Freeze-thaw Treatment Research Articles

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.

Preparation of starch nanoparticles by jet cavitation and enzymatic hydrolysis and their application in starch films

Potato starch was subjected to jet cavitation, freeze-thaw, ultrasound, acid, and enzymatic treatments to prepare starch nanoparticles. Enzymatic hydrolysis after jet cavitation pretreatment was found to be efficient. Therefore, enzymatic hydrolysis conditions of jet cavitation-treated starch were optimized. The smallest starch nanoparticles were obtained when the enzyme concentration was 66.68 nkat, starch concentration was 10 g/dL, and enzymatic hydrolysis duration was 3 h. The prepared starch nanoparticles showed a mixture of B and V-type crystalline structures with reduced relative crystallinity. A combination of potato starch nanoparticles and tea polyphenols was incorporated into potato starch-based edible films. The elongation at break of edible films significantly improved with the incorporation of starch nanoparticles. Additionally, the water resistance, tensile strength, and antioxidant activity of films improved with the addition of starch nanoparticles and tea polyphenols. Furthermore, the FTIR analysis indicated comparable spectra for all the starch-based films, except for the tea polyphenols-incorporated film, which exhibited a distinct band at 1605 cm−1.

Effects of freeze–thawing treatment on mechanical and structural properties of konjac glucomannan gels containing additives

The mechanical, structural, and water-holding properties of freeze-thawed konjac glucomannan (GM) gels prepared using sodium carbonate as a solidifying agent were examined using various techniques. For GM gels prepared at pH = 11, the freezing-thawing (FT) treatment considerably enhanced the compressive stress because treatment promotes the crystallization and aggregation of GM. Additionally, we examined the effect of three additives, such as curdlan (CUD), antifreeze glycoprotein (AFGP), and tremella fuciformis polysaccharide (TFP), on the various properties of freeze-thawed GM gels prepared at pH = 8.5. The compressive stress of the CUD-added GM gels was almost unchanged after the FT treatment but it lowered the water-holding capacity (WHC) of the gel. The compressive stress of the freeze-thawed GM gels containing AFGP and TFP moderately increased after the FT treatment, whereas both gels possessed high WHC even after the FT treatment. Synchrotron simultaneous small-angle X-ray scattering and wide-angle X-ray scattering experiments were performed to examine the structures of these GM gels and their structural changes during the FT process. The GM gels containing additives formed a network with a fractal dimension of 2.4–2.5 that was constructed by the aggregates with partly crystallized GM. The aggregated phase contains a large amount of water, which causes concentration fluctuations within the phase. During freezing, water molecules transitioned to a solid state and formed ice crystals, whereas during thawing, the water molecules returned to their original phase, but the gel network did not revert to its original state. Among freeze-thawed GM/additive gels, the GM/CUD gel was restored to the original structure most closely before FT treatment.

Alleviative effects of chitooligosaccharides on the quality deterioration of frozen dough subjected to freeze–thaw cycles

Chitooligosaccharides (COS), a group of cationic derivatives, have a number of potential applications in the food industry. However, their alleviative effects on frozen dough products have not previously been well explored. In this work, the effects of adding COS to frozen steamed bread dough later subjected to freeze–thaw (FT) treatment were systematically investigated. The results revealed that COS significantly improved the quality of frozen dough, the specific volume of the steamed bread with the addition of COS increased by 25.4% and the hardness was reduced by 5.9% compared to the control group. In addition, COS also significantly restrained the water migration and retarded the increase in the freezable water content of the dough during FT treatment (P < 0.05). After FT-4, the freezable water content of COS group was decreased by 12.5% in comparison with the control group. In addition, the COS facilitated the prevention of disulfide bond cleavage. The free sulfhydryl content of 4.46 μmol/g in the control group was significantly higher than that of other groups after FT treatment (P < 0.05), which enabled the dough to maintain its rheological properties. Moreover, dough with higher concentrations (0.15% and 0.25%) of COS exhibited better gas-holding capacity. These results revealed that COS can effectively maintain the characteristics of frozen dough, improve the quality of frozen steamed bread, and also provide new insights concerning the cationic polysaccharides used in the preparation of frozen dough.

