Disposable Food Packaging and Serving Materials—Trends and Biodegradability

Polysaccharides

Cellulose

Cellulose is the most abundant polymer in the natural environment, and can be obtained from rice, wood, cotton, plant biomass, algae, and specific strains of bacteria [ 71 ]. It is a linear homopolymer, comprised of glucose units connected by β-(1→4) glycosidic bond. Cellulose extraction is considered to be a difficult process with expensive pre-treatment. Enzymatic hydrolysis with exoglucanases, endoglucanases, and β-glucosidase is used to isolate cellulose from biomass. After purification, cellulose can be chemically modified to cellulose derivatives with improved properties [ 72 73 ]. In general, cellulose is water insoluble because of the presence of inter- and intramolecular hydrogen bonding between OH groups, but properties of cellulose depend on the degree of polymerization as well as the source of this biopolymer [ 74 ]. Cellulose and its derivatives possess good film-forming properties, which are generally biodegradable, non-toxic, and transparent, with excellent mechanical, thermal, and barrier properties [ 75 76 ]. Cellulose, as well as starch, belongs to hydrophilic polymers, being water wettable or swellable and consequently biodegradable; thus, their application in terms of technology is limited. On the other hand, the poor solubility of cellulose is one of the challenges in the commercialization of cellulose in the food industry. Therefore, modifications of these material are still being sought after. Transparent films by industrial cellulose pulp solubilization in tetramethylguanidine-based ionic liquids were investigated by Ribeiro et al. [ 77 ]. Carboxymethyl cellulose, an ionic, water-soluble derivative of cellulose, is one of the most promising cellulose derivatives, characterized by good surface properties, mechanical strength, tunable hydrophilicity, viscous properties, availability, and low-cost synthesis process [ 78 ]. It is used in various fields such as food, paper, textile, and pharmaceutical industries. However, cellulose acetate, which is used in films and filters, is biodegraded in the environment, but this process is very long [ 79 ]. Conjunction of bacterial cellulose (with incorporated yeasts) with carboxymethyl cellulose (CMC) and glycerol to extend the shelf life of packaged food materials were also studied [ 80 ]. What is more, the hybrid fiber strategy of long bamboo fibers with short sugarcane fibers was applied in the production of tableware with high tensile strength, superior oil stability, excellent hydrophobicity, and low heavy metal content [ 81 ]. Additionally, cellulose with starch can be used to make compostable cups and trays through the hot-pressing method [ 82 ].

Achromobacter, Alcaligenes, Aerobacter, Agrobacterium, Azotobacter, Komagataeibacter

(formerly

Gluconacetobacter

),

Pseudomonas, Rhizobium, Sarcina, Dickeya,

and

Rhodobacter

genera [

Komagataeibacter

are most commonly used in research and the commercial production of bacterial cellulose [

