Effect of pre-treatment temperatures on the film-forming properties of collagen fiber dispersions

Fabrication, characterization, and in vitro digestion of gelatin/gluten oleogels from thermally crosslinked electrospun short fiber aerogel templates

In this work, the electrospun short fiber-based oleogels (ESFO) were formed by thermal crosslinking. Gelatin and gluten nanofibers were obtained via electrospinning, then homogenized and transformed into short fiber dispersions. Through freeze-drying, electrospun short fiber-based aerogel (ESF-A) templates were obtained for oil adsorption. All ESF-A exhibited the micromorphology of loose fibrous pore structure and prominent changes of characteristic peaks in the thermal and infrared analyses. Moreover, the highly crosslinked templates owned excellent hydrophobicity and mechanical performances (elastic modulus: 0.25 kPa, yield strength: 14.56 kPa, compressive strength: 52.54 kPa, and the final compression recovery: 91.27%). Meanwhile, the oil adsorption/oil holding capacity could reach 76.56 g/g and 80.04%, respectively. Through thermal crosslinking, ESF-O presented good and controllable rheological/in vitro digestion properties, which were further confirmed by PCA analysis. According to different application conditions, ESF-O properties could be adjusted by different degrees of fiber addition or thermal crosslinking.

Collagen and gelatin: Structure, properties, and applications in food industry

Food-producing animals have the highest concentration of collagen in their extracellular matrix. Collagen and gelatin are widely used in food industry due to their specific structural, physicochemical, and biochemical properties, which enable them to improve health and nutritional value as well as to increase the stability, consistency, and elasticity of food products. This paper reviews the structural and functional properties including inherent self-assembly, gel forming, water-retaining, emulsifying, foaming, and thickening properties of collagen and gelatin. Then the colloid structures formed by collagen such as emulsions, films or coatings, and fibers are summarized. Finally, the potential applications of collagen and gelatin in muscle foods, dairy products, confectionary and dessert, and beverage products are also reviewed. The objective of this review is to provide the current market value, progress as well as applications of collagen and its derivatives in food industry.

Mesostructured Fibrils Exfoliated in Deep Eutectic Solvent as Building Blocks of Collagen Membranes

The mesoscale components of collagen (nanofibrils, fibrils, and fiber bundles) are well organized in native tissues, resulting in superior properties and diverse functions. In this paper, we present a simple and controlled liquid exfoliation method to directly extract medium-sized collagen fibers ranging from 102 to 159 nm in diameter from bovine Achilles tendon using urea/hydrochloric acid and a deep eutectic solvent (DES). In situ observations under polarized light microscopy (POM) and molecular dynamics simulations revealed the effects of urea and GuHCl on tendon collagen. FTIR study results confirmed that these fibrils retained the typical structural characteristics of type I collagen. These shed collagen fibrils were then used as building blocks to create independent collagen membranes with good and stable mechanical properties, excellent barrier properties, and cell compatibility. A new method for collagen processing is provided in this work by using DES-assisted liquid exfoliation for constructing robust collagen membranes with mesoscale collagen fibrils as building blocks.

pH-shift strategy improving the thermal stability and oxidation stability of rice starch/casein-based high internal phase emulsions for the application in fish cake

The thermal stability of the different pH-shift rice starch/casein-based high internal phase emulsions (SC-HIPE) were evaluated in the present study to verify potential in improving the quality of fish cake. The results showed that the pH-shift treatment improved thermal stability (from 27.23% to 76.33%) and oxidation time (from 5.01 h to 6.86 h) of SC-HIPE, which showed the smaller droplet size (decreased from 15.14 to 1.64 μm) and higher storage module. The breaking force of FC with thermal stable SC-HIPE (average 64.95 g) was higher than that with thermal unstable SC-HIPE (51.05 g). The cohesiveness, adhesiveness and chewiness could be improved by adding thermal stable SC-HIPE, compared with pork fat. Additionally, combining sensory evaluation, the thermal stable SC-HIPE improved the gel quality, thus it could be completely replaced pork fat in the preparation of FC, which provided theoretical guidance for the preparation and application of fat substitutes.

