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Food Biopackaging Based on Chitosan

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DOI: 10.1007/978-3-319-48281-1_68-1

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Food Biopackaging Based on Chitosan

María R. Ansorena, Norma E. Marcovich, and Mariana Pereda

AbstractChitin, available from waste products of the shellfish industry (shells of the crab,shrimp, etc.), is one of the most abundant natural polymers in the world, and it isused for the production of chitosan by deacetylation. Chitosan, a cationic poly-saccharide, natural, nontoxic, biodegradable, biocompatible, bioadhesive, andavailable commercially, has been employed in a variety of applications rangingfrom membrane separation, tissue engineering, wound healing, and dressing tohydro gels formation and biodegradable films for food packaging. It is also awell-known biopolymer for its broad antimicrobial activity against bacteria andfungi. Chitosan possesses high positive charge on NH3

+ groups when dissolved inaqueous acidic solution, and therefore it is able to adhere to or aggregate withnegatively charged molecules forming three-dimensional networks. Moreover,chitosan acts as stabilizer of hydrocolloids, lipids, and mixtures, promotingemulsion formation and interfacial stabilization, so it is frequently used asemulsifier in film-forming solutions. Due to all these advantageous characteristicsadded to its excellent film-forming properties and low cost, chitosan has gener-ated enormous interests, and thus the quantity and quality of research using thispolymer in the area of packaging have increased steadily in the last few years.Chitosan-based food packaging can be classified as “active” because they includesystems capable of inhibiting microorganism action and avoiding loss of foodquality. In particular, the antimicrobial packaging is one of the most innovative

M.R. Ansorena (*)Food Engineering Group, Chemical Engineering Department, Engineering Faculty, NationalUniversity of Mar del Plata, Mar del Plata, Argentinae-mail: ransorena@fi.mdp.edu.ar

N.E. Marcovich • M. PeredaEcomaterials, Instituto de Investigaciones en Ciencia y Tecnología de Materiales(INTEMA-CONICET), Mar del Plata, Argentinae-mail: marcovic@fi.mdp.edu.ar; mpereda@fi.mdp.edu.ar

# Springer International Publishing AG 2018L.M.T. Martínez et al. (eds.), Handbook of Ecomaterials,https://doi.org/10.1007/978-3-319-48281-1_68-1

1

and promising active packaging types developed over the last decade. Accord-ingly, this chapter discusses in detail the latest advances on films for foodpackaging based on chitosan.

ContentsFood Biopackaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Chitosan-Based Films: Final Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Strategies to Improve Chitosan Film Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Cross-Linked Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Chitosan Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Blends or Multilayer Films Based on Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Active Biopackaging Based on Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Combination of Several Strategies Previously Mentioned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Food Biopackaging

Most of the packaging available in the market is developed from synthetic traditionalpolymers such as polyethylene, polypropylene, or polystyrene causing health haz-ards due to migration of toxic additives into the consumables. Consumer health andenvironmental concerns produced by the solid waste after use of nondegradablepetrochemical-based packaging materials have attracted increasing interest in thefood packaging materials based on biodegradable and natural polymers. Foodbiopackaging can be one of the most promising solutions against the environmentpollution and toxicity caused by nonbiodegradable plastics. What is more, over thelast 15 years, packaging derived from renewable resources is becoming a drivingleader in terms of innovation. The worldwide production of biopolymers was of 3.5billion tons in 2011, and it is expected to reach 12 billion tons in 2020 [1]. Most ofthe biodegradable polymers are derived from replenishable agricultural feed stocks,animal sources, marine food processing industry wastes, or microbial sources [2]such as fruit and vegetables pulp, tone powder, algae, shellfish powder, etc. Poly-mers extracted from such materials begin to be used as films, thermoforming slabs,or bottle trays for packaging applications [3].

Among them, proteins and polysaccharides are popular candidates for the fabri-cation of coating materials to protect the quality and safety of fruits, vegetables, fish,and meats because they are nontoxic, biocompatible, biodegradable, and renewable[4, 5]. The carbohydrates have several advantages such as biodegradability, non-toxicity, relatively good oxygen barriers, and abundance in nature. Polysaccharidesobtained from plant, algae, animal, and microbial origin (e.g., starch, alginate,chitosan, gellan gum, pectin) have been widely used for the development of edibleand/or biodegradable films [6, 7].

2 M.R. Ansorena et al.

Chitosan

Among the various carbohydrates which can be used for food biopackaging,chitosan (CH), a heteropolysaccharide derived from chitin by N-deacetylation,comes out of key interest for the development of films and in particular activepackaging for foods or pharmaceuticals, due to its intrinsic antimicrobial, antifungal[8], and antioxidant properties, good biodegradability and biocompatibility, goodoxygen and carbon dioxide barrier, and excellent film-forming properties [8–10].

Chitosan is a linear polysaccharide of randomly distributed β-(1–4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit)(Fig. 1) [11]. This polymer, available mainly from shellfish processing waste,represents the second most abundant natural biopolymer, after cellulose [12].

Chitosan is insoluble in water and in common organic solvents [13]; it shows bestsolubility in a 1% (v/v) acetic acid solution (pH = 4.4) but remains soluble at pHlower than 6.4; although at concentrations >2% wt./wt., the resulting solutionbecomes very viscous [14]. Chitosan is, without doubt, one of the main biopolymersthat constitute the new generation of active food packaging performing interestingfunctions in the preservation of foods [11].

Currently, most of the commercial chitosan is derived from crustaceans, such aslobster, shrimps and crabs, fungi, and insects [15]. However, mushroom cellularwalls have high chitin content, which might be transformed into chitosan through adeacetylation reaction. For example, Bilbao-Sainz et al. [16] extracted chitosan fromthe stalk bases of brown mushrooms and compared physicochemical properties of

Fig. 1 Structure of chitin andchitosan [11]

Food Biopackaging Based on Chitosan 3

fungal chitosan with high-molecular-weight (HW) and low-molecular-weight(LW) chitosan from animal origin. It was demonstrated that fungal chitosan is agood film-forming material that possesses film properties similar to those of chitosanfilms from animal origin [16].