Komagataeibacter xylinus

is considered a microbial model in BC production [

Bacterial cellulose (BC) is an extracellular polymer of bacteria belonging to(formerly),andgenera [ 83 84 ]. However, the strains belonging to the genusare most commonly used in research and the commercial production of bacterial cellulose [ 85 86 ];is considered a microbial model in BC production [ 87 88 ]. The primary structure of the bacterial cellulose consists of long-chain β-1,4-linked glucose (glucan chains), reaching a degree of polymerization up to 20,000 [ 89 ]. Physicochemical properties of BC depend on the specific characteristics of the architecture, its nanostructure, and macrostructure. They therefore depend on both intracellular biosynthesis and extracellular self-assembling [ 87 ]. BC is identical in chemical composition to plant cellulose, but characterized by a higher crystallinity, degree of polymerization, purity, water-holding capacity, but also high mechanical strength, elasticity, and shapeability, and gas and liquid permeability [ 83 90 ]. It is worth noting that BC was approved by the FDA (the United States Food and Drug Administration) as Generally Recognized As Safe (GRAS) and can be used as a safe food product or food component [ 91 ]. The interest in bacterial cellulose as a packaging material is constantly growing, and several studies have demonstrated that BC shows many advantages in its application in food packaging. The latest review article written by Ludwicka and others [ 92 ] describes the application of bacterial cellulose in active and intelligent food packaging. Antibacterial activity and higher elastic modulus were obtained by BC impregnation in chitosan solution and described in the study of Kingkaew et al. [ 93 ]. The improvement of the tensile strength and barrier performance can be achieved by crosslinking with proteins, which are more easily involved in crosslinking reactions than polysaccharides. The effect of gelatin content on the tensile properties of BC/gelatin composition was studied by Chang et al. [ 94 ]. The authors found that a higher gelatin concentration enhances the tensile properties of the composite. On the other hand, the properties of bacterial cellulose can be modified by the addition of other biopolymers (pectin, xylan, gelatin, or carboxymethylcellulose) to the culture medium, which can stimulate the synthesis of BC and enhance its mechanical properties [ 95 96 ]. Another approach in the production of composites from bacterial cellulose is the isolation of BC crystalline regions, leading to bacterial cellulose nanocrystals (BCNC) [ 97 ]. BCNC with nisin [ 98 ] or cinnamon essential oil [ 99 ] was successfully used as an antimicrobial composition. What is more, antimicrobial activity and enhanced barrier and tensile properties of films with BCNC were achieved by the incorporation of BCNC into a chitosan dispersion with silver nanoparticles [ 100 ]. In general, this strategy can be used for cellulose-based formulations for varied food applications [ 101 ]. On the other hand, there are many challenges for the commercial production of BC-based materials for food application [ 92 ].

Starch

Starch is a polymeric carbohydrate consisting of two types of molecules: the linear and helical amylose branched amylopectin. Amylose, which is responsible for film-forming properties, is a polymer of α-1,4 anhydroglucose, while amylopectin is a highly branched polymer of short α-1,4 chains linked by α-1,6 glycosidic branching points occurring every 25–30 glucose units [ 66 ]. Depending on the plant, starch contains 20–25% of amylose and 75–80% of amylopectin. A higher amylose content results in a greater surface roughness of obtained starch-based materials [ 102 ]. Various starch-based products have been developed and commercialized, and conventional processing techniques (extrusion, injection, compression molding, casting, and foaming) as well as novel techniques (reactive extrusion) are used for processing starch-based polymeric materials [ 103 ]. Starch is considered as an alternative to plastics derived from petroleum derivatives in the production of packaging films [ 104 ]. However, due to their high moisture absorption and poor mechanical properties, starch materials are unstable during processing and storage, and modified starch materials from different plant origins are the subject of numerous studies. Due to the higher lipid content, glutinous rice starch and normal rice starch-based materials are characterized by higher contact angle values than cassava starch [ 105 ], while for films containing blackberry pulp, the increased contact angle and lowered surface roughness were observed. Simultaneously, a lower in vitro digestibility rate and higher resistant starch content were noticed. What is more, for films containing blackberry pulp, higher anti-inflammatory activity and higher cell viability were confirmed [ 106 ]. Combinations of plasticized starch with protein in order to improve processability and storage properties were examined in the study of Huntrakul et al. [ 107 ]. The authors found that pea protein isolate stabilized films during blown extrusion but decreased their flexibility. An increase in the concentration of pea protein decreased the solubility and improved the crystallinity, surface hydrophobicity, and barrier properties against water vapor and oxygen [ 107 ]. Films with starch and yerba mate extract were found to be more hydrophobic and tensile resistant [ 108 ]. Yerba mate extract and poly(vinyl alcohol) mats were incorporated within potato starch in the study of López-Córdoba [ 109 ]. The authors concluded that PVA mat and the yerba extract caused a synergistic effect that increased the elastic module of the biocomposites, while the tensile strength and strain at break were maintained. The results of the study conducted by Righetti et al. (2019) show that starch in the biocomposites of poly(lactic acid) (PLA) with potato acts as filler for PLA and the additional application of biobased and petroleum-based waxes improves the mechanical properties of the composites [ 110 ]. In order to improve the mechanical and water-resistance properties of starch bioplastic, epoxidized palm oil or soybean oil can also be used [ 111 ]. Improved mechanical properties of obtained polymer were also noted when dolomite filler was introduced into thermoplastic starch, and sonicated dolomite-thermoplastic starch shows better mechanical properties than pristine dolomite [ 112 ]. Ren et al. [ 113 ] found that sorbitol has a negative effect on the dispersion of the halloysite nanoclay in the starch matrix, but the addition of halloysite improves the mechanical properties for glycerol plasticized system, compared to composites based on sorbitol and glycerol/sorbitol.

