Fascinating Properties and Applications of Nanocellulose in the Food Industry

Abstract

Nanocellulose, a material derived from cellulose fibers, has gained significant attention in various industries due to its unique properties and potential applications. From an economic perspective, using nanocellulose in industry offers several advantages, such as cost-effectiveness, enhanced product performance, environmental benefits, and diversified applications. Also, it is utilized in the food industry because of its distinct properties, including high surface area, rheological behavior, water absorption ability, crystallinity, and no cytotoxicity. A significant application of nanocellulose is its potential to replace fats, carbohydrates, and proteins and serve as stabilizing agents in high-calorie foods. Moreover, nanocellulose has demonstrated exceptional efficacy as a delivery system, making it an ideal choice for preserving nutrients and active ingredients in food products. A primary objective in the packaging industry is to maintain food quality, extend its shelf life, and minimize waste. Since nanocellulose is both renewable and natural and offers oxygen and water vapor barrier properties, it emerges as a suitable candidate for the packaging industry. However, despite its promising features and applications, there are uncertainties around its non-toxicity and the potential impact on human health, issues that are currently being examined by scientists in the food industry.

1. Introduction

Cellulose (C₆H₁₀O₅)_n, one of the most abundant natural polymers in the world, was first discovered by Anselme Payene. Cellulose is the main component of the cell walls of most plants. The main sources of cellulose are wood pulp, cotton stalks, straw, bacteria, sea animals, and agricultural waste (fruits and vegetables) [1]. Renewability, non-toxicity, environmentally-friendly, wide availability, excellent mechanical properties, low weight, reinforcing capabilities, and biodegradability, with no adverse effects on health and environment, are among the important and practical features of cellulose used in various industries such as food, paper, bio-material, and pharmaceutical industries [2, 3]. Cellulose is a homopolysaccharide compound formed by joining large numbers of β-D-glucose monomers with β (1,4) glycosidic bonds [4]. Cellulose forms intra- and intermolecular hydrogen bonds due to hydroxyl groups in its structure. In general, these hydroxyl groups and their ability to create hydrogen bonds affect the biodegradability, chirality, and hydrophilic properties of cellulose and also create important functions, such as microfibrillated structure, hierarchical organization (crystalline and amorphous fractions), and cohesive nature [5, 6].

Cellulose derivatives, including cellulose acetate, cellulose sulfate, cellulose nitrate, carboxymethyl cellulose, ethyl cellulose, methylcellulose, and nanocellulose, exhibit distinct properties (sizes and shapes) and characteristics based on the production method and materials employed [1].

Nanocellulose consists of cellulose particles with dimensions less than 100 nm. The nanocellulose fibers can be obtained through chemical modification, such as acid hydrolysis, or physical modification, such as ultrasonication [7]. Nanocellulose possesses several practical and significant properties that make it an ideal choice for preparing various polymer composites, including low density, non-abrasiveness, combustibility, excellent potential for chemical modification, crystalline structure, increased specific surface area, advantageous rheological properties, outstanding resistance to water vapor transmission and oxygen permeation, effective barrier against aqueous liquids and oil grease, non-toxicity, and inexpensiveness compared to other synthetic polymers [8, 9].

Nanocellulose, an environmentally friendly and biodegradable biomaterial, has emerged as a promising alternative to synthetic materials. In recent years, cellulose nanocomposites have found applications in various industries, including food, medical, biomedical, pharmaceutical, civil construction, automotive, electronics, packaging, construction, and wastewater treatment [8, 10].

For example, nanocellulose-based biomaterials have properties similar to natural tissue, making them proper for cell attachment and growth. Nanocrystalline suspensions can be used as a cell culture environment, and cellulose nanofibers have been studied to grow membranes containing healing and bacteriostatic agents for treating skin burns [11]. Also, in the field of application in the construction industry, it is possible to mention the efforts of researchers to produce products compatible with the environment. For example, in 2019, a study was conducted to investigate the mechanical performance of integrating cellulose fibers into cement systems. The findings showed that the material had improved properties, including compressive strength, modulus of elasticity, and toughness, indicating its potential as a promising material with ductile and more resistant behavior [12].

