Toxicological studies and some functional properties of carboxymethylated cellulose nanofibrils as potential food ingredient

Characterization and safety assessment of bamboo shoot shell cellulose nanofiber: Prepared by acidolysis combined with dynamic high-pressure microfluidization

The preparation of cellulose nanofiber (CNF) using traditional methods is currently facing challenges due to concerns regarding environmental pollution and safety. Herein, a novel CNF was obtained from bamboo shoot shell (BSS) by low-concentration acid and dynamic high-pressure microfluidization (DHPM) treatment. The resulting CNF was then characterized, followed by in vitro and in vivo safety assessments. Compared to insoluble dietary fiber (IDF), the diameters of HIDF (IDF after low-concentration acid hydrolysis) and CNF were significantly decreased to 167.13 nm and 70.97 nm, respectively. Meanwhile, HIDF and CNF showed a higher crystallinity index (71.32 % and 74.35 %). Structural analysis results indicated the successful removal of lignin and hemicellulose of HIDF and CNF, with CNF demonstrating improved thermostability. In vitro, a high dose of CNF (1500 μg/mL) did not show any signs of cytotoxicity on Caco-2 cells. In vivo, no death was observed in the experimental mice, and there was no significant difference between CNF (1000 mg/kg·bw) and control group in hematological index and histopathological analysis. Overall, this study presents an environmentally friendly method for preparing CNF from BSS while providing evidence regarding its safety through in vitro and in vivo assessments, laying the foundation for its potential application in food.

A 28-Day Repeated Oral Administration Study of Mechanically Fibrillated Cellulose Nanofibers According to OECD TG407

The impact of oral administration of mechanically fibrillated cellulose nanofibers (fib-CNF), a commonly used nanofiber, on toxicity and health remains unclear, despite reports of the safety and beneficial effects of chitin-based nanofibers. Thus, evaluating the oral toxicity of fib-CNF in accordance with OECD Test Guideline 407 (TG407) is essential. This study aimed to assess the safety of orally administered fib-CNF through an acute toxicity study in rats, following the OECD TG407 guidelines for 4 weeks. CNF "BiNFi-s" FMa-10005, derived from mechanically fibrillated pulp cellulose, was administered via gavage to male and female Crl:CD(SD) rats at doses of 50, 150, 500, and 1000 mg/kg/day for 28 days, with a control group receiving water for injection. The study evaluated the toxic effects of repeated administration, and the rats were monitored for an additional 14 days post-administration to assess recovery from any toxic effects. The results showed no mortality in either sex during the administration period, and no toxicological effects related to the test substance were observed in various assessments, including general condition and behavioral function observations, urinalysis, hematological examination, blood biochemical examination, necropsy findings, organ weights, and histopathological examination. Notably, only female rats treated with 1000 mg/kg/day of CNF exhibited a consistent reduction in body weight during the 14-day recovery period after the end of treatment. They also showed a slight decrease in pituitary and liver weights. However, hematological and blood biochemical tests did not reveal significant differences, suggesting a potential weight-suppressive effect of CNF ingestion.

Adjustable strength and toughness of dual cross-linked nanocellulose films via spherical cellulose as soft-phase

Nanocellulose films possess numerous merits ascribing to their inherent biocompatibility, non-toxic and biodegradability properties. The potential for practical applications would be improved if their mechanical strength and toughness requirements could be met simultaneously. Herein, dual cross-linked nanocellulose (DC) film was fabricated by the treatments of chemical and physical cross-linking, which was mechanically superior to pure nanocellulose (CNF) films. To further increase the toughness of DC films, spherical cellulose (Sph) was incorporated into DC film (DC-Sph film), and analyzed under different humidity conditions (RH) (from 10 % to 90 %). The changes of functional groups of CNF, DC and DC-Sph films were detected by FTIR and XPS spectrum. The epichlorohydrin and Sph content were optimized, followed by the investigation of RH on the toughness of films. The highest tensile strength (146.6 ± 4.6 MPa) was obtained in DC film at 50 % RH, while the DC-Sph film showed the largest toughness (40.3 ± 3.7 kJ/m2) at 70 % RH. Furthermore, the possible toughening mechanism of DC-Sph film was also discussed.

Modulating in vitro gastrointestinal digestion of nanocellulose-stabilized pickering emulsions by altering particle surface charge

An in vitro model of human gastrointestinal digestion was introduced to investigate the effects of surface charge of cellulose nanoparticles on emulsion structure during gastric phase, lipase activity, bile salt diffusion, and free fatty acid (FFA) release. Four carboxymethylated cellulose nanofibrils (CNF; C0, C0.36, C0.72, and C1.24) were used, showing different surface charge (p < 0.05). First, four carboxymethylated CNFs had no inhibition effects on lipase activity and bile salt diffusion. Moreover, we found that the lipid emulsion containing CNF formed gel structure to induce oil droplets aggregation during simulated gastric phase. Additionally, the particle surface charge greatly influenced the gel structure of emulsion where a denser gel structure was observed in the C0 (lowest surface charged CNF) stabilized emulsion. Finally, the released FFA results showed that the formed gel structure lowered the lipid emulsion digestion attributed to the restricted adherent area of oil droplets for lipase and bile salt.

