On the investigation of composite cooling/heating set gel systems based on rice starch and curdlan

In pursuit of advancing the understanding of composite gel systems, this study delves into the intricate realm of rheology, structural elucidation, and mechanical attributes. Specifically, it scrutinizes the symbiotic interplay between rice starch, a cooling-set gel, and curdlan, a thermo-irreversible heating-set gel. A higher curdlan content enhances the inter-chain hydrogen bonding between rice starch and curdlan, resulting in a denser gel structure and thus increased moduli, solid-like behavior, and mechanical properties, and reduced frequency-dependence, especially at high temperatures (>65 °C). For example, with 50 % curdlan incorporation, G' (90 °C) improved by 252 %. Notably, thermal treatment can compromise the structural integrity of the rice starch gel, reducing strength and softening texture. However, this textural degradation can be effectively mitigated with, for example, 30 % curdlan incorporation, resulting in a 55-fold hardness increase at 85 °C. The knowledge gained from this work offers valuable guidance for tailoring starch-based gel products to specific properties.

Design and fabrication of functionalized curdlan-curcumin delivery system to facilitate the therapeutic effects of curcumin on breast cancer

We developed a facile method for the fabrication of a biodegradable delivery system composed of two blocks: curdlan and curcumin. This was achieved by chemical functionalization of curdlan through tosylation, amination followed by complexation with curcumin. A comprehensive evaluation of structural characterization and component stability showed that cur-cum complex exhibited better anticancer properties with enhanced thermal properties. The cur-cum complex shows pH sensitive sustained release behaviour with higher release at acidic pH and kinetic data of drug release follows the Korsmeyer-Peppas model. The cur-cum complex has ability to block the proliferation of the MCF-7 cell line as revealed by MTT assay which showed increased toxicity of cur-cum complex against these cell lines. The results obtained from western blot analysis demonstrated that the co-administration of cur and cum effectively induced apoptosis in MCF-7 cells. This effect was observed by a considerable upregulation of the Bcl-2/Bax ratio, a decline in mRNA expression of LDHA, level of lactate and LDH activity. The results clearly depict the role of functionalized curdlan as efficient carrier for curcumin delivery with prolonged, sustained release and enhanced bioavailability, thereby improving the overall anticancer activity.

Study of chondrogenesis of umbilical cord mesenchymal stem cells in curdlan- poly(vinyl alcohol) composite hydrogels and its mechanical properties of freezing-thawing treatments

The curdlan gel is a natural material produced by bacteria. It utilizes chemical cross-linking reactions to form a 3D porous composite hydrogel, increasing its porosity and water content, and improving its mechanical properties. It can be used in tissue repair and regenerative medicine. Curdlan-Poly(vinyl alcohol) (PVA) composite hydrogel can rapidly swell within 1 min due to its porous structure. Compression tests confirmed that it still maintains its original mechanical strength, even after five repeated freeze-thaw (FT) processes, making it suitable for long-term cryopreservation. The purpose of this study is to transplant umbilical cord mesenchymal stem cells (UC-MSCs) on Curdlan-PVA composite hydrogel and observe the chondrocytes on the material. The results of using 4',6-diamidino-2-phenylindole (DAPI), hematoxylin and eosin (H&E), calcein-acetoxymethyl ester (calcein AM), and Collagen type II-Fluorescein isothiocyanate (FITC) staining, confirmed that UC-MSCs can attach and differentiate into chondrocytes on 3D Curdlan-PVA composite hydrogel.

Phase behavior of the gelation process of myofibrillar protein-curdlan blended system: Discussion based on rheology and gel properties

The phase behavior in protein-polysaccharide blended systems is the main factor affecting the physical properties of composite gels; however, the phase behavior at room temperature and during heated gelation is lacking discussion. In this research, extracted grouper myofibrillar protein (MP) and curdlan (CUR) were used as models for the MP-CUR blended system. The phase behavior of the MP-CUR blended system was analyzed using rheology and microstructure analysis, and the accuracy of the phase behavior analysis was verified by measuring the physical indices such as gel properties of the MP-CUR composite gels. At room temperature, MP and CUR showed good co-solubility, so the blended system with 0.8% CUR content obtained the best apparent viscosity, structural recoverability, and other rheological properties. After heating gelation, MP and CUR had strong thermodynamic unaffinity leading to phase separation, and the best storage modulus was obtained for the MP-CUR blended system with 0.6% CUR content. Therefore, it is concluded that 0.6% CUR content is the critical concentration for the MP-CUR blended system. The results were also confirmed by the best gel properties of 0.6% CUR composite gel when the physical properties of the composite gel were determined. The phase behavior evaluation was used to determine the appropriate polysaccharide concentrations as a means to improve the physicochemical properties of the composite gels and to exploit the value of polysaccharides in protein-based food applications.

The antibacterial and hemostatic curdlan hydrogel-loading epigallocatechin gallate for facilitating the infected wound healing

The infected wounds pose one of the major threats to human health today. To address this issue, it is necessary to develop innovative wound dressings with superior antibacterial activity and other properties. Due to its potent antibacterial, antioxidant, and immune-boosting properties, epigallocatechin gallate (EGCG) has been widely utilized. In this study, a multifunctional curdlan hydrogel loading EGCG (Cur-EGCGH3) was designed. Cur-EGCGH3 exhibited excellent physicochemical properties, good biocompatibility, hemostatic, antibacterial, and antioxidant activities. Also, ELISA data showed that Cur-EGCGH3 stimulated macrophages to secrete pro-inflammatory and pro-regenerative cytokines. Cell scratch results indicated that Cur-EGCGH3 promoted the migration of NIH3T3 and HUVECs. In vivo experiments confirmed that Cur-EGCGH3 could inhibit bacterial infection of the infected wounds, accelerate hemostasis, and promote epithelial regeneration and collagen deposition. These results demonstrated that Cur-EGCGH3 holds promise for promoting healing of the infected wounds.

Structural insights into curdlan degradation via a glycoside hydrolase containing a disruptive carbohydrate-binding module

BACKGROUND

Degradation via enzymatic processes for the production of valuable β-1,3-glucooligosaccharides (GOS) from curdlan has attracted considerable interest. CBM6E functions as a curdlan-specific β-1,3-endoglucanase, composed of a glycoside hydrolase family 128 (GH128) module and a carbohydrate-binding module (CBM) derived from family CBM6.

RESULTS

Crystallographic analyses were conducted to comprehend the substrate specificity mechanism of CBM6E. This unveiled structures of both apo CBM6E and its GOS-complexed form. The GH128 and CBM6 modules constitute a cohesive unit, binding nine glucoside moieties within the catalytic groove in a singular helical conformation. By extending the substrate-binding groove, we engineered CBM6E variants with heightened hydrolytic activities, generating diverse GOS profiles from curdlan. Molecular docking, followed by mutation validation, unveiled the cooperative recognition of triple-helical β-1,3-glucan by the GH128 and CBM6 modules, along with the identification of a novel sugar-binding residue situated within the CBM6 module. Interestingly, supplementing the CBM6 module into curdlan gel disrupted the gel's network structure, enhancing the hydrolysis of curdlan by specific β-1,3-glucanases.

CONCLUSIONS

This study offers new insights into the recognition mechanism of glycoside hydrolases toward triple-helical β-1,3-glucans, presenting an effective method to enhance endoglucanase activity and manipulate its product profile. Furthermore, it discovered a CBM module capable of disrupting the quaternary structures of curdlan, thereby boosting the hydrolytic activity of curdlan gel when co-incubated with β-1,3-glucanases. These findings hold relevance for developing future enzyme and CBM cocktails useful in GOS production from curdlan degradation.