Chitosan-Based Films: Final Properties

The casting is the method mostly used to obtain films based on chitosan. It consistsin the pouring of a slightly acidified water solution of chitosan on a flat surface,allowing the solvent to evaporate under controlled conditions (temperature andrelative humidity). Chitosan offers immense advantages as an edible packagingmaterial owing to its good film-forming properties [8–10]. However, unlike conven-tional thermoplastic polymers, chitosan cannot be extruded or molded, and the filmscannot be heat-sealed. This behavior limits the production of chitosan films at acommercial level and narrows their applications [17]. Nevertheless, chitosan can beblended with thermoplastic polymers like poly(butylene succinate), poly(butyleneterephthalate adipate), and poly(butylene succinate adipate) [13], which improve itsthermal properties allowing their processing by extrusion.

Physical and functional properties of chitosan films and coatings rely on numer-ous factors such as molecular weight and degree of deacetylation (DD), type andconcentration of acid solutions and plasticizers, and factors (e.g., pH, temperature)related to film preparation. For instance, the acid used for film preparation signifi-cantly affects the film mechanical properties. Acetic and formic acid-based filmshave shown the highest tensile strengths followed by the films prepared with lactic,propionic, and citric acids [18], confirming that increasing molecular weight ofchitosan improved the films strength, but did not significantly affect their watervapor permeability (WVP). Nunthanid et al. [19] also characterized physicochemicalfilms prepared from chitosan with different molecular weights and DDs and reportedthat an increase in molecular weight of chitosan increased the tensile strength and theelongation as well as the moisture absorption of the films due to chain entanglementnetwork forming in high-molecular-weight chitosan [11]. Additionally, they foundthat films prepared from 100% DD chitosan had a higher mechanical strength thanthose from 80 to 85% DD. The authors explained that the higher mechanical strengthof chitosan with higher degree of deacetylation arises from the denser packing of thechitosan polymer chains substituted with small amino groups, leading to higherinterchain interactions. Moreover, an increase in the DD of chitosan decreases themoisture absorption but also the elongation at break (the ability of a film to stretch)of the films.

Films made from pure chitosan tend to be rigid and brittle, and so plasticizers areneeded to reduce the frictional forces between the polymer chains and therebyimprove their mechanical properties [20]. However, this sometimes compromisesgas and moisture barrier properties of the films. Water vapor permeability of chitosanfilms increased with the addition of plasticizer due to the structural modifications ofthe chitosan network. Incorporation of plasticizers increases the free volume and the

4 M.R. Ansorena et al.

molecular mobility of the polymer network. The network becomes less dense and,consequently, more permeable [11]. Incorporation of hydrophilic plasticizers hasbeen reported to increase the WVP of hydrocolloid-based films, which can also berelated to the hydrophilicity of plasticizer molecules [21]. For instance, chitosanfilms plasticized with sorbitol had lower WVP than those plasticized with glycerol atsimilar concentration due to the fact that sorbitol has less ability to bind water thanglycerol [11].

Chitosan has attracted attention as a potential food preservative due to its anti-oxidant capacity and antimicrobial activity against a wide range of fungi, yeasts, andbacteria [8, 22]. Although the mechanism of the antimicrobial activity of chitosan isnot discerned yet, there are some hypotheses. The most accepted hypothesis attri-butes the antimicrobial activity to a change in cell permeability due to interactionsbetween the positively charged chitosan molecules and the negatively chargedmicrobial cell membrane [23]. The other hypothesis is the interaction of diffusedhydrolysis products with microbial DNA inhibiting the mRNA and protein synthesisand chelating metals, spore elements, and essential nutrients [24].

The good film-forming properties of chitosan allow the production of films andcoating materials with good permeability to CO2 and O2 which provide somemechanical and barrier protection for foods and, consequently, maintain qualityand prolong shelf life [25]. However, chitosan films have poor mechanical properties,and, due to their hydrophilic nature, they are poor barriers to moisture, which limittheir uses in applications where the control of moisture transfer is desirable, such asfood coating/packaging [26]. For this reason, several strategies have been proposedto improve the functional and physical properties of chitosan films, as is discussed inthe following sections.

Strategies to Improve Chitosan Film Properties

Cross-Linked Chitosan

Chitosan has two types of reactive groups in its structure, the free amine groups andthe hydroxyl groups (at C3 and C6 carbons). These functional groups on chitosanmolecules can be chemically modified to enhance the mechanical attributes ofchitosan films and to broaden its applications. A common technique used to chem-ically modify chitosan films is based on the formation of a Schiff base between theamino groups of the chitosan chain and the aldehyde groups of cross-linking agents[27]. Schiff base reactions have been widely applied in the fields of biomedicine,chemistry, and food science, due to mild reaction conditions and high reactionrates [28].

Due to environmental concerns, in recent years, most of the attention has beenfocused on the green and natural cross-linking agents, such as proteins, starch, andplant extracts (polyphenols and aldehyde compounds) [27]. Natural aldehydes, suchas cinnamaldehyde, can be used to modify the properties of chitosan-based materialsby covalent cross-linking. These natural cross-linkers have the additional advantage

Food Biopackaging Based on Chitosan 5

of their intrinsic antimicrobial activity. Cinnamaldehyde has been shown to beeffective against a broad spectrum of food-borne pathogens [27]. Imino–chitosanfilms have also been fabricated using the Schiff base reaction from cinnamaldehyde,vanillin, piperonal, and other natural aldehydes [29]. Typically, nonpolar aldehydesneed to be dissolved in water-miscible organic solvents (such as methanol, ethanol,or acetone) before they can be mixed with aqueous chitosan solutions. Then, highreaction efficiency between aldehydes and chitosan can be greatly achieved by theslow water removal. Chen et al. [30] investigated the Schiff base cross-linking ofchitosan films at low pH by first converting cinnamaldehyde into a water-dispersibleoil-in-water nanoemulsion. The film was formed by the vacuum drying method toremove water. The cross-linked chitosan films exhibited antimicrobial activityagainst both bacteria and fungi. The method described by Chen et al. [30] mayprovide an environmentally friendly strategy to prepare active chitosan films forpreserving fresh food.

Zhang et al. [31] evaluated the effects of vanillin on chitosan films. Resultsshowed that the tensile strength of composite films increased by 53.3% and theWVP decreased by 36.5% compared with pure chitosan film, which was attributed tothe formation of the dense network structure, as confirmed by Fourier transforminfrared spectroscopy (FT-IR). Besides, there were almost no changes on the thermalstability of the composite films compared with the pure chitosan film, as confirmedby thermogravimetric analysis (TGA). In addition, from the scanning electronmicroscopy (SEM) images, it was proved that films containing 0.5–10% vanillinexhibited good compatibility. Vanillin/chitosan films, as a kind of green, safety, andgood physicochemical properties of food packaging materials, have a broad appli-cation in the food industry.

