Perspective Chapter: Cellulose in Food Production – Principles and Innovations

Abstract

For several decades, cellulose and its derivatives have been used in various fields of food processing and their applications have become increasingly important. Nutritionally, cellulose is known as dietary fiber and is used as a functional food component. Many new technological needs were recognized since developing of industrial products and, therefore, cellulose modifications (chemically or physically) also have been considered. The various important properties for using these compounds include organic solubility, gel and film formation ability, make mucoadhesive system, high swelling, hydrophilic and hydrophobic features, act as viscosifying agent, and thermoplastic effects in food systems. Thus, the most typical technological role of these cellulose’s characteristics can be mentioned as edible coating (in fruits and fried products), edible film, emulsification, stabilizing agent, rheology control, suspending agent, diffusion barrier, encapsulation, extrusion, molding, and foam stabilizer in food industry. The new innovations can be mentioned as the production of bacterial cellulose, developing the smart packaging, and the preparation of nanocellulose with environmentally friendly processes. Finally, with the expansion of the usage of cellulosic materials, a reevaluation of their food safety has been carried out. Also, the legal guidelines related to the use of these compounds as raw materials have been provided for manufacturers.

1. Introduction

Cellulose is the most considerable biopolymer (naturally occurring polymer) on the ground with 1.5 × 10¹² heaps of annual manufacturing. This organic polymer is most regularly obtained from plants, and nowadays its significance in food applications and personal and scientific care cannot be dominated out. Cellulose is additionally obtained via in vitro synthesis with the assistance of enzymatic pathways, the chemical synthesis from glucose derivatives, and the biosynthesis via various microorganisms, such as algae and fungi, as nicely as a number of cardio nonpathogenic bacteria of the genera Agrobacterium, Sarcina, Rhizobium, and Acetobacter [1]. Also, cellulose can be modified using chemical reactions to manufacture some compounds with special characteristics. The changes in cellulose polymer enhance and develop its chemical and physical facets, which allow the usage of derivatives for many purposes and applications [2]. Structurally according to Figure 1, cellulose is a polysaccharide that is composed of quite a few lots to over ten hundred D-glucose units as a linear chain [3].

Figure 1.

Linear molecule of cellulose polymer with D-glucose units.

Cellulose is recognized as “Dietary fiber.” Dietary fiber includes remains of plant cells resistant to hydrolysis as digestion procedure via the alimentary enzymes of gastrointestinal system in the human body, whose components are cellulose, hemicellulose, lignin, waxes, pectins, gums, and mucilages. These compounds are naturally current in nuts, cereals, fruits, and vegetables. The quantity and composition of fibers vary from meal to meal based on food structure. A fiber-rich diet is less in calorie density, frequently has a limited fat content, is large in extent, and is richer in micronutrients. This large mass of meals takes longer to consume and its presence in the belly might also deliver a feeling of satiety sooner, although this feeling of fullness is quick time period. It is advised that healthy adults need to devour between 20 and 35 g of dietary fiber every day [4]. There are two kinds of dietary fiber: soluble and insoluble. The insoluble substances structure a bulky mass and velocity transit time through the gastrointestinal tract due to the fact of their bulk; cellulose, hemicellulose, lignin, and waxes fall into this category. Among the soluble dietary fibers are the pectins, gums, and mucilages. All of these have the capability to hold water and thereby expand the viscosity of the food mixtures [5]. Cellulose polymer and its various derivatives have long been applied in manufacturing formulated foods. The modified celluloses (chemical or physical) are beneficial in many food products and the place bulk properties are acceptable targets. This would consist of healthy products, reduced or low-fat foods, taste oil imbibers, or flowable products such as synthetic sweeteners and taste packets. The use of these cellulosic compounds in food processing is typically due to their rheology, managed water interaction, textural attributes, and no longer to solubility or different chemical properties [6]. In this chapter, the use of cellulose biopolymer and its various derived compounds are investigated in the food industry with regard to the principles and innovations.

2. Structure modification of cellulose

Cellulose is a suitable polymer in terms of its potential to create chemical and physical modifications. Considering that the variety of food products needs to provide certain conditions of cellulose behavior and eliminate deficiencies of efficiency, the modified structures of cellulose are widely used in the food industry. Applied biopolymer is derived from cellulose that enables beneficial functions or allows really useful features in various food systems [7]. The list of commercial compounds derived from cellulose as an additive in the food and pharmaceutical industries is as follows:

• Methyl Cellulose (MC): It is produced through the substitution of hydroxyl groups on the polysaccharide molecule with methoxyl groups from the reaction between cellulose in an alkaline medium with a methylating agent, such as methyl iodide, methyl chloride, or dimethyl sulfate. Some features that make it suitable for food use are tough material, absolutely nontoxic, tasteless, odorless, and high-viscosity solutions at very low concentrations [8].