Curdlan/sodium carboxymethylcellulose composite adsorbents: A biodegradable solution for organic dye removal from water

Composite adsorbent comprised of curdlan (CURD) and sodium carboxymethylcellulose (CMC) were fabricated through a single-step heating process, targeting the removal of methylene blue (MB) from wastewater. The CURD/CMC composite adsorbents had a honeycomb porous structure. The integration of CMC not only increased the storage modulus of the CURD/CMC composite hydrogels but also affected the thermal stability and swelling behavior of the composite adsorbents in different pH solutions. Specifically, the addition of 1.2 % CMC increased the peak temperature (184.73 °C) of CURD/CMC composite adsorbent melting by 5.99 °C compared to CURD adsorbent. The addition of CMC improved the swelling ratio of the composite adsorbent at pH 3,7, and 12 with swelling ratio up to 918.07 %. The synergistic interaction between CURD and CMC led to an enhanced adsorption capacity of the aerogel for MB, achieving a maximum adsorption capability of 385.85 mg/g. Adsorption isotherm assessments further demonstrated that the Langmuir isotherm model well fitted the adsorption data of the composite adsorbent on MB. Collectively, these findings underscore the potential of the developed biodegradable adsorbents as promising adsorbents for efficiently eliminating organic dyes from water.

Recent innovations (2020-2023) in the approaches for the chemical functionalization of curdlan and pullulan: A mini-review

Chemical modification represents a highly efficacious approach for enhancing the physicochemical characteristics and biological functionalities of natural polysaccharides. However, not all polysaccharides have considerable pharmacologic activity; so, appropriate chemical modification strategies can be selected in accordance with the distinct structural properties of polysaccharides to aid in improving and encouraging the presentation of their biological activities. Hence, there has been a growing interest in the chemical alteration of polysaccharides due to their various properties such as antioxidant, anticoagulant, antiviral, anticancer, biomedical, antibacterial, and immunomodulatory effects. This paper offers a comprehensive examination of recent scientific advancements produced over the past four years in the realm of unique chemical and functional modifications in curdlan and pullulan structures. This review aims to provide readers with an overview of the structural activity correlations observed in the backbone structures of curdlan and pullulan, as well as the diverse chemical modification processes employed for these polysaccharides. Additionally, the review aims to examine the effects of combining various bioactive molecules with chemically modified curdlan and pullulan and explore their potential applications in various important fields.

Utilization of heat-induced curdlan gel to improve the cooking qualities of thermally sterilized fresh rice noodles

Thermal sterilization is the most economical and efficient method to guarantee the shelf life of extruded fresh rice noodles, but it often leads to a high cooking breakage rate and poor elongation at break of the noodles. The aim of this study was to improve the edible quality of sterilized fresh rice noodles through the addition of low concentrations of curdlan (0.38 %-1.13 %), which can form a thermal-irreversible gel to resist high-temperature sterilization. Compared with the control group without curdlan, the cooking breakage rate of sterilized fresh rice noodles with 1.13 % curdlan decreased from 16.85 % to 5.22 %, the tensile strain increased from 91.15 % to 147.05 %, and the microstructure was more dense and uniform. The results showed that adding the proper amount of curdlan is an effective strategy to improve the quality of sterilized fresh rice noodles.

Improvement of gelation properties of Penaeus vannamei surimi by magnetic field-assisted freezing in combination with curdlan

Traditional methods of freezing and thawing may harm the quality of meat products. In order to reduce the negative impact of freezing on surimi products, the magnetic field-assisted freezing method is combined with various curdlan ratios to enhance the gelation characteristics of Penaeus vannamei surimi in this study. The results showed that the magnetic field-assisted freezing technique significantly improved the quality of thawed surimi compared with soaking freezing (SF), whereas the addition of curdlan further improved the gelation properties, and the gel strength, water-holding capacity, textural properties, whiteness, and G' value were significantly improved when its content was increased to 0.6 %. However, excessive amounts of curdlan interfered with protein covalent cross-linking, leading to a decrease in gel quality. Additionally, the addition of magnetic field and curdlan encouraged the shift of the α-helix to the random coil and β-sheet transition, which stimulated the growth of myofibril molecules, exposed the hydrophobic groups and thiols, improved protein-molecule interactions, and promoted systematic gathering of proteins, leading to the formation of the microstructure of dense and small pores. It also resulted in a drop in water release, an increase in the proton density and a shift in the water condition from free water to more immobile water, which had higher sensory qualities. These effects together resulted in a reduction in thawing and cooking loss to 11.41 % and 13.83 %, respectively. These results also help to clarify the gelation process of shrimp surimi and help to regulate the gelation characteristics of shrimp surimi products.

High-moisture extrusion of curdlan: Texture and structure

High-moisture extrusion is a promising thermomechanical technology extensively employed in manufacturing fibrous meat analogues from plant-based proteins, garnering considerable research attention. However, polysaccharide-based extrusion has been rarely explored. The present study investigates the effects of varying extruder barrel temperatures (130 °C-200 °C) on the texture and structure of curdlan extrudates, and highlights the formation mechanism. Results showed that the single chain of curdlan aggregates to form triple-helix chains upon extrusion, consequently enhancing the crystallinity, particularly at 170 °C. The hardness, chewiness, and mechanical properties improved with increasing barrel temperature. Moreover, barrel temperatures affected the macrostructure, the extrudates maintained intact morphologies except at 160 °C due to the melting of curdlan gel as confirmed by the differential scanning calorimetry thermogram. Microstructural analysis revealed that curdlan extrudates transited through three phases: original gel (130 °C, 140 °C, and 150 °C), transition state (160 °C), and regenerated gel (170 °C, 180 °C, 190 °C, and 200 °C). The steady state of regenerated gel (170 °C) exhibited higher crystallinity and smaller fractal dimension, resulting in a more compact and crosslinked gel network. This study elucidates the structure transition of curdlan gel at extremely high temperatures, offering valuable technical insights for developing theories and methods with respect to polysaccharide-based extrusion that may find applications in food-related fields.

Study of alkali-soluble curdlan/bacterial cellulose/cinnamon essential oil blend films with enhanced mechanical properties

In response to the growing demand for biodegraded film with high mechanical properties for complex preservation application scenarios, we developed a curdlan (CD) blended films with exceptional mechanical strength through an alkali dissolution method. Notably, the alkali-soluble CD film exhibited five-fold increase in tensile strength (TS) when compared to its water-soluble counterpart. Furthermore, the inclusion of 2 % bacterial cellulose (BC) resulted in a significant 41.1 % augmentation of the film's TS. Thermal stability improvements were observed through differential scanning calorimetry (DSC) analysis and thermogravimetric analysis (TGA). X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) results provided insights into alterations in film crystallinity and intermolecular interactions. Specifically, the incorporation of 10 % CEO led to an additional improvement in TS. Our experimental investigations involving the packaging of chilled fresh meat with these blended films unveiled their capacity to effectively inhibit microorganism growth, maintain meat color stability, delay protein decomposition and fat oxidation, and extend the storage time up to 9 days. Our study offers a promising solution for food packaging, emphasizing the development of a high-strength degradable CD/BC/CEO blended film, which holds potential for extending the shelf life of food products.