Failure Mechanism of the Corrugated Medium under Simulated Cold Chain Logistics.

It is necessary to develop corrugated medium food packaging, which is suitable for highly humid environments, to meet the demands of cold chain logistics. In this paper, we investigated the influence of the transverse ring crush index of different environmental factors of corrugated medium and the failure mechanisms during cold chain transportation. After freeze-thaw treatment of corrugated medium, XRD and DP showed a decrease in crystallinity and polymerization of 3.47 and 7.83%, respectively. Also, the FT-IR spectra of the paper showed that the number of intermolecular hydrogen bonds decreased by about 3.00% after freezing. SEM and XRD showed CaCO3 precipitation on the paper surface and a 26.01% increase in pore size. This study would be beneficial in further expanding the applications of cellulose-based paperboard cold chain transportation.

Evaluation of functional properties and freeze-thaw stability of Chinese quince (Chaenomeles sinensis) seed gum

Hydrophilic natural gums have gained increasing attention as food cryoprotectants due to their special functional properties. In this study, the functional properties of Chinese quince seed gum (CQSG), i.e., rheological, textural, emulsifying and foaming properties, were characterized. Effects of gum concentration (0.50–3.00% in w/v) and freezing temperature (−18 °C and −34 °C) were investigated. During freeze–thaw process, there was insignificant change in the flow behavior of the CQSG solution, presumably due either to the random distribution or to the flexibility of the gum molecular chains. After freeze–thaw treatment, the textural properties were stable at low gum concentrations, and the cohesiveness and springiness were relatively stable at high gum concentrations. The hardness and gumminess were enhanced after being frozen at −34 °C and then thawed. The CQSG solutions at all concentrations exhibited enhanced emulsifying and foaming capacities after freeze–thaw treatment, and their stabilities were improved significantly. These results suggest that Chinese quince seed gum can be used as a cryoprotectant in frozen foods.

Low-Temperature-Tolerant Strain-Sensing Flexible Composite for Soft Body Armor.

Developing soft body armor with sensing characteristics in various application scenarios is a challenge but important for creating a peaceful world and personal safety, whereas existing materials suffer from indefinite protective effects and stimulus response at subzero temperatures in the long term. Herein, an anti-freezing and flexible puncture-resistance composite with strain-sensing ability is developed by compounding a NaCl-soaked poly(vinyl alcohol) (PVA)/sodium alginate (SA)/glycerol (Gly) hydrogel (PSGN hydrogel) with Kevlar fabric. After freezing-thawing treatment once and NaCl immersion for 10 h, the Kevlar/PSGN-10 composite has excellent puncture-resistance properties and linear, rapid response, wide band, and stable strain-sensing behaviors at 25 and -30 °C. The composite's maximum puncturing force and energy dissipation at -30 °C are 53.92 N and 370 mJ, respectively, increased by 285 and 302% compared with neat Kevlar fabric. The flexibility reduction and the mass addition of the Kevlar/PSGN-10 composite are merely 19 and 40%, respectively, showing superior wearable comfortability and protection efficiency. The composites also reveal remarkable strain-sensing abilities at -30 °C (linear strain sensitivity with GF = 0.27 and R2 = 0.981, a wide working frequency range of 0.16-1.3 Hz, and sensing stability for 1500 cycles). Moreover, the composite could respond to multipart body motion directly, including fingers, elbows, wrists, and knees. Consequently, the Kevlar/PSGN composite developed in this paper is promising for intelligent soft body armor at various temperatures.