• Hydroxypropyl Methyl Cellulose (HPMC): It is manufactured by the replacement of hydroxyl groups on the polysaccharide molecule with methoxyl and hydroxypropyl groups [9]. During the production of HPMC, the methylcellulose is then further reacted with the staged addition of an alkylene oxide as propylene oxide. By making these changes, some desired modifications occur on the cellulose polymer, which should be noted. HPMC gelling temperature in hot water is considerably greater than that of MC [10]. In contrast with MC, the dissolution in cold water has additionally been noticeably improved. The viscosity of HPMC is much less affected by means of the temperature than MC, and its solution is stable during storage at room temperature. In terms of the potential of the polymer to retain water, it should be pointed out that with the equal addition amount, the water-retention rate (the amount of water that can be retained in a material) of HPMC is greater than that of MC. HPMC has higher enzyme resistance than MC, and the possibility of enzymatic degradation of HPMC is much less than that of MC. HPMC has higher adhesion than MC. HPMC can combine with water-soluble polymers and then form a uniform solution of higher viscosity, such as polyvinyl alcohol, starch ethers, and vegetable gums [11].

• Carboxymethyl Cellulose (CMC): It is produced by binding of carboxymethyl groups (-CH2-COOH) to some hydroxyl groups present in the glucopyranose or monomers of cellulose backbone [12]. CMC is also known as cellulose gum [13]. The manufacturing of CMC includes 4 major processes: The isolation of alpha-cellulose from the water hyacinth and the synthesis by means of the alkalization (alkali-catalyzed reaction) of cellulose with chloroacetic acid with the aid of carboxymethylation and eventually the purification of the CMC itself to cast off undesirable compounds. In other words, it can be expressed that there are two principal reactions in order to turn the cellulose into CMC: alkalization and carboxymethylation [14]. Compared to MC, which is only soluble in cold water, CMC can be dissolved in both hot and cold water, however, its solubility is still poor. CMC and HPMC showing not same water retention rates in such a way that HPMC results in a higher water retention rate when compared to the same amounts [15].

• Croscarmellose Sodium (CCS): CMC is regularly used as its sodium salt named sodium carboxymethyl cellulose (Sodium CMC, SCMC, or NaCMC) to enhance the solubility. NaCMC has a cross-linked polynomial and so it is also recognized as CCS [16]. This polymer is made in two stages, in the first step, crude cellulose is soaked in sodium hydroxide, and then in the second step, NaCMC is formed during the reaction of cellulose with sodium monochloroacetate [17]. Therefore, the main difference between NaCMC and CMC is that NaCMC is easily soluble in hot and cold water, while CMC is poorly soluble in water. NaCMC is white and free-flowing powder that is very slightly soluble in ether. Nary organic solvents [18].

• Ethyl Cellulose (EC): It is produced by means of the reaction between ethyl chloride and alkali cellulose. EC is insoluble in glycerin, propylene glycol, and water, however soluble in different organic solvents [19].

• Hydroxyethyl Cellulose (HEC): It is a hydroxyethyl ether that is produced by soaking the cellulose with sodium hydroxide and then reacting with ethylene oxide. HES indicates high solubility in water over a wide temperature range even at greater than 50 degree Celsius [20].

In terms of chemical formula, repeating structure and substitution group for cellulose derivatives including MC, HPMC, EC, HEC, and NaCMC are altogether shown in Figure 2.

• Hydroxypropyl Cellulose (HPC): HPC is a cellulose-based compound in which hydroxyl groups have been hydroxypropylated. It is produced by reacting alkali cellulose with propylene oxide at high pressure and temperature. In comparison with other water-soluble cellulose ethers, HPC is more plastic and relatively hydrophobic due to the high degrees of hydroxypropylation. Because of its chemical structure, it is absolutely soluble in water and also in polar organic solvents such as methanol, ethanol, isopropyl alcohol (IPA), and acetone. HPC solution has lower viscosity and slow hydration or uptake of water compared to HPMC [21]. Based on the degree of substitution, HPC is divided into two types and solubility behavior of each one is different and which are: High substitute hydroxypropyl cellulose (H-HPC) and low substitute hydroxypropyl cellulose (L-HPC) [22].

