development of edible films and coatings from alginates

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Carbohydrate Polymers 137 (2016) 360–374

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Carbohydrate Polymers

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evelopment of edible films and coatings from alginates andarrageenans

lham Tavassoli-Kafrani, Hajar Shekarchizadeh ∗, Mahdieh Masoudpour-Behabadiepartment of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran

r t i c l e i n f o

rticle history:eceived 20 July 2015eceived in revised form 20 October 2015ccepted 21 October 2015vailable online 28 October 2015

eywords:dible films

a b s t r a c t

The use of renewable resources, which can reduce waste disposal problems, is being explored to producebiopolymer films and coatings. Renewability, degradability, and edibility make such films particularlysuitable for food and nonfood packaging applications. Edible films and coatings play an important role inthe quality, safety, transportation, storage, and display of a wide range of fresh and processed foods. Theycan diminish main alteration by avoiding moisture losses and decreasing adverse chemical reaction rates.Also, they can prevent spoilage and microbial contamination of foods. Additionally, nanomaterials andfood additives, such as flavors, antimicrobials, antioxidants, and colors, can be incorporated into edible

dible coatingslginatesarrageenans

films and coatings in order to extend their applications. Water-soluble hydrocolloids like polysaccharidesusually impart better mechanical properties to edible films and coatings than do hydrophobic substances.They also are excellent barriers to oxygen and carbon dioxide. Recently, there has been much attentionon carrageenan and alginate as sources of film-forming materials. Thus, this review highlights productionand characteristics of these films.

© 2015 Elsevier Ltd. All rights reserved.

ontents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3612. Alginate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3613. Carrageenan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3644. Edible film and coatings applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3665. Film/coating production methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368

5.1. Edible film formation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3685.2. Edible coating formation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

5.2.1. Spraying method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3685.2.2. Dipping method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3685.2.3. Spreading method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368

6. Composite films and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3686.1. Carrageenan/alginate – lipid composite films and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3696.2. Carrageenan/alginate-polysaccharide composite films and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3696.3. Carrageenan/alginate-inorganic particles composite films and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3696.4. Carrageenan/alginate-fruit purees composite films and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

7. Combination of different components with edible films and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3707.1. Plasticizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3707.2. Antimicrobial agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3707.3. Antioxidant agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3717.4. Antibrowning agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .371
7.5. Other agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
∗ Corresponding author.E-mail address: [email protected] (H. Shekarchizadeh).

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8. Advantages and adverse biological effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3719. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372. . . . . .

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in the United Kingdom and Norway during 1934 to 1939 and afterWorld War II, respectively (ITC 1981). The 2 largest producers, KelcoCompany in the USA and Alginate Industries Ltd, in the UK were

Table 1Main hydrocolloids used for the formation of edible films and coatings (Milani &Maleki, 2012; Skurtys et al., 2010).

Type of hydrocolloid Principal function

PolysaccharideAgar (E406) Gelling agentAlginate (E400-404) Gelling agentCarrageenan (E 407) Gelling agentCarboxymethyl cellulose (E466)

Hydroxypropyl cellulose (E463)Hydroxypropyl cellulose (E464)Methyl cellulose (E461)

ThickenerThickener and emulsifierThickenerThickener, emulsifier andgelling agent

Chitosan Gelling and antimicrobial agentArabic gum (E414)

Guar gum (E412)Xanthan gum (E415)

EmulsifierThickenerThickener

Pectin (E440) Gelling agentStarches Thickener and gelling agent

Protein

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. Introduction

The quantity of packaging materials has been increasing by 8%nnually (Muizniece-Brasava, Dukalska, & Kantike, 2011). Less than% of all plastics are being recycled, leading to a high accumulationf plastics in the environment (Espitia, Du, Avena-Bustillos, Soares,

McHugh, 2014). Besides, increasing consumer concerns on foodafety led to development of biodegradable, edible, and renewablelms and coatings suitable for food and nonfood packaging applica-ions (Alves, Costa, & Coelhoso, 2010; Espitia et al., 2014). However,ue to the low cost of synthetic polymers, biodegradable materialsad been ignored (Hambleton, Voilley, & Debeaufort, 2011). Today,ith traditional agricultural commodities being a source of film-

orming material, wide commercialization of biopolymer films hasained more significance (Arvanitoyannis, 2010).

Biopolymers such as polysaccharides, proteins, and lipids cane used for the formation of edible films and coatings (Albert &ittal, 2002; Espitia et al., 2014; Lee, Shim, & Lee, 2004). They can

e used as complement or replacement of traditional materials inrder to reduce traditional polymeric packaging (Barreto, Pires, &oldi, 2003; Mate & Krochta, 1998).

Edibility and biodegradability are the most beneficial character-stics of edible films and coatings. Edibility of films and coatingsould be achieved if films and coatings components includingiopolymers, plasticizers, and other additives be food grade ingre-ients. Meanwhile, all the processes and equipment should becceptable for food processing. To claim biodegradability of filmsnd coatings, their toxicity and environmental safety must be eval-ated by standard analytical protocols (Han & Aristippos, 2005).

An edible coating is a thin layer of edible material formed as aoating on a food product (Kang, Kim, You, Lacroix, & Han, 2013),hile an edible film is a preformed thin layer, made of edible mate-

ial, which can be placed on or between food components (Espitiat al., 2014; Guilbert, Gontard, & Gorris, 1996). The main differenceetween these 2 food systems is that the edible coating is applied

n liquid form on the food, usually by immersing the product inhe solution of edible material, and edible film is first molded asolid sheets, then applied as a wrapping for food products (Falguera,uintero, Jiménez, Munoz, & Ibarz, 2011).

The concept of employing edible films and coatings for foodsates back to 1950s. Their growing application is attributable toeduction of moisture loss, adverse chemical reactions (Baldwin

Wood, 2006; Osorio, Molina, Matiacevich, Enrione, & Skurtys,011), spoilage, and microbial contamination (Arvanitoyannis,010). Additionally, they can be used for controlled release of fooddditives (Barreto et al., 2003). Edible coatings are also effectives a post-harvest treatment to preserve fruit quality (Valero et al.,013).

Hydrophobic substances such as resins, waxes, or some insol-ble proteins are better moisture barriers, but water-solubleydrocolloids like polysaccharides and proteins usually impartetter mechanical properties (tensile strength and elongation atreak) to edible films and coatings than do lipids and hydrophobicubstances (Arvanitoyannis, 2010). They also are excellent barri-rs to oxygen and carbon dioxide (Nussinovitch, 2009) because
f their tightly packed and ordered hydrogen-bonded networktructure (Atarés, Pérez-Masiá, & Chiralt, 2011; Bonilla, Atarés,argas, & Chiralt, 2012). So, they can be used to extend the shelf-
ife of foods by preventing dehydration, oxidative rancidity, and

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372

surface-browning (Dhanapal et al., 2012). Besides, food hydrocol-loids can act as nutritious food ingredients. Some health benefitsinclude lowering risk factors for cardiovascular disease, for immunefunction, for weight management, and for intestinal problems(Viebke, Al-Assaf, & Phillips, 2014). Table 1 shows the main hydro-colloids that can be used for the preparation of edible films andcoatings. The uses of alginates and carrageenans in edible films andcoatings are summarized in Table 2.

In recent years, there has been much attention on carrageenanand alginate as sources in edible film formation (Cian, Salgado,Drago, Gonzalez, & Mauri, 2014). According to FDA, carrageenansand alginates are GRAS materials thereby they have been passedthe mentioned standards and are considered as edible films andcoatings. To the best of our knowledge, there is no review arti-cle about carrageenan and alginate films and coatings. Thus, thisreview highlights production and characteristics of these films.