Pectins

Pectin forms the most complex class of polysaccharides, composed of heterogeneous groups of glycanogalacturonans and acidic structural polysaccharides. Generally, pectin is a structural acidic heteropolysaccharide of galacturonic acid monomers (70%), a sugar acid derived from galactose [ 64 ]. D-galacturonic acid residues are linked at α-1,4 positions, and the acid monomers can be acetylated or methyl esterified. Pectins can be divided into three groups: (1) Homogalacturonans (HGs), Arabinogalactans (AGs), and Rhamnogalacturonans (RGs). Homogalacturonans, the most abundant pectins (up to about 65% of pectins), are homopolymers of α-(1→4)-D-galactopyruronic acid (Galp) methyl esterified units [ 114 ]. Arabinogalactans can be distinguished in two groups: AG I (arabino-4-galactans, constituted by a β-(1→4)-Galp backbone with side chains of arabinans) and AG II (arabino-3,6-galactans, constituted by a linear backbone of 1→3 and 1→6-linked galactopyruronic acid units, branched with arabinan chains). Rhamnogalacturonans, known as “the real pectins” are heteropolymers of galactopyruronic acid and rhamnopyranose branched with arabinogalactans chains. Rhamnogalacturonans I have linear a backbone of alternating α-1,4-linked galactopyruronic acid units and α-1,2-rhamnopyranose units, while rhamnogalacturonans II are constituted by a homogalacturonan backbone of about 9–10 methyl esterified galactopyruronic acid monomers [ 115 ]. Homogalacturonans are also known as the “smooth region” of pectins, while the rhamnogalacturonans and arabinogalactans are the “hairy regions” of pectins. Pectins are present in all the higher plants and occur in the intercellular or middle lamellar region [ 116 ]. Citrus peel, apple pomace, and sugar beet pulp are widely distributed sources of pectin. In the food industry, they are used as stabilizers, thickening and gelling agents, crystallization inhibitors, and encapsulating agents. Pectin gel is formed when homogalacturonans are cross-linked to form a three-dimensional crystalline network in which water is trapped [ 117 ]. Coatings from pectin and its derivatives are considered to be used in food-related applications due to their barrier to oxygen, aroma preservation, barrier to oil and good mechanical properties; however, due to their hydrophilic nature, they are not effective against moisture transfer [ 64 ]. They are used as coating in fresh and minimally processed fruits and vegetables [ 118 ]. It was described that pectin-based coating can enhance the shelf life of lime fruits [ 118 ], which can be used for preservation for a short time application [ 119 ]. Priyadarshi (2021) found that a 50:50 ratio of pullulan and pectin exhibits the highest thermal stability and surface hydrophobicity, reduced water and oil absorption values, as well as increased strength, at the same time maintaining flexibility and stiffness [ 120 ].