In recent years, many different phenolic compounds including curcumin, ferulicacid (FA), gallic acid (GA), quercetin, and tannic acid (TA) have been individuallyincorporated into chitosan films [32–34]. Silva-Weiss et al. [35] suggested thatphenolic compounds could interact with chitosan chains through ester linkage,electrostatic interaction, and hydrogen bond to enhance the mechanical strength ofcomposite films. Other researchers indicated that phenolic compounds might play arole as cross-linking agents in chitosan composite films [33, 34]. According toRivero et al. [34], tannic acid acts as a cross-linker, leading to a more rigid andcompact chitosan matrix and improving the film physical properties. Talón et al. [36]confirm that thyme extract (TE) and TA’s polyphenols, when mixed with chitosan,interacted with chitosan chains, acting as cross-linkers and enhancing the tensilebehavior of films. Besides, the development of polyphenol–chitosan interactionscontributed to a better protection of the functionality of polyphenols during filmformation and conditioning. TE improved tensile properties of the films in the sameway as TA, while the ratio of polyphenol–chitosan seems to play an important role inthis response.

Recently, chitosan tensile properties were also increased considerably by theincorporation of turmeric extract, the film being stiffer than pure chitosan film, andit is attributed to the interaction between �OH group of curcuminoids and otherphenolics and �NH2 groups in chitosan (see Fig. 2) [37]. Similar results have been

6 M.R. Ansorena et al.

obtained with chitosan films incorporated with standard curcumin addition, and theincrease in tensile strength (TS) was reported as two times [32]. This increase wasinterpreted by authors as the strong interaction between curcumin and chitosanbackbone.

As an important category of phenolic compounds, phenolic acids are potentantioxidants and can be further divided into two subcategories: hydroxybenzoicacids and hydroxycinnamic acids based on their carbon frameworks. In recentyears, several efforts have been made to graft natural phenolic acids including gallicacid, ferulic acid, caffeic acid, and catechin onto CH backbones [38]. The introduc-tion of phenolic groups into the CH structure allows obtaining new matrices withsatisfied antioxidant properties and extending CH-based films’ functional properties.

Nowadays, four kinds of grafting techniques including carbodiimide-based cou-pling, enzyme-catalyzed grafting, free radical-mediated grafting, and electrochemi-cal methods are frequently used for the synthesis of phenolic acid-grafted chitosan(phenolic acid-g-chitosan) [39].

GA-g-chitosan film was firstly developed by Schreiber et al. [40] and applied aspeanut powder packaging material. GA-g-chitosan film showed superior preserva-tion effect on peanut powder by reducing the levels of thiobarbituric acid-reactivesubstances, peroxide, and conjugated trienes. Wu et al. [41] further investigated thephysicochemical properties of the gallic acid-g-chitosan film. As compared withchitosan film, gallic acid-g-chitosan film exhibited decreased mechanical strengthand water resistance, whereas it enhanced antioxidant and antimicrobial activities.Nunes et al. [42] prepared caffeic acid-g-chitosan film by using genipin as the cross-linker. The film showed improved antioxidant activity and ideal low solubility inacidic media. However, the surface wettability, mechanical properties, and thermalstability of chitosan film were not significantly influenced after grafting with caffeicacid and cross-linked by genipin. FA-g-chitosan film was developed by Aljawishet al. [43] and byWoranuch et al. [44]. By contrast with chitosan film, FA-g-chitosanfilm showed decreased moisture content, water sorption capacity, and mechanicalproperties but improved oxygen barrier property and antioxidant activity [43, 44], aswell as decreased water vapor barrier property and extensibility [44]. Recently,protocatechuic acid (PA)-g-chitosan films with different grafting ratios have beenprepared and characterized in terms of physicochemical, mechanical, and

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turmeric incorporatedchitosan film

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Fig. 2 Tensile stress–straincurves of chitosan-based films[37]

Food Biopackaging Based on Chitosan 7

antioxidant properties [45]. Results showed that the grafting ratio was a key factoraffecting the properties of protocatechuic acid-g-chitosan films, e.g., PA-g-CH filmwith medium grafting ratio exhibited the highest tensile strength and elongation atbreak. Liu et al. [46] also grafted five kinds of hydroxybenzoic acids including gallicacid, gentisic acid, protocatechuic acid, syringic acid, and vanillic acid onto chitosanthrough carbodiimide-mediated coupling reaction. WVP of chitosan film wasreduced, while UV light barrier, mechanical, and antioxidant properties wereenhanced after grafting. The films were affected by the type of hydroxybenzoicacid grafted and grafting ratio: gallic acid-grafted chitosan film showed the bestphysical, mechanical, and antioxidant properties.

Chitosan Nanocomposites

The practical use of chitosan as a film-forming material remained restricted due to itsinadequate mechanical and barrier properties. In order to use chitosan as a potentialalternative for synthetic polymers, its mechanical properties need to be boosted up toan acceptable level. It has been suggested that use of reinforcements and preparationof composites can improve the inherent shortcomings of biopolymers [47].

Bionanocomposites consist of well-dispersed nanofillers (having a minimum ofone dimension within the nanometer range) into a biopolymeric matrix. Whennanoparticles with excellent mechanical and thermal properties are filled into bio-polymers, they can interact with polymer chains at nanoscale, leading to significantimprovements on the properties of the resulting nanocomposites as a result of theirhigh surface area and high aspect ratio. Therefore, keys to prepare composite filmswith satisfying performances are homogeneous dispersion of nanofillers in thematrix and strong interface interactions [48].

Several research efforts were made to improve the physical and mechanicalproperties of chitosan film by incorporating reinforcing nanofillers such as cellulosenanofibers (CNFs) [49, 50], cellulose nanowhiskers (CNWs) and nanocrystals(CNCs) [51], chitin nanoparticles [52], lignin [1] and polylactide nanoparticles[53], graphene oxide (GO) nanosheets [54], montmorillonite (MMT) [55], etc.