• Microcrystalline Cellulose (MCC): It is manufactured with the aid of subjecting to a high shear treatment, at increased temperature and pressure, a reaction combination of a cellulose material, an active oxygen compound and water, for a time effective to depolymerize the cellulose material. MCC is an isolated, colloidal crystalline component of cellulose fibers and an extra purified structure of cellulose. It is a white, odorless, and tasteless carbohydrate polymer powder that usually consists of up to 350 glucose units. It is dispersible in water but not soluble, requiring large strength to disperse and hydrate [23].

• Polyanionic Cellulose (PAC): It is produced from the isopropyl alcohol solution of alkalized cellulose and chloroacetic acid by means of etherification reaction. The raw materials for the obtaining of PAC are comparable to those for the manufacturing of excessive viscosity CMC, however, in the production process, one-of-a-kind degradation technique is employed so that the substitution of hydroxyl group in the ring shape structure of β-glucose group will be extra uniform. PAC shows markedly solubility both in cold water and hot water. It exhibits the best thermal stability, salt-resistance, and strong antibacterial activity. PAC has a molecular aspect similar to CMC [24].

• Hydroxypropyl Methyl Cellulose Phthalate (HPMC-P): It is manufactured using the esterification of HPMC with phthalic anhydride and is also known as hypromellose phthalate. The dissolution properties of HPMC-P can be controlled by altering the phthalyl content that affects the pH ranges solubility. It is soluble in pH 5 to 5.5 [25].

• Hydroxypropyl Methyl Cellulose Acetate Succinate (HPMCAS): It is obtained via the esterification of HPMC with acetic anhydride and succinic anhydride in a reaction medium of a carboxylic acid (acetic acid) and the usage of an alkali carboxylate (sodium acetate) as catalyst. HPMCAS is blended ester of HPMC acetate and succinic acid. HPMCAS begins to swell and dissolve at pH > 5 relying on the extent of substitution. The pH of dissolution will increase as the ratio of acetyl over succinoyl substitution becomes greater [26, 27].

• Powdered Cellulose (PC): It is typically produced by means of mechanical micropulverizing cellulose. It has an excessive quantity of amorphous regions and is regularly used as filler and binder in tablet manufacture. In comparison with PC, MCC has a greater degree of crystallinity due to the fact that it is usually obtained via partly hydrolyzing cellulose with mineral acid [28]. It does not dissolve in water, ethanol, ether, and dilute mineral acids and it should be said that PC is slightly soluble in sodium hydroxide solution [29, 30].

• Carboxymethylhydroxyethyl Cellulose (CMHEC): It is a combination of water-soluble cellulose ethers, each with the nature of CMC and HEC. CMHEC has an excessive bonding potential and hydration on the suspended solids with very good flocculation, however, due to nonionic hydroxyl the presence of ethyl group, in contrast with the CMC and salt, it is extra compatible. Also, another advantage is the cross-linking ability of multivalent cation, which can significantly improve the viscosity of solutions [31].

Figure 2.

Repeating structure of cellulose derivatives. R: Substituent group.

3. Behavior of cellulosic compounds in food systems

A wide range of cellulose derivatives due to their nontoxic nature for a long time have been developed, in particular, acetate, nitrate and sulfate esters, cellulose ethers (MC, HPMC, CMC, EC, HEC, and HPC), and sodium CMC are the most broadly used cellulose derivatives for foodstuffs [32]. Table 1 indicates the different properties of cellulose-derived compounds, which are used to achieve a specific behavior in food and pharmaceutical systems. As it turns out, the polymers of MC, HPMC, CMC, and HPC exhibit the widest range of properties. Food polymers play an essential role in food structure, food functional properties, food processing, and shelf life. The information in this field is commercially essential as it will provide a beneficial practical guideline for food improvement and industrial production. The application of each of these compounds should be considered in food systems according to the important characteristics of food such as stability, the importance of resistance to stress, maintaining product uniformity, and improving physical properties [36].

Properties	Cellulosic Polymers
	MC	HPMC	CMC	CCS	HPC	EC	HEC	MCC	PAC	HPMC-P	HPMCAS	PC	CMHEC
Water solubility	●	●	●	●	●		●		●	●			●
Organic solubility	●	●			●	●				●	●
Gel; forming	●	●	●	●	●	●	●	●	●	●			●
Film; forming	●	●	●		●	●	●	●	●	●	●		●
Mucoadhesive; system	●	●	●		●	●	●						●
High; swelling	●	●	●	●	●		●	●	●	●		●	●
Hydrophilic; features	●	●	●	●	●		●	●	●	●		●	●
Hydrophobic; features						●					●
Viscosifying agent	●	●	●	●	●	●	●	●	●	●	●	●	●
Thermoplastic; compound								●			●	●
Drug solubilizer	●	●	●	●	●	●	●	●				●	●

Table 1.