2. Alginate

Alginate is an appealing film-forming compound because ofits non-toxicity, biodegradability, biocompatibility, and low price(Vu & Won, 2013). Its functional properties, thickening, stabilizing,suspending, film-forming, gel-producing, and emulsion-stabilizinghave been well studied (Dhanapal et al., 2012; Zactiti & Kieckbusch,2006).

Alginic acid was first discovered in 1881 by Stanford. Around1923, Thornley, in Orkney, UK, established a briquette businessbased on using alginate as a binder for anthracite coal dust. Hemoved to San Diego, USA, and by 1927 his company was producingalginate for use in sealing cans. After some difficulties, the companychanged its name to Kelp Products Corp. and in 1929 it was reor-ganized as Kelco Company. Alginate production was established

Bovine gelatinFish gelatinPig gelatin

Gelling agentGelling agentGelling agent

Whey protein –

362 E. Tavassoli-Kafrani et al. / Carbohydrate Polymers 137 (2016) 360–374

Table 2Various edible films and coatings from alginates and carrageenans.

Type of hydrocolloid Application Product Main results Source

Alginate Film Microwaveable food Increasing warmingefficiency

Albert et al. (2012)

Alginate/gellan/antibrowning agent Coating Fuji apple Less browning Rojas-Graü, Avena-Bustillos,et al., 2007

Polycaprolactone/alginate/antimicrobialcompounds

Packaging(film)

Broccoli Inhibitory effect on growthof pathogens

Takala et al. (2013)

Alginate/clay nanocomposite/essential oil Film – Inhibitory effect onbacterial growth

Alboofetileh et al. (2014)

Alginate Coating Poached and deli turkeyproducts

Inhibition of listeriamonocytogenes growth,good adherent and stablefilm

Juck et al. (2010)

Alginate/antioxidant Coating Refrigerated bream Less chemical and bacterialspoilage

Song et al. (2011)

Alginate/Lemongrass essential oil Coating Fresh-cut pineapple Extention shelf life Azarakhsh et al. (2014)Carrageenan Coating Papaya Reduction moisture loss,

delayed ripening, retentionof firmness

Hamzah et al. (2013)

�-Carrageenan/pectin/mica flakes Film – Improvement of barrierproperties

Alves et al. (2010)

�-Carrageenan/chitosan/model bioactivecompound (methylene blue)

Coating – Dependent release ofmethylene blue onconcentration gradient andpolymer relaxation ofnanolayers

Pinheiro, Bourbon, Medeiros,et al. (2012)

Cellulose/alginate Film – Good mechanical andbarrier properties

Sirvio et al. (2014)

Alginate/pectin Film – Homogenous andtransparent film

Galus and Lenart (2013)

Alginate Coating Dog biscuits – González-Forte, Bruno, andMartino (2014)

Sodium alginate/�-carrageenan/aromacompound

Film – Dependence ofpermeability, diffusion, andstructure of film on aromacompound characteristics

Hambleton et al. (2011)

Sodium alginate (SA)/whey protein isolate(WPI)/gelatin(G)

Film – – Wang et al. (2010)

�-Carrageenan/agar/clay/polylactide Film – Improving film properties Rhim (2013)Alginate Coating UV-activated oxygen indicator

filmsReduction of dye leachinginto water

Vu and Won (2013)

Alginate/pullulan Film – Moisture sensitive Xiao et al. (2012)�-Carrageenan/locust bean gum Film – Improving barrier

properties and tensilestrength

Martins et al. (2012)

Alginate-acerola puree/cellulose Film – Improvement of tensileand water vapor barrierproperties of films

Azeredo et al. (2012)

Alginate-apple puree/plant essential oils Film – Antimicrobial activity, noadverse effect onmechanical properties offilm

Rojas-Graü, Avena-Bustillos,et al., 2007

Alginate/nano-Ag Coating Shiitake mushroom Spoilage Reduction,improvement of sensoryatribiutes, lower weightloss

Jiang et al. (2013)

�-Carrageenans Film Encapsulating aromacompound

Suitable for flavorencapsulation

Hambleton et al. (2009)

�-Carrageenans/aroma compound Film – Controlled release ofaroma componds,encapsulation capacity

Marcuzzo et al. (2010)

Alginate/beta-cyclodextrin/trans-cinnamaldehyde

Coating Fresh-cut watermelon Shelf-life extention,inhibitory effect on growthof psychrotrophics,coliforms, yeast and molds

Sipahi et al. (2013)

Alginate/ascorbic acid/citric acid Coating Fresh-cut Kent mangoes Color retention, highantioxidant activity

Robles-Sánchez et al. (2013)

�-Carrageenan Film Encapsulating aromacompound

Fast release of aromacompound in water

Fabra et al. (2012)

�-Carrageenan/chitosan/allylisothiocyanate/mustard extract

Coating Fresh chicken breasts Inhibition of C. jejuni, lacticacid bacteria, and aerobicbacteria growth

Olaimat et al. (2014)

Agar/�-carrageenan/konjac glucomannan Film Fresh spinach Antimicrobial andantifogging film with highwater holding capacity

Rhim and Wang (2013)

Alginate/chitosan Film – Rougher structure Arzate-Vázquez et al. (2012)

E. Tavassoli-Kafrani et al. / Carbohydrat

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ig. 1. Structural characteristics of alginates: (a) alginate monomers, (b) chain con-ormation, (c) block distribution.

eproduced with permission from Draget and Taylor (2011).

cquired by Merck and Co. Inc., USA. These combined companiesroduce about 70% of the world’s alginate (McHugh, 1987).

To extract the alginate, seaweed is broken into pieces and stirredith a hot solution of an alkali, usually sodium carbonate. After

bout 2 h, the alginate dissolves as sodium alginate to give veryhick slurry, and it contains undissolved parts of seaweed, mainlyellulose. The solution is diluted with very large amounts of water.hen, the solution is forced through a filter cloth in a filter presslong with a filter aid such as diatomaceous earth. The last steps precipitation of the alginate from the filtered solution, eithers alginic acid or calcium alginate (McHugh, 2003). Pretreatmentbefore alkaline extraction) of the seaweed with acid leads to a

ore efficient extraction, a less colored product, and reduced lossf viscosity during extraction because lower amounts of phenolicompounds are present (McHugh, 1987).

Based on its linear structure, alginate can form strong films anddequate fibrous structures in the solid state, hence, it is considered

good filmogenic material (Blanco-Pascual, Montero, & Gómez-uillén, 2014). Alginates have many applications. They can be used

n foods for limiting dehydration of meat (Varela & Fiszman, 2011),sh and fruits (Hambleton et al., 2011), in beverage industriess thickening, gel-forming and colloidal stabilizing agents (Liakost al., 2013), in nonfood industries such as textile printing, as wells manufactories welding rods, binders for fish feed, immobilizediocatalysts (carrying enzymes), release agents, and paper, and alsoor pharmaceutical and medical uses (Skurtys et al., 2010; Vu &

on, 2013). Alginates can also be employed as matrix polymers forncapsulation of drugs, proteins, cells, and DNA (Ashikin, Wong, &aw, 2010).