Chitosan

Nephrops

spp. and

Homarus

spp. (60–75%). Methods of chitosan preparation include three stages: (1) removing calcium carbonate from the shell (demineralization), (2) removing protein and organic compounds other than chitin (deproteinization), and (3) converting chitin to chitosan (deacetylation). This polymer is characterized by many functional properties; on the other hand, a major limiting factor is its poor solubility, which would enable wider industrial application. Chitosan can be modified by physical or chemical processes such as grafting, cross-linking, and substituent incorporation [126,

N-acetylglucosamine (chitin), a precursor of chitosan, is considered to be the second most abundant biopolymer; however, unlike cellulose, it is mainly found in exoskeletons of crabs, lobsters, crayfish, shrimp, and other crustaceans, as well as in the cell walls of fungi. The form that shows increased solubility in acidic environments is chitosan—partially deacetylated form of chitin. Chitosan consists of β-(1→4)-2-amino-2-deoxy-D-glucose monomers [ 121 ] and can be possessed from different sources: crustacean shell waste (20–30%),spp. andspp. (60–75%). Methods of chitosan preparation include three stages: (1) removing calcium carbonate from the shell (demineralization), (2) removing protein and organic compounds other than chitin (deproteinization), and (3) converting chitin to chitosan (deacetylation). This polymer is characterized by many functional properties; on the other hand, a major limiting factor is its poor solubility, which would enable wider industrial application. Chitosan can be modified by physical or chemical processes such as grafting, cross-linking, and substituent incorporation [ 122 ]. Modified forms of chitosan, such as phenolic acid-grafted-chitosan, exhibit enhanced antioxidant, antimicrobial, antitumor, anti-allergic, anti-inflammatory, and anti-diabetic activities [ 123 ]. PLA/chitosan composite film is an interesting alternative to plastics [ 124 ]. Chitosan and chitosan derivatives show antimicrobial activity with high potential within a number of industries [ 124 ]. Chitosan incorporated with extracts of propolis, mango leaf, thermoplastic maize starch, silver nanoparticles, and tea polyphenols show antimicrobial activity against Gram-positive and Gram-negative bacteria as well as against molds and yeasts [ 125 127 ]. Interestingly, the incorporation of tea polyphenols together with silver nanoparticles cause an improvement in the mechanical properties of the obtained composite, as well as in a higher antioxidant resulted [ 128 ]. More importantly, it is considered as sustainable, environment friendly, alternative to synthetic packaging materials, with gas and aroma barrier properties, as well as increased shelf life of the products.

Sulfated Polysaccharides

Sulfated polysaccharides (SPs) are present in the cell wall of marine algae or seaweeds constituted mostly of cellulose and hemicellulose with high carbohydrate content but low calories and fat content. Due to the cross-linkage of sulfate group ions with complex molecules of polysaccharides, the molecules of SPs are negatively charged [ 129 ]. Fucoidans (from brown algae), carrageenans (from red seaweeds), ulvans (from green seaweeds) are main SPs.

Fucoidans

Stoechospermum marginatum, Sargassum (S. ilicifolium, S. marginatum, S. marginatum, S. myriocystum, S. wightii

, which yields 71.5 mg of fucoidan from 1 g of seaweed dry weight),

Dictyota dichotoma, Turbinaria (T. conoides, T. decurrens, T. ornate

). The main sugar found in the polymer is fucose, while other sugars are galactose, xylose, arabinose, and rhamnose. Fucoidan is composed of two chain structures: one with (1→3)-α-L-fucopyranose as the chain and the second with α-L-fucopyranose linked by (1→3) and (1→4) bonds. Sulphate groups at the C-2 or C-4 of both skeletons can occur [

Fucus vesiculosus

is composed of fucose and sulfate, whereas

Padina pavonia

contain fucoidan constituted with fucose, sulfate, xylose, mannose, glucose, and galactose [