Effects of direct addition of curdlan on the gelling characteristics of thermally induced soy protein isolate gels

In this study, the effects of the direct addition of curdlan on the physicochemical, structural, and functional properties of heat-induced soy protein isolate (SPI) gels were evaluated. Results demonstrated that the direct incorporation of curdlan enhanced the gel-forming performance, water-holding capacity, and gel strength of heat-induced SPI gels. The presence of curdlan reduced the free water molecules and α-helix content in the SPI structure and contributed to the construction of stable SPI gels with uniform and compact network structures, as visually proven by microstructure observations. Moreover, compared with the SPI gel alone, the curdlan-SPI composite gels presented a more pronounced viscoelastic property and thermal stability mainly due to the intermolecular hydrogen bonding interaction between curdlan and the SPI molecules. Our findings suggest that the direct incorporation of curdlan can effectively ameliorate the gelling characteristics of heat-induced SPI gels, indicating its potential application as a promising gel improver in the food industry.

Halapricum hydrolyticum sp. nov., a beta-1,3-glucan utilizing haloarchaeon from hypersaline lakes

Two strains of neutrophilic haloaloarchaea were selectively enriched from hypersaline lakes in southwestern Siberia using β-1,3-glucans as a substrate. The strains were nearly identical in their phenotypes and according to phylogenomic analysis, and represent a distant novel species group in the genus Halapricum of the family Haloarculaceae. The main phenotypic property of the novel isolates is the ability to hydrolyze and grow with the polysaccharides curdlan and pachyman. Such potential has, to date, not been seen in any other haloarchaea in pure cultures. The strains are obligately aerobic saccharolytics. Apart from the insoluble β-1,3-glucans, they utilized soluble α-glucans (starch, pullulan and glycogen) and a limited number of sugars. The major ether-bound polar phospholipids include PGP-Me and PG. The glyco- and sulfolipids were absent. The major respiratory menaquinone is MK-8:8. On the basis of their unique physiological properties and the results of phylogenomic analysis, the isolates are suggested to be classified into a novel species Halapricum hydrolyticum sp. nov. (type strain HArc-curdl5-1T = DSM 114193T = UQM 41587T).

Insight into curdlan alleviating quality deterioration of frozen dough during storage: Fermentation properties, water state and gluten structure

Curdlan was effective in alleviating quality deterioration of frozen dough during storage. This research explored the mechanisms from perspectives of fermentation properties, water state and gluten structure of frozen dough during storage, and the performance of corresponding steamed bread. Results showed that curdlan addition improved the gas-releasing capability and gas-holding capability of frozen dough, meanwhile enhanced the specific volume and textural properties of corresponding steamed bread. The melting enthalpy and NMR results demonstrated that curdlan restricted the conversation of bound water into freezable water, and inhibited the moisture migration in frozen dough. Frozen dough with 0.5% curdlan had significantly lower gluten macropolymers (GMP) depolymerization degree and free sulfhydryl (SH) content than the control, indicating that curdlan alleviated the depolymerization of GMP. Microstructure results proved that the deterioration of the structure was retarded by curdlan. This study contributes to understanding the theories for curdlan alleviating the deterioration of frozen dough during storage.

A general route to strong, conductive and antibacterial curdlan-based purely natural eutectohydrogels with self-assembled layer-by-layer network structure

To promote the application extension of curdlan from food industry- dominant to advanced flexible biomaterials, a novel group of purely natural curdlan gels with noticeable performance was developed through a simple heating-cooling approach, i.e., heating the dispersion of pristine curdlan in mixed acidic natural deep eutectic solvents (NADESs) and water at 60-90 °C, and cooling at ambient temperature. The NADESs employed are composed of choline chloride and natural organic acids (lactic acid as the representative). The as-developed gels (called eutectohydrogels) are not only compressible and stretchable but conductive, which traditional curdlan hydrogels are not attainable. The compressive stress at 90 % strain exceeds 2.00 ± 0.03 MPa, the tensile strength and fracture elongation reach 0.131 ± 0.002 MPa and 300 ± 9 % respectively, attributed to the distinctive, reciprocally linked self-assembled layer-by-layer network structure formed during gelation. An electric conductivity up to 2.22 ± 0.04 S‧m^-1 is achieved. The excellent mechanics and conductivity confer them good strain-sensing behavior. Additionally, the eutectohydrogels display high antibacterial activity against S. aureus (a model Gram-positive bacterium) and E. coli (a model Gram-negative bacterium). The outstanding comprehensive performance together with the purely natural attribute makes them broad application prospects in biomedical fields like flexible bioelectronics.

by attenuating the exopolysaccharide encapsulation

During curdlan production by Agrobacterium sp., the secreted exopolysaccharide (EPS) gradually encapsulated Agrobacterium sp., accompanied by cell aggregation, resulted in inhibited substrate uptake and curdlan synthesis. To relieve the EPS encapsulation effect, the shake-flask culture medium was quantitatively supplemented with 2 % to 10 % endo-β-1,3-glucanase (BGN), while obtaining curdlan with a decreased weight-average molecular weight ranging from 18.99 × 10⁴ Da to 3.20 × 10⁴ Da. In a 7-L bioreactor, the 4 % BGN supplement substantially attenuated the EPS encapsulation, resulting in increased glucose consumption and curdlan yield to 66.41 g/L and 34.53 g/L after fermentation of 108 h, which improved 43 % and 67 %, respectively compared with the control. The disruption of EPS encapsulation with BGN treatment accelerated the regeneration of ATP and UTP, resulting in sufficient uridine diphosphate glucose for curdlan synthesis. The upregulation of related genes at the transcription level reveals that the respiratory metabolic intensity, the energy regeneration efficiency, and the curdlan synthetase activity were enhanced. This study presents a simple and novel strategy of relieving the effects of EPS encapsulation on the metabolism of Agrobacterium sp. for the high-yield and value-added production of curdlan, which could be potentially applied in producing other EPSs.

Ultrasonic treatment combined with curdlan improves the gelation properties of low-salt Nemipterus virgatus surimi

In this study, the gel properties of ultrasonic alone, curdlan treatment alone, and the combination of both at low-salt surimi levels were investigated, mainly in terms of textural properties, water holding capacity, water distribution, dynamic rheology, protein secondary structure, microstructure and correlation analysis. The results showed that the springiness, gel strength, water holding capacity and energy storage modulus (G') of the low-salt surimi gels without ultrasonic or curdlan treatment were lower than those of the high-salt concentration surimi gels. Compared with the 1 % low-salt group, the ultrasonic treatment combination with curdlan resulted in a significant improvement (p < 0.05) in the texture, water holding capacity and energy storage modulus (G') of the low-salt surimi at the same salt concentration. The gel strength increased significantly from 3386.360 g·mm to 5457.203 g·mm, but there was no significant improvement in whiteness (p > 0.05). In addition, ultrasonic treatment combined with curdlan promoted the shift of the α-helix to the random coil and the β-turn angle shift, thus exposing the internal groups, enhancing protein intermolecular interactions, and promoting the orderly aggregation of proteins, resulting in a microstructure of dense, and obtained the lowest porosity of 14.534 %. The present study might be necessary for promoting the high-value use of aquatic surimi products and the development of low-salt foods.

Characterizations of konjac glucomannan/curdlan edible coatings and the preservation effect on cherry tomatoes

In this study, konjac glucomannan (KGM) and curdlan were used to fabricate composite coating (KC). The coating solutions were investigated using a rheological method, and the coatings were characterized by water solubility tests, water vapor permeability (WVP), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The preservation effect of KC coating on cherry tomatoes stored at room temperature was determined. Results indicated that the curdlan addition can adjust the hydrophilicity/hydrophobicity of KGM coatings. Curdlan addition enhanced intermolecular entanglement and film-forming property. Increasing curdlan content in KC coatings significantly decreased the moisture content, dissolution and swelling ratio, and WVP. The KGM-curdlan composites behaved as high-performance coatings with good compatibility and uniformity. The K₃C₂ coating showed the best uniformity, water barrier, and thermal stability. The application of K₃C₂ coating significantly reduced the weight loss, decay loss, and delayed the decreases of firmness, soluble solids, total acid, and VC contents of cherry tomatoes. The KGM/curdlan edible coatings have promising potential for prolonging the shelf life of cherry tomatoes and applications in fruits preservation in the future.