Alginate can be isolated from brown algae (Laminaria digitatand Ascophyllum nodosum) cell walls where it is present as the cal-ium, magnesium, and sodium salts of alginic acid (McHugh, 2003).t can also be synthesized by microorganisms (Alboofetileh, Rezaei,osseini, & Abdollahi, 2014; Blanco-Pascual et al., 2014). Alginate

s a linear anionic (Vu & Won, 2013) water-soluble polysaccharideHambleton et al., 2011) consisting of monomeric units of 1-4-inked �-d-mannuronate (M) and �-l-guluronate (G) (Fig. 1a, b)Alboofetileh et al., 2014; Blanco-Pascual et al., 2014). The poly-

er chain of alginate is made up of 3 kinds of regions or blocksn different proportions and different distributions in the chainFig. 1c). In these the physical properties of alginates depend on
he relative proportion of these 3 blocks (Liakos et al., 2013; Xiao,u, & Tan, 2014). The G blocks contain only units derived from l-uluronic acid which cause greater gel strength, the M blocks arentirely based on d-mannuronic acid, and the MG blocks consist of
e Polymers 137 (2016) 360–374 363

alternating units of d-mannuronic acid and l-guluronic acid whichdetermine the solubility of alginates in acid (McHugh, 1987). Mand G blocks are known as homopolymeric blocks and MG blocksare heteropolymeric blocks (Gómez-Ordónez & Rupérez, 2011). Therelative fraction of each unit depends on species, part, and age ofseaweeds from which the alginate is isolated (Ashikin et al., 2010).The biological source, growth, and seasonal conditions are alsodeterminative (Zactiti & Kieckbusch, 2006).

Alginate monomer composition and sequence affect seriouslythe final properties of alginate gels since selective binding of ions isa pre-requisite for gel formation (Draget & Taylor, 2011). The M/Gratio and distribution of M and G blocks in the chain of alginateaffect the physical properties of the alginate. M/G ratios < 1 indi-cate a large amount of guluronic acid, which has the ability to formstrong junctions. M/G ratios > 1 are indicative of a lower guluronicproportion, which might result in softer, more elastic structures(Blanco-Pascual et al., 2014).

Alginate solutions can form gels either by lowering the pH belowthe pKa value of the guluronic residue or in the presence of diva-lent ions (Hambleton, Perpinan-Saiz, Fabra, Voilley, & Debeaufort,2012; Hambleton et al., 2011). These ions include calcium, magne-sium, manganese, aluminum, and iron (Dhanapal et al., 2012). Theaffinity of alginates toward divalent ions decreases in the follow-ing order: Pb > Cu > Cd > Ba > Sr > Ca > Co, Ni, Zn > Mn (Pawar & Edgar,2010).

The most useful and unique property of alginates, which causesthe strong gel or low-soluble polymer, refers to their ability to reactwith polyvalent metal cations, specifically calcium ions (Zactiti &Kieckbusch, 2006). These ions help the formation of associationbetween M and G blocks. The length of G blocks determines the algi-nate ability and selectivity to form these interactions (Hambletonet al., 2012). M blocks and MG blocks are almost without selec-tivity. The diffusion of ions into the alginate solution causes anion exchange process where the water soluble alginate (for exam-ple sodium or potassium form) has to exchange its counter-ionswith Ca2+ to obtain a sol/gel transition. This ionic cross-linking willbe form a rapid cold setting and heat stable gel. When formingalginate gels, two contiguous, diaxially linked guloronic residuesform a cavity that act as a binding site for calcium ions (Cuadros,Skurtys, & Aguilera, 2012). This arrangement is pictured as the “egg-box” model (Fig. 2). The mechanical properties of films are directlyrelated to the number of “eggbox” sites. As a result, film charac-teristics like water and mechanical resistant, barrier properties,cohesiveness, and rigidity can be improved (Zactiti & Kieckbusch,2006).

However, the definite mechanism of alginate gelation is stillunder controversy. The polyvalent metal cations tend to chelatethe carboxylate and hydroxyl groups of the alginate. This chelationis not just simple, but a sort of bridge between the metal ion and twocarboxylate and one or more pairs of the hydroxyl groups occursthrough partially ionic and partially coordinate bonds, respec-tively. Therefore, a two- stage mechanism has been suggested forsuch chelation by numerous studies (Fig. 3): first, the formation ofstrongly intramolecular linked dimer associations with importantcontributions from van der Waals and hydrogen bonding interac-tions in which the functional groups involved in chelation belong tothe same chains, followed by the formation of weaker intermolec-ular dimer associations in which the carboxylate and hydroxylfunctional groups are related to different chains that display noparticular specificity, and being mainly governed by electrostaticinteractions (Cuadros et al., 2012; Hassan, Gobouri, & Zaafarany,2013; Li, Fang, Vreeker, & Appelqvist, 2007).

3 kinds of alginate blocks have different interactions withcations. M blocks bind cations externally near their carboxylategroups, while G blocks integrate cations into pocket-like structuresformed by adjacent G residues. In MG blocks, cations preferentially


ox” dR

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ocate in a concave structure formed by M–G pairs (Emmerichs,ingender, Flemming, & Mayer, 2004).A direct mixing of alginates and polyvalent metal cations does

ot produce homogeneous gels due to the very rapid and irre-ersible formation of junctions between these two components.he formation of gel lumps (fish-eyes) is the result of such mixing.he only exception is for very small volumes of alginate under highhear. To overcome this problem, the ability to control the intro-uction of the crosslinking ions is essential. This control is possibley two different gel preparing methods: diffusion and the inter-al setting. In the diffusion method (Fig. 4a), cross-linking ions, forxample Ca2+, diffuse from an outer reservoir into an alginate solu-
ion. In the internal setting method (sometimes also referred to asn situ gelation) (Fig. 4b), an inert ion is converted into an active
ig. 3. Intermolecular and intramolecular interactions of alginate and metal cations.

eproduced with permission from Hassan, Gobouri, and Zaafarany (2013).

uring gelation of alginate.

cation by a change of pH of the alginate solution or by a limitedsolubility of the calcium salt source.

In the diffusion method, the Ca2+ will first cross-link the film sur-faces drawing the polymer chanis closer to form a less permeablesurface to the diffusion of Ca2+. Thus, the diffusion method yieldsgels having a Ca2+ ion concentration gradient across the thickness,while internal setting gives gels with uniform ion concentrationsthroughout (Pawar & Edgar, 2010).

By increasing the cation concentration during gelation of algi-nate, a more densely cross-linked structure will be formed whichcauses a less porous structure as well as reduction in water contentand permeability of the gel (Aslani & Kennedy, 1996). However,there is an optimal amount of cross-linker that can be used andfurther increase in amount of cation employed does not exert sig-nificant changes in the gel properties (Chan, Lee, & Heng, 2006).

Sodium alginate among the other kinds of alginates, can formfilms with the properties of being water-soluble, strong, glossy,tasteless, odorless, flexible, low permeable to oxygen and oils (Xiaoet al., 2014).

During the formation of alginate film by diffusion settingmethod, the Ca2+ in the cross-linking solution will first cross-linkthe film surface drawing the polymer chains closer to form a lesspermeable surface to the diffusion of calcium ions into the inte-rior. So, using an optimal amount of cross-linker to produce matrixwith the desired characteristics (instead of a matrix with a highlycross-linked surface and a less well cross-linked interior) is essen-tial in diffusion setting method. In internal setting, by using CaCO3,as the source of calcium ions, the reaction between the acid andcarbonate leads to the formation of CO2 which cause formationof cavities within the film. Therefore, prepared films and coatingby diffusion setting which use external cross-linking are thinnerfilms with smoother surface, greater matrix strength, stiffness andpermeability than films and coatings prepared by internal settingwhich are internally cross-linked (Chan et al., 2006).