Fucoidans are a long-chain SP found in various species of brown algae:, which yields 71.5 mg of fucoidan from 1 g of seaweed dry weight),). The main sugar found in the polymer is fucose, while other sugars are galactose, xylose, arabinose, and rhamnose. Fucoidan is composed of two chain structures: one with (1→3)-α-L-fucopyranose as the chain and the second with α-L-fucopyranose linked by (1→3) and (1→4) bonds. Sulphate groups at the C-2 or C-4 of both skeletons can occur [ 130 ]. In general, the structure of fucoidans is dependent inter alia on seaweed species; for example, fucoidan fromis composed of fucose and sulfate, whereascontain fucoidan constituted with fucose, sulfate, xylose, mannose, glucose, and galactose [ 131 ]. Biological activities of the polymer include antitumor, antioxidant, anticoagulant, antithrombotic, immunoregulatory, antiviral, and anti-inflammatory effects [ 130 ], while functional properties include gelling, chemical reactivity, improving quality, and controlling moisture [ 129 132 ].

Carrageenans

Rhodophyceae

family are most often used for this purpose [

Kappaphycus alvarezii

. Carrageenan contains 15–40% of ester-sulfate. Units of 3,6-anhydrous-galactose (3,6-AG) and D-galactose are linked by α-1,3 and β-1,4-glycosidic bond forming carrageenan [

Carrageenans are natural polysaccharides obtained by extraction from seaweed containing large amounts of sulfur, which is closed in the form of sulphate groups in the structure of the plant. The red algae of thefamily are most often used for this purpose [ 133 ]. A high level of carrageenan is obtained from. Carrageenan contains 15–40% of ester-sulfate. Units of 3,6-anhydrous-galactose (3,6-AG) and D-galactose are linked by α-1,3 and β-1,4-glycosidic bond forming carrageenan [ 134 ]. From a chemical point of view, there are many isomers, but three main forms have been used in particular: kappa, lambda, and iota [ 135 ]. Carrageenan acids are unstable in their pure form; therefore, only the salts of these acids have found industrial application. The most commonly used salts are calcium, sodium, and potassium. Not all isomers are able to react with specific ions, e.g., the lambda isomers do not form gels by reaction with ions. It is believed that mixtures of individual isomers are the most promising. For example, the combination of two kappa isomers with one iota resulted in a gel of high elasticity. The attractiveness of carrageenan is based on its gelling properties, but it has no nutritional benefits. The gel strength, solubility, and temperature stability are affected by the level of ester sulfate, and increased ester sulfate level lowers the mechanical property of SP. They are used in the production of edible packaging, film coatings, and blends, and the addition of starch improves the mechanical strength, gelling strength, and barrier properties [ 129 ]. Carrageenans show great potential as an ingredient in gradual-release drugs. Hydrogels obtained as a combination of carrageenans and alginates can be used in targeted drug delivery [ 136 ]. What is more, they can be applied in milk products and dietetic formulations, but >2% of carrageenan in food products results in adverse health effects and degraded carrageenan is prohibited as it causes cancer [ 137 ].

Ulvans

Ulva

(

U. conglobate

and

U. prolifera

) [

U. flexuosa

to 40% in

U. armoricana

[

Ulvans are a polyanionic heteropolysaccharide constituted by β-(1–4)-xyloglucan, glucuronan, and cellulose in a linear arrangement, occurring in green algaeand) [ 138 ]. The ulvan content varies from 2.7% into 40% in 139 ]. Ulvan can be applied in food, pharmaceutical, and biomedical products [ 140 ]. The biological activity of ulvan as antioxidant and antimicrobial activity against human, plant, and animal pathogens were demonstrated in the study of Amin [ 141 ]. Ulvan-based gels, fibers, films, nanomaterials, and composites arouse more and more interest [ 142 ]. Morelli et al. (2019) obtained ulvan-based emulsions with promising properties as a stabilizing agent for food and cosmetic application [ 143 ]. Shalaby and Amin (2019) found that a 1–2% addition of ulvan polysaccharides stimulated the growth and activity of probiotic bacteria [ 144 ]. The potential of ulvan as a carrier of antimicrobial agent (nisin) against Gram-positive bacteria was evaluated by Gruskiene [ 145 ]. What is more, Guidara and others (2019) found that ulvan can be used as a film layer forming system, showing solubility, barrier, optical, and good mechanical properties, which are important for food and packaging products [ 146 ]. Ulvan-based film with glycerol was also obtained by Ganesan et al. (2018) and improved physicochemical and mechanical properties with decreasing water vapor permeability were noted [ 147 ]. Active films based on ulvan with glycerol or sorbitol as a plasticizer were studied by Guidara and co-workers (2019). The authors found that enzymatic–chemical extraction results in more beneficial impacts on the optical, thermal, structural properties, and glycerol results in the compact structure of films, lower temperature of transition, and greater antioxidant property of the obtained films [ 146 ]. It is believed that ulvan functions have broad potential, but further research into this polymer is required [ 148 ].