The variety of polymer properties [33, 34, 35].

Variations of the molecular structure and size of polymer chains or networks consequences in one of kind polymers with special properties. In using each of these polymers, vital behaviors in that food system need to be identified. In a food whose stability in the aqueous phase is important, the preference of a polymer that is soluble in water will be desired. In the design of food formulations based on water-insoluble compounds, it is important to select derivatives with similar properties to the main ingredients of that formulation. Generally, in various applications of cellulose derivatives for the food systems, such as emulsifiers, stabilizers, coatings, film production, gel formation, creating adhesive, and thickening structures, these different and compatible properties of the polymer are considered. Sometimes, several polymers may be suitable for a formulation or purpose, in this situation, a polymer should be chosen that is economical and can be used on an industrial scale. In fact, in a low-scale trial and error, polymers are replaced with each other, and rheological properties and sensory evaluation or textural indicators are tested. In a food system, some positive properties of a polymer may compensate for the disadvantages of another polymer, and a more suitable structure can be created by using a combination. In the research and development departments in the food industry, the application of each of the replaceable polymers is constantly being investigated. Today, the design of stabilizers for different food products has become a profitable industry and business in the world. Many companies supplying industrial raw materials are known for introducing new stabilizing formulations in the food industry [37, 38].

4. Function results of cellulosic structures in foods

Cellulose and its derivatives have shown special roles and results in the industrial production of food and have solved many problems. In the food industry, for a research and development specialist, it is important to know about these roles and their definitions and to substitute different ingredients in a way that is effective. In order to understand the function of cellulose and its derivatives in food systems, its specific roles and applications need to first be defined in following terminology:

• Edible coating (EC): It is described as a thin layer of safe-to-eat material formed on a food. Edible coatings may additionally be described as defensive layers created around food surfaces by using solutions made from suitable for eating polymers like polysaccharides, proteins, lipids, or their combinations. This protective layer acts as a barrier between the food and exterior surroundings and as a result prolongs the ripening and spoilage process. Different kinds of industrial safe-to-eat coatings are broadly used to prevent moisture loss and to add shine to fruits and vegetables. Other business purposes of edible coating consist of coating nuts, fried foods, seafood, minimally processed foods, vegetables, and especially fruits [39].

• Edible Film (EF): It is a preformed, thin layer, made of safe-to-eat material, which once formed can be positioned on or between food components. The main distinction between EC and EF is that the EC is applied in liquid form on the food, commonly through immersing the product in a prepared solution, and EF is first molded as solid sheets using polymers as edible film formers, which are then applied as a wrapping on the food product [40].

• Emulsification: It is the technique of dispersing two or greater immiscible liquids together to structure a semi-stable mixture. In food applications, these two liquids commonly consist of an organic type (oil) section and an aqueous type (water) section that is stabilized by means of the addition of a food-grade emulsifier or surface-active agent. Emulsifiers work by means of forming physical barriers that maintain droplets from coalescing. The surface-active agent or surfactant includes both polar head and nonpolar tail. Therefore, emulsifier as a surfactant is attracted to both hydrophilic and hydrophobic compounds and assists products containing immiscible food ingredients, such as oil and water, to combine [41]. The water-holding capacity of cellulose derivatives such as carboxymethyl cellulose can be used in the formulation of food products such as doughnuts to prevent their staleness by maintaining the product’s moisture during storage. Also, in interaction with other oil-uptake inhibitors hydrocolloid polymers, such as xanthan, their negative effects on the texture of the final product were eliminated using CMC and it helps to maintain the proper volume of the final product [42].

• Stabilizing agent: It is an ingredient added to foods to assist, keep, or decorate their unique texture and physical and chemical attributes. Stabilizing agents or stabilizers serve both the practical purpose of maintenance while additionally making products some distance extra appetizing to consumers. They can also work synergistically with emulsifiers to permit food ingredients that would now not in any other case combine well and hold a homogenous dispersion. This will increase the stability and viscosity of the food by means of binding its giant molecules. This component is used for a number of features in foods and its major characteristic is to act as a thickening agent to gel the ingredients into the required consistency [43].

• Rheology control: It is important in the food industry in order to maintain product quality. Rheology of food is tofind out about the consistency and flow of food under certain utilized forces, to recognize the underlying physicochemical concepts of food substances and their interaction. Rheology modifiers assist to obtain preferred rheological behavior, supporting to manage a range of characteristics, consisting of shelf stability, ease of application, sag or bend, resistance, leveling, settling, film forming, regulation compliance, and more [44].