3. Carrageenan

Carrageenan and agar are 2 major groups of galactans presentedin red seaweeds (de Araújo et al., 2011). Carrageenans are natu-ral hydrophilic polymers (Osorio, Molina, Matiacevich, Enrione, &Skurtys, 2011) with a linear chain of partially sulphated galactans,


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hich presents high potential of film-forming. These sulphatedolysaccharides are extracted from the cell walls of various red sea-eeds (Skurtys et al., 2010). The most usual seaweeds for extraction

f carrageenans are Kappaphycus alvarezii and Eucheuma denticu-atum seaweeds (McHugh, 2003). However, some scientists extractarrageenans from Hypnea musciformis (Wulfen) Lamoroux sea-eeds (Cosenza, Navarro, Fissore, Rojas, & Stortz, 2014) and Solierialiformis (de Araújo et al., 2011). The main source of commercialarrageenan is Chondrus crispus species of seaweed known as Car-ageen Moss or Irish Moss in England and Carraigin in Ireland. Theame Carraigin was first used by Stanford in 1862 for the extractf C. crispus. It has been used in Ireland since 400 AD as a gelationgent and as a home remedy to cure coughs and colds. The termcarrageenan” is more recent and has been used by several authorsfter 1950 (Necas & Bartosikova, 2013; Rosa, 1972).

There are 2 different methods for carrageenan production.irst, is the original method, based on extraction of carrageenano an aqueous solution and after removing the filtrate con-aining seaweed residue, carrageenan should be recovered fromhe solution. This method was expensive and was only usedntil the late 1970s to early 1980s. In the second method,eaweeds are washed to remove solid impurities before treat-ng with alkali to extract the carrageenan. After extraction, theilute extracts (1–2% carrageenan) are filtered, concentrated, andhen precipitated with isopropanol to give a fibrous coagulum.he coagulum is pressed to remove solvent and washed. It is
hen dried and milled to an appropriate particle size (McHugh,003).
Carrageenan has many applications in food and even non-ood industries and is a high value functional ingredient in foods

om Juarez, Spasojevic, Faas, & de Vos, 2014), internal setting (b) (reproduced with

(Hambleton, Fabra, Debeaufort, Dury-Brun, & Voilley, 2009; Necas& Bartosikova, 2013). Carrageenan can be used as stabilizer (Hsu& Chung, 1999) in dairy products such as flavored milks (Necas &Bartosikova, 2013). They also can be used in water-based foods,meat products (as oxygen barrier to retard lipid oxidation (Varela& Fiszman, 2011), pet food (McHugh, 2003), infant food, and nutri-tional supplement beverages. The ability of suspending cocoa inchocolate milk at very low concentrations (ca. 300 ppm) is uniquein carrageenan (Necas & Bartosikova, 2013). They mostly have beenused to delay microbial growth in gels containing antimicrobialagents (Varela & Fiszman, 2011). They are also used in pharma-ceuticals, cosmetics, printing, and textile industries (Cosenza et al.,2014). Preparation of edible films using carrageenan is not abun-dant in literature because carrageenan is mostly used as a coating(Campos, Gerschenson, & Flores, 2011).

There are 3 main types of carrageenans differing in chem-ical structures and properties (Fig. 5): kappa carrageenan(�-carrageenan) with a 3-linked, 4-sulfated galactose and a 4-linked 3,6-anhydrogalactose, iota carrageenan (�-carrageenan)with a structure like the former, but with an additional sulfateester group on C-2 of the 3,6-anhydrogalactose residue, and lambdacarrageenan (�-carrageenan) with a 2-sulfated, 3-linked galactoseunit, and a 2,6-disulfated 4-linked galactose unit (Cosenza et al.,2014).

Carrageenans are water-soluble polymers which their solubilitydepend on the content of ester sulfate and the presence of potential
associated cations. Higher levels of ester sulfate mean lower solu-bility temperature. Presence of cations such as sodium, potassium,calcium, and magnesium promote cation-dependent aggregationbetween carrageenan helices.


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The presence of anhydro-bridges in �- and �-carrageeenaneduces the hydrophilicity of the sugar residue and inverts the chaironformation and allows the carrageenan to undergo conforma-ional transitions which are conducive to the gelation properties ofarrageenans (Rhein-Knudsen, Tutor Ale, & Meyer, 2015).

Iota carrageenan forms elastic and clear gels with no synere-is in the presence of calcium salts (McHugh, 2003). Its gels arehermoreversible (50–55 ◦C). The blending of iota carrageenan withalcium salts makes it a suitable hydrocolloid as a functional ingre-ient for stabilization, thickening, and gelation in dairy productsuch as milk gels and ice cream (Hambleton et al., 2009). It canorm a three-dimensional network with double-helix chains. Eachair of helixes being 13.9 A laterally spaced, therefore it has a com-act, dense, and organized film structure (Hambleton et al., 2012).

ota carrageenan-based edible films have good mechanical char-cteristics. They are emulsion stabilizers and can decrease oxygenransfer, and limit surface dehydration and taste deterioration ofruits and cheeses (Hambleton et al., 2012). They can also be useds encapsulation agents for active substances (Hambleton et al.,011). Lambda carrageenan dose not form gel and just forms highiscosity solutions (de Araújo et al., 2011). So, these polysaccha-ides are used as cold soluble thickeners in syrups, fruit drinks,izza sauces, and salad dressings (Milani & Maleki, 2012). Kappaarrageenan is one of the most common forms of carrageenans,hich can be used in foods. It has a double-helix conformation. The

inear helical portions can associate and form a three-dimensionalel in the presence of appropriate cations. This gel is freeze-thawtable. Kappa carrageenan is also able to interact with variousood proteins through electrostatic interactions and increase theirggregation stability (Lopez-Pena & McClements, 2014). Kappa car-ageenan forms strong and rigid gels with potassium salts as well asrittle gels with calcium salts. Kappa carrageenan gels are opaque,ut by sugar addition they become clear (McHugh, 2003).

The mechanism of gel formation of carrageenans which is ahermo-reversible gel depends on temperature and gel-inducinggents. Structure of carrageenans at high temperature (above0 ◦C) is as random coil which is due to the electrostatic repul-ions between neighboring chains. Upon temperature reducing,
he conformation of chains changes to helical structure. Furtherooling and presence of cations lead to intermolecular interactionsetween the carrageenan chains which cause aggregation of theelical dimers and formation of a stable three dimensional network.
es of carrageenans.

For �-carrageenan and �-carrageenan, typically potassium andcalcium respectively stabilize the junction zones between the twohelixes by binding to the negatively charged sulfate groups withouthindering cross-linking of the two helices (Fig. 6). However, thecharged sulfate esters on the other side of the �-carrageenan causean extensive conformation via a repulsion effect of the negativeSO3

− groups and inhibit gelation while promoting viscosity in thesolution (Rhein-Knudsen et al., 2015).

Carrageenans, especially poligeenan (degraded carrageenan)have been known to induce colonic inflammation, (Chen, Yan,Wang, Xu, & Zhang, 2010) and to be toxic to macrophages (Thomson& Horne, 1976). However, toxicological properties of carrageenanshave been shown at high doses that do not occur with the foodadditive. Average molecular weight greater than 100,000 Da witha low percentage of smaller fragments is necessary for food gradecarrageenan (Cohen & Ito, 2002; Prajapati, Maheriya, Jani, & Solanki,2014).

4. Edible film and coatings applications

An ideal edible coating forms a thin layer on the surface of thecoated food product and supplies an effective barrier to water,vapour, moisture, or temperature. In addition, it does not absorboxygen and forms a selective barrier to gases, significantly car-bon dioxide (Chlebowska-Smigiel, Gniewosz, & Gaszewska, 2008).Alginate and carrageenan are highly hydrophilic. So, they presentonly a limited barrier to moisture. However, they are a goodbarrier to fats and oils. They are also good oxygen barriers andcan provide protection against lipid oxidation (Varela & Fiszman,2011).

The diffusion of compounds within edible films and coatingsdepend strongly on the physicochemical properties of the com-pounds such as molecular weight, structure, hydrophobicity, andpolarity. Permeability of compounds is affected by the interactionsbetween the compounds and the film matrices. Also the mobility ofthe diffusing molecule has an important role on the permeability.On the other hand the diffusion of compounds within alginates andcarrageenans which are water-soluble polymers can be affected by
water. Water is a solvent, so it can induce a modification of thematrix structure, such as swelling of polymers, and can modify thediffusion of molecules showing an affinity for water (Hambletonet al., 2011, 2012).