Assessing the Safety of Mechanically Fibrillated Cellulose Nanofibers (fib-CNF) via Toxicity Tests on Mice: Single Intratracheal Administration and 28 Days' Oral Intake

Mechanically fibrillated cellulose nanofibers, known as fib-CNF (fiber length: 500 nm; diameter: 45 nm), are used in composites and as a natural thickener in foods. To evaluate their safety, we conducted a 28-day study in mice with inhalation exposure at 0.2 mg/body and oral administration of 400 mg/kg/day. Inhalation exposure to fib-CNF caused transient weight loss, changes in blood cell counts, and increased lung weights. These changes were attributed to adaptive responses. The oral administration of fib-CNF for 28 days resulted in no apparent toxic effects except for a slight decrease in platelet counts. The fib-CNF administration using the protocols studied appears to be safe in mice.

Improving the emulsifying capacity of brewers' spent grain arabinoxylan by carboxymethylation

Arabinoxylan derived from brewers' spent grain was carboxymethylated, and the emulsifying capacity of carboxymethylated arabinoxylans (CMAX) with different degrees of substitution (DS) was investigated. Results showed that carboxymethylation greatly enhanced the emulsifying capacity and emulsion stability of CMAX compared to the initial arabinoxylan. CMAX developed decreased ζ-potential, higher hydrophilicity, and improved interfacial adsorption capacity. Consequently, the denser and stronger interface on the oil droplet was formed, and the stabilizing mechanism was altered. Moreover, CMAX with lower DS could effectively stabilize emulsions during storage at a concentration of 0.5 % and pH between 6 and 7. Higher DS, however, led to poorer emulsion stability and greater flocculation as a result of the fragile interface formed by excess intermolecular ionic force. The research found CMAX potential in emulsion stabilizing and further applications in food processing.

Inhibition of α-amylase and amyloglucosidase by cellulose nanofibrils with different surface charge and spectroscopic analysis of their interaction mechanism

We investigated the inhibition effect of carboxymethylated cellulose nanofibrils with four different surface chargeon α-amylase and amyloglucosidase via enzyme activity inhibition assay, fluorescence spectra and secondary structure change analysis. These results revealed that cellulose nanofibril with lowest surface charge displayed the greatest inhibition effects against α-amylase (9.81 mg/mL) and amyloglucosidase (13.16 mg/mL). All cellulose nanofibrils in starch model significantly (p < 0.05) inhibited the starch digestion, where the inhibition effect was negatively correlated with the magnitude of particle surface charge. Cellulose nanofibrils could bind α-amylase or amyloglucosidase to form new complex in the manner of static quenching. The thermodynamic parameters demonstrated that the cellulose nanofibrils-starch hydrolase (α-amylase or amyloglucosidase) complexes were formed spontaneously via hydrophobic effects. Additionally, Fourier transform Infrared spectra exhibited the changes in the fraction of secondary structures of starch hydrolase after the interactions with carboxymethylated cellulose nanofibrils. These data provide a convenient and simple method tailor gastrointestinal digestion of starch by changing cellulose surface charge, to control postprandial serum glucose upsurge.

Toxicological Assessment of Cellulose Nanomaterials: Oral Exposure

Cellulose nanomaterials (CNMs) have emerged recently as an important group of sustainable bio-based nanomaterials (NMs) with potential applications in multiple sectors, including the food, food packaging, and biomedical fields. The widening of these applications leads to increased human oral exposure to these NMs and, potentially, to adverse health outcomes. Presently, the potential hazards regarding oral exposure to CNMs are insufficiently characterised. There is a need to understand and manage the potential adverse effects that might result from the ingestion of CNMs before products using CNMs reach commercialisation. This work reviews the potential applications of CNMs in the food and biomedical sectors along with the existing toxicological in vitro and in vivo studies, while also identifying current knowledge gaps. Relevant considerations when performing toxicological studies following oral exposure to CNMs are highlighted. An increasing number of studies have been published in the last years, overall showing that ingested CNMs are not toxic to the gastrointestinal tract (GIT), suggestive of the biocompatibility of the majority of the tested CNMs. However, in vitro and in vivo genotoxicity studies, as well as long-term carcinogenic or reproductive toxicity studies, are not yet available. These studies are needed to support a wider use of CNMs in applications that can lead to human oral ingestion, thereby promoting a safe and sustainable-by-design approach.