Freeze-thaw assisted maleic acid pretreatment of eucalyptus to prepare cellulose nanocrystals and degraded lignin

A green and effective method is proposed for the pretreatment of eucalyptus by freeze–thaw assisted maleic acid tactic, wherein the effects of freeze–thaw, maleic acid concentration, reaction time, and temperature on the fractionation were examined. Results showed that under optimal conditions (60% maleic acid, 120 °C, and 2 h), a remarkable removal of 74.5% lignin and 95.2% hemicellulose was achieved after freeze–thaw treatment. The resulting cellulose-rich solid residues were further processed with maleic acid to prepare cellulose nanocrystals, which displayed uniform sized rod-like structures and high crystallinity (62.51%). Moreover, maleic acid pretreatment resulted in lignin with low molecular weight (2110–2530) and excellent homogeneity (PDI ≤ 1.86), while maintaining a relatively intact structure. The lignin had high β-O-4 aryl ether bond contents (≥77.5%) and abundant phenolic hydroxyl contents (2.33–3.63 mmol/g). Overall, the process exhibits notable benefits in effectively separating lignocellulose for high valorization.

Changes in overall and inter-variability of runoff and soil loss for a loess soil resulted from a freezing-thawing cycle.

The soil freeze-thaw process is a transition phase of soil water in cold areas that influences the soil's hydrological behavior. However, dynamic phenomena and corresponding consequences have yet to be studied adequately. Therefore, the present study was planned to comparatively analyze the effects of a freezing-thawing cycle on the hydrologic behaviors of loess soil from northeast Iran. Small-size (0.5 × 0.50m) erosion plots were subjected to a freezing-thawing cycle under governing conditions of the region of the origin soil. The plots were subjected to a freezing-thawing treatment by inducing cold air until the temperature declined to below - 20°C and lasted for 3days using a cooling compartment system and then were kept in the laboratory with an ambient temperature of above 10°C for 2days. The treated plots and untreated plots were then exposed to a simulated rainfall with an intensity of 72mmh-1 and 0.5h duration while they were placed on a slope of 20%. The results indicated that the hybrid processes of freezing-thawing and splash and inter-rill erosions significantly increased runoff generation and soil loss. The time to runoff, runoff volume, and soil loss were 1.65 times less and 1.38 and 2.90 times more, respectively, compared to those reported for the control treatment with significant differences (p < 0.006). The performance of ice lenses, freezing fronts, and the creation of near-saturation moisture after completing the cycle were identified as the most critical factors affecting the different soil behaviors under the frozen-thawed cycle.

Effect of Freeze–Thaw Cycles on Physicochemical and Functional Properties of Ginger Starch

Ginger (Zingiber officinale Roscoe.) starch is a waste product generated during the extraction of bioactive compounds from ginger. This study aimed to treat ginger starch with different freeze–thaw cycles and explore the effect on the functional components, physicochemical properties, and structural properties of ginger starch. The results of the study showed that as the number of freeze–thaw cycles increased, the content of resistant starch, amylose, total starch, and recrystallization in ginger starch increased significantly (p &lt; 0.05). Freeze-dried ginger starch exhibited a C-type crystal structure in the X-ray diffraction pattern. The Fourier-transform infrared spectroscopy results also showed that the value of A1047/1022 increased, indicating that the freeze–thaw cycle would increase the degree of starch recrystallization. In terms of physical and chemical properties, compared with gelatinized starch, freeze–thawed starch had low swelling power, high solubility, low peak viscosity and breakdown, indicating higher thermal stability. In conclusion, freeze–thaw treatment can promote the formation of resistant starch from ginger starch and reduce starch hydrolysis, reflecting the potential of low–GI foods. We hope that ginger starch can be used as a raw material for new applications in functional foods.

Effect of Liquid Nitrogen Cooling and Heating on Mechanical Properties and Acoustic Emission Characteristics of Coal