Intranasal immunization with curdlan induce Th17 responses and enhance protection against enterovirus 71

Mucosal surfaces are in contact with the external environment and protect the body from infection by various microbes. To prevent infectious diseases at the first line of defense, the establishment of pathogen-specific mucosal immunity by mucosal vaccine delivery is needed. Curdlan, a 1,3-β-glucan has a strong immunostimulatory effect when delivered as a vaccine adjuvant. Here, we investigated whether intranasal administration of curdlan and antigen (Ag) could induce sufficient mucosal immune responses and protect against viral infections. Intranasal co-administration of curdlan and OVA increased OVA-specific IgG and IgA Abs in both serum and mucosal secretions. In addition, intranasal co-administration of curdlan and OVA induced the differentiation of OVA-specific Th1/Th17 cells in the draining lymph nodes. To investigate the protective immunity of curdlan against viral infection, intranasal co-administration of curdlan with recombinant VP1 of EV71 C4a was administered and showed enhanced protection against enterovirus 71 in a passive serum transfer model using neonatal hSCARB2 mice, although intranasal administration of VP1 plus curdlan increased VP1-specific helper T cells responses but not mucosal IgA. Next, Mongolian gerbils were intranasally immunized with curdlan plus VP1, and they had effective protection against EV71 C4a infection, while decreasing viral infection and tissue damage by inducing Th17 responses. These results indicated that intranasal curdlan with Ag improved Ag-specific protective immunity by enhancing mucosal IgA and Th17 against viral infection. Our results suggest that curdlan is an advantageous candidate as a mucosal adjuvant and delivery vehicle for the development of mucosal vaccines.

The alleviative effect of curdlan on the quality deterioration of konjac glucomannan thermo-irreversible gels after commercial sterilization at 121 °C

This work employed different curdlan concentrations (0.00 %, 1.00 %, 1.50 %, 2.00 %, and 2.50 %) to alleviate the quality degradation of konjac glucomannan (KGM) gels after commercial sterilization at 121 °C for 15 min. The results showed that all levels of curdlan could retard the deterioration of KGM gels, with the best effect at 2.00 %. After commercial sterilization, incorporating curdlan into KGM gels greatly reduced the Tan σ (G"/ G'), total relaxation time and half-free water from 0.52, 89.85 ms and 98.26 % to 0.27, 38.48 ms and 21.42 %, respectively. Moreover, the addition of curdlan imparted a better texture to KGM gels, as reflected in the increase of hardness, springiness, water-holding capacity and whiteness value from 1400.85 g, 0.42, 87.92 % and 33.33 to 3461.68 g, 0.80, 96.50 % and 49.27, respectively. Furthermore, SEM images revealed that curdlan endowed KGM gels with a tighter structure and smaller pores, and the pore size distribution was reduced from 113.46 μm to17.91 μm, indicating a stronger interaction among molecules, as evidenced by XRD and FTIR results. KGM gels with curdlan possessed less proportion of complete crystallites and crystalline region. These findings suggested that curdlan can be the potently protectant for improving the quality of commercially sterilized KGM gel-based products.

Sustainable curdlan biosynthesis by Rahnella variigena ICRI91 via alkaline hydrolysis of Musa sapientum peels and its edible, active and modified hydrogel for Quercetin controlled release

Despite the high demand for curdlan (Curd), its industrial implementation has not reached a mature stage due to the high cost of simple sugar feed stocks. Herein, Musa sapientum peels hydrolysate (MPH) was proposed for the first time as a sustainable medium for Curd generation and as an ameliorated functional biomaterial for quercetin (Quer) sustained release. In this study, banana peels have been hydrolysed by 3 % NaOH catalyst/ 60 °C, yielding high concentration of glucose 20.5 ± 0.04 and 24.3 ± 0.11 g/L and reducing sugar amount, respectively. Meanwhile, a novel local Rahnella variigena ICRI91 strain was isolated from soil, that was useful for Curd production and identified by 16S rRNA analysis. Furthermore, three-batch fermentation models were carried out using MPH for obtaining a sufficient yield of Curd. R. variigena ICRI91 accumulated a satisfactory Curd concentration; 10.3 ± 0.25 g/L; using 60 g/L MPH. On the other hand, the strain produced an impressive Curd yield; 21.5 ± 0.13 g/L with an attained productivity of 0.179 ± 0.01 g/L/h and a sugar consumption of 68 ± 0.25 % as the MPH content increased to 100 g/L. For the first time, Curd hydrogel was modified by different amount of Xylitol (Xyl), reaching good mechanical performance; 3.1 MPa and 75 % for tensile strength (TS) and elongation at break (EB), respectively. Curd/Xyl (3/5) hydrogel was then integrated with nanometer-sized quercetin nanocrystals (Quer NCs, 83 ± 0.12 nm) with high colloidal stability of -23 ± 0.05 mV. The interconnected H- bonding between Xyl and Curd was confirmed by FTIR and SEM. The generated biomaterial was tailored to exhibit a sustained Quer release over 72 h. It also has improved antibacterial efficacy against four bacterial pathogens compared to that of a free drug. In recognition of these merits, an edible polymeric nanomaterial has been proposed for the functional food and biomedicine sectors.

Cell membrane-camouflaged DOX-loaded β-glucan nanoparticles for highly efficient cancer immunochemotherapy

Biomimetics plays an important role in cancer treatment since it can prolong the circulation of nanoparticles, enhance their delivery and retention in target tissues, and reduce the systemic toxicity of drugs and their carriers. In this study, we developed a biomimetic nanosystem consisting of chemotherapeutic and immunotherapeutic agents wrapped in cell membranes. Specifically, the anti-tumor drug doxorubicin (DOX) was loaded into a bacterial-derived immunomodulatory agent (low molecular weight curdlan, lCUR), and the lCUR-DOX was further wrapped in the red blood cell membrane for camouflage and prolonged circulation. The successful preparation of the lCUR-DOX@RBC nanosystem was supported by various optical and morphological characterizations. In vitro studies indicated that the nanosystem can escape uptake by macrophages, inhibit the invasion of tumor cells, and reprogram M2 macrophages with an immunosuppressive phenotype into M1 macrophages with an immunopromoting phenotype via the MAPK signaling pathway while promoting the phagocytosis of macrophages. In vivo studies showed that the nanosystem effectively inhibits tumor growth in the A-375 tumor-bearing mouse model. Taken together, the above results support further development of the lCUR-DOX@RBC platform for cancer immunochemotherapy in clinical applications.

Preparation of a novel curdlan/bacterial cellulose/cinnamon essential oil blending film for food packaging application

With the increasing attention to food preservation and environmental safety, there is great pressing demand to explore novel edible and environment-friendly food packaging films. In the present study, a new kind natural curdlan (CD) film was developed with the addition of bacterial cellulose (BC) and cinnamon essential oil (CEO) at 2% and 10% (w/w) amounts, with regard to improve mechanical properties and investigate potential food applications. Our results showed that the tensile strength, the crystallinity and the thermal stability of the CD/BC blending film were improved, while the water vapor permeability, moisture content and the lightness were reduced. Moreover, the CEO addition to the CD/BC film further increased the barrier properties and also mechanical properties. The results of FTIR and XRD were applied for analyzing the potential interactions of the film matrix. Finally, addition of CEO endowed the blending films with good antibacterial activity and antioxidant capacity, which could effectively inhibit the bacterial growth and the lipid oxidation of chilled chicken during the preservative period. Thus, this work demonstrates that the novel CD/BC/CEO blending film with improved mechanical and barrier properties can be of great potential for developing food packaging material for promising applications.