Chitosan–cellulose combinations are compatible due to chemical structures sim-ilarity, which results in films with the physicochemical properties of chitosan and themechanical properties of cellulose fibers [50]. CNFs have been researched for theiruse in biodegradable packaging due to their renewable, low cost, low density, andnonabrasive nature. This allows them to formulate bio-based nanocomposites witheasy processability. CNCs have been added into chitosan biopolymers to producegreen nanocomposite films, with improved thermal, mechanical, and oxygen barrierproperties [51]. However, in this research work, WVP and transparency of the filmswere not evaluated. Mujtaba et al. [56] added CNCs from flax into chitosan films andshow improvements in mechanical properties and crystallinity index of chitosanfilms, while thermal properties and water vapor permeability were unchanged.Furthermore, Coelho et al. [52] showed that the addition of different concentrations

8 M.R. Ansorena et al.

of microcrystalline cellulose as well as the application of moderate electric field tochitosan films led to hydrophobic films with reduced WVP values.

TEMPO-oxidized cellulose nanofibers extracted from cotton stalks [49] wereproduced by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxi-dation. Hydrogen bonds and electrostatic attraction between the negatively chargedcarboxylate groups (COO�) and the positively charged ammonium groups (NH3

+)of chitosan ensure the high compatibility between both biopolymers (see Fig. 3).Soni et al. [49] prepared transparent and high-performance bionanocomposite filmsbased on chitosan matrices, sorbitol as plasticizer, and TEMPO-oxidized cellulosenanofibers as reinforcing agents. Incorporation of TEMPO-CNFs enhanced themechanical strength of the films due to the high aspect ratio (3–20 nm width and10–100 nm length) of the fibers and the strong interactions developed with thechitosan matrix. SEM and atomic force microscopy (AFM) images indicated thatnano-sized TEMPO-CNFs were completely embedded in the chitosan matrix.

Fig. 3 The schematic representation of intermolecular hydrogen bonds and electrostatic interac-tions in chitosan/TEMPO-CNFs nanocomposite film [49]

Food Biopackaging Based on Chitosan 9

Besides, these bionanocomposite films had good thermal stability and the oxygenand WVP of the films containing 15–25% wt. TEMPO-CNFs were significantlyreduced. Summarizing, Soni et al. [49] showed that it is possible to producebionanocomposite films that are flexible and transparent and thus have potential infood packaging applications.

Coelho et al. [52] added chitin nanofibers (CHNF) as two-dimensional organicnanofillers and AgNPs as inorganic three-dimensional nanoparticles into chitosanfilms. The results showed that the AgNPs had a negative effect on mechanical andcolor properties of chitosan films, but incorporation of CHNF improved theirmechanical and barrier properties significantly. Lowest WVP, solubility, and swell-ing of nanocomposite films were, respectively, for 6, 2, and 2% wt. of CHNFcontent.

Polylactide (PLA) nanoparticles are safe biopolymers originating from catalyzedpolymerization of lactic acid monomers. Unlike chitosan, PLAs are hydrophobic atthe surface and carry anionic charges. Basu et al. [53] used PLA nanoparticles todevelop uniform chitosan nano-biocomposite films. They proved that the nano-particle array incorporated in the chitosan films served as cargo loaders for activemolecules, by using quercetin, a bioflavonoid ubiquitous in many plant species, asmodel cargo molecule. Sustained quercetin release imparted synchronized antimi-crobial and antioxidant properties in finished packaging films. Nanocomposite filmmicrostructure showed a homogenous nanoparticle dispersion throughout the filmmatrix.

Recently, GO nanosheets, a novel two-dimensional nanomaterial prepared fromnatural graphite, have attracted significant attention owing to its novel structure,greater chemical stability, superior mechanical properties, biocompatibility, and,most importantly, its hydrophilic character [54]. Ahmed et al. [54] preparedchitosan-based nanocomposite films by blending chitosan and GO nanosheets insolution at selected concentrations (0.5, 1, and 2% w/w). By introducing GO, a morecompact CH/GO network structure was formed with improved tensile properties andglass transition temperature (Tg) for the composite films. The addition of GO to theCH significantly lowered the lightness (L*) value and UV light transmittance. GOwas effective in enhancing the tortuosity of the diffusive path for oxygen and watervapors to diffuse through the CH nanocomposite film. FT-IR indicated anintermolecular hydrogen bond formation between CH and GO. These CH/GOfilms with improved thermomechanical and barrier properties could be competitivecandidates for various food packaging applications.

MMT, a natural multilayer silicate, is one of the most extensively studiednanofillers due to its low cost, high aspect ratio and specific surface area, goodbiocompatibility, nontoxicity, high strength, and other outstanding properties. Dis-persion of MMT in the polymeric matrix at a minimal loading level was reported toenhance thermal, mechanical, functional, and barrier properties of biopolymer-basedcomposites while maintaining their biodegradability. It is a promising nano-reinforcement for chitosan films due to suitable chitosan–nanoclay interactions[57]. When filled into polymers, there are three basic dispersion degrees of MMT,which are tactoids, intercalated layers, and randomly exfoliated lamellae. In the latter

10 M.R. Ansorena et al.

two cases, polymer chains can interact with MMT lamellae at nanoscale obtainingnanocomposites with excellent properties. There are various reports on the effect ofMMT on the final properties of chitosan-based nanocomposites [18, 55]; for exam-ple, Beigzadeh Ghelejlu et al. [55] prepared chitosan/nanoclay nanocomposite filmscontaining three different levels of MMT (1, 3, and 5% w/w based on chitosan). Theexfoliated dispersion form of MMT nanolayers was confirmed by X-ray diffractionanalysis, while SEM images showed an increase in films’ surface roughness by theaddition of MMT. WVP, solubility of films, and mechanical properties were reducedsignificantly ( p < 0.05) by incorporation of MMT. The incorporation of MMT gaverise to films darker in appearance.

Blends or Multilayer Films Based on Chitosan

It is known that polymer blending can result in an improvement of the physical andfunctional properties of pure components [30] by the formation of new bonds.Blends and bilayer films of chitosan and anionic polymers have shown to improvemechanical and barrier transport properties comparing to single-component-basedfilms. This fact was attributed to the formation of polyelectrolyte complexes throughelectrostatic interactions between the protonated amino groups of chitosan and thenegatively charged side-chain groups in the other biopolymer at the operating pH [9,58]. Improvement in mechanical properties, better performance in terms of WVP,and lower water solubility have been reported for blends and bilayer films ofchitosan with starch, pectin, or alginate [58, 59], gelatin [60], or whey [61], com-paring to chitosan stand-alone films. Bilayer systems are reported to have betterwater vapor barrier properties than blend films [60, 61].