Changes in Structures and Properties of Collagen Fibers during Collagen Casing Film Manufacturing

Collagen casing is an edible film, which is widely used in the industrial production of sausages. However, the detailed changes in the collagen fibers, from the raw material to the final collagen film, have rarely been reported. In this research, the changes in the collagen fibers during the manufacturing process, including the fiber arrangement, the triple-helix structure and the thermal stability, were investigated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy. The relationship between the structure stability and the arrangement of the collagen fibers was also discussed. According to the SEM, XRD, TGA, DSC and FTIR results, the collagen fibers were depolymerized during the acid swelling and became uniformly aligned after the homogenization process. Degassing had no obvious effect on the triple-helix structure. Alkaline neutralization with ammonia destroyed the triple-helix structure, which could be partly reversed through the washing and soaking processes. During the final drying step, the depolymerized triple helix of the collagen fibers recombined to form new structures that showed decreased thermal stability. This study expands our knowledge about the behavior of collagen fibers during the industrial process of producing collagen biobased casings.

Collagen processing with mesoscale aggregates as templates and building blocks

Collagen presents a well-organized hierarchical multilevel structure. Microfibers, fibers, and fiber bundles are the aggregates of natural collagen; which achieve an ideal balance of mechanical strength and toughness at the mesoscopic scale for biological tissue. These mesostructured aggregates of collagen isolated from biological tissues retain these inherent organizational features to enable their use as building blocks for constructing new collagen materials with ideal mechanical performance, thermal and dimensional stability. This strategy is distinct from the more common bottom-up or molecular-level design and assembly approach to generating collagen materials. The present review introduces the hierarchical structure of biological collagen with a focus on mesostructural features. Isolation strategies for these collagen aggregates (CAs) are summarized. Recent progress in the use of these mesostructural components for the construction of new collagen materials with emerging applications is reviewed, including in catalysis, environmental applications, biomedicine, food packaging, electrical energy storage, and flexible sensors. Finally, challenges and prospects are assessed for controllable production of CAs as well as material designs.

Rheological Method for Determining the Molecular Weight of Collagen Gels by Using a Machine Learning Technique

This article presents, for the first time, the results of applying the rheological technique to measure the molecular weights (Mw) and their distributions (MwD) of highly hierarchical biomolecules, such as non-hydrolyzed collagen gels. Due to the high viscosity of the studied gels, the effect of the concentrations on the rheological tests was investigated. In addition, because these materials are highly sensitive to denaturation and degradation under mechanical stress and temperatures close to 40 °C, when frequency sweeps were applied, a mathematical adjustment of the data by machine learning techniques (artificial intelligence tools) was designed and implemented. Using the proposed method, collagen fibers of Mw close to 600 kDa were identified. To validate the proposed method, lower Mw species were obtained and characterized by both the proposed rheological method and traditional measurement techniques, such as chromatography and electrophoresis. The results of the tests confirmed the validity of the proposed method. It is a simple technique for obtaining more microstructural information on these biomolecules and, in turn, facilitating the design of new structural biomaterials with greater added value.

A comparative study on cross-linking of fibrillar gel prepared by tilapia collagen and hyaluronic acid with EDC/NHS and genipin

Chemical cross-linking is an important step to grant satisfying properties to collagen-based materials. However, there are few comparative studies on crossing-linking of collagen-based fibrillar gels which are preferred biomaterials for similar properties to native tissues with different cross-linking agents. In this study, a fibrillar gel was fabricated with tilapia collagen and hyaluronic acid, and cross-linking conditions with EDC/NHS and genipin were discussed. Genipin gave gels much higher equilibrium cross-linking degree than EDC/NHS. ATR-FTIR and XPS showed EDC/NHS offered short-range cross-linking formed by amino and carboxyl groups in fibrils, while genipin induced long-range cross-linking by nucleophilic reaction through attack of amino groups in fibrils on carbon atoms at C-3 as well as ester groups in genipin, besides improved hydrogen bonds. XRD and SEM revealed the structural integrity of gels was strengthened after cross-linking, whereas fibril bundles disaggregated into thin fibrils. Consequently, swelling capacity and anti-degraded property were enhanced significantly, while thermal stability weakened. The fibrillar gels had good biocompatibility, but interestingly the appearance and migration of L929 fibroblasts were influenced by cross-linking degree. These results demonstrated that aquatic collagen-based fibrillar gel cross-linked by genipin had greater potential in biomaterials than EDC/NHS, whereas the cross-linking degree should be controlled.

Tunable mechanical behavior of collagen-based films: A comparison of celluloses in different geometries

Collagen (Col) films were reinforced by celluloses in different geometries: microcrystalline cellulose (MCC), cellulosic fines (CF), cellulose nanofiber (CNF) and cellulose nanocrystals (CNC). The reinforcement mechanisms were investigated by the elastoplasticity and fracture appearance. Compared with the fracture stress of collagen film (67.5 MPa), the Col-CNF films effectively borne the stress (95.8 MPa) by intercrystalline fracture, ascribing the abundant hydrogen bonding and mechanical locking between cellulose and collagen. The toughness of Col-CF films was increased by the interfibrillar slippage of CF and pull-off of CF within the matrix, improving the strain-to-break from 8.37% to 12.13%. The films added with MCC and CNC weaken the mechanical behavior, due to the defects and lack of mechanical locking. Besides, the effects of celluloses' geometries on the thickness, density, water-tightness, thermal stability, crystallinity and FTIR of films were also investigated. These provide the evidence that the geometries of fillers diversely improve the behaviors of collagen film offering strategies for the film with adjustable mechanical properties.

