Freeze-thaw Treatment Research Articles

Elastic and conductive gellan gum/polyvinyl alcohol physical hydrogels with low swelling potential for sustainable flexible electronics

Conductive hydrogels are considered to be promising materials for flexible electronics, but those nondegradable are bound to produce substantial undesirable electronic wastes once widely applied, inconsistent with the long-term sustainable development goals. To develop biodegradable conductive hydrogels for sustainable flexible electronics, a green chemical reaction-free strategy was developed to manufacture a novel type of composite hydrogels, exploiting biodegradable gellan gum and polyvinyl alcohol as the matrices and natural-derived tannic acid as the crosslinking agent. The technique involves successive cool-induced sol−gel transition, freeze-thawing and Na2SO4 solution treatment. A universal electronic testing machine, scanning electronic microscope, X-ray diffractometer, thermogravimetric analyzer, and electrochemical work station were employed to study the mechanics, structure and morphology, swelling and conductivity of the hydrogels. The results indicate strong, elastic and tough hydrogels were achieved owing to the multi-crosslinked multiple-network structure. The maximum compressive stress (90% strain), tensile strength, breakage elongation and fracture energy reach 10.7 MPa, 1.2 MPa, 890% and 480 kJ/m3 respectively. The stress recovery rate still remains 86% after 10 consecutive loading-unloading under 200% strain. The highest conductivity reaches 3.27 S/m, which along with the excellent mechanics confers them good strain-sensing behavior. Moreover, the final hydrogels show low swelling in both water (the equilibrium swelling ratio (ESR) < 300%) and physiological saline (ESR < 90%). The excellent mechanical performance, high conductivity and good strain sensing, low swelling and inherent biodegradability as well as the ecofriendly manufacturing process imply potential prospect in sustainable flexible electronics.

Mechanical properties and damage modeling of unloaded marble under freezing and thawing with different temperature ranges

The seasonal freeze-thaw environment is a primary factor contributing to the deterioration of manually excavated disturbed rock masses on reservoir bank slopes in highland alpine areas. To investigate the mechanical properties and damage deterioration mechanism of excavation-unloading rock under seasonal freeze-thaw environment in cold region, the freeze-thaw cycle tests with different temperature difference levels (−10–10 °C, −15–25 °C, −20–40 °C) and different cycle times (0,10,20,30) were simulated for the triaxial unloading damaged marble. Then, the mechanical parameters of unloaded marble after freezing and thawing were obtained by uniaxial compression and triaxial compression tests, and the influence laws of temperature ranges, number of freezing and thawing cycles and confining pressure on the mechanical properties of unloaded marble were analyzed. Finally, the damage model of unloaded marble considering freeze-thaw action was established. The results show that the strength of unloaded marble is significantly weakened under the combined effect of F-T (freezing and thawing) and loading, and that the deterioration effect of the number of F-T cycles is stronger than that of the temperature ranges. The increase in the confining pressure increased the compressive strength and elastic modulus of the unloaded marble, and suppressed the damage of the unloaded marble after the freeze-thaw treatment. The porosity of the unloaded marble developed gradually and increased exponentially with the increase of the number of freeze-thaw cycles, the compressive strength and elastic modulus had a negative exponential relationship with the number of freeze-thaw cycles, and the shear strength parameter had a quadratic polynomial relationship with the number of freeze-thaw cycles. In addition, the softening mechanism of unloaded marble by natural water plays a key role in the process of freeze-thaw cycle, and the damage model considering freeze-thaw is established, and the theoretical curves are well matched with the experimental results. The outcomes of this study hold significant theoretical and engineering importance for evaluating the stability of excavated unloaded rock in highland alpine regions.

N-rich chitosan-derived porous carbon materials for efficient CO2 adsorption and gas separation.