The instability of rock fractures has been extensively studied in domestic and international research. This paper investigates two coal types from the Jiaozuo area, which were subjected to liquid nitrogen cyclic treatment using Brazil’s indirect tensile testing (BITT). The study analyzes the characteristics of acoustic emission (AE) and crack formation during the coal cracking process and evaluates the impact of freeze-thaw treatment with liquid nitrogen cycles on the mechanical properties of coals. The results demonstrate that liquid nitrogen has a significant impact on the formation and development of coal fractures under the Brazil splitting test conditions. As the number of cyclic treatments increases, the maximum load-bearing capacity of coal decreases, indicating a gradual reduction in the effective stress on coal samples. Furthermore, the acoustic emission activity intensity of coal mass during phased loading increases as the number of freeze-thaw cycles of liquid nitrogen increases. Finally, during phased loading of coal specimens, the primary factor is the germination, extension, and failure of tensile cracks, while the secondary factor is the development, extension, and failure of shear cracks. Overall, this study provides valuable insights into the behavior of coals under freeze-thaw cycles of liquid nitrogen treatment and highlights the importance of understanding the characteristics of coal fracture instability.

Stability of protein particle based Pickering emulsions in various environments: Review on strategies to inhibit coalescence and oxidation.

The emerging research interests in fabrication of protein particles as soft-particle emulsifiers show the prospective potential of using protein particles in novel poly-phase dispersing food systems. This review first provides a comprehensive summary and analysis on the dominant role of key physicochemical properties of protein particles including wettability, morphology, surface charge and protein concentration on their emulsifying abilities to construct Pickering emulsions. It was found that the constructed emulsions showed high sensitivity to changes in pH, ionic strength and temperature (thermal and freeze-thaw treatment). Moreover, oxidation remains as a challenge for protein particle based Pickering emulsions during prolonged storage, reducing their acceptance in food products. Current strategies for improving the stability of these emulsions to variable aqueous conditions and variable temperatures, and restricting oxidation event are summarized. In summary, an "ideal" protein particle-based Pickering emulsion system is proposed, encompassing aspects of interfacial property, emulsion network and texture, and antioxidant enrichment, thus promoting industrial translation into novel food and nutraceutical products.

Behavior of protein-polysaccharide conjugate-stabilized food emulsions under various destabilization conditions.

The sensitivity of protein-stabilized emulsions to flocculation, coalescence, and phase separation under destabilization conditions (i.e., heating, aging, pH, ionic strength, and freeze-thawing) may limit the widespread use of proteins as effective emulsifiers. Therefore, there is a great interest in modulating and improving the technological functionality of food proteins by conjugating them with polysaccharides, through the Maillard reaction. The present review article highlights the current approaches of protein-polysaccharide conjugate formation, their interfacial properties, and the behavior of protein-polysaccharide conjugate stabilized emulsions under various destabilization conditions, including long-term storage, heating and freeze-thawing treatments, acidic conditions, high ionic strength, and oxidation. Protein-polysaccharide conjugates are capable of forming a thick and cohesive macromolecular layer around oil droplets in food emulsions and stabilizing them against flocculation and coalescence under unfavorable conditions, through steric and electrostatic repulsion. The protein-polysaccharide conjugates could be therefore industrially used to design emulsion-based functional foods with high physicochemical stability.

Freeze-thaw treatment of bacteria significantly affects bacterial transport behaviors in both saturated and unsaturated porous media: Deep investigation the roles of flagella and extracellular polymeric substances

The effects of freeze-thaw (FT) treatment and mechanisms on bacteria transport/retention in porous media with different moisture contents remain unclear. The transport/retention behaviors of bacteria with different FT treatment cycles (0, 1, and 3) in sand columns with different moisture contents (100 %, 90 %, 60 %, and 30 %) in NaCl solutions (10 and 100 mM) thus were investigated. Regardless of moisture content and solution chemistry, FT treatment increased bacteria deposition in sand columns, consistent with the results of QCM-D and visible parallel plate flow chamber (PPFC) systems. Via deep investigation of the contribution of flagella through using genetic-modified bacteria strain without flagella and that of extracellular polymeric substances (EPS) through analyzing its overall quantity, composition as well as the secondary structure of its two major components (proteins and polysaccharides), the mechanisms of FT treatment controlling bacterial transport/deposition were revealed. Although FT treatment induced flagella loss, it was not the major contributor to driving to the enhanced FT-treated cell deposition. Instead, FT treatment stimulated EPS secretion and increased its hydrophobicity (via increasing hydrophobicity of both proteins and polysaccharides), mainly contributing to the enhanced bacterial deposition. Even with copresent humic acid, FT treatment still enhanced bacterial deposition in sand columns with different moisture contents.

