Search

Jerky is a type of meat product traditionally produced using a hang-drying process to achieve desirable textural properties. Inspired by the jerky processing, we present a strategy for fabricating strong alginate hydrogels with highly anisotropic structures via stretching and drying under constant stress. The tunable stretching process endowed the alginate hydrogels with adjustable mechanical properties and structural features by promoting the orientation and aggregation of the constituent polymers. At a high water content of about 80%, the tensile strength of the obtained hydrogel was increased to 20 MPa, which was 10 times higher than that of the hydrogel without the stretching process. Moreover, these hydrogels can be favorably compared with other common structural materials. This paper introduces a facile strategy to tune the structural alignment and mechanical properties of hydrogels, which will expand the applicability of the natural hydrogels formed by non-covalent interactions.

Agarose/fish gelatin (AR/FGA) double-network hydrogels (DNs) were fabricated via a one-step heating-cooling method. The structure, mechanical and textural properties, water-holding capacity, swelling behavior and sensory characteristics of the DNs were analyzed and compared with the corresponding single-network hydrogels (SNs) and beef tendons. An increase in FGA concentration (10-40 wt%) significantly enhanced the mechanical strength and toughness of DNs, while a moderate increase in AR concentration (0.5-1.5 wt%) only improved their mechanical strength. The 1.5 wt% AR/40 wt% FGA DNs attained excellent fracture stress and strain compared with the single AR and single FGA gels. This can be attributed to the energy dissipation effect, intermolecular hydrogen bond interactions and higher entanglement density of molecule chains. Furthermore, AR/FGA DNs attained a higher hardness, water holding capacity and lower swelling rate compared with SNs. The principal component analysis and correlation analysis showed that the 1.5 wt% AR/30 wt% FGA DNs displayed the most comparable correlation with beef tendons, which was consistent with the results of the sensory evaluation, showing great potential as artificial beef tendons. Our findings provide guidance for the modulation of gel properties and development of artificial foods.

The combination of fiber and hydrogel in a system can provide substantial benefits for both components, including the development of three-dimensional structures for the fiber, followed by modifications in the rheological and mechanical properties of the hydrogel. Despite a large increase in the use of fiber-hydrogel composites (FHCs) in various sciences and industries such as biomedicine, tissue engineering, cosmetics, automotive, textile, and agriculture, there is limited information about FHCs in the realm of food application. In this regard, this study reviews the mechanism of FHCs. The force transmission between fiber and hydrogel, which depends on the interactions between them during loading, is the main reason to enhance the mechanical properties of FHCs. Moreover, articles about such FHCs that have the potential for foods or food industries have been described. Additionally, the information gaps about edible FHCs were highlighted for further research. Finally, the methods of fiber formation have been summarized., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Alginate is an important natural biopolymer and has been widely used in the food, biomedical, and chemical industries. Ca 2+ -induced gelation is one of the most important functional properties of alginate. The gelation mechanism is well-known as egg-box model, which has been intensively studied in the last five decades. Alginate also forms gels with many other monovalent, divalent or trivalent cations, and their gelation can possess different mechanisms from that of Ca 2+ -induced gelation. The resulted gels also exhibit different properties that lead to various applications. This study is proposed to summarize the gelation mechanisms of alginate induced by different cations, mainly including H + , Ca 2+ , Ba 2+ , Cu 2+ , Sr 2+ , Zn 2+ , Fe 2+ , Mn 2+ , Al 3+ , and Fe 3+ . The mechanism of H + -induced gelation of alginate mainly depends on the protonation of carboxyl groups. Divalent ions-induced gelation of alginate show different selection towards G, M, and GM blocks. Trivalent ions can bind to carboxyl groups of uronates with no selection. The properties and applications of these ionotropic alginate gels are also discussed. The knowledge gained in this study would provide useful information for the practical applications of alginate., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Enhancement on the mechanical properties of hydrogels leads to a wider range of their applications in various fields. Therefore, there has been a great interest recently for developing new strategies to reinforce hydrogels. Moreover, food gels must be edible in terms of both raw materials and production. This paper reviews innovative techniques such as particle/fiber-reinforced hydrogel, double network, dual crosslinking, freeze-thaw cycles, physical conditioning and soaking methods to improve the mechanical properties of hydrogels. Additionally, their fundamental mechanisms, advantages and disadvantages have been discussed. Important biopolymers that have been employed for these strategies and also their potentials in food applications have been summarized. The general mechanism of these strategies is based on increasing the degree of crosslinking between interacting polymers in hydrogels. These links can be formed by adding fillers (oil droplets or fibers in filled gels) or cross-linkers (regarding double network and soaking method) and also by condensation or alignment of the biopolymers (freeze-thaw cycle and physical conditioning) in the gel network. The properties of particle/fiber-reinforced hydrogels extremely depend on the filler, gel matrix and the interaction between them. In freeze-thaw cycles and physical conditioning methods, it is possible to form new links in the gel network without adding any cross-linkers or fillers. It is expected that the utilization of gels will get broader and more varied in food industries by using these strategies., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Injectable hydrogels have gained great attentions for cell therapy and tissue regeneration as a result of the applications in minimally invasive surgical procedures with the ease of handling and complete filling of the defect area. Here, a novel biodegradable, thermosensitive and injectable carboxymethyl chitin (CMCH) hydrogel was developed for three-dimensional (3D) cell culture. The obtained CMCH solution remained transparent liquid flowing easily at low temperatures and gelled rapidly at 37 °C. The gelation time of CMCH hydrogels could be easily tuned by varying temperature and the degree of carboxymethylation, which facilitates the cell encapsulation process at room temperature and in-situ forming hydrogel at body temperature. Moreover, the CMCH-14 hydrogels in PBS buffer remained stable and continuous porous structure and could be degraded in the presence of lysozyme or hyaluronidase. HeLa cells proliferated sustainably and self-assembled to form 3D multicellular spheroids with high cell activity on the surface of CMCH-14 hydrogel. Encapsulation of COS-7 cells within the in-situ forming CMCH hydrogel demonstrated that CMCH hydrogels promoted cell survival and proliferation. In vivo mouse study of the CMCH hydrogels showed good in-situ gel formation and tissue biocompatibility. Thus, the biodegradable thermosensitive injectable CMCH hydrogels hold potential for 3D cell culture and biomedical applications. Statement of Significance Biodegradable hydrogels have been widely studied for cell therapy and tissue regeneration. Herein, we report a novel thermosensitive injectable carboxymethyl chitin (CMCH) hydrogel for 3D cell culture, which was synthesized homogeneously from the bioactive natural chitin through the “green” process avoiding using organic solvent. The CMCH solutions exhibited rapid thermoresponsive sol-to-gel phase transition behavior at 37 °C with controllable gelation times, which facilitates the cell encapsulation process at room temperature and in-situ forming hydrogel at body temperature. Importantly, in vitro 3D cell culture and in vivo mouse study of the CMCH hydrogel showed promotion of cell survival and proliferation, good in-situ gel formation and biocompatibility. We believe that such thermosensitive injectable CMCH hydrogels would be very useful for biomedical applications, such as tumor model for cancer research, post-operative adhesion prevention, the regeneration of cartilage and central nervous system and so on. [ABSTRACT FROM AUTHOR]