Capturing and separating carbon dioxide, particularly using porous carbon adsorption separation technology, has received considerable research attention due to its advantages such as low cost and ease of regeneration. In this study, we successfully developed a one-step carbonization activation method using freeze-thaw pre-mix treatment to prepare high-nitrogen-content microporous nitrogen-doped carbon materials. These materials hold promise for capturing and separating CO2 from complex gas mixtures, such as biogas. The nitrogen content of the prepared carbon adsorbents reaches as high as 13.08wt%, and they exhibit excellent CO2 adsorption performance under standard conditions (1 bar, 273K/298K), achieving 6.97mmol/g and 3.77mmol/g, respectively. Furthermore, according to Ideal Adsorption Solution Theory (IAST) analysis, these materials demonstrate material selectivity for CO2/CH4 (10 v:90 v) and CO2/CH4 (50 v:50 v) of 33.3 and 21.8, respectively, at 1 bar and 298K. This study provides a promising CO2 adsorption and separation adsorbent that can be used in the efficient purification process for carbon dioxide, potentially reducing greenhouse gas emissions in industrial and energy production, thus offering robust support for addressing climate change and achieving more environmentally friendly energy production and carbon capture goals.

Efficient production of γ-aminobutyric acid using engineered Escherichia coli whole-cell catalyst

γ-Aminobutyric acid (GABA) has been widely used in the food, feed, pharmaceutical, and chemical industry fields. Previously, we developed a whole-cell catalyst capable of converting L-glutamate (L-Glu) into GABA by overexpressing the glutamate decarboxylase gene (gadz11) from Bacillus sp. Z11 in Escherichia coli BL21(DE3). However, to enhance cell permeability, a freeze-thaw treatment is required, and to enhance GADZ11 activity, pyridoxal 5′-phosphate (PLP) must be added to the reaction system. The aim of this study is to provide a more efficient approach for GABA production by engineering the recombinant E. coli above. First, the inducible expression conditions of the gadz11 in E. coli were optimized to 37 °C for 6 h. Next, an ideal engineered strain was produced via increasing cell permeability by overexpressing sulA and eliminating PLP dependence by constructing a self-sufficient system. Furthermore, an efficient whole-cell biocatalytic process was optimized. The optimal substrate concentration, cell density, and reaction temperature were 1.0 mol/L (the molecular ratio of L-Glu to L-monosodium glutamate (L-MSG) was 4:1), 15 and 37 °C, respectively. Finally, a whole-cell bioconversion procedure was performed in a 3-L bioreactor under optimal conditions. The strain could be reused for at least two cycles with GABA yield, productivity and conversion ratio of 206.2 g/L, 117.8 g/L/h and 100.0%, respectively. This is currently the highest GABA productivity from a mixture of L-Glu and L-MSG reported without the addition of cofactors or additional treatment of cells. This work demonstrates that the novel engineered E. coli strain has the potential for application in large-scale industrial GABA production.

Removal of plant endogenous proteins from tobacco leaf extract by freeze–thaw treatment for purification of recombinant proteins

Plants are useful as a low-cost source for producing biopharmaceutical proteins. A significant hurdle in the production of recombinant proteins in plants, however, is the complicated process of removing plant-derived components. Removing endogenous plant proteins, including ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), a major photosynthetic plant enzyme that catalyzes photosynthesis through carboxylation and oxygenation, is important for the purification of recombinant plant proteins. In particular, RuBisCO accounts for 50% of the soluble leaf protein; thus, the removal of RuBisCO is critical for the purification of recombinant proteins from plant materials. An effective conventional method, known as freeze–thaw treatment, was developed for the removal of RuBisCO from Nicotiana benthamiana, which expresses recombinant green fluorescent protein (GFP). Crude extracts or supernatants were frozen at − 30 °C. Upon thawing, most of the RuBisCO was precipitated by centrifugation without significant inactivation and/or yield reduction of GFP. Based on the proteomics analysis, using this method, RuBisCO large and small subunits were reduced to approximately 10% and 20% of those of the unfrozen supernatant solutions, respectively, without the need for specific reagents or equipment. The proteomic analysis also revealed that many ribosomal proteins were removed from the extracts. This method improves the purification process of recombinant proteins from plant materials. Prolonged freezing damaged recombinant β-glucuronidase (GUS), suggesting that the applicability of this treatment should be carefully considered for each recombinant protein.