3D Printing of Multifunctional Conductive Polymer Composite Hydrogels

AbstractFunctional conductive hydrogels are widely used in various application scenarios, such as artificial skin, cell scaffolds, and implantable bioelectronics. However, their novel designs and technological innovations are severely hampered by traditional manufacturing approaches. Direct ink writing (DIW) is considered a viable industrial‐production 3D‐printing technology for the custom production of hydrogels according to the intended applications. Unfortunately, creating functional conductive hydrogels by DIW has long been plagued by complicated ink formulation and printing processes. In this study, a highly 3D printable poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)‐based ink made from fully commercially accessible raw materials is demonstrated. It is shown that complex structures can be directly printed with this ink and then precisely converted into high‐performance hydrogels via a post‐printing freeze–thawing treatment. The 3D‐printed hydrogel exhibits high electrical conductivity of ≈2000 S m−1, outstanding elasticity, high stability and durability in water, electromagnetic interference shielding, and sensing capabilities. Moreover, the hydrogel is biocompatible, showing great potential for implantable and tissue engineering applications. With significant advantages, the fabrication strategy is expected to open up a new route to create multifunctional hydrogels with custom features, and can bring new opportunities to broaden the applications of hydrogel materials.

Effects of freeze-thaw intensities on N2O release from subsurface wastewater infiltration system

Subsurface wastewater infiltration system (SWIS) is a low-investment and cost-effective wastewater treatment technology. Nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, is a major by-product of biological denitrification processes within SWIS. Although SWIS has been widely applied in varying zones, until now, whether and how periodical freeze-thaw cycles (FTCs) occurring in aerobic layers affect N2O release still remain unclear? In this study, two runs were arranged, which covered two freeze-thaw (FT) intensities of − 5 °C/5 °C and − 15 °C/5 °C, respectively. An in-situ simulation system of SWIS was carried out to monitor N2O release and microbial community structure in different profiles. The result revealed that raising FT intensity decreased the rate of nitrogen removal of SWIS. Average removal rate of TN under strong FTCs was 88.65–88.97%, which was 1.32–2.47% lower than that under weak FTCs conditions. In addition, a positive correlation was found between FT numbers and N2O release. The contribution of anaerobic zone increased from 29.24% to 75.16% with extending the FT cycles from 1 to 9. High-throughput sequencing results showed that different FT intensities had distinct effects on microbial communities. Euryarchaeota abundance increased significantly under strong FT treatment, while Proteobacteria abundance sharply decreased from 49.5% to 7.6% at day 27 of stable operation. PCA analysis shows that bacterial community composition of samples treated with weak FT and CK is similar. While significant differences in sample composition were found between strong and weak FT treatments, which was the main reason resulting in different N2O release patterns.

Pickering emulsions synergistically stabilized by sugar beet pectin and montmorillonite exhibit enhanced storage stability and viscoelasticity

Sugar beet pectin (SBP) is a naturally occurring emulsifying type of pectin fabricated into nanocomposites with montmorillonite (MMT) and then introduced as a stabilizer for high internal phase emulsions (HIPEs). SBP-MMT composites performed well in emulsifying medium-chain triglyceride with an oil volume fraction (φ) of 0.1–0.85 and SBP/MMT mass ratios of 1:0.1–1:0.75. The two representative high internal phase emulsions stabilized by SBP-MMT composites at different SBP/MMT mass ratios exhibited good stability against creaming and coalescence. In these emulsion systems, SBP and MMT formed a network in the continuous phase that markedly improved the rheological properties, including the storage modulus (by 3 orders of magnitude). Confocal light scattering microscopy analysis indicated that a fraction of MMT could work synergistically with SBP in adsorbing on oil droplet surfaces, enhancing stability. SBP-MMT composites stabilized high internal phase emulsions destabilized after the freeze-thaw treatment (−40 °C for 20 h and 25 °C for 4 h) but could be facilely re-emulsified via high-speed shearing. The gastrointestinal digestion behaviors were also modified by stabilizing SBP and MMT. Overall, this work reveals a hitherto undocumented strategy for fabricating highly stable emulsions based on SBP-MMT composites which have huge prospects for application in the food and related industries.