Protein-Based Systems for Topical Antibacterial Therapy

Recently, proteins are gaining attention as potential materials for antibacterial therapy. Proteins possess beneficial properties such as biocompatibility, biodegradability, low immunogenic response, ability to control drug release, and can act as protein-mimics in wound healing. Different plant- and animal-derived proteins can be developed into formulations (films, hydrogels, scaffolds, mats) for topical antibacterial therapy. The application areas for topical antibacterial therapy can be wide including bacterial infections in the skin (e.g., acne, wounds), eyelids, mouth, lips, etc. One of the major challenges of the healthcare system is chronic wound infections. Conventional treatment strategies for topical antibacterial therapy of infected wounds are inadequate, and the development of newer and optimized formulations is warranted. Therefore, this review focuses on recent advances in protein-based systems for topical antibacterial therapy in infected wounds. The opportunities and challenges of such protein-based systems along with their future prospects are discussed.

Liquid-Exfoliated Mesostructured Collagen from the Bovine Achilles Tendon as Building Blocks of Collagen Membranes

Mesoscaled assemblies are organized in native collagen tissues to achieve remarkable and diverse performance and functions. In this work, a facile, low-cost, and controllable liquid exfoliation method was applied to directly extract these collagen mesostructures from bovine Achilles tendons using a sodium hydroxide (NaOH)/urea aqueous system with freeze-thaw cycles and sonication. A series of collagen fibrils with diameters of 26-230 nm were harvested using this process, and in situ observations under polarizing microscopy (POM) and using molecular dynamics simulations revealed the influence of the NaOH/urea system on the tendon collagen. FTIR and XRD results confirmed that these collagen fibrils preserved typical structural characteristics of type I collagen. These isolated collagen fibrils were then utilized as building blocks to fabricate free-standing collagen membranes, which exhibited good stability in solvents and outstanding mechanical properties and transparency, with potential for utility in optical and electronic sensors. Moreover, in vitro and vivo evaluations demonstrated that these new resulting collagen membranes had good cytocompatibility, biocompatibility, and degradability for potential applications in biomedicine. This work provides a new approach for collagen processing by liquid exfoliation with utility for the formation of robust collagen materials that consist of native collagen mesostructures as building blocks.

Strategies for Fabricating Protein Films for Biomaterials Applications

Proteins are naturally occurring functional building blocks that are useful for the fabrication of materials. Naturally-occurring proteins are biodegradable and most are biocompatible and non-toxic, making them attractive for the fabrication of biomaterials. Moreover, the fabrication of protein-based materials can be conducted in a green and sustainable manner due to their high aqueous solubility. Consequently, the applicability of protein-based materials is limited by their aqueous and mechanical instability. This review summarizes strategies for the stabilization of protein films, highlighting their salient features and potential limitations. Applications of protein films ranging from food packaging materials, tissue engineering scaffolds, antimicrobial coatings etc. are also discussed. Finally, the need for robust and efficient fabrication strategies for translation to commercial applications as well as potential applications of protein films in the field of sensing, diagnostics and controlled release systems are discussed.

Impact of heating and drying temperatures on the properties of konjac glucomannan/curdlan blend films

The impact of preparation conditions including heating temperature (from 60 °C to 90 °C) and drying temperatures (from 25 °C to 90 °C) on the properties of pure curdlan film and konjac glucomannan (KGM) and curdlan blend films were analyzed. Microstructure analysis indicated the KGM addition could significantly improve the relatively poor film-forming property of curdlan. FTIR and X-ray analysis showed that at high heating temperature 90 °C, molecular interaction might be enhanced in the films due to the stretched structure of curdlan and dissociation of curdlan bundles or triple-helix structure. This was supported by the changes in the mechanical property, surface hydrophobicity, moisture barrier, and moisture tolerance property. The impacts of drying temperature were some different for the curdlan film and KGM/curdlan blend film, and were explained from the molecular hydrophilicity-hydrophobicity, compactness of the films, curdlan conformation, and molecular interaction. This work guided biodegradable film production especially with curdlan added.