2. Economic aspects of using nanocellulose in industry

Nanocellulose can be produced from different raw materials, which depend on the availability of the raw material, its cost, and environmental conditions, and these factors can directly affect the cost of nanocellulose production. This is observed, even though the properties of the produced nanocellulose and its application in the industry are influenced by the raw material and production method. As research and innovation in nanocellulose-based technologies continue, new sources and production methods are expected to be recognized and developed, further expanding its potential applications over the years [13]. In general, the economic advantages of the use of nanocellulose in industry can be mentioned as follows:

1. Cost-effectiveness: nanocellulose can be produced from renewable sources such as wood pulp, agricultural residues, or waste paper. This makes it a cost-effective and supportable alternative to customary materials. Additionally, the production processes for nanocellulose are becoming more efficient, further reducing production costs; 2. Lightweight and strong: nanocellulose is lightweight yet incredibly strong, making it an attractive material for industries such as automotive, aerospace, and construction. Its high strength-to-weight ratio can lead to cost savings in manufacturing and transportation; 3. Enhanced product performance: the interpolation of nanocellulose into various products can improve their mechanical strength, barrier properties, and persistence. This can result in longer-lasting products with reduced maintenance and replacement costs; 4. Environmental benefits: nanocellulose is biodegradable and non-toxic, making it an environmentally friendly alternative to synthetic materials. As sustainability becomes increasingly important to consumers and regulatory bodies, the use of nanocellulose can provide a competitive advantage for companies looking to reduce their environmental impact; 5. Variegated applications: nanocellulose has a wide range of potential applications across industries such as packaging, textiles, electronics, healthcare, and energy storage. This versatility opens up new market opportunities for companies utilizing nanocellulose in their products.

Apart from the economic benefits of using nanocellulose in the industry, there are several disadvantages and barriers facing nanocellulose and its wide application in various industries, which can be mentioned as 1. Initial investment: implementing and developing efficient and valuable methods of nanocellulose production can be expensive, which is the biggest challenge for manufacturing companies; 2. Competition: nanocellulose faces competition from other materials, and companies may need to invest in marketing and education efforts to promote its advantages and gain market share; 3. Uncertain demand: due to the novelty of using nanocellulose in the industry, this material may face uncertainty in the market and price; 4. Regulatory challenges: regulatory requirements and standards for nanocellulose products may impact production costs and market access, requiring companies to navigate complex regulatory landscapes [13, 14].

3. Types of nanocellulose

In general, depending on the source of cellulose, the production method, their size, and function, there are three types of nanocellulose with similar chemical composition and different morphology, namely nano-fibrillated cellulose (NFC), cellulose nanocrystals (CNCs), and bacterial nanocellulose (BNC) [15].

Nano-fibrillated celluloses are 1–100 nm in diameter and 500–2000 nm in length (depending on the type of raw material), and all are long, entangled, and flexible. Moreover, they consist of 100% cellulose in both amorphous and crystalline forms, and in comparison to CNCs, NFCs possess a greater surface area, higher aspect ratio, and longer length [16]. Also, among various types of nanocelluloses, NFCs have the simplest production method, owing to their avoidance of harsh chemical processes that degrade the molecular structure of cellulose. Generally, they are prepared by the physical separation of cellulose fibers, such as grinding, homogenization, and ultrasonication, or by chemical methods, including oxidation of wood raw material by 2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO) under gentle stirring, and finally by a combination of two chemical and physical methods that include carboxymethylation and high-pressure homogenization [17].

Mostly, CNCs are obtained through acid hydrolysis of cellulose nanofibrils. Their diameter and length are 2–20 μm and 100–500 nm, respectively. Their structure is rod- or whisker-shaped and consists entirely of crystalline cellulose (around 54–88% crystallinity). CNCs exhibit an exceptionally high crystallinity [18]. The production of nanocellulose involves two fundamental steps. First, impurities of the raw material are eliminated using an alkaline (NaOH) solution or by a bleaching method. Subsequently, the raw material is heated in an acidic environment to eliminate the amorphous portion of cellulose, and after centrifugation and dialysis, CNC is obtained. It is worth noting that the type of raw material, type of acid, and hydrolysis temperature and time affect the dimensions of CNCs [19, 20].