High-temperature glycosylation of saccharides to modify molecular conformation of egg white protein and its effect on the stability of high internal phase emulsions

This paper investigates the freeze–thaw stability of oil-in-water emulsions stabilized by high-temperature wet heating glycosylation products. Glucose (Glu), D-fructose (Fru), xylose (Xyl), maltodextrin (MD), oligofructose (FO), and oligomeric isomaltulose (IMO) were chosen as sugar sources for the glycosylation reaction with egg white proteins (EWPs) at 120 °C to prepare the GEWPs. The study reveals that the type of sugar significantly influences the Maillard reactions with EWPs. The degree of glycosylation was highest in the Xyl group with the greatest reducing capacity and lowest in the MD, FO, and IMO groups. High-temperature wet glycosylation treatment induced changes in the secondary and tertiary structures of EWP. Elevated temperature exposed hydrophobic groups within the protein, while covalent binding of hydrophilic carbohydrates via the Maillard reaction decreased the protein's H0 value. Improved foaming and emulsifying properties were attributed to the increase in α-helix content, disulfide bond formation, and reduced surface tension. Emulsions prepared from GEWPs exhibited higher apparent viscosity and G' compared to those from natural EWPs, with the GEWP/Xyl group showing the highest values. After freeze–thaw treatment, the GEWP/Fru and GEWP/FO groups demonstrated superior stability and reduced freezing point, along with minimal microstructural alterations. These findings underscore the importance of sugar type in the stability of high internal phase emulsions (HIPEs) stabilized by GEWPs, indicating that a tailored Maillard reaction can yield stabilizers with exceptional freeze–thaw stability for emulsions.

Quality deterioration of frozen dough bread during terminal freezing and thawing: From the insight of moisture and starch properties

The temperature at the terminal cold chain changes sharply, which severely affects the quality of frozen dough products. This study focused on the variations of texture, moisture distribution, starch-ordered structure, and microstructure of frozen dough bread during terminal freeze-thaw (TFT) treatment. The specific volume of the frozen dough bread after TFT-6 decreased by 45% and obvious holes appeared on the surface. Meanwhile, TFT-6 (TFT with 6 cycles) increased the bread hardness by 205 gf and chewiness by 190 gf compared to the frozen storage (FS). The maximum fermentation height of dough bread under the TFT-6 decreased by 21.19%, the gas holding rate decreased by 23%, and proportion of bound water (A21) decreased by 36.88% compared to the fresh dough bread (p<0.05). Then, the starch was reordered after TFT treatment, compared with the fresh dough bread, the relative crystallinity of TFT-6 treated bread increased by 8.7% and the R1047/1022 (proportional relationship between ordered and amorphous structures) increased by 89.33%, while scanning electron microscope (SEM) images illustrated that the internal structure of the TFT-treated bread showed obvious loose and porosity characteristics. TFT negatively affected frozen dough breads, such as bread hardening, larger empty spaces, and reduced volume, which was related to water migration and deterioration of starch structure. The above experiments provided a theoretical basis for revealing the effect of TFT in production applications.

Study on deterioration mechanism of granite with a natural single weak surface after freeze-thaw treatment

Natural weak plane of rock is a great threat to the stability of the rock project in cold areas due to the freeze-thaw environment. However, the effect of both weak plane and freeze-thaw cycles is rarely considered. This paper investigated the deterioration mechanism of granite with a natural single weak surface after 0, 20, 40, and 60freezing-thawing cycles. Experimental results show that as the number of freeze-thaw cycles increased, the peak strength of samples decreased while the axial strain gradually increased. The weak plane angle has a significant impact on the sample strength. The strength and elastic modulus changed in a ‘U' shape with the increase of weak plane angle. The samples exhibited a shift from brittle failure to ductile failure with the increase of freeze-thaw cycles. A theoretical model for predicting rock strength is proposed with consideration of weak plane and freeze-thaw effects by combining the single weak plane theory with the decay function. The proposed model is verified by experimental data. The predicted values based on the proposed model match well with experimental data. Samples with lower porosity but higher tensile strength and elastic modulus have larger frost resistance. The research results can provide a scientific basis for the safety assessment of geotechnical engineering in cold regions.