Alginates

Ascophyllum nodosum, Laminaria hyperborean

, and

Macrocystis pyrifera

. Alginic acids, as these compounds are referred to, are chemically converted into calcium or sodium salts, since only in this form do they exhibit favorable properties. Salts made with monovalent cations, such as sodium, are liquids that exhibit high viscosity [2+ ions, which affect higher gel rigidity. On the other hand, if they are present in smaller amounts, the gel will be softer and more flexible. Due to its antimicrobial, antioxidant, and immunostimulatory abilities, alginates are widely used in the food and beverage industry as well as in the biomedical industries [

In terms of chemical structure, alginates are mannuronic and guluronic acid polymers can be obtained from specific species of algae, mainly, and. Alginic acids, as these compounds are referred to, are chemically converted into calcium or sodium salts, since only in this form do they exhibit favorable properties. Salts made with monovalent cations, such as sodium, are liquids that exhibit high viscosity [ 149 ], while bivalent cations, such as calcium, result in gel structure [ 150 ]. The structure and properties of the resulting product are also influenced by ratio of the number of individual acid units, which defines its further properties, e.g., flexibility. The higher content of guluronic acid in the structure will ensure a higher concentration of Caions, which affect higher gel rigidity. On the other hand, if they are present in smaller amounts, the gel will be softer and more flexible. Due to its antimicrobial, antioxidant, and immunostimulatory abilities, alginates are widely used in the food and beverage industry as well as in the biomedical industries [ 151 152 ].

Curdlan

Agrobacterium

(former taxonomy:

Alcaligenes faecalis

var.

myxogenes

) [

Curdlan is a polysaccharide formed from glucose monomers linked by beta bonds between the first and third carbon of successive monomers. It belongs to the compounds that are soluble in alkaline solutions with a pH above 12; it is insoluble in water and other organic solvents such as methanol and ethanol. Curdlan is produced by bacteria belonging to the genus(former taxonomy:var.) [ 153 154 ]. It is believed that the synthesis of the compound depends on the environmental stressors. Bacteria are able to synthesize it from various carbon sources, including glucose, maltose, fructose, and sucrose. According to Wu et al. (2018), 2% glucose, maltose, and sucrose as the carbon source showed better curdlan production than 2% galactose or fructose [ 155 ]. Similar results were obtained by Lee’s team, where the highest amount of curdlan was obtained in the medium with 10% maltose [ 156 ]. An interesting ability of a polysaccharide is to change its elasticity as a gel under the influence of temperature. As a result of heating, it gains considerable strength. The fact that it has no taste, smell, or color speaks for its use in food. It also does not require additional chemical transformations, such as alginates [ 154 ].

Agar, fucoidan, carrageenan, ulvan, and others can be used for both edible as well as non-edible film or wraps, bags, and covers with enhanced barrier properties. What is more, these natural polymers can be blended with other polymers (polylactic acid, polyolefins, polyhydroxy butyrate) as well as with nanoparticles and nanocrystals [ 157 ]. Due to their biodegradability and low environmental impact, they are an interesting alternative to synthetic polymers used in the production of single-use plastic materials.