Fig. 6. The gelation mechanism of �-carrageenan in the presence of potassium ions.R

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eproduced with permission from Rhein-Knudsen et al. (2015).

The diffusion of water soluble material is expected to occurhrough aqueous pores or channels in the alginate film matrix. A

ore cross-linked film has lower or smaller pores or channels. Theistribution of cross-linkages in the matrix has a significant effectn substances permeation. Inhomogeneous alginate films impedeubstances permeation more than homogeneous films.

Internal setting method produces a more uniformly cross-linkedatrix. However, the liberation of CO2 forms microscopic cavities

n internally cross-linked films which impede diffusion of sub-tances. The cavities are air vesicles which disrupt liquid continuityn the matrix. The internal gelation method is useful in producingross-linked alginate films and coatings for retarding or controllingelease of material in comparison to diffusion setting (Chan et al.,006).

The functionality and performance of edible coatings mostlyepend on the production method of coating and the coating abilityo adhere to the product surface (Dhanapal et al., 2012). Edible filmsan be defined as a thin protective layer for food packaging, which
an be eaten with food (Hambleton et al., 2009). Edible films caneduce the environmental pollution; improve the sensorial prop-rties of packaged products, decrease moisture loss, and increasehe nutritional value of the foods (Zactiti & Kieckbusch, 2006).
Alginate and carrageenan can be used to form film coatingfor meat and meat products. The coatings can prevent shrinkage,microbial contamination, and surface discoloration by delayingmoisture transport (Nussinovitch, 2009). The effect of alginategel coating as an edible susceptor in combination with saltin microwaveable chicken nuggets was investigated by Albert,Salvador, and Fiszman (2012). Results showed that salty algi-nate coating could act as an effective susceptor during heatingby microwave and therefore decrease cooking times. Alginate andcarrageenan based edible coatings are effective as post-harvesttreatments to maintain quality of fruits such as tomato, peach,sweet cherry, and so on. Edible coatings are able to delay ripen-ing and can extend shelf-life of products (Hamzah, Osman, Tan,& Mohamad Ghazali, 2013; Valero et al., 2013). Minimally pro-cessed products such as fresh cut fruits are susceptible to microbialspoilage. Edible coatings are able to control the microbial spoilageby preventing microbial proliferation and delaying respiration(Mastromatteo, Conte, & Del Nobile, 2012). Alginate and car-
rageenan film coatings are applied to carry different functionalagents in order to improve their application. For example, alginatesolution diminished dye leaching out of colorimetric oxygen indi-cator due to its ability to ion bind with the cation dye (Vu & Won,

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013). Lu, Ding, Ye, and Liu (2010) also indicated that the use oflginate coating with nisin and cinnamon could maintain qualityf northern snakehead fish filets. Application of nisin containinglginate film for sliced beef could reduce the amount of Staphylococ-us aureus. It could be suggested that nisin containing edible filmsould control the growth of pathogens at the surface of ground beefr other meat products (Millette, Tien, Smoragiewicz, & Lacroix,007).

Hydrogels are highly hydrophilic polymer gels with the ability ofwelling by absorbing and retaining large amounts of water with-ut dissolving or losing their integrity in water. They can be used forood packaging. Rhim (2013) prepared hydrogel films composed ofgar, �-carrageenan, konjac glucomannan, and nanoclay. This filmhowed a high water-holding and water vapour adsorptive capac-ty. These properties makes hydrogel film a suitable packaging filmor highly moisture foods or foods contacting with high humidityondition.

. Film/coating production methods

Principal technologies for producing edible films are similar tohose for thermoplastic structures: solvent casting and extrusion.bviously, the conditions are different, but the principles are allied.or the coating production the main techniques are spraying andipping (Skurtys et al., 2010).

.1. Edible film formation methods

One of the most used techniques to form edible films is solventasting or wet process (Nussinovitch, 2009). Dispersions of edibleaterials are spread on a suitable base material and then let to

e dried. During drying of the solution, solubility of the polymerecreases as a result of solvent evaporation, until polymer chainslign themselves to form films (Skurtys et al., 2010). It is importanto carefully control drying rate and environmental conditions dueo their high influence on final thickness and structural character-stics of the resultant film (Campos et al., 2011). Infrared drying canasten the drying process and so is advantageous.

Easy removing of film without any tearing and wrinkling is verymportant, which is dependent on the type of base material. Forasy peeling off dried film from one edge of the base material, opti-um moisture content (5–8%) is desirable (Tharanathan, 2003).The other technique is a dry process in which compression

olding and extrusion are done, rely on the thermoplastic sta-us of some polysaccharides and proteins at low moisture levelsNussinovitch, 2009). Among three techniques of film production,nly casting method exemplifies. Because films produced via thisethod are stand-alone. Hence, it is possible to evaluate the phys-

cal and chemical properties of film forming material alone (Lee &an, 2006).Casting method has been used to form alginate films. Algi-

ate reaction with calcium ions is fast, but casting to make films difficult. So, 2 steps procedures are used to preparing castedlms. The first step is to cast a partially dry alginate film solu-ion and then immersing into a calcium solution. Alternatively,t is possible to spray calcium solution to the pre-formed filmCampos et al., 2011). This method was used for preparation of algi-ate/chitosan (Arzate-Vázquez et al., 2012), alginate/pectin (Galus

Lenart, 2013), and alginate/cellulose films (Sirvio, Kolehmainen,iimatainen, Niinimaki, & Hormi, 2014).

Cha, Cooksey, Chinnan, and Park (2003) prepared nisin-ncorporated films and assayed the effect of casting and heat-press

ethods as film preparation methods and the type of edible filmsmethylcellulose (MC), hydroxypropyl methyl cellulose (HPMC), �-arrageenan and chitosan) on antimicrobial activity of the films.esults showed that heat-pressed films exhibited less inhibitory

te Polymers 137 (2016) 360–374

zones in comparison with casting method. The antimicrobialactivity of nisin- incorporated MC films was most effective in heat-pressed films as well as chitosan films in the cast films category.Casting method was also used for preparation of polycaprolac-tone/alginate based antimicrobial films (Takala, Vu, Salmieri, Khan,& Lacroix, 2013) and for production of pectin/�-carrageenan com-posite films containing organically modified nanoclays (Falgueraet al., 2011).

5.2. Edible coating formation methods

5.2.1. Spraying methodThis method can be used for low viscosity coating solutions,

which can be easily sprayed at high pressure (60–80 psi) (Dhanapalet al., 2012; Tharanathan, 2003). The drop-size distribution ofsprayed coating-forming solution in classic spraying system can beup to 20 �m, whereas electrospraying can produce uniform parti-cles of less than 100 nm from polymer and biopolymer solutions.Furthermore, the formation of polymeric coatings by spraying sys-tems can be affected by other factors such as drying time, dryingtemperature, drying method, and so on (Skurtys et al., 2010).

5.2.2. Dipping methodAmong different coating formation methods, only dipping tech-

niques can form high thick coating (Dhanapal et al., 2012). Dippingmethod is used to form coatings on fruits, vegetables, and meatproducts (Lu et al., 2010; Tharanathan, 2003). Properties such asdensity, viscosity, and surface tension of coating solution are impor-tant to estimate the film thickness (Skurtys et al., 2010). In thismethod, a thin membranous film is formed over the product surfaceby directly dipping the product into the aqueous medium of coatingformulations, removing, and allowing to air dry. Foam applicationmethod is another coating formation method. This method is usu-ally used by applying emulsions. In here the foam will break byextensive tumbling action, and therefore uniform distribution ofthe coating solution will be over the product surface (Tharanathan,2003).