Boosting emulsion properties: The role of β-sheet content and fibril length in soy protein isolate emulsions

This study aimed to research the effects of β-sheet content and fibril length in three categories ((low, medium, and high β-sheet) and (short, medium, and long fibrils)) on soy protein isolate (SPI) emulsions. The highest surface hydrophobicity (H0) (27,600 ± 100) was detected in the sample with the highest β-sheet content and the longest fibril length. The interfacial tension presented that the sample with the highest β-sheet content and longest fibril length could adsorb quickly at the oil (O)/water (W) interface. The emulsion stabilized by high β-sheet content and long fibril length had a lower droplet size (202 ± 4.35 nm) with more homogenous distribution and higher viscosity (8.75 ± 0.13 cP) due to more entanglement. According to the environmental stresses results (i.e., various ionic strengths (0–400 mM), pH changes (2–9.5), thermal treatment, and 30 days of storage), the emulsion prepared by the sample with the highest β-sheet content and the longest fibril length was more stable than other emulsions. Moreover, all emulsions were unstable against freeze-thaw treatment. Finally, it could be concluded that higher content of β-sheet and longer fibril led to the stability of emulsion through higher initial absorption at the O/W interface, formation of a continuous and thicker membrane coating at the O/W interfaces, viscosity improvement, and H0 enhancement.

Bio-impedance measurements for meat quality determination of pork loins under repeated freeze-thaw treatments

Evaluation of key quality traits in the cold chain is an important factor in ensuring meat safety. To meet the demands of consumers, development of non-destructive detection methods is essential for quality assessment of meat products. Electrical impedance spectroscopy (EIS) has emerged as one promising non-destructive technique in the food industry. In this study, EIS was developed to investigate the effects of freeze-thawing on quality parameters of porcine meat. Bioimpedance from 20 Hz to 200 kHz was collected from frozen-thawed meat, and the experimental impedance data were fitted to a Cole impedance model. The model fitting resulted in corresponding determination coefficient values of the resistance R and the reactance X, for needle electrodes (R2R=0.9683; R2X =0.9063) and plate electrodes (R2R=0.9442; R2X =0.8347). The Cole-impedance model well represented the collected bioimpedance datasets with standard deviations of 0.9611 Ω for needle electrodes and 0.9272 Ω for plate electrodes. Furthermore, there were significant differences in the Cole-impedance model parameters, which were attributed to the formation of ice crystals that implied cell membrane degeneration during freeze-thawing. Our results highlight the potential of bio-impedance measurements, gaining better insight on quality defects assessing in freeze-thawed meat.

Engineering pH-sensitive erodible chitosan hydrogel composite containing bacteriophage: An interplay between hydrogel and bacteriophage against Staphylococcus aureus

Encapsulation of phages represents a key approach for improving phage stability and controlling phage delivery dosage. The hydrogel made from positively charged quaternized chitosan (QCS) and multivalent crosslinker, aldehyde-modified poly(xylitol sebacate)-co-poly(ethylene glycol) (APP) was introduced for the first time for drug (phage 44AHJD) delivery. The freeze-thawing (FT) treatment enhanced the porous structure and the stress resistance of native hydrogel with increased compression stress (stiffness) from 10 to 20 kPa. The stiffness of the phage-loaded hydrogel (FTP) was suitable for the proper release of phage particles and polymer chains, both working synergistically against bacterial growth. The FTP followed the Korsmeyer-Peppas model's anomalous diffusion of phage particles at different temperatures (30–45 °C) and pH (6.6–8.5) conditions. FTP was sensitive to pH, which released more phage particles at pH-neutral conditions, while the release under acidic and alkaline conditions was more based on gel degradation. The high biocompatibility of FTP hydrogel at its working concentration of 30 mg mL−1 was demonstrated through a hemolysis ratio of <2 %. Sixty percent of the total encapsulated phages and 6 mg mL−1 of hydrogel debris were released after 10 h of hydrogel submerge treatment, which can fight the growing bacteria and the emergence of phage-resistant bacteria.

