Gel Hardness Research Articles

Effects of pH, kappa‐carrageenan concentration and storage time on the textural and rheological properties of pea protein emulsion‐gels

SummaryThis study examined the rheological and textural properties of gels produced through emulsion gelation using pea protein isolate (PPI). Emulsions were prepared with varying PPI concentrations (2%–10%) and 0.25 oil fraction, followed by heat treatment. Higher PPI concentrations improved encapsulation efficiency (EE), but heat slightly reduced it, though EE remained above 90%. Droplet size decreased with higher PPI. The emulsion was then gelled with different kappa‐carrageenan (KC) concentrations (1%–2%) and pH levels (4–7). Gel hardness increased with KC content, while adhesiveness decreased. Springiness, cohesiveness and water‐holding capacity (WHC) rose with pH and KC, while meltability decreased. Rheological tests showed stronger gels with higher KC and lower pH. Storage time generally increased gel strength, except at pH 4. This work highlights the interplay between PPI, KC, pH and storage time in shaping the properties of pea protein‐based emulsions and gels.

Impact of diverse mineral hardness in electrodialysis water on the ionotropic gelation mechanism of low methoxyl pectin

In this study, the effect of desalinated lava seawater via electrodialysis (ED water) on the formation and properties of low methoxyl pectin (LMP) gels was investigated. Additionally, the syneresis, microstructure, gelation mechanism, and thermostability of the gel samples were analyzed. When the ED water content exceeded 25 %, pectin gels with viscosities and textures that differed from those of the sol were formed. The highest gel hardness (9.38 N) was observed when 50 % ED water was mixed with LMP. However, when 75 % ED water was added, the pore size of the LMP gel became the largest, and excess water was released from the gel, resulting in a weak gel strength (4.98 N). The formation and properties of the gel structure were found to be mainly due to the ionic bonds between the minerals in the ED water and the free carboxyl groups of pectin, and it was confirmed that the hydrogen bonds within the pectin chains also had an effect. These results suggest that the interaction between the ED water and LMP can be widely used in various industrial fields, including low-sugar gels or viscosity-enhancing agents with diverse rheological properties.

Insight into the effect of potassium carbonate on the physicochemical and structural properties of starch isolated from hot-dry noodles

The objective of this study was to investigate the changes in physicochemical and structural properties of starch isolated from hot-dry noodles (HDNS) treated with different contents of potassium carbonate (K2CO3). The results demonstrated that the existence of K2CO3 increased the WHC and hardness of HDNS gel with an elevated storage modulus. Meanwhile, K2CO3 promoted the gelatinization of HDNS, which displayed higher viscosity and swelling power. Moreover, the relative crystallinity of HDNS were improved. K2CO3 facilitated the transformation of HDNS from an amorphous to a more ordered and crystalline structure. Simultaneously, the microscopic characteristics exhibited that K2CO3 promoted the partial fusion of starch particles to form aggregates, and the particle size became larger. In conclusion, the physicochemical and structural properties of HDNS were improved effectively with the incorporation of K2CO3, and the research results provided new insights for the processing of high-quality hot-dry noodles.

Arabinan branches in the RG-I region of citrus pectin aid acid-induced gelation

Gelation is a critical property of citrus pectin. However, the roles played by neutral sugar side-chains on acid-induced pectin gelation remain poorly understood. Herein, galactan- or/and arabinan-eliminated pectins (P-G, P-A, and P-AG) were used to investigate the effects of side-chains on gelation. The gel hardness values of citrus pectin, P-G, P-A, and P-AG were 42.6, 39.9, 5.3, and 2.1 g, respectively, suggesting that arabinan contributed more to gelation than galactan. We next found that arabinan branches promoted pectin chain entanglement more effectively than arabinan backbones. Destabilizer addition experiments showed that hydrogen bonding, electrostatic interaction, and hydrophobic interaction were the main forces affecting pectin gel networks and strength, which was further validated by molecular dynamic simulations. The total number of hydrogen bonds between the arabinan branches and galactan/HG (65.7) was significantly higher than that between the arabinan backbones and galactan/HG (39.1), indicating that arabinan branches predominated in terms of such interactions. This study thus elucidated the roles played by neutral-sugar side-chains, especially the arabinan branches of acid-induced pectin gels, in term of enhancing high-methoxyl pectin gelation, and offers novel insights into the structure-gelling relationships of citrus pectin.