Bacterial nanocelluloses have a twisted ribbon-like shape and length of 20–100 nm, which are chiefly obtained from Gluconacetobacter xylinus, Acetobacter, Rhizobium, Agrobacterium, Aerobacter, Achromobacter, Azotobacter, Salmonella, Escherichia, and Sarcina systems or cell-free systems [21, 22]. BNCs form a hydrogel at the water-air interface. Their synthesis involves the production of β-1,4-glucan chains within the bacterial cell excreted through the cell membrane as protofibrils. These protofibrils then crystallize to create ribbon-shaped microfibrils, leading to the formation of a pellicle. The physical and mechanical properties of BNCs are different depending on the type of bacterial strain, synthesis method (cell and cell-free systems), cultural conditions (carbon and nitrogen source), structural features, and arrangement of fibers [23].

4. Application of nanocellulose in the food industry

Nanocelluloses possess exceptional utility and distinctiveness across various industries, particularly in the food sector, attributed to their remarkable capacity for forming hydrogen bonds, expansive surface area, and aspect ratio compared to cellulose fibers. Additionally, their inexhaustible primary sources further enhance their significance. Different types of nanocellulose are used in the food industry as emulsifiers, fat substitutes, thickeners, and in food packaging. Nanocellulose also acts as a carrier agent in biological systems to carry nutrients like curcumin, vitamins, omega-3-fatty acids, minerals, amino acids, nutraceuticals, probiotics, polyphenols, antioxidants, micronutrients, enzymes, and essential oils [23].

4.1 Stabilizer and emulsifier

In the food industry, many natural substances such as gums (like xanthan, carrageenan, gellan, and locust bean gum) [24] and hydrophilic polysaccharides extracted from seaweed and microorganisms are used as natural stabilizers and emulsifiers [25]. The use of stabilizers in products like gravies, creams, sauces, frostings, additives, icings, salad dressings, foams, soups, puddings, dips, desserts, texture enhancers, thickeners, and frozen dairy products is highly prevalent [26]. However, subjects such as thinning, phase separation, and lack of phase stability over time are the main problems of the food industry. Hence, it is crucial to employ a cost-effective and easily extractable natural material that not only preserves the quality but also prevents any physical changes in the products [27]. Nanocellulose (NC), as a natural emulsifying and stabilizing ingredient, is of great interest in food products due to its unique rheological properties. Also, it can extend the shelf life and preserve the shape of frozen desserts. While increasing the amount of other stabilizers can improve shape retention, it may negatively impact the texture and flavor of the dessert. However, NC can prolong the structure retention time without compromising other desirable characteristics of the dessert [28]. In 2022, researchers successfully created medium internal phase oil-in-water (O/W) Pickering emulsions using bamboo shoots nanocellulose (BSNC) as a stabilizer. The nanocellulose extracted from bamboo shoots demonstrated promising potential as an emulsifier in the Pickering emulsions. Emulsions with a BSNC content of 0.5 wt% at a 5:5 oil-to-water volume ratio had smaller particle sizes of around 25. However, increasing the BSNC content resulted in larger droplet sizes and even demulsification. Subjecting the emulsions to twice shearing improved their physicochemical properties significantly by reducing droplet size. As the BSNC content increased, the apparent viscosity initially increased and then decreased, with all emulsions exhibiting elastic behaviors [29].

Another application of NC is the development of Pickering emulsions in various industries such as dairy, meat, and bakery. For example, in the dairy industry, it is a suitable option for replacing butter in baking cakes and replacing cream in preparing frozen yogurt and ice cream. In 2019, research was conducted to investigate the addition of NC to ice cream and its effect on the structure and performance of the frozen product. The results showed that NC has a direct effect on fat absorption. So, the presence of NC caused enhanced sensory attributes in samples containing less fat, and crystal growth, ice cream hardness, and rheology remained unchanged at subzero temperatures [30]. The surface tension between oil and water decreases by adding NC to different emulsions, which improves the stability of the emulsion system [31]. In this regard, the effect of adding NC as a stabilizer on meat sausage was investigated. The findings revealed that the addition of NC enhanced the binding capacity of fat and moisture, the sausage’s hardness, elasticity, and chewability, resulting in reduced cooking loss and improved emulsion stability [32]. So, in general, Pickering emulsions stabilized with NCs have more stability and better compatibility than traditional surfactants.