• Suspending agent: It is a substance added to fluids or liquids to help suspend or disperse particles and reduce sedimentation. This is important in the stability of beverages and maintaining the integrity of liquid products that contain fine solids. If the suspension is no longer maintained, particularly in some beverage products, the structure of the product will change in taste, decrease in quality, and not be accepted by the consumer [45].

• Diffusion barrier: It is a thin layer of polymer generally positioned in multilayer films between two different layers or on surface of a layer. Gas diffusion barriers are vital for a number of purposes in food packaging’s capability to resist the absorption of light, moisture, and oxygen. These properties come from the accumulation of the individual films used in the development of the packaging. The oxygen, water vapor, and carbon dioxide barrier properties are of specific significance in food packaging applications. The correct barrier and proper gas combination will make the shelf life of food products longer. Several physical factors can have an effect on the barrier properties of a polymer that consist of temperature, humidity, orientation, and cross-linking [46].

• Encapsulation: It is a technique or industry term in which active agents or dietary supplements are surrounded by using a coating to supply small capsules with controlled migration. This procedure includes the incorporation of food ingredients or different substances in small capsules. Also, encapsulation refers to an object’s capability to conceal taste and smell that are now not necessary to sense by its consumer [47].

• Extrusion: It is a mechanical procedure in which certain substances as soft blended components are forced, underneath pressure, via a die or perforated plate opening to create products of a preferred shape, structure, size, and/or texture. This technique is used in food processing and described as a machine of pushing out, combined components in form of paste, especially via a small opening referred to as a die that is designed to produce the required shape [48].

• Molding: The operation of molding is to form the dough piece, in accordance to the bread variety being produced, so that it appropriate fits and matches into pans. The dough molding tools can be set to obtain the preferred form with a minimal quantity of stress and strain on the dough [49].

• Foam stabilizer: Liquid foams are often made pretty long-lasting by means of including some substance, known as a foam stabilizer, that prevents or retards the coalescence of the gas bubbles. A stronger foam structure is to add polymer to a foam-making system. The polymer will increase the liquid viscosity for that reason extend the foam stability and also additionally minimize the adsorption of foaming agents. Thus, the synergistic effect in a foam system is achieved [50].

• Thermoplastic system: It is thermo-softening plastic or binder that turns soft and flexible at certain temperatures and solidifies when cooled [51].

Table 2 shows the main specific use of cellulose derivatives in the food and drug industry.

Application	Cellulosic compound	Reference
Edible coating	MC, HPMC, and NaCMC	[52, 53]
Edible Film	MC, HPMC, CMC, andHPC
Emulsification	EC and NaCMC	[54, 55]
Stabilizing agent	EC, HPC, and NaCMC
Rheology control	MC, HPMC, NaCMC, and HPC	[56]
Suspending agent	MC, HPMC, NaCMC, and HPC
Diffusion barrier	MCC	[57, 58]
Encapsulation	HEC, HPC, HPMC, MC, and NaCMC	[59]
Extrusion	HPMC	[60]
Molding	HPMC
Foam stabilizer	MC, HPMC, NaCMC, andMCC	[61]
Thermoplastic system	CMC and MCC	[62]

Table 2.

The main applications of cellulose compounds.