Assessment of curcumin self-emulsion containing high methoxyl pectin-whey protein complex: Quality stability by thermal, freeze-thaw treatment, and release characteristics

Polysaccharide-protein complexes have been commonly used in recent years to improve the quality and stability of emulsions. In this study, we evaluated the effect of high methoxyl pectin-whey protein complex (HWC) on the storage stability and in vitro release characteristics of curcumin self-emulsion systems. The droplet size and loading of the curcumin self-emulsion system were approximately 306.60–353.45 nm and 2.21 mg/mL, respectively, with good dispersibility. The thermal stability of HWC was significantly increased (p < 0.05) by the formation of amide groups at pH 5, as confirmed by Fourier transform infrared spectroscopy. After three rounds of freeze-thaw cycles, the stability and retention rate of curcumin approached 92.98 and 97.83%, respectively (p < 0.05). The retention rate increased from 43.81 to 51.76% during a 20-day storage test in a light environment by adding whey protein to improve photostability. In the in vitro gastrointestinal test, the release rate in simulated gastric fluid decreased from 67.71 to 47.50% in 60 min and increased from 62.22 to 73.17% in simulated intestinal fluid in 90 min. Thus, emulsification technology can be used to improve the quality and stability of curcumin processing and can be applied to health food development.

Peculiar properties of tuber starch in a potato mutant lacking the α-glucan water dikinase 1 gene GWD1 created by targeted mutagenesis using the CRISPR/dMac3-Cas9 system.

Glucose chains in starch are phosphorylated and contribute to structural stabilization. Phosphate groups contained in starch also play a role in retaining moisture. α-Glucan water dikinase 1 (GWD1) is involved in the phosphorylation of glucose chains in starch. In this study, we generated potato mutants of the GWD1 gene using the CRISPR/dMac3-Cas9 system. Observation of the phenotypes of the GWD1-deficient mutants revealed their physiological roles in tuber starch formation. The 4-allele mutants showed growth retardation and a delay in tuber formation. A significant decrease in phosphorus content was detected in the tuber starch of the gwd1 mutant. This mutant starch showed a higher amylose content than the wild-type starch, whereas its gelatinization temperature was slightly lower than that of the WT starch. The peak viscosity of the mutant starch was lower than that of the WT starch. These observations revealed that the starch of the gwd1 mutants had peculiar and unique properties compared to those of WT, sbe3 and gbss1 mutant starches. The amount of tissue-released water due to freeze-thawing treatment was determined on tubers of the gwd1 mutant and compared with those of WT and the other mutants. Significantly less water loss was found in the gwd1, sbe3 and gbss1 mutant tubers than in the WT tubers. Our results indicate that the GWD1 gene is not only important for potato growth, but also largely effective for the traits of tuber starch.

Green modification of corn starch through repeated freeze-thaw cycles (RFTC), microwave assisted solid state acetic acid esterification (MSAE), and by dual RFTC/MSAE treatment

Freeze-thaw treatment as a green technology has been extensively applied to improve the functional properties in types of starches. The present work aimed to compare the effects of repeated freeze-thaw cycles (RFTC), microwave assisted solid state acetic acid esterification (MSAE), and their combination (RFTC/MSAE) on structural and functional properties of corn starch (NS). RFTC/MSAE treatment provided higher esterification efficiency (68.7%) for the esterified starches compared to MSAE alone (32.6%) due to raised surface area of starch granules after applying RFTC. Esterification of starch chains by using acetic acid was confirmed through FTIR (1700 cm−1) and 1H NMR (2 ppm). SEM images showed that the pores and channels were formed on granules after applying RFTC treatment, while no change in their size was observed. Also, XRD and DSC were employed to scrutinize the changes in crystalline structure of granules after applying each modification. The dual treatment decreased crystallinity, viscosity, swelling power, digestibility rate, and gelatinization temperatures, while increased amylose extent, whiteness, solubility, and paste clarity compared to those of NS. The conformity of the dual treatment with principles of green chemistry was investigated by Eco-scale methodology. Starch acetate synthesized through the dual modification can be utilized in formulation of low-calorie foods due to its highlighted features such as low digestibility rate (RS: 54.7%) and viscosity (455 cp).