4.2 Fat replacer

Today, with the progress of science, the world has moved toward consuming healthy and smart foods with low fat and sugar content and, as a result, suitable calories. Obesity and overweight are some of the basic problems among people of different societies, which have forced scientists to research the replacement of fattening factors, especially fat, with appropriate and natural substances. The use of NC in many foods, especially high-consumption and high-demand foods such as ice cream and processed meats, is one of the effective options for reducing the amount of fat and, as a result, reducing calories, maintaining the quality of the product’s texture, and improving nutritional and health aspects. In this regard, Velásquez-Cock et al. [30] added NC to the ice cream formulation to produce ice cream with low fat and calories. The results showed that the presence of NC in low-fat ice creams caused a significant decrease in the melting rate of reduced-fat ice cream. A study conducted in 2022 aimed to develop reduced-fat mayonnaise formulations with 5, 15, and 30% fat content using varying concentrations of nanocellulose synthesized from palm-pressed fiber. The study also included a 20-day stability assessment. The results showed that the reduced-fat mayonnaise had smaller oil droplets closely packed together when viewed under a light microscope. However, significant oil droplet coalescence was observed during storage, which could lead to viscosity loss. These findings suggest that nanocellulose was effective as a fat mimetic during mayonnaise formulation, but its effectiveness during long-term storage is uncertain [33].

4.3 Dietary fiber

Nanocellulose, as a dietary fiber, has a significant impact on the general health of the body through three mechanisms: promoting satiety (effect on protein), regulating blood sugar (effect on glucose), and regulating blood lipids (impact on lipid and fat). Foods containing high protein are mainly used to control obesity and weight due to their high satiety effect; therefore, a more complex protein has a slower digestion rate, and as a result, the time to induce satiety in the body increases. In general, the speed of food digestion determines the availability of nutrients in the body, and the delay in emptying the stomach may evoke the satiety effect [34, 35]. The results of recent years have shown that NC, like anionic polysaccharides (pectin or carrageenan), effectively enhances digesta viscosity, impedes proteolysis, and decelerates gastric emptying through their interaction with protein solutions. NCs with a negative charge can decrease protein proteolysis in the stomach by attracting proteins with opposite charges through electrostatic forces. Consequently, this leads to stable satiety and reduced consumption of other foods (Figure 1) [36].

Figure 1.

Schematic of the effect of NC on protein digestion [36].

Another benefit of NC as a dietary fiber is its role in the treatment of obesity and diabetes. NC impedes glucose absorption in the body by slowing down the digestion and absorption of glucose. NC spontaneously combines with glucose-decomposing enzymes to form a hydrophobic complex, which changes the protein structure of the enzyme and disrupts the activity of α-amylase and amyl glucosidase (Figure 2) [37]. In 2019, scientists also investigated the effect of NC, extracted from bleached softwood pulp, on digestive viscosity, glucose digestion, and absorption. The findings indicated that concentrations exceeding 0.5 wt% substantially enhanced digesta viscosity, slowed hydrolysis, minimized glucose release, and delayed glucose diffusion [39]. Also, in 2023, to increase the value of waste chili stems and promote the recycling of green resources, cellulose was extracted from chili stems using a nitric acid-ethanol method, and nanocellulose was then prepared using a sulfuric acid hydrolysis method. The study demonstrated that biscuits with satisfactory overall quality could be made using 7% nanocellulose, resulting in a regular appearance and a relatively smooth surface. Mice experiments revealed that consuming biscuits containing nanocellulose reduced food intake significantly and inhibited weight gain in mice. Therefore, the research suggests that whole wheat biscuits with nanocellulose could be considered as a high-fiber food option [40].

Figure 2.

Schematic of NC effect on glucose digestion [37, 38].

