%). After homogenization by the colloid mill, the heat-induced gel transformed into a smooth, viscous fluid state, which subsequently turned into a weak gel as the pH continuously decreased under the effect of lactic acid bacteria fermentation. In the second gelation stage (i.e., acid gelation), the proportion of hydrophobic interactions increased from ∼12% to ∼49%, whereas the proportion of disulfide bonds decreased from ∼74% to ∼45%, indicating that hydrophobic interactions played a crucial role in the second gelation, while disulfide bonds still showed great importance in stabilizing the gel structure, although their percentage decreased significantly. In summary, egg proteins form a hard gel by heating, and this heat-induced gel has the ability to gel twice after homogenization, making it possible to form egg-based yoghurt with a fine texture and good taste under the action of lactic acid bacteria fermentation.

Lactiplantibacillus plantarum strains with proteolytic abilities showed diverse effects on casein gel formation during fermentation

Proteolysis is often used to improve gel-forming properties of protein, however, the proteolytic effect of lactic acid bacteria on protein gel properties has been rarely reported. The purpose of this study is to investigate the potential role of proteolysis by Lactiplantibacillus plantarum in casein gel formation during fermentation. A total of fifty-four L. plantarum strains were subjected to a screening of proteolytic ability and twenty-one strains were found possessing extracellular protease-producing abilities. The top nine strains with varying proteolytic abilities were investigated for their impacts on casein gel formation. Interestingly, the casein gels fermented by the strains with the highest and lowest proteolytic abilities both showed relatively low hardness and lower storage modulus (G′) and loss modulus (G″) in rheological analyses. However, two strains, namely L. Plantarum YM13-8.1 and L. Plantarum YN22-3.1, which possess a relatively moderate level of proteolytic ability among the nine strains, significantly improved the hardness and water-holding capacity of casein gels and presented a more dense and uniform gel structure, which was accompanied by an increased hydrophobicity and disulfide bond content. The results indicate that the strains YM13-8.1 and YN22-3.1 can facilitate the formation of casein gel by improving the aggregation of protein molecules in fermentation. Concludingly, we propose that the proteolysis by L. plantarum proteinases dramatically influences the casein gel properties, and the effects, to a certain degree, are strain-specific.

Heat-moisture treatment to modify structure and functionality and reduce digestibility of wrinkled and round pea starches

Heat-moisture treatment (HMT) was employed to modify wrinkled pea (74.2 % and 76.5 % amylose) and round pea starches (35.9 % and 34.8 % amylose) at 35.0 % moisture, 110 or 130 °C, and 6 h. HMT increased the gelatinization temperatures and decreased the gelatinization enthalpy changes, reduced the pasting viscosities and gel hardness, and enhanced the enzymatic resistance of the pea starches in comparison with the native counterparts, with greater extents of changes observed for HMT at 130 °C overall. Although HMT decreased the relative crystallinity and elevated the proportion of amorphous conformation, the remaining double-helical crystallites in the modified samples showed improved thermal stability as revealed by differential scanning calorimetry (DSC). More importantly, the HMT-modified pea starches required a higher heating temperature of 120 °C, rather than 95 °C, in Rapid Visco Analyser to provide greater pasting viscosities and develop firmer gels, suggesting that the modified samples had stronger molecular entanglement than the native counterparts. Such molecular entanglement could also reduce enzymatic digestion of HMT-modified starches after boiling in water. With more diverse functional profiles and increased resistant starch (RS) contents (particularly for the HMT-modified wrinkled pea starches having 22.7–29.9 % RS), the HMT-modified pea starches could be promising new ingredients for food applications.

Fibrous cellulose improves the strength and water retention of heat-induced myofibrillar protein gel by microstructure enhancement

In this study, four kinds of cellulose were prepared by mechanical grinding and/or acidolysis methods, including fibrous microfibrillated cellulose (MFC), fibrous nanofibrillated cellulose (CNF), rod-like microcrystalline cellulose (MCC) and acicular nanocrystalline cellulose (CNC). Subsequently, the effects of different amounts of these celluloses (0.1, 0.3, 0.5, 0.7 and 1.0 wt%) on properties of chicken myofibrillar protein (MP) gel were investigated. The results showed that the addition of all celluloses induced the compact and uniform gel microstructure, which significantly improved the gel hardness and water holding capacity (p < 0.05), stabilized the internal water content of gel and improved its viscoelasticity. Compared with MCC and CNC, CNF and MFC with 0.5 wt% significantly improved the gel performance (p < 0.05), indicating that the enhancement of MP gel by cellulose was largely dependent on the shape and length-diameter ratio rather than the size. In addition, the filling of cellulose had percolation threshold, in other words, excessive filling was not conducive to the strengthening effect of cellulose. Finally, two mechanical models (Halpin-Kardos and Ouali) were introduced to explain the enhancement mechanism of MP gel by cellulose, it was found that the formation of CNF filler network in MP matrix was the main reason for the enhancement of MP gel.