Curcumin-loaded antioxidant oleogels based on native and modified bean starches

Oleogels show promise in the food industry as potential substitutes for saturated fats, providing a medium for incorporating bioactive compounds. Starch modified with octenyl succinic anhydride (OSA) can serve as a structuring agent for vegetable oils due to its amphiphilic nature. This study aimed to develop oleogels based on native starch (NS) or modified starch (MS) bean, sunflower oil, beeswax, and curcumin. The oleogels were evaluated for gel hardness, oil holding capacity, structural stability, weight loss, X-ray diffraction, peroxide value, and antioxidant activity during 30 days of storage. The modification reduced the amylose content by 36%, viscosity by 32%, breakdown by 78%, and retrogradation by 54% of the starch. The oleogels exhibited structural stability and oil binding capacity above 96% during 30 days. Oleogels with NS and 0.5% curcumin were 20% softer than those without curcumin. Over 30 days, the hardness of the oleogels increased by 21%–48%. The addition of 0.5% curcumin in native and OSA starch oleogels increased their antioxidant activities to 41% and 35%, respectively. The texture and antioxidant properties of the oleogels indicate the feasibility of their application in food products.

Highly ordered aggregation of soy protein isolate particles for enhanced gel-related properties through konjac glucomannan addition

This study assessed the effect of konjac glucomannan (KGM) on the aggregation of soy protein isolate (SPI) and its gel-related structure and properties. Raman results showed that KGM promoted the rearrangement of SPI to form more β-sheets, contributing to the formation of an ordered structure. Atomic force microscopy, confocal laser scanning microscopy, and small-angle X-ray scattering results indicated that KGM reduced the size of SPI particles, narrowed their size distribution, and loosened the large aggregates formed by the stacking of SPI particles, improving the uniformity of gel system. As the hydrogen bonding between the KGM and SPI molecules enhanced, a well-developed network structure was obtained, further reducing the immobilized water's content (T22) and increasing the water-holding capacity (WHC) of SPI gel. Furthermore, this gel structure showed improved gel hardness and resistance to both small and large deformations. These findings facilitate the design and production of SPI-based gels with desired performance.

Modulation of acid-induced pea protein gels by gellan gum and glucono-δ-lactone: Rheological and microstructural insights

This study investigated the effect of gellan gum (GG) and glucono-δ-lactone (GDL) on the acid-induced gel properties of pea protein isolate (PPI) pretreated with media milling. The inclusion of GG substantially enhanced the gel hardness of PPI gel from 18.69 g to 792.47 g though slightly reduced its water holding capacity (WHC). Rheological analysis showed that GG increased storage modulus (G’) and decreased damping factor of gels in the small amplitude oscillatory shear region and transformed its strain thinning behavior into weak strain overshoot behavior in the large amplitude oscillatory shear region. SEM revealed that GG transformed the microstructure of gel from a uniform particle aggregate structure to a chain-like architecture composed of filaments with small protein particles attached. Turbidity and zeta potential analysis showed that GG promoted the transformation of PPI from a soluble polymer system to an insoluble coagulant during acidification. When GG content was relatively high (0.2 %-0.3 %), high GDL content increased the electrostatic interaction between PPI and GG molecules, causing their rapid aggregation into a dense irregular aggregate structure, further enhancing gel strength and WHC. Overall, GG and GDL can offer the opportunity to modulate the microstructure and gel properties of acid-induced PPI gels, presenting potential for diversifying food gel design strategies through PPI-GG hybrid systems.