Another application of NC in the food industry is its use as an agent that disrupts the digestion and absorption of lipids in the body. The presence of lipids and fats in daily meals, including milk, ice cream, hamburgers, bread, and dairy products, plays a significant role in weight gain and blood pressure increase. Therefore, the production of targeted and intelligent food holds a key role in the future of the food industry. In general, NCs, with their absorption power and high water content, increase food’s viscosity, which in turn reduces the food’s caloric content and causes disorders in fat digestion. So, NCs effectively hinder the digestion and full absorption of lipids in the body through various fundamental mechanisms. These include (1) thickening or gelling gastrointestinal fluids to prevent digestive enzymes from reaching the fat; (2) combining with gastrointestinal constituents such as bile salt to form a precipitate; (3) reducing the surface area exposed to digestive enzymes by promoting flocculation of fat; and (4) forming a thin coating around the fat to reduce its exposure to digestive enzymes (Figure 3) [41]. To investigate the effect of NC on lipids, scientists simulated the conditions and environment of the digestive system. They found that NC reduces the activity of the lipase enzyme, increases the viscosity of intestinal digesta, and is more effective than cellulose in blocking the effect of bile salts and absorbing cholesterol in the body [42].

Figure 3.

Schematic of NC effect on fat digestion [41].

4.4 Retrogradation inhibitor in starchy food

Another nutritional application of NC is its use in the starchy food industry. Scientists have found that nanocellulose (especially CNC) can be used to produce healthy starchy foods and support weight loss efforts. A major issue in the starchy food industry is “retrogradation,” which typically occurs during the cooling and storage stage of gelatinized starch, reducing the quality of the product [43]. With a large specific surface area and abundant hydroxyl groups, CNC effectively interacts with amylose through hydrogen bonding, inhibiting short-term retrogradation. Furthermore, the interaction between CNC and amylopectin inhibits long-term retrogradation (Figure 4) [44]. There have been extensive studies on the effect of NC on starch. For example, a 2017 study investigating the impact of NC on oxidized potato starch found that NC influenced enzyme activity and the amount of resistant starch. Notably, the addition of NC to gelatinized starch reduced the amount of quickly digestible and slowly digestible starch but increased the amount of resistant starch. Resistant starch is a type of starch that resists enzymatic digestion and cannot be digested in the small intestine. However, it can be fermented with volatile fatty acids in the human intestinal tract, specifically in the colon [45].

Figure 4.

Schematic of NC effect on starch digestion [37, 38].

4.5 Food additive

Today, nanocelluloses, especially BNCs, due to small diameter, hydrophobicity, and water-holding capacity, are added to food and are used to reduce calories, increase and improve their absorption in the body, and improve nutritional properties. Among the applications of nanocellulose as a food additive, it can be mentioned to replace BNCs instead of flavonoids, cara gum, and other stabilizers to the ice cream formula to obtain a new type of ice cream. For example, in 2018, Guo et al. [46] showed that adding bacteria to ice cream increased its resistance to melting and could maintain its shape for at least an hour after being taken out of the freezer. Since BNCs are easily digested and absorbed by the digestive system, they are used as a quality improver based on meat. For example, in 2019, Guo et al. [47] demonstrated that BNC can effectively reduce moisture loss in chicken cake without altering the chemical structure or protein groups in the chicken. Another application of nanocellulose is the enrichment of beverages and dairy products in the market. For example, nanocelluloses can produce quality yogurt with a soft texture and higher stability [48].

4.6 Encapsulating agent

The food industry faces a significant challenge in preserving micronutrients, vitamins, minerals, and active components (such as probiotics) during production, preparation, transportation, and storage. Moreover, digestive enzymes often compromise these nutrients in the stomach and bile salts before reaching their intended destination in the body, primarily the intestine [49]. Therefore, food industry scientists are striving to protect nutrients from adverse factors and conditions and improve the performance of the delivery system using encapsulation techniques. Encapsulation is an active substance transfer system that uses natural polymer materials to safeguard nutrients, thereby enhancing the bioavailability and biological activity of substances. The polymer materials used in encapsulation should ideally be natural, readily available, inexpensive, non-toxic, free of pollution, easily modifiable, and have good biodegradability and biocompatibility [34]. Among the materials used for encapsulation, NC has drawn the attention of numerous researchers due to its distinctive biological properties, such as high safety, excellent biodegradability, and non-toxicity. A noteworthy study in this area has explored the use of alginate and NC in the microencapsulation of probiotics. The results of the study indicated that the inclusion of NC increases the compression strength of the produced hydrogels by more than 30% and diminishes the porosity induced by freeze-drying. Additionally, the introduction of 13% NC significantly extended the survival time of the probiotic strain (Lactobacillus rhamnosus) within the alginate microbeads [50]. In 2020, researchers encapsulated the probiotic Lactobacillus rhamnosus using a mixture of whey protein isolate, inulin, and NC (CNC). They found that NC significantly improved the resistance and survivability of the microcapsules under simulated digestive system conditions [51]. Also, Wang et al. [52] developed a soy protein isolate combined with CNC composite nanoparticles for the delivery of curcumin. The resulting complex composite nanoparticles demonstrated improved encapsulation efficiency and controlled release in simulated gastrointestinal conditions. CNC was found to be essential in the delivery system for the active compounds. In 2021, a compelling study was conducted on the encapsulation of ascorbic acid (Vitamin C) using NC. In this experiment, Vitamin C was encapsulated through an electrostatic interface with glycidyltrimethylammonium chloride-modified chitosan (GCS) and then cross-linking with phosphorylated CNC (PCNC) to produce Vitamin C-GCS-PCNC nanocapsules. The results of the investigation revealed that the inclusion of NC in the encapsulation formulation enhanced the efficiency, provided better control of the release action, and increased the antioxidant and antibacterial capabilities of vitamin C [53].