Chitosan–Polysaccharides FilmsBlending chitosan with other polysaccharides should impart better functional prop-erties than pure chitosan films, which would be achieved by hydrogen and/orelectrostatic interactions between carboxylate groups of carbohydrates and proton-ated amino groups of chitosan [9, 58]. As an example, Vargas et al. [62] showed thatthe association of chitosan and methylcellulose improved water barrier properties incomparison to both pure films while leading to transparent with also better gasbarrier, mechanical properties, and good appearance.

Several studies with blends of chitosan and pectin have demonstrated that there isa high cross-linking potential between both components; i.e., polymer–polymercomplexes can be formed as a result of interchain interactions (electrostatic interac-tions) when these two macromolecules are mixed in solution [59]. Baron et al. [63]developed and characterized films based on blends of chitosan extracted from bluecrab and pectin (P) extracted from orange from industrial wastes. The CH–P-basedfilms were prepared by the casting method in different CH–P ratios [0:100, 25:75,50:50, 75:25, and 100:0] and compared to two controls [0:100 and 100:0] ofcommercial pectin and chitosan. The addition of high concentrations of pectin inthe formulations resulted in films with high solubility and increased moisture

Food Biopackaging Based on Chitosan 11

sorption. No significant difference in the degree of swelling (DS) and WVP of thefilms was observed. CH–P blend films were less stiff and therefore more elastic andflexible than films based on only one biopolymer. The control films presented betterresults in terms of color, being brighter and less opaque than other film formulations.

Chitosan–Protein FilmsProteins have properties that are advantageous in the preparation of packagingbiomaterials; for example, their ability to form networks, their plasticity, and elas-ticity [4]. Polysaccharide–protein mixed systems are increasingly used in variousfood, pharmaceutical, and biotechnology applications. The protein–polysaccharidecomplexes could exhibit better functional properties than that of the proteins andpolysaccharides alone [64]. Thus, it is also important to look for the combinations ofbiopolymers that yield a better performance as a natural and edible package. In theproduction of these films, advantage can be taken from chitosan acting as a cationicpolymer that can establish electronic interactions through the NH3

+ groups withanionic groups, such as the COO� present in proteins or polyanions. These interac-tions are responsible for the formation of polymeric complexes [9, 58].

Sodium caseinate (SC) is a commercially available water-soluble polymerobtained by acid precipitation of casein, the main protein in cow milk. Caseinatepresents thermoplastic and film-forming properties due to its random coil nature andits ability to form weak intermolecular interactions; i.e., the partially denaturedpeptide chains bond together primarily through hydrophilic and hydrogen bondsresulting in the formation of the protein matrix [4]. Pereda et al. [65, 66] preparedSC/CH films by casting from aqueous solutions. The complex films showed amoderate improvement in the tensile strength (19.6 MPa) and an increase in theimpact strength (35.6 GPa) with respect to those corresponding of chitosan films(17 MPa and 26.6 GPa, respectively). At the same time, SC/CH films show lowerequilibrium moisture content than either CH or SC neat ones. Moreira et al. [67]analyzed the antimicrobial properties of SC/CH films showing an improvement inthe bactericidal properties of the CH/SC blend with respect to those of the neat CHfilm. The strong interactions developed between the cationic polymer chitosan andthe SC carboxyl groups (confirmed by FTIR) lead to polyelectrolyte complexation,which is proposed as the reason for improvement with respect to caseinate orchitosan films [66].

Gelatin (Ge), a product of partial hydrolysis of collagen, is a traditional water-soluble biopolymer with distinctive advantages of biodegradability, nontoxicity,biocompatibility, and low cost. Gelatin can form films and coating with good opticalproperties, adequate mechanical properties, and excellent gas barrier properties atlow relative humidity able to act as biopackaging materials [68]. The influence ofchitosan molecular weight and degree of deacetylation and gelatin origin on thephysicochemical properties of gelatin–chitosan composite films were investigated,founding that interactions between Ge and CHwere stronger in the blends made withchitosan of HWor higher DD than the blends made with LWor DD [69]. Accordingto the gelatin origin, the interactions between gelatin and chitosan were stronger in

12 M.R. Ansorena et al.

the blends made with tuna-skin gelatin than in the blends made with bovine-hidegelatin [70].

Composite films of chitosan and gelatin (or collagen) have been reported to haveimproved mechanical, transport, and physical properties compared with those ofsingle-component-based films [60, 71]. This was attributed to the formation of bothelectrostatic interactions and hydrogen bonds occurring between gelatin andchitosan [71]. Furthermore, these strong interactions lead to the formation of mul-tiple complexes of the two biopolymer molecules [71]. Despite the numerous workson composites from chitosan and gelatin, information about bilayer films is limited,although it was reported that bilayer chitosan/gelatin films had higher performancein terms of water vapor permeability and mechanical properties than the compositecounterpart [60]. On the other hand, Pereda et al. [72], who developed bilayer andcomposite CH–Ge films, found that both resulted effective alternatives to reduceWVP of chitosan control film, while the tensile strength of composite and bilayersystems did not differ significantly. Regarding antimicrobial activity, their resultsindicated that only Escherichia coli was sensitive to the combination CH–Ge.

Chitosan–Lipid FilmsOne approach to improve the low moisture barrier properties of chitosan filmsconsists in the incorporation of hydrophobic compounds, such as lipids, in thefilm formulation [73, 74]. However, the decrease in the WVP sometimes is at theexpense of sensorial alterations that have been shown to characterize foods coatedwith composite films featuring high amounts of lipids such as saturated acids andwaxes. On the other hand, some authors reported composite films featuring unsat-urated oils rich in oleic acid that can potentially improve the moisture-barrierproperties of hydrophilic films and prevent, at the same time, drastic changes intheir mechanical properties. Moreover, the liquid nature of oils at room temperaturemakes them easily mixable with biopolymers [72]. When hydrocolloid and lipidingredients are combined, they may interact favorably, resulting in edible films withimproved structural and functional properties, as the mechanical and barrier proper-ties depend not only on the compounds used for the polymer matrix but also on theircompatibility [73].