Effect of melting combined with ice recrystallization on porous starch preparation: Pore-forming properties, granular morphology, functionality, and multi-scale structures

In this work, critical melting (CM) combined with freeze-thawing treatment (FT, freezing at −20 ℃ and −80 ℃, respectively) was used to prepare porous starch. The results showed that CM combined with the slow freezing rate (−20 ℃) can prepare porous starch with characteristics of grooves and cavities, while combined with the rapid freezing rate (−80 ℃) can prepare with holes and channels, especially after repeating FT cycles. Compared with the native counterpart, the specific surface area, pore volume, and average diameter of CMFT-prepared porous starch were significantly increased to 4.07 m2/g, 7.29 cm3/g × 10−3, and 3.57 nm, respectively. CMFT significantly increased the thermal stability of starch, in which the To, Tp, and Tc significantly increased from 63.32, 69.62, and 72.90 (native) to ∼69, 72, and 76 °C, respectively. CMFT significantly increased water and oil absorption of porous starch from 91.20 % and 72.00 % (native) up to ∼163 % and 94 %, respectively. Moreover, CMFT-prepared porous starch had a more ordered double-helical structure, which showed in the significantly increased relative crystallinity, semi-crystalline lamellae structure, and the proportion of the double helix structure of starch. The synergistic effect of melting combined with ice recrystallization can be used as an effective way to prepare structure-stabilized porous starch.

Fracture behavior of yellow sandstone under freeze–thaw cycles with varied saturation states: An investigation of mode I fracture

In cold regions, the behavior of fissured rock in rock engineering is significantly affected by freeze–thaw (F–T) cycles. To investigate the impact of freeze–thaw cycles on rock fracture behavior, freeze–thaw cycle treatment, and fracture tests were conducted on Cracked Straight Through Brazilian Disc (CSTBD) specimens. The freeze–thaw treatment notably degraded the physical and mechanical properties of the rock, marked by a downward trend in fracture load, toughness, and energy. A considerable volume of data suggests that the impact of freeze–thaw (F–T) on yellow sandstone was predominantly during the initial stages of cycling, with this trend stabilizing as the number of cycles increased. Microscopic analysis via Scanning Electron Microscopy (SEM) uncovered the patterns of freeze–thaw damage in yellow sandstone. Dry rocks exhibited crack propagation, while water-saturated rocks displayed pore and crack expansion. The Digital Image Correlation (DIC) method illuminated the evolution of the high strain zone during the fracturing process. The mode I fracture process revealed a gradual expansion of the high strain zone originating from the crack tip, intensifying with increased load. As freeze–thaw cycles progressed, damage accumulation was gradual, and the path of mode I crack propagation grew increasingly intricate from a macroscopic perspective. Additionally, the quantification of fractal dimensions, achieved through the analysis of binarized SEM images, corroborates these observations at a microscopic level.

Konjac glucomannan and xanthan synergistic interaction gel: Underlying mechanism for improvement of gel mechanical properties induced by freeze-thaw treatment

Synergistic interaction gels (SIGs) formed by mixing konjac glucomannan (KGM) and xanthan at an appropriate ratio have gained increased interest due to its inherent versatility. However, their mechanical properties were not high enough to meet the needs of practical applications. This work demonstrated that freeze-thaw treatment (FT) significantly improved their mechanical properties, and the underlying mechanisms were proposed. Relative lower frozen temperature (−40 °C or −80 °C) and more freeze-thaw cycles reduced the pore size, decreased the average size of orderings (crystalline structure) and increased the ordering content (at −40 °C or under third cycle at −80 °C, except for KGM/xanthan SIGs with a ratio of KGM to xanthan at 2:8) for KGM/xanthan SIGs. Those undoubtedly increased the crosslinking density and improved the gel structure, which was responsible for the increment of G' (at 25–30 °C) and gel hardness, and reduction of water holding capacity. Freeze-thaw treatment with −15 °C did not increase the ordering contents and gel hardness, but enhanced the G' (at 25–30 °C). It is possible that freezing at −15 °C enhanced gel structure rigidity by increasing the molecular entanglement via squeezing of ice crystals and rearrangement of molecular chains. Those results are helpful to rational design and production of KGM/xanthan SIGs with physical methods.