With reference to eq. (5) in the original article, the authors have neglected to specify the description of some terms in the text. They correct the mistake in the present erratum. [ABSTRACT FROM AUTHOR]

Emulsion-templating techniques have been used to develop structurally anisotropic hydrogels. This paper proposes a method to couple biopolymer assembly behavior with a phase-separated aqueous two-phase system (ATPS) to construct a hierarchical structure on protein-polysaccharide hydrogels. Based on the phase separation of Artemisia sphaerocephala Krasch polysaccharide (ASKP) and whey protein isolate (WPI) fibrils, a bi-continuous hydrogel was fabricated through spontaneous iron-facilitated molecular chelation. The impact of WPI fibrils under ultrasonic treatment for varying durations on gel structurization and physicochemical properties was also exploited. Shorter length of WPI fibrils facilitated stepwise cross-linking gelation during the oxidation of ferrous ions to ferric ions. Specifically, ultrasonic treatment for 6 min and 8 min promoted the accumulation of shorter fibrils, resulting in the formation of a more intensive clockwise-oriented hierarchical network. Compared to the hydrogels with longer linear aggregates without the ultrasonic treatment, the incorporation of the shorter aggregates resulting from ultrasonic treatment for 6 min and 8 min significantly increased the gel's water holding capacity and mechanical properties. Additionally, the fibrils that underwent ultrasonic treatment for 6 min resulted in a more stable three-dimensional network with optimal elastic performance. This study presents a new water-in-water emulsion-templated strategy for structural regulation and stabilization of multiform hydrogel. [Display omitted] • A hierarchical structured hydrogel was created using a phase-separated ATPS. • WPI fibril length effectively impacted the properties of the hierarchical hydrogel. • Shorter fibrils resulted in an oriented network, improving the mechanical properties. [ABSTRACT FROM AUTHOR]

Polymer hydrogels have attracted considerable attention as functional materials. The conventional single network hydrogels (SNs) are mechanically either too soft or brittle to be used as load-bearing substances. Therefore, the interpenetrating network hydrogels (IPNs) with unique physical characteristics paid more and more attention and they have shown great potentials in fabricating a variety of food structures with desired functionalities. This review provided a summary of the latest developments and applications of IPNs in terms of synthesis strategies (heating-cooling, enzymatic, and ionic-induced technique), physical performance (mechanical property, water holding capacity, swelling capacity, and thermal property), formation and strengthening mechanisms, as well as food applications. The major future trends of IPNs in food systems were also discussed. As compared with SNs, IPNs generally exhibited more favorable mechanical performance, water holding capacity and thermal stability. The strengthening mechanisms of IPNs were mainly attributed to the filling of polysaccharides in other biopolymers, the increased density of entangled network, and the possible interactions between individual networks. IPNs with tunable mechanical property could be fabricated, showing great potential for various food applications such as edible films, three-dimensional printing, delivery of bioactive/aroma compounds, as well as fat replacers. • IPNs can be fabricated by heating-cooling, ionic and enzymatic crosslinking. • IPNs exhibit favorable mechanical properties, high WHC and thermal stability. • IPNs provide approving texture and pleasant sensory quality for food. • Strengthening of IPNs is due to "filler effect" and enhanced noncovalent actions. • IPNs show potential application in meat analogues, 3D printing and fat replacers. [ABSTRACT FROM AUTHOR]