As indicated in the previous sections, chitosan possesses high positive charge onNH3

+ groups when dissolved in aqueous acidic solution, and therefore it can adhereto or aggregate with negatively charged lipids and fats [75]. Moreover, chitosan actsas stabilizer of hydrocolloids–lipids mixtures, promoting emulsion formation andinterfacial stabilization, since its molecules are composed of both hydrophilic andhydrophobic portions. Thus, it is frequently used as emulsifier to uniformly stabilizeoil droplets in emulsion systems [76]. Wong et al. [77] added saturated fatty acidsand fatty acid esters to chitosan-based films, obtaining the higher resistance to watervapor transmission when lauric and butyric acids were used. On the other hand, Parkand Zhao [78] incorporated vitamin E into the chitosan matrix obtaining a significantdecrease in the WVP at expenses of an increase in opacity and a significant reductionin the tensile strength of the composite films. There are some reports on the effect ofunsaturated oils, such as olive oil, on the properties of chitosan-based films and few

Food Biopackaging Based on Chitosan 13

works dealt with the study of the interactions between chitosan and olive oil orchitosan and olive oil components [79–81]. Moreover, the study published by Vargaset al. [81] focused in the improved physicochemical quality of the strawberriescoated with the edible coatings and not in the physical and mechanical characteri-zation of the chitosan-based films themselves; the data reported by Muzzarelli et al.[80] dealt with the capacity of chitosan to alter the composition of olive oil uponpercolation of the oil through a bed of chitosan powder; and the paper published byHam-Pichavant et al. [79] was focused in the potential replacement of fluorocarbontreatment of paper-based materials by chitosan coating, to produce oil barrierpackaging. Pereda et al. [82] investigated the properties of plasticized chitosan–oliveoil emulsion films prepared with increasing oil concentrations. They found that theemulsifying nature of chitosan was enough to stabilize olive oil droplets in the film-forming emulsions; hence, homogeneous, thin, and translucent films were obtainedin all cases. The homogeneity of the lipid globules distribution in the films wasconfirmed by contact angle measurements and optical microscopy. All the tensileproperties increased with olive oil concentration and were explained considering theinteractions developed between lipid and carbohydrate phases in addition to thelubricant characteristics of the oil, which were also confirmed by total soluble mass(TSM) determinations. Moisture sorption, water vapor permeation through the films,and effective diffusion coefficients decreased as oil concentration increases, as aresult of the nonpolar nature of the lipid.

Active Biopackaging Based on Chitosan

The oxidative processes, along with the microbiological growth, is one of themechanisms of food quality deterioration, being responsible for many importantchanges such as loss of nutritional values, texture modifications, and development ofundesirable compounds such as off flavors, colored, and even toxic substances tohumans [83]. Although the potential of chitosan, due to its inherent antimicrobialactivity against bacteria and fungi, to act as active food packaging to maintainqualities, improve safety, and prolong shelf life of foods has been widely reported[8, 72], it can be also increased by the addition of active compounds. Therefore,antioxidant and antimicrobial active packaging [83] that can use natural compoundsis being highlighted as a new mechanism to prevent food oxidation and growth ofpathogenic and/or spoilage microorganisms [8, 10, 23, 83]. In this sense, edibleplants, especially those ones rich in secondary metabolites (e.g., essential oils,polyphenols), have an increasing interest due to their high concentrations of bioac-tive ingredients with antioxidant and/or antimicrobial activity [11].

Chitosan–Phenolic Compounds FilmsPhenolic compounds are the most abundant secondary metabolites in the plantkingdom. It has been demonstrated that the incorporation of phenolic compoundsinto chitosan can improve the physical, mechanical (see section “Cross-LinkedChitosan”), and biological properties of composite films [11]. The properties of

14 M.R. Ansorena et al.

chitosan–phenolic composite films mainly depend on the chemical structure, addi-tion content, and dispersion degree of phenolic compound in the films. In practicalapplications, the incorporated phenolic compounds can be released from film matri-ces to the packed food, providing sustained release of antioxidant activity duringfood storage [11].

Chitosan films incorporated with plant polyphenols have been proved to be ableto provide effective gas barrier, mechanical strength, and competent functionalproperties beneficial to maintain quality and prolong shelf life of fruits and vegeta-bles, processed meat products, and fish and seafood [11].

Polyphenols from green tea have proved to be effective antimicrobials andantioxidants and can be efficiently incorporated into chitosan-based films [11]. Theantimicrobial effects of propolis (PE) against Gram-positive (Bacillus cereus,Listeria monocytogenes, and Staphylococcus aureus) and Gram-negative (Salmo-nella typhimurium, E. coli, and Pseudomonas fluorescence) bacteria have beenpreviously reported [84]. Siripatrawan and Vitchayakitti [84] studied active filmfrom chitosan incorporated with 0, 2.5, 5, 10, and 20% w/w propolis extract (seeFig. 4) and found that incorporation of PE into chitosan films improved mechanicaland barrier properties, as well as antimicrobial and antioxidant activities. Themodification of film properties could be attributed to the interactions betweenfunctional groups of chitosan and polyphenols and other constituents of propolisas verified by FT-IR analysis.

Recently, Sun et al. [85] prepared and characterized chitosan film incorporatedwith thinned young apple polyphenols (YAP), in which the content of total poly-phenols is approximately ten times higher than that in ripe apples. Films showed anenhancement of WVP, while their opacity was significantly increased (see Fig. 5).Besides, the YAP-chitosan films showed antimicrobial effects on both bacteria andmolds.

The milk thistle plant (Silybum marianum L. Gaertn. Asteraceae) (SME) is anannual or biennial plant mostly known for its medicinal and antioxidant activity andis being introduced as a potential new source of natural antioxidants to replacesynthetic ones [55]. The addition of SME at minimal loading of 0.5–1.5% v/vsignificantly improved the DPPH radical scavenging activity, WVP, and watersolubility of chitosan films, bringing about films with higher antioxidant activityand enhanced barrier properties compared to other natural extracts. However, theincorporation of SME decreased the mechanical properties of resulted films and gaverise to films darker in appearance [55].

Curcumin is widely known for its antibacterial, antioxidant, and wound-healingproperties [32]. Liu et al. [32] analyzed chitosan film with curcumin. The Cur-CHfilm (1% weight of chitosan) possessed a good compatibility evidenced by SEM andacceptable thermal behavior. Moreover, Cur-CH specimens improved the anti-bacterial effect against S. aureus (the diameter of the inhibition zone was increasedfrom 10 to 12 mm) and exhibited an excellent antifungal effect.