Effect of caseinate salt addition on the structural characteristics of kefiran systems.

Sodium caseinates-kefiran systems were studied to explore whether any potential interactions between them might exist. The study was performed using low-deformation rheological techniques, which were dynamic and creep tests. The systems were prepared under various experimental conditions such as heating and acidification. Besides, the structure development of the systems in relation to time was also monitored using oscillatory shear rheometry. The results indicated that the structural characteristics of the systems were mainly affected by the state of the caseinates such as the formation of aggregates and to a lesser degree by the interactions of kefiran molecules with the caseinates. Freeze-thaw treatment produced cryogels with good thermal stability and fairly satisfactory mechanical properties. The morphology of the caseinate-kefiran systems was also investigated by means of confocal laser scanning microscopy.

Assessing the emulsifying properties of Tenebrio molitor larvae protein preparations: Impact of storage, thermal, and freeze-thaw treatments on o/w emulsion stability

Insect proteins have gained attention as novel ingredients, which may contribute to the development of high-value-added products. This study evaluates the emulsifying and emulsion-stabilizing properties of Tenebrio molitor larvae protein preparations obtained through different procedures, leading to the following rich-in-protein samples: ASP (∼67 %), AIP (∼75 %), and SSP (∼62 %). The method applied for protein isolation influenced the molecular and structural characteristics of the preparations, thus affecting their adsorption behaviour at oil-water interfaces and ability to stabilize emulsions. O/w emulsions were prepared, and their physicochemical stability was assessed with respect to droplet size, oil droplet flocculation/coalescence, microstructure, and creaming upon storage as well as after thermal and freeze-thaw treatments. The use of ASP and AIP protein preparation as emulsifiers led to higher stability during storage. All emulsions were stable upon heating and able to withstand two freeze-thaw cycles without phase separation, although there was an increase in droplet size. Interestingly, the AIP emulsion remained stable after the 3rd freeze-thaw cycle, indicating remarkable stability under freezing compared to the other two emulsions. These findings are of great importance for the formulation of food-grade emulsions using insect protein preparations and their future exploitation in developing food items subjected to different treatments.

Formation mechanism of cold-set bitter apricot kernel protein isolate-gellan gum binary gels with excellent freeze-thaw stability

Binary gels with various microstructures, including apricot kernel protein isolate-gellan gum gels with high freeze-thaw stability, were obtained by combining transglutaminase covalent cross-linking and gellan gum modification. Adding 0–0.1% gellan gum (w/w) can form continuous protein network structures dominated by covalent networks and disulfide bonds. In addition to covalent cross-linking, the increase in the strength of hydrophobic and electrostatic interactions at gellan gum concentrations below 0.2% (w/w) facilitated the formation of a bicontinuous network (AGG3). When excess gellan gum was added (0.03%, w/w), gellan gelation occurred in the system, leading to the formation of heterogeneous aggregated structures (AGG4). Confocal laser microscopy revealed a dense porous structure in the continuous protein network after freeze-thaw treatment, and AGG4 showed heterogeneous and loose aggregated microstructure, while the bicontinuous network structure was maintained. The water holding capacity of AGG3 was increased by 21.36% after freezing compared with the gels without gellan gum, and AGG3 maintained high hardness and springiness. Low-field nuclear magnetic resonance and magnetic resonance imaging showed that the bicontinuous network was more conducive to the tethering ability and uniform distribution of hydrogen protons than the continuous network structure of proteins. Therefore, AGG3 exhibited excellent freeze-thaw stability.