Incorporation of amylose improves rheological and textural properties of Moringa oleifera seed salt-soluble protein

The interactions between corn amylose (CA) and Moringa oleifera seed salt-soluble protein (MOSP) were explored to improve the gel properties of MOSP. With increasing CA content, the MOSP-CA gel network structure was improved but the size of the gel porosity decreased firstly and then increased; the water holding retention (WHR) of MOSP-CA was decreased from approximately 94 % to 85.43 ± 2.54 %. The MOSP-CA-2.5 gel exhibited the best water holding stability (WHS), with a value of 37.1 ± 0.33 %. The MOSP-CA gel hardness increased with CA concentration, and MOSP-CA-2.5 showed relatively optimal cohesiveness, elasticity, adhesiveness, and chewiness. Meanwhile, MOSP-CA-2.5 exhibited gel strength. Incorporation of CA significantly increased the exposure of hydrophobic residues and the concentration-dependent increase in disulfide bonds in MOSP-CA gel. Thus, hydrophobic interactions, hydrogen bonds, and disulfide bonds collectively stabilized the structure of MOSP-CA gel. The findings would broaden the application of MOSP and improve the utilization value of MOSP in various industries.

Optimising corn (Zea mays) cob powder as an effective sorbent for diverse gel matrices: exploring particle size and powder concentration effects

SummaryThis study aims to valorise a plant waste, corn cobs (Zea mays) enriched with fibres (cellulose of 19.09–19.18% and hemicellulose of 34.04–60.13%), to create gel‐like sorbents. Corn cobs (CB) were dried, grounded and sieved to obtain 500, 250 and 125 μm powder size fractions. Various CB powder concentrations (10–40% w/w) were mixed with distilled water and rice bran oil for 2 min at ambient temperature to form hydrogel‐like and oleogel‐like sorbents, respectively. Visual appearance indicated that selected gels formed by 250 and 125 μm CB powders were self‐sustained right after mixing, while the largest particles (500 μm) could not fabricate gels at the CB concentrations studied. FTIR results suggested that the gelation process was primarily attributed to physical absorption rather than chemical binding. Comprehensive analyses of microstructure, physicochemical properties and rheological behaviour indicated that gelation was due to fibre–fibre interaction (125 μm) and oil/water–fibre interaction (250 μm). An increase in CB powder concentration enhanced the microstructural density and hardness of gels. Thus, 250 μm particles and higher absorbent concentrations resulted in brittle sorbents characterised by high hardness but low cohesiveness. The 250 μm particles also exhibit a superior antioxidant profile and lower oil/water loss than the 125 μm CB particles due to effective intra‐particle trapping mechanisms.

Effect of freezing on physicochemical properties and microstructure of soy protein gels

This study aimed to analyze the dynamic evolution of physicochemical properties and microstructure in soybean protein gels subjected to freezing conditions. SPI, 7S, and 11S were used in experiments. A 12g/100g protein gel was formulated after 1 and 5 days of freezing. Subsequent determination and analysis encompassed various indices, including texture, subunit composition, sulfhydryl group content, water distribution, and microstructure. The findings revealed a significant increase in the hardness of SPI, 7S, and 11S protein gels with prolonged freezing time. The 11S gel exhibited the most substantial increase, followed by SPI and 7S. And the decreases in the water-holding properties of the protein gels were 10.08%, 1.19%, and 49.34%, with the largest decrease in the water-holding properties of the 11S protein gels. Conversely, the water-holding capacity and total sulfhydryl content of SPI, 7S, and 11S protein gels decreased over time during freezing. Subunit distribution analysis indicated darker bands at the top of concentrated and separation gels. The freezing process induced the formation and growth of ice crystals, altering the spatial network structure of protein gels. Consequently, the proportion of free water in all three soybean protein gels increased, leading to enhanced mobility and a looser network structure.

Effects of alginate synergized with polyphenol compounds on the retrogradation properties of corn starch

This study aimed to investigate the impact of alginate (AG) on the retrogradation properties of corn starch (CS) in conjunction with three phenolic compounds, including naringin (NA), rutin (RT), and soy isoflavones (SI). The findings indicated that AG, NA, RT, and SI collectively resulted in a significant reduction in the hardness, retrogradation enthalpy, and relaxation time of CS gel. This effect was more pronounced when compared to NA, RT, and SI individually. The findings suggested that the elemental system comprising AG, phenolic compounds, and CS yielded enhanced water retention capacity and thermal stability. Moreover, a noticeable decrease in the short-range ordered structure and crystallinity was observed, indicating that AG and phenolic compounds effectively inhibited the retrogradation of CS; notably, the synergistic interaction between AG and SI resulted in the most favorable outcome. The results of this study provide new ideas for the design, development, and quality improvement of starch-based food.