Effect of curdlan on the aggregation behavior and structure of gluten in frozen-cooked noodles during frozen storage

Due to the crucial role of gluten network in maintaining the tensile properties of frozen-cooked noodles (FCNs), the underlying mechanism of protective effect of curdlan on FCNs quality during frozen storage was explored from the perspective of aggregation behavior and structure of gluten in this study. The results showed that curdlan weakened the depolymerization behavior of gluten proteins through inhibiting the disruption of disulfide bonds; Curdlan stabilized the secondary structure of gluten proteins by restraining the transformation of compact α-helices to other secondary structures; Atomic force microscope results implied that curdlan inhibited the aggregation of gluten chains; Confocal laser scanning microscopy observation analyzed by AngioTool software indicated that the connectivity and uniformity of gluten network were enhanced because of curdlan. This study may provide more comprehensive theories for the strengthening effect of curdlan on FCNs quality from the perspective of gluten structure and contribute to the quality improvement of FCN in the food technology field.

DH-2

Curdlan is an edible microbial polysaccharide and can be used in food, biomedical and biomaterial fields. To reduce the cost of curdlan production, this study investigated the suitability of cassava starch hydrolysates as carbon source for curdlan production. Cassava starch was hydrolyzed into maltose syrup using β-amylase and pullulanase at various enzyme dosages, temperature, time and addition order of two enzymes. The maltose yield of 53.17% was achieved at starch loading 30% by simultaneous addition β-amylase 210 U/g starch and pullulanase 3 U/g starch at 60 °C for 9 h. Cassava starch hydrolysates were used as carbon source for curdlan production by Agrobacterium sp. DH-2. The curdlan production reached 28.4 g/L with the yield of 0.79 g/g consumed sugar and molecular weight of 1.26 × 10⁶ Da at 96 h with cassava starch hydrolysate at 90 g/L initial sugar concentration. Curdlan produced from cassava starch hydrolysates was characterized using FT-IR spectra and thermo gravimetric analysis. This work indicated that cassava starch was a potential renewable feedstock for curdlan production.

Properties of soybean protein isolate/curdlan based emulsion gel for fat analogue: Comparison with pork backfat

To obtain an analogue of pork backfat (PBF), we combined emulsion and gel to fabricate emulsion gel, which was prepared by using soybean protein isolate (SPI) and curdlan (CL) through a facile heat-treatment method in this paper. The microstructures, rheology properties, water holding capacity and freeze-thawing stability of the emulsion gel were investigated. The results suggested that the SPI/CL-stabilized emulsion gel was thermal-irreversible, and SPI was the emulsifying agent of the emulsion gel. Oil contents significantly affect the water holding capacity and freeze-thawing stability of emulsion gel. Subsequently, the TPA, gel strength and color of emulsion gels with different oil contents were compared with PBF. The hardness, chewiness, springiness, and gel strength of emulsion gel with 10 wt% oil contents were no significant differences from that of PBF (P > 0.05). Hence, this SPI/CL based emulsion gel can be used as an analogue to PBF, providing an alternative ingredient for the development of plant-based low-fat meat products.

Freeze-thaw and solvent-exchange strategy to generate physically cross-linked organogels and hydrogels of curdlan with tunable mechanical properties

Physical gels from natural polysaccharides present the advantage of no toxic cross-linking agents and no chemical modification during preparation. Herein, novel physical gels, transparent organogels and opaque hydrogels from the microorganism-derived (1,3)-β-D-glucan of curdlan were prepared in dimethyl sulfoxide (DMSO) using the freeze-thaw technique, followed by a solvent-exchange strategy with water. The mechanical and structural properties of these gels were investigated by rheology, scanning electron microscopy, attenuated total reflection infrared spectroscopy, wide-angle X-ray diffraction and small-angle X-ray scattering. Gelation mechanisms and intermolecular interaction models have also been proposed. The good solvent DMSO serves as both a crosslinker and a pore-foaming agent in organogels. The reversible macromolecular conformation changes and phase separation of curdlan endow the gels with reversible transparency, volume change and tunable mechanical strength. The new design strategy of facile preparation and performance tuning provides a platform for developing new organogels and sterile hydrogels of curdlan.

Exopolysaccharide synthesis repressor genes (exoR and exoX) related to curdlan biosynthesis by Agrobacterium sp

Curdlan is a neutral, water-insoluble, unbranched, linear β-(1,3)-glucan. This study explored the roles of exoR and exoX in curdlan biosynthesis in Agrobacterium sp. ATCC 31749. The microcapsule biosynthesis of ΔexoR strain was reduced, and the motility of this strain increased remarkably compared with the wild-type (WT) strain during the cell growth phase. The curdlan yields of ΔexoR and ΔexoX strains enhanced by 19% and 17%, and the glucose utilization increased by 12% and 11%, respectively, compared with the WT strain during batch fermentation. By contrast, the curdlan yields of exoR and exoX overexpression strains decreased by 28% and 33%, respectively. The gel strength produced by ΔexoR and exoX overexpression strains decreased compared with the WT strain. RT-qPCR analysis at the transcriptional level revealed that key genes in exopolysaccharide synthesis and central metabolic pathways were up-regulated in ΔexoX and ΔexoR strains during gel production. Metabolomics analysis of ΔexoR and ΔexoX mutants proved the rates of central metabolic and electron transport chain were accelerated.

The effect of curdlan and the resting process on the quality of the dried whole tofu noodles

The aim of this study is to make dried noodles having high contents of whole tofu (60% (w/w)). To control the high moisture of the whole tofu, curdlan was added and a high-temperature resting process was applied. The elasticity of the dough sample rested at 45°C for 45 min increased over 50% more than the non-rested one. The addition of curdlan and the high-temperature resting process helped to form a compact internal structure in the dough, which might have been induced by the gelation of curdlan and the swelling of starch. In addition, these treatments resulted in about 20% and 15% reduction in cooking time and cooking loss, respectively. Whole tofu noodles having high protein content with improved texture and cookability was developed. These results could be helpful to the development of the bread based on a high hydration dough.

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The online version contains supplementary material available at 10.1007/s10068-021-01020-9.

AMP functionalized curdlan nanoparticles as a siRNA carrier: Synthesis, characterization and targeted delivery via adenosine A2B receptor

Receptor-mediated endocytosis has been used for tissue targeted delivery of short interfering RNA (siRNA) drugs. Herein, we investigated adenosine receptor (AR) as a candidate for receptor-mediated siRNA internalization. We synthesized adenosine functionalized cationic curdlan derivatives (denote CuAMP polymers). One of these polymers, CuAMP4, efficiently delivered siRNA to breast cancer cells expressing high level of A_2B receptor. The internalization of siRNA loaded CuAMP4 by cancer cells was inhibited by free AMP as well as endocytosis inhibitors. Moreover, knockdown of A_2BR by siRNA, or pre-treatment of the cells with anti-A_2BR antibody, strongly inhibited the cellular uptake of CuAMP4. Our findings confirmed that A_2BR can be utilized for cell type specific siRNA delivery, and CuAMP4 NP may be a promising delivery system for cancer cell targeted delivery of therapeutic siRNAs.