5. Food safety of cellulosic compounds

Reevaluation of the food safety of cellulosic compounds has been carried out by international associations such as the European Food Safety Authority (EFSA) in the EFSA’s scientific panels on Food Additives and Nutrient Sources added to Food (ANS). Food safety of cellulose derivatives as food additives including MCC (E 460(i)), PC (E 460(ii)), MC (E 461), EC (E 462), HPC (E 463), HPMC (E 464), ethyl MC (E 465), NaCMC (E 466), enzymatically hydrolyzed CMC (E 469), and cross-linked CMC (E 468) has been investigated (“E numbers” are special codes for components used as food additives and “E” is the abbreviation of Europe) [63]. The ideal everyday consumption as an acceptable daily intake (ADI) “not distinguished” for unmodified and modified celluloses established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Scientific Committee on Food (SCF). Celluloses are not absorbed in the human body and are excreted intact through the feces after digestion of foods. Additionally, MCC, PC and modified celluloses are fermentable by means of intestinal flora in animals and humans. Specific toxicity facts are not available for all different celluloses, which were considered common among all types of cellulose due to their structural and biological similarities. In general, the acute toxicity of all cellulose types was low and there was no genotoxic concern. Short-term and sub-chronic dietary toxicity studies conducted with MCC, Mc, EC, HPC, HPMC, NaCMC, and enzymatically hydrolyzed CMC showed no specific treatment-related adverse symptoms and unfavorable side effects at levels up to 10%. In the performed studies about chronic toxicity with MCC, MC, HPC, HPMC, ethyl MC, and NaCMC, there is no side effect reported up to 9000 mg/kg body weight per day. The carcinogenicity effects were not observed for MCC and other cellulose derivatives. The reproductive problems and growth side effects were not indicated with doses of cellulose higher than 1000 mg/kg. The daily exposure to a variety of cellulosic compounds such as MCC, NaCMC, cross-linked CMC, and enzymatically hydrolyzed CMC for the general population was up to 506 mg/kg body weight. It was reported that there is no requirement for a numerical ADI and there would be no safety concern in consumption and use levels for all considered types of cellulose. Finally, the panel reported the daily indicative total exposure of cellulose derivatives around 660–900 milligrams per kilogram of human body weight. The safety of cellulose and cellulose derivatives has been extensively studied in animals and humans. These studies show that cellulose and cellulose derivatives pass through the gastrointestinal tract unchanged and can be rapidly detected in the feces of experimental animals and humans upon consumption. JECFA stated that viscosity is not recognized as a factor related to the safety of these additives. Many safety research reviewed and analyzed the use of cellulose compounds. All of these research aid the statement that there is no safety impact arising from a variation in viscosity. In general, if it is not definitely claimed that cellulose is nontoxic, it can at least be said that celluloses are of very low toxicity at the ranges of consumption and intake imperative to obtain the preferred impact and do now not pose a hazard or risk to health. Cellulose and its derivatives both are known to be safe in terms of environmental impacts [64, 65].

6. The principles of food regulation in the use of cellulose derivatives

The Code of Federal Regulations (CFR) is an arrangement and codification of general, customary, and everlasting regulations published in the Federal Register by federal government agencies, supervisory departments, and businesses. In relation to the legal guidelines related to the consumption of special raw materials in the food industry, considerable codes have been provided that present appropriate information to industrial producers [66]. In the case of drugs for human use, such as ophthalmic demulcents, the concentrations percentage of each cellulose derivative (NaCMC, HEC, HPMC-P, and MC) has been established within 0.2 to 2.5% in accordance with the standard of 21CFR349.12 [67]. The use of ethyl cellulose in food and feed is stated in the legal standards of 21CFR172.868 and 21CFR573.420, respectively. Ethyl cellulose as food additive may be safely used in foods under the stated conditions: In clause “a”—The food additive is a cellulose ether containing ethoxy groups (OC2H5) linked by an ether bond and containing not more than 2.6 ethoxy groups per anhydro glucose unit on an anhydrous basis. In clause “b”—Ethyl cellulose is used or intended for use as a binder and filler in dry vitamin preparations, as part of protective coatings for vitamin and mineral tablets, and finally in the role of stabilizer in flavoring compounds. For the use of ethyl cellulose as animal feed, it must meet the previously stated conditions of clause “a” in the same way as in clause “b–”—its uses are presented as a binder or filler in dry vitamin preparations to be incorporated into animal feed [68, 69]. Usage rules for hydroxypropyl cellulose are provided in 21CFR172.870. This standard separates HPC with a high degree of substitution (which contains no more than 4.6 hydroxypropyl groups per anhydro glucose unit) and a low degree of substitution (which contains on average 0.1 to 0.4 hydroxypropyl groups per anhydro glucose unit). High substituted HPC may be used as an emulsifier, film former, protective colloid, stabilizer, suspending agent, and thickener according to good manufacturing practice (GMP). HPC with low substitution can be used as a binder and disintegrator in tablets or wafers containing dietary supplements according to GMP. FDA indicated that the proposed use of high-substituted HPC is safe with a minimum viscosity of 10 centipoises and for same using as a binder in dietary supplements similar to low-substituted HPC will not result in an increased intake or harm to human health under the established conditions of use and significantly it is not expected to have different biological properties [70]. Finally, for HPC based on federal regulation of 75FR17928, there is no significant effect on the environment and thus an environmental impact statement is not required [71]. The specific labeling requirements for the use of various hydrophilic gums such as NaCMC in specific drug products are noted in 21CFR201.319 [72].