Investigating the effects of oil type, emulsifier type, and emulsion particle size on textured fibril soy protein emulsion-filled gels and soybean protein isolate emulsion-filled gels.

The effects of oil type, emulsifier type, and emulsion particle size on the texture, gel strength, and rheological properties of SPI emulsion-filled gel (SPI-FG) and TFSP emulsion-filled gel (TFSP-FG) were investigated. Using soybean protein isolate or sodium caseinate as emulsifiers, emulsions with cocoa butter replacer (CBR), palm oil (PO), virgin coconut oil (VCO), and canola oil (CO) as oil phases were prepared. These emulsions were filled into SPI and TFSP gel substrates to prepare emulsion-filled gels. Results that the hardness and gel strength of both gels increased with increasing emulsion content when CBR was used as the emulsion oil phase. However, when the other three liquid oils were used as the oil phase, the hardness and gel strength of TFSP-FG decreased with the increasing of emulsion content, but those of SPI-FG increased when SPI was used as emulsifier. Additionally, the hardness and gel strength of both TFSP-FG and SPI-FG increased with the decreasing of mean particle size of emulsions. Rheological measurements were consistent with textural measurements and found that compared with SC, TFSP-FG, and SPI-FG showed higher G' values when SPI was used as emulsifier. Confocal laser scanning microscopy (CLSM) observation showed that the distribution and stability of emulsion droplets in TFSP-FG and SPI-FG were influenced by the oil type, emulsifier type and emulsion particle size. SPI-stabilized emulsion behaved as active fillers in SPI-FG reinforcing the gel matrix; however, the gel matrix of TFSP-FG still had many void pores when SPI-stabilized emulsion was involved. In conclusion, compared to SPI-FG, the emulsion filler effect that could reinforce gel networks became weaker in TFSP-FG.

Extraction and Structural Analysis of Sweet Potato Pectin and Characterization of Its Gel.

Pectin is widely used in the food and pharmaceutical industries. However, data on sweet potato pectin extraction and structural property analyses are lacking. Here, for the high-value utilization of agricultural processing waste, sweet potato residue, a byproduct of sweet potato starch processing, was used as raw material. Ammonium oxalate, trisodium citrate, disodium hydrogen phosphate, hydrochloric acid and citric acid were used as extractants for the pectin constituents, among which ammonium oxalate had a high extraction rate of sweet potato pectin, low ash content and high molecular weight. Structural and gelation analyses were conducted on ammonium oxalate-extracted purified sweet potato pectin (AMOP). Analyses showed that AMOP is a rhamnogalacturonan-I-type pectin, with a molecular weight of 192.5 kg/mol. Chemical titration and infrared spectroscopy analysis confirmed that AMOP is a low-ester pectin, and scanning electron and atomic force microscopy demonstrated its linear molecular structure. Gelation studies have revealed that Ca2+ is the key factor for gel formation, and that sucrose significantly enhanced gel hardness. The highest AMOP gel hardness was observed at pH 4, with a Ca2+ concentration of 30 mg/g, pectin concentration of 2%, and sucrose concentration of 40%, reaching 128.87 g. These results provide a foundation for sweet potato pectin production and applications.

Assembly behavior and nano-scale microstructure of tamarind gum/xanthan synergistic interaction gels

Synergistic interaction gels (SIGs) hold immense promise for applications in 3D printing, colonic drug delivery, and sustained release. The amalgamation of xanthan and tamarind gum (TMG) gives rise to SIGs through molecular interaction; however, the intricacies of their assembly behaviors remain elusive. This work elucidates that in xanthan-rich systems, the predominant formation of xanthan aggregations shapes network assembly structure, with TMG clusters adhering to them. Conversely, in TMG-rich systems, TMG clusters actively participate in creating a “sea-island” assembly structure enveloped by xanthan aggregations. Higher concentration of TMG contributes to augmenting the association extent of TMG and xanthan. The heightened binding between TMG and xanthan correlates with an increase in chain distance in scatters and the compactness of scatter arrangement. These favor the development of micro-structures with a relatively larger mesh size and the enhancement of gel hardness. This study serves to facilitate the design and production of SIGs-based artificial gel foods with the requisite performance characteristics, such as artificial sea cucumber and porcine back fat.