Effect of formation of the maltodextrin/gelatin emulsion on gel properties of gelatin

This work investigated the influence of formation of the maltodextrin/gelatin emulsion on gel properties of gelatin. When the maltodextrin/gelatin emulsion was formed, adding maltodextrin increased the gelling temperature (Tg) but decreased the hardness of the gelatin gel. However, adding sucrose increased both the Tg and hardness, since no emulsion was formed. Thus, this work further investigated effects of the initial volume ratio of the gelatin and maltodextrin solutions (VGE/VMD), the dextrose equivalent (DE) of maltodextrin and the biopolymer concentrations on microstructure and properties of the emulsion gel. When the VGE/VMD was 3:7, 5:5, and 7:3, the Tg was 21.6, 24.6, and 23.8 °C, respectively, while the hardness was 365.2, 570.1, and 708.7 g, respectively. The droplet size decreased, as the VGE/VMD increased. These results suggested that smaller droplets induced a stronger emulsion gel. Similarly, maltodextrin of higher DE induced smaller droplets, lower Tg and larger hardness. Moreover, the gelatin concentration was positively correlated with the Tg and hardness but had no linear correlation with the droplet size, which suggested that more gelatin improved the gelling ability, and the emulsion gel strength depended on the gelling ability rather than the microstructure. Similarly, more maltodextrin induced higher Tg and hardness but bigger droplets.

Rheological and physicochemical properties of heat-induced ovalbumin gels in presence of sodium carboxymethyl cellulose.

In this study, the effect of sodium carboxymethylcellulose (CMC-Na) on the rheological and physicochemical properties of heat-induced ovalbumin (OVA) gels was evaluated. The OVA/CMC-Na composite gels were prepared by heat-induced (85 °C, pH 7.0) a mixture of CMC-Na (0, 0.2, 0.4, 0.8 and 1%) and OVA. The results revealed that the addition of CMC-Na dramatically reduced the springiness and hardness of the composite gels, while slightly enhancing the intermolecular hydrogen bonding interactions, which facilitated the improvement of the softness of the gels. It can be observed by SEM that the added CMC-Na was stacked on the surface of the OVA, resulting in visible "linear bumps". All gel samples exhibited shear-thinning behavior. The apparent viscosity of the composite gels increased with the addition of CMC-Na, and the OVA gel with 1% CMC-Na showed the highest apparent viscosity and the lowest storage modulus (G'). Additionally, low field nuclear magnetic resonance (LF-NMR) measurements indicated that the increasing CMC-Na boosted the water mobility of the composite gel. This study offers a novel approach to the development of ovalbumin-based soft gel foods, especially for certain populations with swallowing difficulties.

Insight into the improvement in pasting and gel properties of waxy corn starch by critical melting treatments

To improve the pasting and gel properties of waxy corn starch (WCS), the native starch was modified by critical melting (CM) at the onset temperature (TO), peak temperature (TP), and conclusion temperature (TC) (labeled CMO, CMP, and CMC respectively). CM treatments significantly enhanced the thermal stability of the WCS, as indicated by the increase in the peak gelatinization temperature, pasting temperature, and peak time. In addition, after CMP treatment, the storage modulus, hardness, gumminess, springiness, and chewiness of starch gels significantly increased by 43.29 %, 31.14 %, 23.36 %, 8.26 %, and 61.43 %, respectively, and the syneresis rate significantly decreased by 19.69 % (p < 0.05). These results indicated that CMP treatments significantly improved the gelling ability and freeze-thaw stability of the WCS. These results are ascribed to the partial disruption and enhanced rearrangement of the starch crystalline structure. CMP treatment induced the crystalline structure of starch to be partially disrupted and a hard structure was formed on the surface of starch granules. The hard structure in CMP-treated starch supplied more attachment points for crystalline structure rearrangement during gelatinization. Therefore, the above results indicated that CMP treatments can be used to modify starch to improve the pasting and gel properties of starch-based food products.

Characterization of the physiochemical properties, microstructure, and molecular interactions of a novel rice-pea protein gel.

The application of rice and pea proteins in food production is limited due to their undesirable processing performance. The objective of this research was to develop a novel rice-pea protein gel using alkali-heat treatment. This gel had a higher solubility, stronger gel strength, better water retention capacity, and denser bilayer network. This is due to the alkali-heat induced modifications for the secondary structures of proteins (i.e., a decrease in the α-helix, and an increase in the β-sheets) and the interactions between protein molecules. The network structure of gel was more compact by adding 2% and 4% alkali-heat rice protein (AH-RP). This resulted in a stable double-layer network structure of gel. Adding 4% AH-RP significantly improved the hardness and elasticity of gel. This gel will have a good potential use for being the ingredient to produce the functional foods and meat analogs.

Combined effect of heating temperature and content of pectin on the textural properties, rheology, and 3D printability of potato starch gel

Three-dimensional (3D) printing is one of the emerging techniques which fabricates customized foods with desired sensory characteristics. Rheological properties of 3D printing materials are vitally important in printability which govern the flowability and structural stability. Due to its unique gel-forming characteristics, potato starch has been extensively used in myriad food applications, such as 3D printing. However, little attention has been paid to the combined effect of heating temperature and pectin addition on the properties of potato starch gels. Thus, this study investigated the impact of different pectin contents (1, 1.5, and 2 %) on printability and the rheological and textural properties of potato starch gels heated at different temperatures (70, 80, and 90 °C). The gel heating temperature governs pectin-driven modifications in potato starch gels. Pectin addition increased the 3D printability, viscosity, storage modulus, hardness, gumminess, and springiness of starch gel at higher temperatures (80 °C and 90 °C). In contrast, at lower temperatures (70 °C), pectin addition decreased printability, viscosity, storage modulus, hardness, gumminess, and springiness. Therefore, the gel heating temperature influences the impact of pectin on printability, rheology, and textural properties. Accordingly, the combined effects of pectin and heating temperature should be considered in pectin-based 3D food-printing ink formulations.