The prescribed conditions for the safe use of methyl ethyl cellulose are provided in the standard of 21CFR172.872: In clause “a”—The general formula of cellulose ether is as [C₆H_(10-x-y) O₅(CH₃)_x(C₂H₅)_y]_n. In this chemical formula, x is the number of methyl groups and y is the number of ethyl groups. The average value of x is 0.3 and the average value of y is 0.7. In clause “b”—This additive composition must have the following conditions: The methoxy content shall be not less than 3.5% and not more than 6.5%, calculated as OCH₃, and the ethoxy content shall be not less than 14.5% and not more than 19%, calculated as OC₂H₅, both measured on the dry sample. The viscosity of an aqueous solution, 2.5 grams of the material in 100 milliliters of water, at 20°C, is 20 to 60 centipoises. The ash content on a dry basis has a maximum of 0.6%. In clause “c”—The food additive is used as an aerating, emulsifying, and foaming agent, in an amount not in excess of that reasonably required to produce its intended effect [73].

The specified conditions for safely using “Hydroxyethyl cellulose film-water insoluble” for packaging food are stated in accordance with the regulation code of 21CFR177.1400. In clause “a”—Water-insoluble hydroxyethyl cellulose film consists of a base sheet manufactured by the ethoxylation of cellulose under controlled conditions, to which may be added certain optional substances of a grade of purity suitable for use in food packaging as constituents of the base sheet or as coatings applied to impart desired technological properties. In clause “b”—The optional substances that are identified as suitable in terms of food safety can be used in the base sheet of film production and coating as components of water-insoluble hydroxyethyl cellulose film. In clause “c”—Any substance employed in the production of the water-insoluble hydroxyethyl cellulose film described in this section [74].

7. Innovations of the cellulosic application in the food industry

Studies discuss the interrelation between the chemical structure of cellulose and its source and its various physicochemical characteristics. Although cellulose extracted from plants has been most investigated, cellulose purified from microorganisms and animals with special structural features has received increasing attention [75].

Heretofore, enzymatic hydrolysis procedure, TEMPO oxidation reaction (2,2,6,6-Tetramethylpiperidine-1-oxyl), and carboxymethylation process have been widely used to assist in defibrillating cellulose during processing into nanocellulose, which not only helps decrease consumption of energy but also provides additional functional groups for the final products [76].

Acidic hydrolysis, which includes inorganic and organic acids, can remove and eliminate amorphous regions, resulting in cellulose nanocrystal (CNC), although highly corrosive conditions and low CNC yield are persistent issues. Through mechanical treatments such as refining, homogenization, microfluidization, sonication, ball milling, and the aqueous counter collision (ACC) technique, cellulose nanofibrils (CNF) can be produced, however, the very high input energy prohibits the commercialization of these methods [77, 78].

Bacterial cellulose (BC), a special nanocellulose derived from bacteria, has currently attracted numerous research interests. Its higher aspect ratio and larger diameter make it a promising material for food packaging applications. In order to facilitate the application of nanocellulose in food packaging, it is always processed using different manufacturing technologies, including solution casting, layer-by-layer (LBL) assembly, extrusion, coating, gel-forming, spray drying, electrostatic spinning, adsorption, with the aim of producing different forms of materials such as film, gel, coating membrane, and emulsions [79, 80].

Due to their non-toxicity, proper biodegradability and biocompatibility, high aspect ratio, low coefficient of thermal expansion, extremely good mechanical strength, and special optical properties, nanocellulose-based food packaging materials are broadly used for fruit packaging, meat products, fast foods, dairy products, and beverages. Since nanocellulose and functional fillers in cellulose-based nanocomposites provide excellent barrier and mechanical properties, antibacterial activity and stimuli-responsive performance, therefore noticeably improve food quality stability and shelf life [81, 82].

Nanocellulose and its derived nanocomposite have turned out to be a hotspot of research in food packaging due to its great properties including excessive strength, large specific surface area, excellent barrier properties and proper biocompatibility, safety, non-toxicity, and degradability. In food packaging materials, nanocellulose-based nanocomposites can be used as fresh and antibacterial packaging materials, smart packaging materials, and high-barrier packaging materials, which indicates the excessive utility potential of nanocellulose-based composites. Therefore, nanocellulose-based composites, as a type of renewable and environmentally friendly packaging material, enhance the protection and quality of food and are one of the important paths to understand the improvement of “eco-friendly industry” in the food industry [83].

Recently, biopolymer-based hydrogels have been attracting growing attention due to the fact of their promising applications in drug release, biosensors, superabsorbent materials, tissue engineering, and many others [84]. Hydrogels are water-insoluble polymers that have the ability to hold a large amount of water in their network [85, 86]. The considerable hydrophilic groups with hydroxyl, carboxyl, and aldehyde form in the structure of native cellulose or cellulose derivatives make them suitable to prepare hydrogels without difficulty with fascinating constructions and properties for biomedical and food packaging and applications [87, 88].