Dynamic tensile mechanical properties of water-saturated and frozen sandstone after freeze-thaw fatigue damage treatment

To study the physical properties and dynamic mechanical response characteristics of rock materials in seasonally frozen regions, density, P-wave velocity, nuclear magnetic resonance, and dynamics Brazilian disc tests were carried out on sandstones treated with different numbers of freeze-thaw cycles. The experimental results show that the water-saturated density and P-wave velocity of sandstone decrease and the Nuclear magnetic resonance porosity increases as the number of freeze-thaw cycles increases. Under a certain loading rate, the dynamic tensile strength of water-saturated sandstone gradually decreases and that of frozen sandstone gradually increases as the number of freeze-thaw cycles increases; at the same time, the dynamic tensile strength of both water-saturated and frozen sandstone increases as the loading rate increases under the same number of freeze-thaw cycles. The reason for the variability of dynamic tensile strength between water-saturated and frozen sandstones with the increase in the number of freeze-thaw cycles can be attributed to the change in porosity. On this basis, the concept of relative dynamic tensile strength of sandstones was introduced and regression analysis was carried out with the increase ratio of porosity, and it was found that the correlation between the relative dynamic tensile strength and the increase ratio of porosity was strong. The relative dynamic tensile strength of water-saturated sandstone decreases exponentially with the increase ratio of porosity; the relative dynamic tensile strength of frozen sandstone increases exponentially with the increase ratio of porosity.

Modulation of composite hydrogel consisting of TEMPO-oxidized cellulose nanofibers and cationic guar gum

The applications of hydrogels are prominently affected by the modulation of their structure and performance. We herein systematically implemented the modulation of an all-polysaccharide hydrogel consisting of TEMPO-oxidized cellulose nanofibers (TOCN) and cationic guar gum (CGG). Four different factors including the carboxylate content and size of TOCN, the freezing-thawing treatment and solid content of hydrogel were studied to disclose their influence on the structure and property of TOCN/CGG hydrogel. The results indicated that the increase of carboxylate content of TOCN, the number of freezing-thawing cycles and solid content all increased the crosslinking density of hydrogel as a result of the improved interactions. Accordingly, the hydrogels exhibited more compact structures and enhanced rheological properties. The influence of TOCN size on the hydrogel structure and property was demonstrated to be dependent on the compromise between the exposed functional groups of TOCN and their ability in generating entanglements inside the hydrogel. This work helps shed light on the modulation of hydrogel structure and performance, which might facilitate the exploration of hydrogel applications.

Preparation of a Graphene-Enhanced Hydroxyapatite Film on Dolomitic Marble by the Sol-Gel Method

The preparation of continuous hydroxyapatite film on stone is a promising method of protecting marble from erosion. However, many methods negatively affect the calcium in the substrate and forming of struvite on the dolomite surface, leading to a heterogeneous coating and low efficiency. In this study, a continuous hydroxyapatite coating on dolomitic marble was achieved from graphene enhanced Ca(OH)2 nanoparticles as the calcium precursor using the sol-gel method. The morphology and the structure of the film was evaluated by a field emission scanning electron microscope coupled with energy dispersive spectroscopy (FESEM-EDS), an optical microscope, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and analytical techniques. Moreover, the color and the contact angle measurements, as well as the simulated acid rain test and freeze–thaw treatment, were performed to assess the chromatic aberration, hydrophilicity, reliability, and durability of the coating. A suppositional combination model among hydroxyapatite, graphene quantum dots, and dolomite were suggested based on structural similarities between the support material and components of the functional coating. The integrality and efficiency of the hydroxyapatite film was improved by compositing with graphene quantum dots.