The effect of carboxymethylation on the macromolecular conformation of the (1 → 3)-β -D-glucan of curdlan in water

The chain conformational change in curdlan during carboxymethylation was investigated using nuclear magnetic resonance (NMR), circular dichroism (CD) spectroscopy, and atomic force microscopy (AFM). The distributions of carboxymethyl substituents within anhydroglucose unit (AGU) of CMCD were found to follow the order of OH (6) > OH (4) > OH (2) for CMCD with a low DS and OH (6) > OH (2) > OH (4) for CMCD with relatively high DS. The increased carboxymethylation level induced the chain conformation transition of curdlan from triple helix to random coil in water. The DS of 0.25 was the critical value of chain conformation transition, below which CMCD chains were triple helices. For DS larger than 0.25, CMCD existed in the state of random coils. The intermolecular hydrogen bonding between C2 hydroxyls in AGU sustained the triple helical conformation and stiffness of the polymer chain, which weakened with the increase in DS.

Rheological investigation of a versatile salecan/curdlan gel matrix

Hydrogel, as a three-dimensional material with high water content, has unique physicochemical and variable mechanical properties. Natural polysaccharide-based composite hydrogels are very popular within medical industry as these viscoelastic materials are non-toxic, biodegradable, bioabsorbable, and biocompatible. This research investigates the engineering of novel composite hydrogels from natural polysaccharides salecan and curdlan without any structural modification and chemical crosslinking. The scanning electron microscopy, Fourier transform infrared spectroscopy and various rheological methods were employed to investigate the morphology, molecular interaction, and flow behavior of the samples respectively. The key rheological parameters were compared using the Power Law, Herschel-Bulkley and Arrhenius models. This is the first study reporting a novel composite hydrogel made from Salecan and Curdlan with ideal elasticity, enhanced thermostability, good injectability, self-recovery and other rheological properties that will pave the way for application in different fields.

Synthesis of PEGylated cationic curdlan derivatives with enhanced biocompatibility

Cationic polysaccharides have shown excellent ability of nucleic acids delivery. However, cationic curdlan derivatives with high degree of amination cause damage to the cell membrane and induce considerable cytotoxicity, limiting their in vivo application. Herein, we synthesized PEGylated 6-amino-6-deoxy-curdlan derivatives containing cleavable disulfide bonds. The resulting polymers (denote 6AC-2S PEGx) not only showed high affinity to siRNA but also exhibited significantly decreased cytotoxicity and hemolysis effect, while showing remarkable in vitro transfection efficiency. In vivo study demonstrated that 6AC-2S PEG40, which had a lower LD50 value than that of 6AC-100, did not cause liver damage, as the i.v. injection of 6AC-2S PEG40 to mouse did not increase serum level of ALT/AST. Furthermore, tissue distribution results showed that 6AC-2S PEG40 successfully delivered siRNA to liver, lung and spleen. Collectively, our data confirmed that PEGylation can increase the biocompatibility of cationic curdlan derivatives, which is a promising carrier for nucleic acid therapeutics.

Antifracture, Antibacterial, and Anti-inflammatory Hydrogels Consisting of Silver-Embedded Curdlan Nanofibrils

The bacterial exopolysaccharide Curdlan has a unique collagen-like triple helical structure and immune-modulation activities. Although there have been several types of Curdlan gels reported for antibacterial or wound healing purposes, none of them exhibit favorable mechanical properties for clinically applicable wound healing materials. Herein, we present a two-step approach for preparing Ag-embedded Curdlan hydrogels that are highly soft but are very stretchable compared with common polysaccharide-based hydrogels. Ag ions were first reduced in a diluted Curdlan solution to form AgNP-decorated triple helices. Then, the aqueous solution consisting of Curdlan/Ag nanoparticles was mixed with a dimethyl sulfoxide solution consisting of a high concentration of Curdlan. This mixing triggered the conformation transformation of Curdlan random coils into triple helices, and then the helices were further packed into semicrystalline nanofibrils of ∼20 nm in diameter. Due to the presence of semicrystalline fibrils, this novel Curdlan hydrogel exhibits a fracture strain of ∼350% and fracture stress of ∼0.2 MPa at a water content of ∼97%. This nanofibril hydrogel supported the attachment, spreading, and growth of fibroblasts and effectively inhibited the growth of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Moreover, the hydrogels downregulated NO production and proinflammatory gene expression levels in lipopolysaccharide (LPS)-stimulated macrophages but did not change the anti-inflammatory gene expression levels in IL-4-stimulated macrophages. In an animal study, these hydrogels accelerated wound healing in a bacteria-infected mice skin wound model. These results validate the further development of Curdlan/AgNPs nanofibril hydrogels in clinical wound management.

Curdlan intake changes gut microbial composition, short-chain fatty acid production, and bile acid transformation in mice

Indigestible polysaccharides, such as dietary fibers, benefit the host by improving the intestinal environment. Short-chain fatty acids (SCFAs) produced by gut microbial fermentation from dietary fibers exert various physiological effects. The bacterial polysaccharide curdlan benefits the host intestinal environment, although its effect on energy metabolism and SCFA production remains unclear. Hence, this study aimed to elucidate the effect of curdlan intake on gut microbial profiles, SCFA production, and energy metabolism in a high-fat diet (HFD)-induced obese mouse model. Gut microbial composition of fecal samples from curdlan-supplemented HFD-fed mice indicated an elevated abundance of Bacteroidetes, whereas a reduced abundance of Firmicutes was noted at the phylum level compared with that in cellulose-supplemented HFD-fed mice. Moreover, curdlan supplementation resulted in an abundance of the family Bacteroidales S24-7 and Erysipelotrichaceae, and a reduction in Deferribacteres in the feces. Furthermore, curdlan supplementation elevated fecal SCFA levels, particularly butyrate. Although body weight and fat mass were not affected by curdlan supplementation in HFD-induced obese mice, HFD-induced hyperglycemia was significantly suppressed with an increase in plasma insulin and incretin GLP-1 levels. Curdlan supplementation elevated fecal bile acid and SCFA production, improved host metabolic functions by altering the gut microbial composition in mice.

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Curdlan improves gut microbial composition in high-fat diet-fed (HFD) mice.

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The effects of HFD-induced hyperglycemia are mitigated by curdlan supplementation.

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Curdlan supplementation increases plasma insulin and GLP-1 levels.

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Curdlan increases fecal short-chain fatty acids (SCFAs) and secondary bile acids.

Preparation and characterization of curdlan with unique single-helical conformation and its assembly with Congo Red

Elucidating the structure-activity relationship of curdlan is hampered by a lack of characterization with unique specific conformations (i.e., single- or triple-helix). In this study, single-helical curdlan is generated in dilute NaOH solutions at 35-50 °C, and characterized with NMR, SAXS, and GPC. The conformational transition from coil to single-helix and the intramolecular hydrogen bond interaction are explored using NMR. It is found that the two aforementioned types of curdlan interact with Congo Red in very different ways. Single-helical curdlan can encapsulate Congo Red to form a stable, supramolecular dye assembly, which is demonstrated by the shortest distance between the H3 of curdlan and the phenyl groups of Congo Red, and also the same self-diffusion coefficients of Congo Red and curdlan. In contrast, random-coil curdlan interacts weakly with Congo Red and cannot enwrap it. This study offers insight into the specific structure-activity relationship of beta-(1,3)-glucans.