Development and Characterization of Hybrid Meat Analogs from Whey Protein-Mushroom Composite Hydrogels.

There is a need to reduce the proportion of animal-derived food products in the human diet for sustainability and environmental reasons. However, it is also important that a transition away from animal-derived foods does not lead to any adverse nutritional effects. In this study, the potential of blending whey protein isolate (WPI) with either shiitake mushroom (SM) or oyster mushroom (OM) to create hybrid foods with enhanced nutritional and physicochemical properties was investigated. The impact of OM or SM addition on the formation, microstructure, and physicochemical attributes of heat-set whey protein gels was therefore examined. The mushroom powders were used because they have relatively high levels of vitamins, minerals, phytochemicals, and dietary fibers, which may provide nutritional benefits, whereas the WPI was used to provide protein and good thermal gelation properties. A variety of analytical methods were used to characterize the structural and physicochemical properties of the WPI-mushroom hybrids, including confocal microscopy, particle electrophoresis, light scattering, proximate analysis, differential scanning calorimetry, thermogravimetric analysis, dynamic shear rheology, textural profile analysis, and colorimetry. The charge on whey proteins and mushroom particles went from positive to negative when the pH was raised from 3 to 9, but whey protein had a higher isoelectric point and charge magnitude. OM slightly increased the thermal stability of WPI, but SM had little effect. Both mushroom types decreased the lightness and increased the brownness of the whey protein gels. The addition of the mushroom powders also decreased the hardness and Young's modulus of the whey protein gels, which may be because the mushroom particles acted as soft fillers. This study provides valuable insights into the formation of hybrid whey protein-mushroom products that have desirable physiochemical and nutritional attributes.

Modification of pea starch using ternary mixtures of natural crosslinking agents: Vanillin-chitosan-betaine and vanillin-gelatin-betaine

Different methods of starch modification have been proposed to broaden its application. In this study, the effects of ternary mixtures of natural crosslinking agents: chitosan-betaine-vanillin and gelatin-betaine-vanillin on the properties of pea starch were explored. These combinations of substances were selected because they have complementary crosslinking mechanisms. The effects of the ternary crosslinker mixtures on the gelatinization, mechanical properties, thermal stability, and microstructure of pea starch were compared. Both combinations of crosslinkers enhanced the gelatinization viscosity, viscoelasticity, gel hardness, and thermal stability of the pea starch, by an amount that depended on the ratio of the different components in the ternary mixtures. In all cases, the crystal structure of the starch granules disappeared after gelatinization. The modified starch had a more compact and uniform microstructure than the non-modified version, especially when it was crosslinked by vanillin, gelatin, and betaine. The improvement in the gelation properties of the starch were primarily attributed to hydrogen bonding, electrostatic attraction, and Schiff base crosslinking of the various components present. Gelatin enhanced the gel strength more than chitosan, which was probably because of greater hydrogen bonding. Our findings suggest that the properties of starch can be enhanced by adding ternary mixtures of natural crosslinkers.

Molecular regulation of rapeseed protein for improving its techno-functional properties

To improve the techno-functional properties of rapeseed protein (RP), this work tried to regulate the molecular structure of RP via inducing the co-assembly of RP with zein and whey protein (WP). The results showed that WP and zein mainly regulate the folding process of RP through hydrophobic and disulfide bonds, thereby altering the structural conformation and forming stable complex RP (CRP). WP addition not only increased the number of surface charges and hydrophilicity of proteins, but also decreased their sizes, improved the water solubility, as well as the availability of active groups. These changes significantly increased the foaming capacity (from 60 % to 147 %) and in vitro gastric digestion rate (from 10 % to 60 %) of CRP. Besides, WP also contributed to the formation of gels and the regulation of their textural profiles. Comparatively, zein improved the hydrophobicity of CRP and balanced degree of intermolecular forces, which effectively increased the emulsifying activity index of CRP from 22 m2/g to 90 m2/g. Zein decreased the hardness, springiness and water-holding capacity of gel, but increased its gumminess and chewiness. Overall, both WP and zein effectively changed the structural conformation of RP, and improved its techno-functional properties, which provides an effective strategy to modify protein.