4.7 Food packaging materials

Packaging plays an essential role in protecting food from spoilage factors, including light, oxygen, heat, and bacteria. This makes it a vital component within the comprehensive system of the food industry. The use of natural and renewable materials in efficient packaging not only preserves food and extends its shelf life but also maintains the quality and nutritional value of the food until its expiration date, thereby helping to minimize waste in the sector. The prevalent use of plastic and its derivatives in the packaging industry, combined with increasing concern about environmental pollution and public health, has promoted scientists to explore natural and biodegradable materials for the production of suitable packaging. Among these materials, cellulose and its derivatives, especially NCs, have emerged as significant and essential candidates for the creation of biodegradable and intelligent packaging. One of the prominent attributes of NC that inspires scientists to employ it in the packaging industry includes its natural origin, high biodegradability, strength, resistance to oxygen and moisture penetration, and antibacterial properties. Generally, the exceptional oxygen barrier properties of NCs result from a combination of their high crystallinity and a network structure sustained by strong inter- and intramolecular hydrogen bonds [54]. Extensive research is being conducted on the application of NC in the packaging industry, particularly in intelligent packaging. For instance, in 2021, researchers manufactured nanocomposite films to regulate D-limonene permeability by utilizing nanocrystals and starch. Their study results indicated that the amount of NC, along with its appropriate aspect ratio, could autonomously manage D-limonene permeability [55]. In another study, Perumal, et al. [56] discovered that incorporating NC into the formulation of a biocomposite film (comprising clay and polyvinyl alcohol (PVA)) not only prolonged the storage life of mangoes but also enhanced the thermal and tensile properties of the films by increasing the amount of CNC filler up to 6 wt %. Currently, researchers are exploring the use of NC in intelligent packaging systems, leveraging its antibacterial and antioxidant properties. In 2020, researchers produced a probiotic nanocomposite film utilizing Lactobacillus plantarum, NC, and inulin. Their findings indicated that the fabricated probiotic packaging films exhibited potent antibacterial properties and effectively extended the shelf life of chicken fillets [57]. Another study produced composite films using polyhydroxybutyrate (PHB) and nanocellulose (CNC) via the solvent casting method. This study showed that, besides enhancing the barrier performance, mechanical strength, transparency, and other attributes of the composite film, CNC did not impact the inherent PHB [58].

Another beneficial effect of incorporating nanocellulose into packaging systems is enhancing the mechanical properties, such as high tensile strength, elongation, and flexural modulus [59]. For instance, a 2020 study observed a sevenfold increase in tensile strength and a sixfold increase in elongation at break when CNC was added to a PVA film [60]. Moreover, in research conducted by Chen et al. [61], it was found that integrating 0.5% stearic acid-modified microcrystalline cellulose/nanocellulose into cassava starch film significantly increased tensile strength by 484.5%.