Double network hydrogels (DNs) with excellent strength and toughness have been preliminarily applied in the preparation of artificial foods. To evaluate the effect of conformation transition of ductile polymers on the physicochemical properties of DNs, we firstly prepared agarose (AR)/high acyl gellan (HAG) DNs and investigated their mechanical properties, and then calcium ion (Ca2+) was introduced into optimized AR/HAG DNs to regulate the conformation of ductile chains (HAG) for further increasing their mechanical properties. The mechanical strength of the optimized AR/HAG gel is 5 times and 2 times that of AR and HAG gel, respectively. Compared with adding Ca2+ method, immersing Ca2+ solution endowed optimized DNs with 5-fold increase in mechanical strength, outstanding textural properties and lower swelling ratio, which was attributed to the extended conformation of ductile chains. Furthermore, the obtained DNs were reminiscent of beef omasum based on their physicochemical properties. Optimized AR/HAG DNs after immersing in 2 wt% CaCl 2 solution exhibited comparable texture properties with beef omasum by three correlation analysis methods and sensory evaluation, providing a new strategy to fabricate biomimetic food with high chewiness by regulating the conformation of ductile polymers in DNs. • Optimized agarose/high acyl gellan double network gel had outstanding mechanics. • Strength of agarose/high acyl gellan gel increased 5-fold by Ca2+ immersion method. • Extended ductile chain endowed higher DNs mechanics than its folded conformation. • Ca2+-induced agarose/high acyl gellan gel had comparable texture to beef omasum. [ABSTRACT FROM AUTHOR]

Beef tripe is widely consumed in the world due to its favorable texture. However, the large-scale cultivation of cattle for producing tripe would exacerbate living environment, and therefore the development of artificial beef tripe is necessary. To imitate the texture of authentic beef tripe, we fabricated the agarose (AR)/konjac glucomannan (KGM) double network hydrogels (DNs) with outstanding mechanical properties using heating-cooling combined with sodium carbonate immersion strategy, and further compared them with beef tripe. Notably, the optimized DNs demonstrated a significantly increased mechanical strength of 450% and 340% than single AR and KGM gels, respectively. Further study revealed that the soft networks (KGM) mainly maintained the elasticity of the hydrogels, whereas the rigid networks (AR) were integrated inside the large soft network framework and acted as "load carriers" to efficiently dissipate energy. Correlation analysis and sensory attributes analysis indicated that the AR/KGM DNs with a mass ratio of 1:4 presented the most comparable texture properties with beef reticulum and rumen cooked, showing the great potential as artificial beef tripe. [Display omitted] • Agarose/konjac glucomannan double network gel was built by a two-step procedure. • Agarose/konjac glucomannan double network gel had outstanding mechanical property. • Optimized agarose/konjac glucomannan gel showed comparable texture to beef tripe. [ABSTRACT FROM AUTHOR]

• Making two types of WPI nanofibril-gel composites by controlling WPI aggregates. • The concentration of WP amyloid fibril and gel types affected composite properties. • Fibril led to decreasing tan δ-value and condensing structure of stranded WPI gel. • Phase separation and disordering occurred in particulate WPI gels by adding fibril. • The elastic modulus of both types of WPI gel enhanced by adding fibril. Adding fibers to hydrogels is a modern strategy for producing tough hydrogels. Nanofibers usually perform well in hydrogels due to their unique properties. The purpose of this study was to investigate the effects of whey protein amyloid fibril (WPF) on the properties of heat-set whey protein isolate (WPI) gels with fine-stranded or particulate microstructure (at pH 7). The results show that by adding WPF, a homogenous and dense network was observed in fine-stranded gel, while the formation of a coarse and amorphous structure with microphase separation intensified in particulate gel. By adding 1% WPF, the elastic modulus of gels increased about 10.6 and 3.6 times in the case of fine-stranded and particulate gels, respectively. In fine-stranded gels, adding WPF to the gel led to a decrease in the T g value (from 66.33 to 59.36 °C) and a decrease in tan δ (from 0.2328 to 0.0837), indicating an increase in gel strength because of WPF. In contrast, adding WPF to particulate gels did not cause significant changes in the T g and tan δ. There was a decrease in the water holding property of particulate gels when WPF was added, whereas it did not change significantly in fine-stranded gels. These findings imply that the efficiency of WPF in WPI gels depends not only on the WPF concentration but also on the type of the WPI gel. In sum, WPF enhances order in the structural network of fine-stranded gels, while accelerating the formation of inhomogeneous random aggregates in particulate gels. Creating fiber-hydrogels with different microstructures and rheological properties can be possible by controlling WPI aggregation (as in amyloid fibril, fine-strand or particulate aggregates). [ABSTRACT FROM AUTHOR]