Dipping method has been used to coat papaya fruit by using�-carrageenan (Hamzah et al., 2013) and to coat carrot by usingsodium alginate (Mastromatteo et al., 2012).

The formation of edible coatings on minimally processed fruits isproblematic due to the difficulty of obtaining a good coating adhe-sion to the hydrophilic surface of the cut fruit. Multilayer techniqueis used to overcome it by the layer-by-layer electrodeposition.In here 2 or more layers of material are physically or chemicallybonded to each other (Skurtys et al., 2010).

The layer-by-layer method was used to produce multilayerantimicrobial alginate-based edible coating for fresh-cut water-melon (Citrullus lanatus) (Sipahi, Castell-Perez, Moreira, Gomes,& Castillo, 2013). A multilayer coating was also prepared forcontrolled release of polyethylene terephthalate by using �-carrageenan and chitosan (Pinheiro, Bourbon, Quintas, Coimbra, &Vicente, 2012).

5.2.3. Spreading methodIn spreading method or brushing method, the coating solution is

spread on the product. González-Forte, Bruno, and Martino (2014)used this method to coat dog biscuits with 2 different coatings. Onone hand, they spread sodium alginate solution with a brush on thesurface of biscuits and then sprayed a solution of CaCl2 to form agel. On the other hand, they spread a gelatinized suspension of cornstarch on the biscuit.

6. Composite films and coatings

Edible film and coating materials must have favorable physico-chemical and sensory properties to satisfy the consumers’ product

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cceptability (Wang, Marcone, Barbut, & Lim, 2012). As each indi-idual component has some defects, so applying one componentith another one can cover their defects. Composites are hybridaterials, which their properties are different from their individual

omponents of which they are made. For more than one hundredears, many new composite materials had been produced annuallySimkovic, 2013).

It is possible to improve the technological properties of edi-le films and coatings made of single component by usinghemical reactions (such as cross linking) or physical treat-ents (such as ultrasound, heat or radiation) (Wang, Auty, &

erry, 2010). However, film functionality can be improved byombining different proteins, polysaccharides, lipids, as well asynthetic polymers. A synergistic effect of combined features ofure components may be achieved by designing composite filmsnd coatings. Mechanical and barrier properties of compositelms and coatings depend on properties of each forming poly-ers and their compatibility (Bourtoom, 2008; Galus & Lenart,

013).

.1. Carrageenan/alginate – lipid composite films and coatings

Composite films containing both lipid and polysaccharide canorm packaging with good mechanical and water barrier propertiesHambleton et al., 2012). In here, lipids can be either used to obtain-ng an emulsified film by dispersing it in polysaccharide aqueousolution and then drying or can be cast as a layer on the polysaccha-ide film to obtain a bilayer film (Hambleton et al., 2012; Marcuzzo,ensidoni, Debeaufort, & Voilley, 2010). The prior is used in mostf food industry applications because it can improve water barrierroperties and only need one step in manufacture in comparisono 3 step for latter (Hambleton et al., 2009, 2012). In addition,y using lipids to form emulsified films, active molecules can bencapsulated.

Carrageenan emulsion-based film was prepared to encapsulateifferent aroma compounds. The fat was added to the plasti-ized film-forming solution composed of carrageenan and glycerol.

mix of 10 aroma compounds was pre-solubilized in meltedat before being dispersed into the film-forming solution. Glyc-rol monostearate (GMS) was used as emulsifier. It was foundhat carrageenan films as encapsulating matrixes have better per-ormances for retention of more polar aroma compounds. Theyan retain volatile compounds during film formation, and releaseradually with time (Marcuzzo et al., 2010). Hambleton et al.2012) measured permeability, sorption, and diffusion coefficientf the n-hexanal and d-limonene aroma compounds throughmulsified and non-emulsified �-carrageenan and sodium algi-ate based films. In another study, Fabra, Chambin, Voilley, Gay,nd Debeaufort (2012) analyzed the release of n-hexanal and-limonene from �-carrageenan films with and without lipid.hey showed that d-limonene was encapsulated in the lipidhase of edible films and its release was decreased in the saltedium.

.2. Carrageenan/alginate-polysaccharide composite films andoatings

Alves et al. (2010) studied the barrier properties of a polymericatrix composed of �-carrageenan and pectin with the inclusion

f mica flakes. The effect of adding water as plasticizer on bar-ier properties of these composite films was also studied. Results
emonstrated that there is a significant decrease of CO2 and O2 per-eability in the films without mica flakes. Furthermore, above 10%
f mica flakes in the composite, the barrier properties of the filmsere decreased. It was interested that a significant increase of both

e Polymers 137 (2016) 360–374 369

CO2 and O2 permeability was observed in hydrated films with 25%water.

Biocomposite films based on 4 different wood cellulose fibersand alginate were prepared by Sirvio et al. (2014) and the filmproperties were studied. There was a good interaction betweencelluloses and alginate matrix. By increasing the amount of thefiber in the biocomposite films, thickness, tensile strength, andspecific modulus of films were increased but strain and flexibil-ity of films decreased and the mechanical properties of films wereincreased by increasing the amount of the fiber in the biocompos-ite films. Osorio, Molina, Matiacevich, Enrione, and Skurtys (2011)produced edible film coating for fresh blueberries by incorpora-tion of �-carrageenan, plasticizer, and carnauba wax emulsion intothe hydroxy propyl methyl cellulose and studied the film struc-ture and functional properties. An increase in film structure andfunctionality was seen as a result. Martins et al. (2012) developed�-carrageenan/locust bean gum blend films by casting method andstudied films physical properties. The addition of �-carrageenanto locust bean gum improved the barrier properties of the films.For example water vapour permeability of the films decreased.Moreover, the tensile strength of blend films enhanced. It is sug-gested that hydrogen bonds interactions between �-carrageenanand locust bean gum have a significant influence in films properties.

High cost of some polymers such as pullulan has limited theiruse. Blending them with other abundant polymers can overcomethis problem. Alginate was successfully incorporated into the pul-lulan films by Xiao, Lim, and Tong (2012). It reduced not only thecost of pullulan films, but also potentially enhanced the materialproperties of the blend films.

6.3. Carrageenan/alginate-inorganic particles composite filmsand coatings

The addition of inorganic impermeable particles (for examplemica flakes) into the polymer matrix enhances the barrier prop-erties of the films. However, it makes the films less transparentand therefore not suitable for packaging applications. Reducing thesize and the amount of the particles can overcome this drawback.Nanocomposites have obtained significant attention due to theirimprovement in the mechanical and physical properties (Alveset al., 2011).

In the research done by Alves et al. (2011), composite filmcomposed of pectin, �-carrageenan and modified nanoclays wasprepared by casting method. Results indicated that the addition of10% organically modified nanoclay particles to the polymer matrixhas a positive impact on the barrier properties of the films. Rhim(2013) prepared a multilayer film with agar/�-carrageenan/claynanocomposite and polylactide. The result indicated that the filmproperties of prepared film such as optical, mechanical, barrier, andthermal stability properties were improved.

6.4. Carrageenan/alginate-fruit purees composite films andcoatings

Production of edible films from fruit purees has some elab-orations due to the presence of film-forming polysaccharides intheir combination. The mechanical and barrier properties of thosepolysaccharides combine with the sensory and nutritional proper-ties of the fruit in these films. Azeredo, Miranda, Rosa, Nascimento,and de Moura (2012) evaluated the properties of the edible films
from alginate–acerola puree reinforced with cellulose whiskers.Results showed that the whiskers could improve the water vapourbarrier and overall tensile properties (except by elongation) of thefilms.