5. Safety and regulatory aspects

Wood pulp and powdered cellulose are generally recognized as safe (GRAS) and are commonly used as raw materials in food-contact materials or food additives. As NC is one of the most widely used cellulose derivatives in different industries, evaluating its biological effects on the ecosystem and the human body solely based on its chemical characteristics is not sufficient. The interactions of NC with cells and other living organisms can be influenced by various factors, including its size, shape, aggregation characteristics, and other unknown factors [62]. One of the primary routes for NC to enter the body is through the skin and respiratory system. If the amount of NC in the skin and respiratory system exceeds permissible limits, it can cause skin toxicity and pulmonary inflammation [34, 63]. The use of commercial foodborne nanoparticles, such as titanium dioxide (TiO₂) and zinc oxide (ZnO), in the food industry can lead to complications like colitis [64], and this raises significant concerns among consumers and researchers about the safety of NC following ingestion through the gastrointestinal tract. Therefore, extensive studies have been conducted to investigate the effect of NC and related problems on food and the human body, using both in vivo and in vitro methods.

In 2010, the toxicity effect, including the in vitro cytotoxic and genotoxic properties of NC, obtained from birch pulp, with dimensions ranging between 20 and 60 nm to 100 and 350 nm, on human and animal cells was investigated. Additionally, the study examined the lethal effect of NC on human cells. Also, the effect of NC damage on DNA using a bacteriological assay (the Ames test) was also studied [65]. In 2011, another in vitro study focused on the toxicity, health, and environmental safety of NC with dimensions of 20–30 nm. The study evaluated its effect on human and mouse macrophages, its impact on cell survival, as well as the cytokinetic characteristics of cells [66]. Also, in recent years, extensive studies have been conducted on the oral toxicity of NCs using both in vitro cellular models and/or in vivo animal models. For instance, in 2019, the toxicological effects of ingested NC were investigated using both an in vitro intestinal epithelium model and an in vivo rat model [67]. In 2020, the impact of CNF on gut microbial health was studied by examining its cytotoxicity and in vivo toxicity [68], and in 2020, the hepatotoxicity of NC modified with oxalate ester in rats was investigated [69]. Furthermore, in 2021, the oral toxicity of carboxymethylated CNF was evaluated using in vitro cellular studies and an in vivo mice repeated gavage model [70]. All these studies consistently concluded that both original and functionalized NC showed no cytotoxicity. Additionally, it was observed that NC was non-toxic in an in vivo animal model when used at a reasonable concentration, with an upper limit of 3.5 wt%. Therefore, to gather clearer information regarding the safety effects of nanomaterials like NC, it is crucial to establish internationally standardized methods that guarantee their safety. Moreover, prior to the commercialization of food products utilizing new nanotechnologies, it is essential to proactively anticipate, understand, and effectively manage both the potential positive and negative consequences that may arise from consuming nanomaterials [62].

6. Conclusion and prospects

Cellulose, the most abundant polymer in nature, is the primary resource for the production of NC. The unique properties of NC, including its biocompatibility, biodegradability, non-toxicity, inexhaustible nature, nanoscale size, high aspect ratios, large surface area, liquid crystalline, and rheological properties, have made it an appealing choice for use in different industries such as food industry. Generally, NC has a greater affinity for oil than water. It can be used as a barrier to mix water and oil emulsions, making it a valuable stabilizing agent for emulsions and food products. This characteristic explains the use of NC in the food industry, particularly in foods such as sauces, soups, puddings, etc. Moreover, due to its ability to create stable emulsions with low-oil content, NC can contribute to the production of low-oil, low-calorie food products. NC can also serve as a suitable coating and carrier for bioactive compounds, such as probiotics, protecting them from the effects of digestive enzymes. Consequently, NC can play a crucial role in food enrichment. When utilized in packaging systems, NC enhances the mechanical and barrier properties of packaging films. As a result, food products are less exposed to spoilage factors, and their shelf life is increased. From the economic point of view, the use of nanocellulose in the industry due to its cheap source, low weight, and high strength, as well as enhanced product performance, can have a bright future, provided that it can overcome the upcoming obstacles, such as the expensive production method and the instability of the market. Also, there are still significant challenges faced during the application of NC in the food industry. These challenges include improving technology and reducing production costs, developing new methods for modifying the hydrophobicity of NC, further investigating its nutritional properties and impact on consumer health, and conducting more comprehensive research on the safety aspects of NC. As research and development continue to advance the production and utilization of nanocellulose, its economic viability is expected to further improve in the coming years.