Recently, Gul and Bakht [86] showed the antimicrobial potentials of turmericextracts. This property together with its commercial availability and cost-effectivefeatures makes turmeric extracts as good candidates to be incorporated into chitosan

Food Biopackaging Based on Chitosan 15

Fig. 4 Antibacterial action of chitosan film containing propolis extract [84]

16 M.R. Ansorena et al.

Fig. 5 (a) The photographs and (b) SEM micrographs of surface and (c) cross section of chitosanfilms incorporated with different concentrations of YAP [85]

Food Biopackaging Based on Chitosan 17

films aimed as food packaging. This characteristic was also confirmed byKalaycıoğlu et al. [37], who observed that the antimicrobial activity of the chitosanfilms with turmeric incorporation, studied against Salmonella and S. aureus, wasincreased as compared with control films.

On the other hand, Souza et al. [87] tested the incorporation of six differenthydroalcoholic extracts (HAE) (ginger, rosemary, sage, black tea, green tea, andkenaf leaves HAE) on chitosan films. HAE turned the films to a more saturated colorand less bright, reducing the transmittance by 15–80% as compared to CH films, butimproved the mechanical properties. In general, incorporation of HAE in thechitosan increased the moisture content (from 13% in the chitosan to 25% on averageof the HAE films) and solubility (from 17% in the chitosan to 22% on average of theHAE films), while swelling degree decreased (from 191% in the chitosan to 139% onaverage of the HAE films), due to the interaction of water, chitosan, and polyphenolspresent on extracts used.

Chitosan–Essential Oils FilmsEssential oils (EOs) from plant extracts are natural antimicrobial and antioxidantagents, and most of them are classified as generally recognized as safe (GRAS),which makes them interesting additives in food industry, especially because theyhave been used as remedies from ancient times. Incorporation of essential oil inedible films may not only enhance the antimicrobial properties but also reduce watersolubility, vapor permeability, and slow lipid oxidation of the product [26]. Forexample, polyphenols from cinnamon essential oil have proved to be effectiveantimicrobials and antioxidants and can be effectively incorporated into chitosan-based films [11].

Hafsa et al. [88] developed chitosan-containing Eucalyptus species (EG) essentialoil (0, 1, 2, 3, and 4% (v/v)) by casting and solvent-evaporation method and showedthat chitosan-based films containing EG essential oil could be used as active films dueto its low affinity to water and excellent in vitro antimicrobial and antioxidant activities.

Souza et al. [87] test the incorporation of five essential oils (EO) (ginger, rose-mary, sage, tea tree, and thyme EO) on chitosan films. The color of EO films wassimilar to control samples while improving the light barrier of films, conferring tochitosan an extra protection against oxidative processes. In general, incorporation ofEOs in the chitosan increased the moisture content and solubility, while swellingdegree decreased due to the interaction of water, chitosan, and polyphenols presenton extracts used. Moreover, tensile strength of chitosan increased from 20 to26 MPa, on average.

Tastan et al. [89] also showed a higher antimicrobial activity of chitosan filmscontaining carvacrol nanoemulsions with respect to chitosan alone. At the sametime, the minimization of the impact on film appearance (i.e., whiteness index) andthe preservation of surface hydrophobicity occurred.

Recently, Shahbazi [90] analyzed CH films incorporated with Ziziphoraclinopodioides essential oil (ZEO) and grape seed extract (GSE), which are naturalantioxidants and antibacterial agents. When incorporated into CH films, both GSEand ZEO showed good antibacterial and antioxidant efficacies, which can be

18 M.R. Ansorena et al.

important barrier against microbial and chemical contamination in food industries.However, ZEO and GSE reduced swelling index, tensile strength, puncture force,and puncture deformation of CH films [90].

Chitosan–Metallic Nanoparticles FilmsAntimicrobial activity and stability of chitosan can also be enhanced by the incor-poration of conducting polymers, metal nanoparticles, and oxide agents [91]. Metaloxide nanoparticles show excellent antimicrobial properties [47]. Zinc oxide (ZnO)is known as a GRAS compound by Food and Drug Administration and has beenintroduced into a number of food packaging and coatings to maintain food colors,avoid spoilage, and improve packaging material properties, including mechanicalstrength, barrier properties, and stability [92]. Al-Naamani et al. [92] proved thesuccessful interaction of chitosan and ZnO nanoparticles which improved its wateraffinity. Moreover, while chitosan coating provided an effective antimicrobialdefense against Salmonella enterica, E. coli, and S. aureus, chitosan–ZnO nano-composite coatings fully inhibited growth of the pathogens after 24 h incubation.

Recently, much attention has been focused on chitosan–TiO2 nanocompositeswhich were proven to possess favorable mechanical, thermal, and photocatalyticproperties [93]. Zhang et al. [93] prepared chitosan–TiO2 nanocomposite films as anactive antimicrobial packaging material for food preservation. The wettability andmechanical properties of the composite film were enhanced by the addition of TiO2

nanopowder. The chitosan–TiO2 film possessed a decreased transmittance in thevisible light region which facilitated its photocatalytic antimicrobial effect underambient condition. The preservation of red grape was studied with plastic wrap ascontrol. The results showed that the prepared chitosan–TiO2 film successfullyprotects red grapes from microbial infection and extends their shelf life.

Combination of Several Strategies Previously Mentioned

The aim of combining different strategies is to customize the performance of thesenovel and biodegradable materials in food preservation applications, to enhance foodsafety and quality.

For example, Noshirvani et al. [94] described the elaboration of bio-based filmsfrom a binary polysaccharide network (CMC and CH) with oleic acid (OL) as thehydrophobic compound. The film was incorporated with cinnamon essential oil(CEO) or ginger essential oil (GEO). Especially, CEO and also GEO were bothefficient to control the in vitro growth of Aspergillus niger. The presence ofcinnamaldehyde in CEO can create many kinds of interactions with the networkmade by blending CMC, CH, and oleic acid. Regarding mechanical properties,highest concentrations of EOs led to an improvement of 328 and 111% of theelongation with cinnamon and ginger, respectively. EOs and especially cinnamonoil could be used to plasticize binary polysaccharide network of chitosan andcarboxymethyl cellulose while decreasing WVP and maintaining antifungal activityof the resulting films. The films previously mentioned (CMC–CH–OL) were also

Food Biopackaging Based on Chitosan 19

studied, but in this case, the incorporation of different concentrations (0.5–2 wt.%) ofzinc oxide nanoparticles (ZnO NPs) was analyzed. Interactions between ZnO NPsand polymer matrix were confirmed by FT-IR. After addition of ZnO NPs, tensilestrength, lightness, and thermal stability decreased, while elongation at break andcontact angle with distilled water increased, showing a plasticizing effect of ZnONPs on the polymer network. Addition of ZnO NPs led to a considerable absorbanceof UV light at all tested concentrations of ZnO NPs with low adverse effect on thetransparency of films in the visible range. Microbial tests showed superior antifungalactivity of nanocomposite films especially at the highest concentrations of ZnO NPs(2 wt.%) [95].