Regarding the progress of cellulose and its derivatives in the food industry, especially packaging, the following should be mentioned [89, 90]:

• Expanding cellulose resources to different biomass besides traditional raw materials, such as tunicate and BC, for higher quality and greater satisfactory nanocellulose to develop and improve many advanced applications. So far, commercially available nanocellulose is mainly produced from wood and other plant sources. Although numerous research works focused on the preparation of nanocellulose from tunicate and BC, confirmed their higher overall performance than wood-based nanocellulose, further research and evaluation on the preparation-properties-performance correlation of this particular nanocellulose is important and necessary.

• Developing an efficient, cost-effective, eco-friendly, or environmentally-friendly approach for extraction of nanocellulose. Although several new extraction methods have been developed, the most broadly used ones are sulfuric acid hydrolysis and mechanical refining. However, the harsh and extreme acid hydrolysis, high water usage, large amount of polluted wastewater, high demand for energy, and low efficiency have largely prohibited the industrially feasible production of nanocellulose. Therefore, more work efforts should be made to develop novel methods for the preparation of nanocellulose, such as those based on organic acids, which have already been shown to be a green approach (not environmentally harmful strategy) for the preparation of functionalized derivatives as nanocellulose.

• Elaborating new procedures to fabricate cellulosic nanocomposites. In the laboratory, the solution casting technique is still broadly used for research purposes, which is not suitable for industrial-scale production. In the pilot scale, extrusion has been used, although it is not an excellent approach due to the fact the nanocellulose is evermore dispersed in water, which negatively impacts the performance of the extrusion. Accordingly, it is essential to develop a scalable method for the preparation of nanocellulose-based composites for food packaging materials.

• Improving the overall performance of nanocellulose-based composites as packaging materials. The perfect food packaging materials require anti-UV (UV-proof, UV-block, or UV-protect), vapor and gas barrier properties, excellent mechanical strength, and appropriate hydrophobicity. Particularly for the last one, new techniques have to be developed to change the hygroscopic nature of nanocellulose and increase the wet strength or wet tensile value, hence making its functions and applications in daily life more practical. For example, the coating with natural wax or esterification reaction as a pretreatment seems appropriate to achieve this goal.

• Development of smart packaging materials based on nanocellulose. At present, achieving the responsive properties of cellulose nanocomposites is usually performed with the aid of combining different organic and inorganic fillers. However, the migration and release of functional fillers and their potential health risks have not been comprehensively investigated. Future researchers in systematic studies should not only pay attention to the safety issue of nanocellulose itself but also focus on the functionality of selected fillers.

• Designing packaging materials based on nanocellulose for food. Although many studies generally focused on the preparation and properties of packaging materials, little attention is paid to the interaction between materials and food and even neglected the various aspects that affect the application of materials. For example, the impact of environmental prerequisites and conditions on the quality change of both food products and packaging materials has to be investigated to show the feasibility and suitability of packaging materials for a particular food.

8. Conclusions and outlook

In summary, cellulose has been used in various food applications fields for decades, and its impact on the food industries has become increasingly important. The porous network, biocompatibility, high aspect ratio, and abundance of hydroxyl groups are advantages of cellulose for use as a functional food component. Cellulose creates different colloidal conditions such as surface charge, dimensions, crystal structure, solubility, and wettability. The colloidal properties of cellulosic polymers can be controlled by changing the manufacturing parameters or replacing surface hydroxyl groups with the ester groups. In addition, health benefits and functional impacts such as hypoglycemic and hypolipidemic activity and intestinal bioavailability due to cellulose can be affected by colloidal states. Based on the review of major studies related to cellulose in the food industry, it is possible to refer to the following cases for valuable consideration as cellulose-related challenges in the future: (1) the design of functional foods is possible by changing the colloidal states of cellulose, (2) new food properties can be obtained by different colloidal states in food matrix (3) the interaction between cellulose and gut microbiota needs to be further studied and the potential mechanism needs further investigation, (4) the application of nanocellulose in food matrix is ​​increasingly discovered and the potential long-term risk of nanocellulose requires regulatory and safety testing, and (5) the energy consumption and potential environmental pollution should be considered, and new green technologies to extract or prepare different types of cellulose are proposed.

Conflict of interest

The author declares no conflict of interest.

Notes

This chapter was written in such a way that those whose specialty is not food science and technology can understand the uses and effects of cellulose and its derivatives in the food industry.