CGMCC 11546 via energy regeneration

Curdlan is a water-insoluble exopolysaccharide produced by Agrobacterium species under nitrogen starvation. The curdlan production in the ΔmdeA, ΔmetA, ΔmetH, and ΔmetZ mutants of methionine biosynthesis pathway of Agrobacterium sp. CGMCC 11546 were significantly impaired. Fermentation profiles of four mutants showed that the consumption of ammonia and sucrose was impaired. Transcriptome analysis of the ΔmetH and ΔmetZ mutants showed that numerous differentially expressed genes involved in the electron transfer chain (ETC) were significantly down-regulated, suggesting that methionine biosynthesis pathway affected the production of energy ATP during the curdlan biosynthesis. Furthermore, metabolomics analysis of the ΔmetH and ΔmetZ mutants showed that ADP and FAD were significantly accumulated, while acetyl-CoA was diminished, suggesting that the impaired curdlan production in the ΔmetH and ΔmetZ mutants might be caused by the insufficient supply of energy ATP. Finally, the addition of both dibasic sodium succinate as a substrate of FAD recycling and methionine significantly restored the curdlan production of four mutants. In conclusion, methionine biosynthesis pathway plays an important role in curdlan biosynthesis in Agrobacterium sp. CGMCC 11546, which affected the sufficient supply of energy ATP from the ETC during the curdlan biosynthesis.

Molecular dynamic simulation: Structural insights of multi-stranded curdlan in aqueous solution

In this work, by using molecular dynamic simulation we provide microscale structure information which helps to reveal the molecular mechanisms concerning the multi-chain conformational behavior of short curdlan. Through simulations starting with different conformations of curldan dodecasaccharides, it is found that the right-handed triple helix is thermodynamically the most stable conformation in aqueous solutions, which is well maintained and stabilized by an inter-strand hydrogen bonding network of the C₂ hydroxyls. Unlike any predicted forms, the inter-strand hydrogen bonds exhibit a left-handed double helix pattern with preferred global orientations. Temperature REMD results suggest that the formation of triple helix is temperature sensitive, but the already formed triple helix is not. Investigation of curdlan with numbers of repeating units from 3 to 12 captures a critical value of 6, which in a way elucidates the relationship between the formation of triple helix and the chain length.

Effect of alkali-neutralization treatment on triple-helical aggregates and independent triple helices of curdlan

Triple-helical aggregates (THAs) have been proven to affect the biological activities and functional properties of triple-helix polysaccharides. Thus, it's urgent to seek a method to reduce the size of THAs while preserving independent triple helices (ITHs). In this study, the effects of alkali-neutralization (AN) treatment on THAs and ITHs of curdlan were studied. The positive values of the Congo red test data (R²>0.99) fitted using a Logistic model indicated that AN treatment (C_NaOH/HCl>0.28 mol/L) facilitated the disaggregation of THAs. Congo red test, sedimentation test, and turbidity test showed that AN treatment (C_NaOH/HCl = 1.0 mol/L) significantly reduced the size of THAs to approximately 1 μm while effectively increasing the relative amount of ITHs to approximately 199 %. Fourier transform infrared spectroscopy and X-ray diffraction analysis showed that AN treatment basically unchanged the primary structure of curdlan chains, but affected the crystalline structure and the intermolecular and intramolecular hydrogen bonding of curdlan.

Construction of novel curdlan-based and Ca2+-chelated magnetic microspheres (CCMM) for efficient protein purification and oriented immobilization

In this study, curdlan-based and calcium ion (Ca²⁺)-chelated magnetic microspheres (CCMM) were prepared for protein purification and oriented immobilization. Additional purification steps before immobilization were not required. CCMM samples were produced by reverse embedding of Fe₃O₄ nanoparticles with curdlan and chelated with Ca²⁺ in the presence of iminodiacetic acid. The β-xylanase XynII from Trichoderma reesei QM6a was used to investigate the efficiency of CCMM preparation. The resulting CCMM-XynII was found to be very stable, showing 82 % and 60 % of initial activities after storage for 35 days and after being assayed ten times, respectively. In addition, the CCMM-XynII showed higher stabilities in the presence of organic solvents and multiple chemicals than the free XynII, suggesting that the CCMM-XynII could be efficient for applications requiring the presence of organic solvents. In addition, CCMM may be more suitable than commercially available Ni-NTA for purification of proteins intolerant of Ni²⁺.

Chemosensitivity assessments of curdlan-doped smart nanocomposites containing erlotinib HCl

Curdlan (CN)-doped montmorillonite/poly(N-isopropylacrylamide-co-N,N'-methylene-bis-acrylamide) [CN/MT/P(NIPA-co-MBA)] smart nanocomposites (NCs) were developed for efficient erlotinib HCl (ERL) delivery to lung cancer cells. The placebo NCs demonstrated excellent biodegradability, pH/thermo-responsive swelling profiles and declined molar mass (M¯c) between the crosslinks with increasing temperature. The XRD, FTIR, DSC, TGA, and SEM analyses revealed the architectural chemistry of these NC scaffolds. The NCs loaded with ERL (F-1-F-3) displayed acceptable diameter (734-1120 nm) and zeta potential (+1.16 to -11.17 mV), outstanding drug entrapping capability (DEE, 78-99%) and sustained biphasic ERL elution patterns (Q_8h, 53-91%). The ERL release kinetics of the optimal matrices (F-3) obeyed Higuchi model and their transport occurred through anomalous diffusion. The mucin adsorption behaviour of these matrices followed Freudlich isotherms. As compared to pure ERL, the formulation (F-3) displayed an improved anti-proliferative potential and induced apoptosis more effectively on A549 cells. Thus, the CN-doped smart NCs could be utilized as promising drug-cargoes for lung cancer therapy.

Oxidized curdlan activates dendritic cells and enhances antitumor immunity

Curdlan activates dendritic cells (DCs) and enhances DC-based antitumor immunity. However, hydrophobicity and heterogeneity of curdlan particulates hinder perfect binding of curdlan to dectin-1 receptor, resulting in the reduced activation of antigen presenting cells and limited antitumor effects. Herein, we synthesized partially oxidized curdlan derivative (β-1,3-polyglucuronic acid, denote PGA). PGA-45 polymer, the reaction product prepared from curdlan by oxidation with 4-acetamido-TEMPO/NaClO/NaClO₂ systems under acid conditions for 45 min, activated DCs, induced the expression of co-stimulatory molecules and cytokines, and promoted allogenic T cell proliferation as well as the expression of IL-2. Mechanistically, PGA-45 polymer strongly enhanced phosphorylation of IKK-β and reduced the expression of phosphorylated Akt, suggesting that PGA-45 may activate multiple cell surface receptors such as TLR4 and dectin-1. Administration of tumor lysate pulsed DCs pre-treated with PGA-45 particles induced strong antitumor activity in B16F10 melanoma model. Our data suggest that PGA-45 have strong adjuvant effects for anti-cancer immunity and the design of PGA polymers may provide insights in the development of novel adjuvants for cancer immunotherapy.

Preparation and characterization of curdlan/nanocellulose blended film and its application to chilled meat preservation

In this study, to improve the mechanical and thermal properties of curdlan film, a curdlan/nanocellulose (NC) blended film was prepared and characterized for the first time. NC was successfully prepared from microcrystalline cellulose (MCC) with NaOH/urea treatment. The particle size of NC was observed to be 70-140 nm by cryo-electron microscope (cryo-EM). The blended film was prepared by adding the NC to curdlan solution. The tensile strength (TS) of the blended film reached the maximum value of 38.6 MPa, and the elongation at break (EB) was 40%. The DSC curve showed that the heat absorption peak of the film was 240 °C, indicating that the blended film has good temperature stability. Additionally, some other film properties were also improved, including gas barrier properties and transparency. Obvious morphological and molecular differences between the blended film and the pure curdlan film were discovered by SEM and FTIR analysis. Finally, the blended film was used for the preservation of chilled meat and extended the storage time of meat to 12 days. These results provided a theoretical basis for future application and development of biodegradable film.