Bonilla and Sobral [96] studied the effect of incorporating rosemary, cinnamon,boldo-do-chile, and guarana ethanolic extracts at 1% into edible films prepared fromblends of gelatin and chitosan. These extracts are well known for their antioxidantand antimicrobial properties. The antioxidant activity of the blend films was signif-icantly enhanced with the addition of extracts and chitosan up to 50% (GEL50:CH50).

Gabriel et al. [97] synthetized silver nanoparticles (AgNPs) on films of CH/MMTnanocomposites by photochemical method. The increase in clay concentrationresulted in faster synthesis of AgNPs. For 2.5 and 5 wt.% of MMT, the AgNPsexhibited more uniform size and mixture of intercalated/exfoliated structures. Theantibacterial activity of nanocomposite films was determined against the growth ofE. coli and Bacillus subtilis. Films prepared in the absence of AgNPs showed noinhibition zones, indicating that AgNPs are responsible for the antibacterial activity.The presence of clay did not influence the bactericidal activity.

Yu et al. [98] developed biopolymer-based edible nanocomposite films ofchitosan–starch reinforced with CNFs. Results demonstrated that CNFs increasedthe rigidity of the films due to more hydrogen bonds being induced by CNFs(�60%). Incorporating a high content of CNFs (�60%) in the film resulted inenhanced filling effect on the structure of the biopolymer films, which significantlyimproved the light barrier, oxygen barrier, and water vapor barrier capacities. AsCNF content increased to 100%, the film opacity increased by 59%. Furthermore,the antimicrobial properties of the edible films with 80 and 100% CNFs wereincreased by up to 2 log CFU/g on day 8 in a beef model. These results demonstratethat CNFs have great potential in applications of active packaging for food products.Complex chitosan-plasticized films modified with olive oil (OO) and/or cottonnanocrystals (CNCs) were successfully obtained by casting. Due to cellulose–gly-cerol–chitosan interactions, composite films appeared less opaque as the celluloseconcentration increases (up to 7 wt.% CNC), which is an advantage from theconsumer viewpoint. Moreover, both nanocellulose and olive oil additions led tothe reduction of the WVP and the total soluble matter, which are also desirablecharacteristics for a food packaging. The EMC of the chitosan-plasticized matrixwas considerably reduced by adding only 3 wt.% CNC or only olive oil (withoutreinforcing filler), and thus, these films could be considered for special applications.The tensile modulus was significantly increased by CNC addition, while the utili-zation of olive oil moderates the reduction of the elongation at break; this synergistic

20 M.R. Ansorena et al.

effect is an improvement over the expected response (i.e., modifications that lead toan increase in the stiffness and usually also lead to a decrease in the deformationcapability) [99].

Li et al. [100] developed CH/LY (lysozime)/REC (rectorite) films with highstrength and enhanced antibacterial properties via a green method. Lysozyme is akind of natural, nontoxic, and antibacterial protein, and rectorite (REC) is a kind oflayered silicate that has the adsorption and stabilizing effect on bacteria when itcombines with other antibacterial materials [100]. Due to the good chemical stabilityand heat-resisting function, REC improved the strength and thermal property ofcomposites. CH/LY/REC hybrid films were successfully prepared and the surface offilms was smooth and homogeneous (see Fig. 6). The FTIR results confirmed that thehydroxyl group of REC reacted with the chains of CH and LY. The hydrophobic andthermal properties of the CH films were increased by the addition of LY and REC.Besides, LY could be released from the chitosan hybrid films and kept the hydrolyticactivity against bacterial cell wall substrate. Furthermore, the CH/LY/REC filmsexhibited remarkable antibacterial activity due to the synergetic bacteria inhibition ofCH, LY, and REC. Such simple and green method could be used to fabricatecomposite materials with strong antibacterial properties, which could broaden theapplications in the fields of food packaging and biomedical materials [100].

Conclusion

The last 5 years have witnessed an impressive growth of research studies regardingfood biopackaging based on chitosan. Along this chapter, it was demonstrated thatchitosan films have an enormous potential to be used as antimicrobial and antioxi-dant packaging material for a wide range of applications in the food industry, andthus, they are a promising alternative to synthetic materials, potentially contributingto food shelf-life extension. It was shown that the inherent antimicrobial propertiesof chitosan films can be enhanced by the addition of bioactive ingredients withantioxidant and/or antimicrobial activity such as polyphenols, essential oils, metalnanoparticles, oxide agents, etc. Sometimes, these additives also develop strong

00

5

10

15

20

25

30

CSCS/LYCS/LY/REC35

40

2 4 6 8Tensile strain (%)

Ten

sile

str

ess

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a)

10 12 14

ab c

Fig. 6 (a) Stress–strain curves of CH, CH/LY, and CH/LY/REC films and photos of CH/LY/RECfilms (b) transparence, (c) twisting [100]

Food Biopackaging Based on Chitosan 21

physical interactions with the chitosan matrix, not only contributing not only to abetter protection of the enhanced functionality but also improving physical, mechan-ical, or barrier properties of the film. Moreover, the mechanical, physical, and barrierproperties of chitosan-based films can be tailored by the incorporation of compatibleor functional nanofillers into chitosan matrices; by blending chitosan with oppositecharged polysaccharides, proteins, or lipids; by cross-linking chitosan with naturalaldehydes containing compounds; or by grafting it with phenolic acids, which arealso potent antioxidant compounds. Moreover, these strategies could also be com-bined to customize the performance of these novel and biodegradable materials infood preservation applications, to enhance food safety and quality. Yet, furtherresearch is required to evaluate the behavior of these films when in contact withfood matrices, in order to identify which of them are worth to be used by the foodpackaging industry.

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