Effects of Eucommia ulmoides leaf powder on the gelatinization, rheology, and gel properties of sweet potato starch

This study aimed to explore the feasibility of employing Eucommia ulmoides leaf powder (ELP), which is a novel medicinal and food homologous material, to improve the physicochemical properties of sweet potato starch (SPS) gel. The effects of ELP on the gelatinization, rheology, and gel properties of SPS were investigated. The Brabander viscosity test results showed that ELP could reduce the peak viscosity, trough viscosity, final viscosity, and setback value of SPS. The rheological tests showed that the SPS-ELP gels had shear-thinning behavior, and that the ELP could decrease the apparent viscosity, shear stress, G′, G″ of SPS-ELP gels and make the gels exhibit stronger liquid-like behavior. The X-ray diffraction pattern indicated that the ELP could decrease the relative crystallinity and retard retrogradation of SPS-ELP gels, which was cofirmed by microscopic structure analysis. The ELP had a significant effect on the color difference of the gels, resulting in a yellow-green color. The addition of ELP also reduced the hardness of SPS-ELP gels, and increased the median particle size D50, volume mean diameter D [4,3], and area mean diameter D [3,2] of gel particle size distribution. These findings suggest that ELP has a good potential in improving starch gel properties.

Physicochemical characteristics of tea seed starches from twenty-five cultivars

The physicochemical features of starches separated from tea seeds of 25 cultivars were analyzed. The distinct characteristic of tea seed starches was that they had high apparent amylose content (AAC, 28.94–39.91 %) and resistant starch contents (4.64–8.24 %), suggesting that tea starch can be used for production of low glycemic index food. One cultivar (T12) had smallest breakdown (74.2 RVU) and highest gel hardness, indicating it performed stably during shear thinning, resulting in a firm texture. Another cultivar (T25) had a peak viscosity of 417.6 RVU, a large breakdown and small setback, suggesting a low tendency for retrogradation. There was a range of 61.6 °C to 77.5 °C for the peak gelatinization temperature and 0.163 to 0.390 for the flow behavior index values. These parameters could serve for selecting suitable starches with minor differences in physicochemical properties for food use. Correlation analysis indicated that AAC is a key factor determining starch retrogradation properties. The broad genetic diversity in the tea seed starch physicochemical features provided potentially versatile applications in the food industry. The results gained from the present study contribute to a better understanding of tea seed starch quality, and encourage its application in many value-added food products.

Unraveling the mechanisms of pea protein isolate in modulating retrogradation behavior of pea starch

The study investigated the impact of pea protein isolate (PPI) on the short-term and long-term retrogradation behavior of pea starch (PS). Dynamic time scanning and water migration analysis revealed that the presence of PPI enhanced water mobility within the PS gel during short-term storage (4 °C, 8 h) and impeded amylose gelation, effectively suppressing the short-term retrogradation of amylose. Over long-term storage (4 °C, 14 d), PPI reduced the retrogradation enthalpy and the ordered structure of starch molecules. The relative crystallinity and retrogradation degree reduced by 40.6% and 29.9%, respectively, as the PPI content increased from 0 to 12%. Textural profile analysis showed PPI decreased the gel hardness and induced the formation of a weak gel of PS, thereby delaying the long-term retrogradation of amylopectin. Scanning electron microscopy analysis further confirmed that the PS-PPI mixed gel exhibited a more disordered and loose structure compared to the PS gel, which resulted from PPI inhibiting the rearrangement and aggregation of amylose and amylopectin molecules. These findings suggested that PPI exhibited the potential to inhibit the short-term and long-term retrogradation of PS, thus providing valuable theoretical evidence for enhancing the development and research of pea-based products.