Further interpretation of the strengthening effect of curdlan on frozen cooked noodles quality during frozen storage: Studies on water state and properties

Curdlan has been applied to weaken the quality deterioration of frozen cooked noodles (FCN) during frozen storage. However, the underlying mechanism is still unclear. In this paper, an A/LKB-F probe was used for texture profile analysis and mercury intrusion was firstly used for analyzing ice crystals state in three dimensions. Meanwhile, a systematic study on the water state was conducted, as well as the freeze-thawed stability of FCN under curdlan intervention during frozen storage. The results showed that 0.5% curdlan significantly (P < 0.05) alleviated the decrement in hardness, chewiness and extension, and enhanced the freeze-thawed stability of FCN. This was closely associated with the fact that the addition of curdlan minimized freezable water content, inhibited water mobility and migration, and raised the homogeneity of ice crystals in FCN. This study provides more comprehensive theories for the strengthening effect of curdlan on FCN quality from the perspective of water state.

Construction and characterization of folate-functionalized curdlan-trilysine siRNA delivery platform for in vivo hepatic carcinoma treatment

RNA interference technology is a powerful tool with substantially clinical prospects for carcinoma therapy, in which efficiency and specificity of delivery of dsRNA remains a critical issue. Herein, aiming at delivery of dsRNA in efficient and safe way, we constructed targeting delivery platform (CTL-PEG-FA) by grafting curdlan with trilysine through click reaction, then modifying with PEG linked folic acid. The CTL-PEG-FA vector exhibited excellent gene binding capacity to condense siRNA and dramatically reduced cytotoxicity. Increased cell uptake of CTL-PEG-FA/Bcl-2 siRNA was achieved by the synergism of folate mediated endocytosis and charge interaction, and further causing severe HepG2 cells injury through apoptosis mechanism after down-regulation of Bcl-2 protein. In vivo experiments, CTL-PEG-FA/Bcl-2 siRNA complex distinctly accumulated in tumor site and significantly inhibited the growth of tumor, while no obvious toxicity was observed. Therefore, well-performed CTL-PEG-FA with excellent biocompatibility, has the potential to be the candidate of gene therapy for clinical applications.

Emulsifying properties of a ferulic acid-grafted curdlan conjugate and its contribution to the chemical stability of β-carotene

A biopolymer-polyphenol conjugate-stabilized oil-in-water emulsion system was established to improve the chemical stability and bioaccessibility of β-carotene (BC). In this study, the emulsifying properties and contribution of a ferulic acid-grafted curdlan conjugate (Cur-D-g-FA) to the chemical stability of BC were investigated. Results showed that the emulsification ability of emulsions stabilized by Cur-D-g-FA remarkably increased with an increasing concentration from 0.05% to 0.8% (w/v) along with decreasing average droplet sizes, negatively charged zeta potentials, and uniform size distributions. The emulsions stabilized by 0.8% Cur-D-g-FA exhibited pronounced shear thinning and solid-like elastic properties as well as satisfactory oxidation stability. The emulsions stabilized by 0.8% Cur-D-g-FA had excellent ability to improve the chemical stability of BC when exposed to different environmental stresses and resulted in the favorable bioaccessibility of BC in vitro. The results prove that Cur-D-g-FA as a promising stabilizer has great potential to protect liposoluble nutrients in food-grade emulsion-delivery systems.

Construction of functional curdlan hydrogels with bio-inspired polydopamine for synergistic periodontal antibacterial therapeutics

Curdlan, a bacteria-derived polysaccharide resource, possesses substantial potential for periodontal antimicrobial delivery. Here, the facile engineering of a functionalized curdlan/polydopamine (PDA) composite hydrogels was reported. The physiochemical evaluations of composite hydrogels proved their tunable properties associated with concentration of PDA including pore size, rheological property and swelling behavior. We have systematically assessed biocompatibility in vitro and found these hydrogels toxicity-free. Moreover, photothermal performance upon near infrared light (NIR) exposure was conducted and eventually indicated the best matches for antibacterial application. The acetate chlorhexidine (CHX) was chosen as a model antimicrobial and the release profiles demonstrated the entrapped CHX could be triggered and nicely controlled by NIR. The optimized bacteriostatic rate reached 99.9 %. Overall, we aimed to provide new curdlan-based hydrogels for periodontal antibacterial treatment by combining photothermal effect and antimicrobial simultaneously.

In vitro prebiotic potential, digestibility and biocompatibility properties of laminari-oligosaccharides produced from curdlan by β-1,3-endoglucanase from Clostridium thermocellum

Curdlan or laminarin, a β-1,3-glucan was hydrolysed by β-1,3-endoglucanase (CtLam81A) from Clostridium thermocellum to produce laminari-oligosaccharides. TLC analysis of hydrolysed curdlan showed the presence of laminari-oligosaccharides of the degree of polymerization, DP2-DP7. This mixture of laminari-oligosaccharides displayed prebiotic properties. Laminari-oligosaccharides showed an increase in the growth of probiotic bacteria such as Lactobacillus plantarum DM5 and Lactobacillus acidophilus, while they did not promote the growth of non-probiotic bacteria (Escherichia coli and Enterobacter aerogenes). Laminari-oligosaccharides showed higher prebiotic activity score of 0.92 ± 0.01 and 0.64 ± 0.08 for L. plantarum DM5 and L. acidophilus NRRL B-4496, respectively, similar to those shown by inulin. Laminari-oligosaccharides showed higher resistance or low digestibility against α-amylase, artificial gastric juice and intestinal fluid than inulin indicating their bioavailability to the probiotic bacteria present in the gastrointestinal tract of human. The probiotic bacteria consumed laminaribiose and laminariotriose more readily than higher laminari-oligosaccharides as carbon source for their growth. The in vitro cytotoxicity assay of laminari-oligosaccharides (1 mg/ml) on human embryonic kidney (HEK 293) cells showed that the cell viability was not affected even after 72 h indicating their biocompatible nature. All the results amply indicated that laminari-oligosaccharides can serve as potential prebiotic additives for functional food products.

Chemistry and microbial sources of curdlan with potential application and safety regulations as prebiotic in food and health

Curdlan - a homopolysaccharide is comprised of glucose using β-1,3-glycosidic bond and produced by different types of microorganisms as exopolysaccharide. Curdlan gel is stable during freezing and thawing processes which find several applications in food and pharmaceutical industries. It acts as a prebiotic, stabilizer and water-holding, viscosifying and texturing agent. Additionally, curdlan gel is used as a food factor to develop the new products e.g. milk fat substitute, non-fat whipped cream, retorting (freeze-drying) process of Tofu, low-fat sausage, and low-fat hamburger. However, a great variation exists among different countries regarding the regulatory aspects of curdlan as food additives, dietary components or prebiotic substances. Therefore, the present review paper aims to discuss safety issues and the establishment of common guidelines and legislation globally, focusing on the use the applications of curdlan in the food sector including the development of noodles, meat-based products, and fat-free dairy products. This review analyzes and describes in detail the potential of curdlan as a sustainable alternative additive in health and food industries, emphasizing on the chemical composition, production, properties, and potential applications.