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. Combination of different components with edible filmsnd coatings

Edible films and coatings can incorporate other componentsuch as antibrowning, antimicrobial, antioxidant, and texture mod-fier agents (Bonilla et al., 2012; Osorio, Molina, Matiacevich,nrione, & Skurtys, 2011; Zactiti & Kieckbusch, 2006), colorants,avors, nutrient, spices (Kang et al., 2013; Nussinovitch, 2009;astromatteo et al., 2012), surfactants, emulsifiers plasticizers, and

o on (Osorio, Molina, Matiacevich, Enrione, & Skurtys, 2011). Inhe other hand, blending with other food additives and modifiergents can extend applications of edible films and coatings. This isecause of the weak mechanical properties (tensile strength andensile elongation) and poor barrier properties of biodegradablelms and coatings (Lee et al., 2004; Sorrentino, Gorrasi, & Vittoria,007). For example, hydrocolloids are hydrophilic materials, and sore poor moisture barriers (Alves et al., 2011; Atarés et al., 2011).his property can be compensated by adding lipids, which are veryood moisture barriers (Tharanathan, 2003).

.1. Plasticizers

Plasticizers are non-volatile and low-molecular weight com-ounds, which are added to polymers in order to reduce brittleness,

mpart flow and flexibility, and enhance toughness and strength forlms. As a specific definition for coatings, plasticizers impact resis-ance of the coating and reduce flaking and cracking by improvingoating flexibility and toughness. As a disadvantage, plasticizersenerally increase film permeability to oxygen, moisture, aroma,nd oils due to reducing intermolecular attractions along the poly-er chains (Barreto et al., 2003; Rojas-Graü, Avena-Bustillos, et al.,

007; Sothomvit & Krochta, 2005).Small size, high polarity, more polar groups per molecule, and

ore distance between polar groups within a molecule are plas-icizer characteristics, which enhance plasticizing effects on aolymeric system. Plasticizers are generally required for polysac-harides or proteins based edible films (Skurtys et al., 2010).

Monosaccharides, disaccharides, or oligosaccharides (for exam-le: fructose–glucose syrups, sucrose, honey, corn syrup) areommonly used as plasticizers in film systems (Azeredo et al.,012). Polyols (for example glycerol, sorbitol, glyceryl derivatives,nd polyethylene glycols) (Galus & Lenart, 2013; Hambleton et al.,012; Hamzah et al., 2013; Myllärinen, Partanen, Sppälä, & Forssell,002; Song, Liu, Shen, You, & Luo, 2011), lipids (Campos et al., 2011),nd derivatives (for example phospholipids, fatty acids, and sur-actants) are also used as plasticizers (Sothomvit & Krochta, 2005).

ater can act as a plasticizer in hydrophilic biopolymers due toisruption of hydrogen bonds between polymer chains (Xiao et al.,012).

.2. Antimicrobial agents

The incorporation of antimicrobial agents into the edible filmsnd coatings has demonstrated to act as a stress factor to decreaseathogen growth and to protect foodstuff against spoilage flora.he use of chemical antimicrobial agents such as benzoic acid,odium benzoate, propionic acid, sorbic acid, and potassium sor-ate is limited in food systems due to health concerns of consumersMastromatteo et al., 2012; Skurtys et al., 2010). Therefore, con-umers demand for natural and healthy preservatives is caused tose of generally recognized as safe (GRAS) compounds (Campost al., 2011). The most frequently used biopreservatives for antimi-
robial packaging are lysozyme and nisin (Skurtys et al., 2010).ther antimicrobial compounds include organic acids (lactic, acetic,alic, and citric acids), chitosan, the lactoperoxidase system, and
ome plant-derived secondary metabolites such as essential oils

te Polymers 137 (2016) 360–374

and phytoalexins. Cassia, clove, garlic, sage, oregano, pimento,thyme, rosemary, lemongrass, scutellaria, and forsythia suspenseare examples of such plants (Campos et al., 2011; Mastromatteoet al., 2012; Shojaee-Aliabadi et al., 2014). Edible films and coatingswith antimicrobial properties can be named as active packaging(Juck, Neetoo, & Chen, 2010).

Metal nanomaterials as a noble kind of antimicrobial agentsfor food packaging system have received increasing attention inrecent years. Among metal nanomaterials, nanosilver has beenshown to be a promising antimicrobial material. Nanosilver par-ticles can interrupt bacterial processes such as respiration andcell division and finally lead to cell death by attaching to thecell membranes and penetrating into bacteria. Bactericidal activityof nanosilver enhances by release of silver ions within bacte-rial cells. Jiang, Feng, and Wang (2013) investigated the effect ofalginate/nanosilver coating on the microbial and physicochemi-cal quality of shiitake mushroom during storage. Results indicatedthat the alginate/nanosilver coating has beneficial effect on thequality of shiitake mushroom and therefore, could be used forits preservation and shelf-life expansion. The antimicrobial prop-erty of alginate/clay nanocomposite films containing 3 essentialoils (marjoram, clove, and cinnamon) against food pathogens wasstudied. Results showed that in all films marjoram had the highestantimicrobial activity (Alboofetileh et al., 2014).

Azarakhsh, Osman, Ghazali, Tan, and Mohd (2014) studied theinfluence of adding lemongrass essential oil to alginate based ediblecoating in microbial and physicochemical of fresh-cut pineapple.Results indicated that the incorporation of 0.3% (w/v) lemongrassin coating had potential to access both extension in the shelf-lifeand maintenance the quality of fresh-cut pineapple. In anotherstudy Takala et al. (2013) incorporated two antimicrobial formu-lations into alginate films, namely, A and B. The former containedorganic acids mixture, rosemary extract, and Asian spice essentialoil and the latter contained organic acid mixture, rosemary extract,and Italian spice essential oil. The inhibitory effect of each for-mulation on the growth of Listeria monocytogenes, Escherichia coli,and Salmonella typhimurium was investigated on fresh broccolistored at 4 ◦C. Results showed a good inhibitory capacity of algi-nate films containing formulation A against growth of mentionedbacteria.

Olaimat, Fang, and Holley (2014) evaluated the bacteri-cidal property of allyl isothiocyanate incorporated into �-carrageenan/chitosan coating against Campylobacter jejuni on freshchicken. They found that �-carrageenan/chitosan coatings contain-ing allyl isothiocyanate had excellent potential to reduce C. jejuniviability on raw chicken. Chitosan and �-carrageenan are oppo-sitely charged polysaccharides, so a mixture of them has goodbarrier properties and can cause delayed release of incorporatedbioactive compounds.

The effect of incorporation of antimicrobial agents includingnisin, Novagard CB 1, Guardian NR100, sodium lactate, sodiumdiacetate, and potassium sorbate into edible coatings includingalginate, �-carrageenan, pectin, xanthan gum, and starch ongrowth control of L. monocytogenes in poached and deli turkeyproducts was studied by Juck et al. (2010). Results showed thatalginate based antimicrobial coatings can enhance the microbio-logical safety and quality of turkey poultry products by inhibitingthe growth of L. monocytogenes. Meanwhile, the incorporation ofnicin/sodium lactate and sodium lactate/sodium diacetate into thealginate coating effectively inhibited the growth of this pathogen.In another study, Mastromatteo et al. (2012) investigated theeffectiveness of combined use of ethanol as antimicrobial com-
pound and alginate based coating on the shelf-life of fresh carrotspacked under passive and active modified atmosphere packaging.Results showed that the combination of dipping in ethanol andapplication of an alginate coating controlled both dehydration and

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espiration of sliced carrots. So, it caused a good preservation ofensory properties and prolonged the shelf-life of carrots.

.3. Antioxidant agents

Adding lipids to edible films and coatings in order to reduceater vapour transfer is popular. So, incorporation of antioxidants

n edible films and coatings materials leads to increase producthelf-life by protecting foods against oxidative rancidity, degra-ation, and discoloration. It is interested that most antimicrobialgents have antioxidant properties. Natural and synthetic antiox-dants are widely used in food packaging (Skurtys et al., 2010).henolic compounds, vitamins E and C, essential oils (Oregano andosemary), sodium ascorbate, citric acid, and ferulic acid are theost common used antimicrobial compounds (Bonilla et al., 2012;

ong et al., 2011).Blanco-Pascual et al. (2014) extracted edible film-forming mate-

ials from brown seaweeds L. digitata and A. nodosum and studiedhe antioxidant activity of extracts. Results indicated that A.odosum films had higher antioxidant activity than L. digitata. Innother experiment Song et al. (2011) investigated the effect ofncorporation of different antioxidants (vitamin C and tea polyphe-ols) into the alginate based edible coating on shelf-life and qualityf refrigerated bream (Megalobrama amblycephala). They found thatuality of treated product with vitamin C and tea polyphenols wasigher than untreated ones. Vitamin C had the best effect in thease of reducing the degree of chemical spoilage, retarding wateross, and enhancing the overall sensory values of bream.

.4. Antibrowning agents

Great efforts have been done to increase the shelf-life of freshut fruits and vegetables by preventing cut surface browning. Incor-oration of antibrowning agents into the films and coatings can

mprove color preservation of fruits and vegetables. Ascorbic acid,itric acid, and some sulfur-containing amino acids (cysteine andlutathione) have been widely incorporated into edible coatings torevent enzymatic browning (Conte, Scrocco, Brescia, & Del Nobile,009; Robles-Sánchez, Rojas-Graü, Odriozola-Serrano, González-guilar, & Martin-Belloso, 2013).

The ability of alginate and gellan based edible coatings to carryntibrowning agents (N-acetylcysteine and glutathione) and theffect of antibrowning agents on water vapour resistance of coat-ngs for fresh-cut apples were investigated by Rojas-Graü, Tapia,odríguez, Carmona, and Martin-Belloso (2007). Results indicatedhat both antibrowning agents could be carried in the coatingsnd exerted their effects on fresh-cut apples. N-acetylcysteine hadositive effect on water vapour resistance in the alginate coating,hile in the gellan coating, its effect was negatine. Citric acid as

n antibrowning agent was incorporated into the sodium alginateoating. The coating was used to prolong the shelf-life of minimallyrocessed lampascioni. Results showed that the respiratory activ-

ty and the browning process of coated lampascioni were delayed.esult also indicated that the coated lampascioni packaged in aolyester based biodegradable film showed the best performance

n prolonging the shelf-life of the fresh-cut produce (Conte et al.,009).

In another research, ascorbic and citric acid were used asntibrowning agents in alginate edible coating and their effectsn color of fresh-cut mangoes was evaluated. The application oflginate coating with antibrowning agents maintained the color ofresh-cut mangoes (Robles-Sánchez et al., 2013).

.5. Other agents

Functional ingredients such as probiotics (Tapia et al., 2007),rebiotics (Rößle, Brunton, Gormley, Wouters, and Butler, 2011),

e Polymers 137 (2016) 360–374 371

minerals (Rhim & Wang, 2014), and vitamins (Robles-Sánchez et al.,2013) are other agents incorporated into the edible films and coat-ings in order to increase their functionalities. Edible films andcoatings can also be used as a carrier to convey nutrients andnutraceuticals that are lacking or are present in only low quantityin food products (Rößle et al., 2011; Tapia et al., 2007). Flavor andpigments agents may also be incorporated into the edible films andcoatings to improve the sensory quality of products (Skurtys et al.,2010).

8. Advantages and adverse biological effects

As mentioned before, edible films and coatings should have notoxic effect on biological systems. Some known positive biologi-cal effects of carrageenans such as antitumor, immunomodulatory,anticoagulant, antithrombotic, and antiviral activities have beenknown. Furthermore, the antioxidant activity of all carrageenansespecially lambda carrageenan is reported (Campo, Kawano, daSilva, & Carvalho, 2009; Prajapati et al., 2014).

Despite the positive biological effects, some researchers havefocused on the adverse biological effects of carrageenans. Theseeffects are mostly related to degraded carrageenan (poligeenan)which have molecular weights below 50 kDa (Chen et al., 2010; Liu,Zhan, Wan, Wang, & Wang, 2015; Prajapati et al., 2014). However,Tobacman (2001) reported the carcinogenic effects of undegradedcarrageenans.

Degraded carrageenans are responsible for intestinal inflamma-tion (Tobacman, 2001) and also, they are toxic to macrophages(Thomson & Horne, 1976). Feeding 2 g/kg body weight of degradedcarrageenan to guinea pigs for 20–45 days caused ulcerative lesions(Prajapati et al., 2014). Silva et al. (2010) evaluated the inflamma-tory properties of kappa, iota and lambda carrageenans. Lambdacarrageenan was seen to have the most inflammatory activity andthe least activity was reported for kappa carrageenan. Their resultsdemonstrated that an increase in the sulfate groups led to inhancedinflammatory activity of carrageenan.

However, toxicological properties of carrageenans have beenshown at high doses that do not occur with the food additive. Itis necessary for food grade carrageenan to have average molecularweight greater than 100,000 Da with a low percentage of smaller(Cohen & Ito, 2002; Prajapati et al., 2014).

Unlike carrageenans, the majority of articles have been justmentioned the advantages of alginate. However, it should be notedthat only highly purified alginates have been reported to haveno immunogenic response in mice. This means some impuritiesincluding heavy metals, endotoxins, proteins, and polyphenoliccompounds may cause immunogenic responses (Lee & Mooney,2012).

Alginates are known as dietary fiber (Houghton et al., 2015). Thepositive effects of alginates on intestinal absorption and colonichealth have been reported by Dettmar, Stugala, and Richardson(2011). Some research has been reported the pharmaceutical activ-ity of alginate molecule. This ability refers to alginates with highmannuronate residues which could induce cytokine production 10times more than alginates containing high guluronate blocks (Lee& Mooney, 2012).

9. Conclusion

Consumer demands for more natural foods, and also for environ-mental protection have excited the development of new packaging
materials. Edible films and coatings have been received consider-able attention over the last years due to their possibility to useas edible packaging materials over synthetic ones and to reducethe environmental pollution. Besides, development of edible films

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nd coatings can reduce the post-harvest losses and also can pro-ide less expensive packaging materials for industry and lower therices of the food products. Edible films and coatings are defined ashin layers of materials used on food products that have importantffects on their conservation, distribution, and marketing. Ediblelms and coatings can protect the product from mechanical dam-ge, physical, chemical, and microbiological activities. Such filmsan be a carrier of antioxidants, antimicrobial, nutraceuticals, andavorings agents or other additives to improve the mechanical

ntegrity, handling, and quality of food products. Different biopoly-ers such as polysaccharides, proteins, and their blends are applied

o form edible films and coatings. Among these biopolymers, algi-ates and carrageenans have been frequently used in recent yearsue to their good barrier properties to oxygen, carbon dioxide,nd lipids as well as their superb mechanical properties (tensiletrength and elongation at break). Commercialization of biopoly-er films is limited due to their high sensitivity to moisture and

heir compatibility with other emergent stress factors such asigh pressures, electric fields, ultrasound, microwave radiation, andamma radiation. Technical information on edible films and coat-ngs is far from adequate, so the food scientist has the formidableask of developing a film for each food application.

cknowledgments

The authors would like to acknowledge the Isfahan University ofechnology for providing an excellent library facilities and supportor the preparation of review article.

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development of edible films and coatings from alginates

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