Edible coatings and films have been used for centuries and extensively studied for the last 20 years (Rossman, 2009)� These materials do not pretend to fully replace traditional packaging; instead, the idea is to provide additional properties and add benefits by incorporating natural additives such as antioxidants, antimicrobials, and nutrients to be applied, for example, for food preservation or enrichment (Pavalath and Orts, 2009)� These materials can be used to protect the product from mechanical damage, physical, chemical, and microbiological activity and also to prevent mois- ture loss, create a shiny surface, as well as control gas and lipid migration (Olivas and Barbosa-Cánovas, 2009)� Edible coatings and films are mostly applied in highly perishable products such as fruits and vegetables, highly conditioned by the attain- ment of characteristics such as adequate cost, functional attributes, mechanical, and optical properties (Rojas-Grau et al�, 2009)� The term “edible” coating or film has been related to food applications� Edible coatings and films are defined like thin layers of edible materials applied on food products that play an important role on their conservation, distribution, and marketing (Falguera et al�, 2011)� Specifically, an edible coating is a thin layer of edible material formed as a coating on a food product that is applied in liquid form (structural matrix) on the food� On the contrary, an edible film is a preformed thin layer made of edible material that is first molded 4�3�4 Plasticizer Properties ������������������������������������������������������������������������ 134 4�3�5 Applications of Edible Coatings and Films Based on Lipids ����������� 134 4�4 Edible Coatings and Films Based on Natural Waxes ����������������������������������� 138 4�5 Concluding Remarks ������������������������������������������������������������������������������������ 138 References �������������������������������������������������������������������������������������������������������������� 142
as solid sheets and can be placed on or between food components (Falguera et al�, 2011; McHugh, 2000)� All its components must be safe to eat or composed of gen- erally recognized as safe (GRAS) materials and must have approval of regulatory agencies (e�g�, the Food and Drug Administration [FDA], in the United States, or the European Food Safety Authority [EFSA], in the European Union)� Characteristics of edible coatings and films depend on different parameters such as the kind of material implemented, the structural matrix, the conditions under which films are preformed and the type and concentration of additives (Guilbert et al�, 1996)�
Usually edible coatings and films are classified according to their structural mate- rial� They can be composed of hydrocolloids, which consist of polysaccharides or proteins, or hydrophobic compounds (e�g�, lipids, waxes, and resins) or a mixture of these components� In this latter case, they are known as “composite films” with the aim of taking advantage of the properties of each compound and the synergy between them (Altenhofen et al�, 2009; Falguera et al�, 2011)� All the components have a function into the system� The polymer or mixture of polymers to be used will form the base matrix of the film and is crucial to be compatible with all the ingredients to provide the required properties for the end use� Plasticizers are often included in the system and are added to the solution to enhance softness, flexibility, elongation, clarity, among others, and their choice will depend on the type of poly- mer used� Waxes, lipids, and resins can be included in the formulation to provide good moisture barrier properties because of their low affinity for water (Krochta, 1997)� The properties that lipids confer to the matrix will depend on the character- istics of the lipid component, such as physical state, degree of saturation, and fatty acid content� The efficiency of an edible film as a barrier to moisture transfer cannot be simply improved with the addition of hydrophobic materials to the formulation, unless the formation of a homogeneous and continuous lipid layer inside the hydro- colloid matrix is achieved (Karbowiak et al�, 2007)� Several techniques are used for introducing lipids into edible films: (i) they can be the only constituent of the film, (ii) they can form a layer over a hydrocolloid layer, or (iii) they can form an emulsion with the hydrocolloid� The influence of lipids in edible coatings and films is particu- larly important when they are added to these systems� In water, lipid molecules form micelles, monolayers, bilayers, or vesicles due to the strong cohesive self-attraction of water molecules that repels the hydrocarbon chains� Variations in polarity can explain their different efficiency when integrated in edible films� Waxes belong to the class of nonpolar lipids, which means that they have no polar constituents or pos- sess a hydrophilic part that in practice does not permit interaction with water; this character explains why waxes are the most efficient lipid barriers� The interactions with proteins and polysaccharides result from a subtle balance between forces of dif- ferent nature, mainly electrostatic and hydrophobic, due to their amphiphilic charac- ter� The efficiency of lipids depends on several factors but mainly to the homogeneity of the film, structure, and physical state, among others (Callegarin, 1997)�
4.1.1 Why use edible Coatingsand Films?
Food preservation helps food to maintain its original properties/quality up to the point of consumption� It is accomplished by protecting the food product from
surrounding environment conditions by controlling migration and mass transfer, including water loss� Indeed, product quality depends on the organoleptic, microbio- logical, nutritional, and functional properties (Lin and Zhao, 2007)� These properties are subjected to changes during storage and distribution, mainly due to moisture migration either from the food to the environment or between different parts within a composite heterogeneous product (Debeaufort and Voilley, 2009)�
The use of edible coatings and films improves appearance, being an effective bar- rier to transmission of gases, solving problems of migration of moisture, oxygen, car- bon dioxide, and aromas (Campos et al�, 2011; De León-Zapata et al�, 2015), and reducing maturation processes, thus extending storage time and quality of vegetables or fruits (Beristain et al�, 1999)� Several lipids, for example, candelilla wax (De León- Zapata et al�, 2015), carnauba wax (Chiumarelli and Hubinger, 2012; Jo et al�, 2014), beeswax (Fagundes et al�, 2014; Khanzadi et al�, 2015); polysaccharides, for example, pectin (Otoni et al�, 2014; Sánchez et al�, 2015), chitosan (Arancibia et al�, 2015), mesquite gum (Bosquez-Molina et al�, 2003), tara gum (Antoniou et al�, 2014), starch (Chen et al�, 2010), galactomannans (Chen and Nussinovitch, 2000; Martínez-Ávila et al�, 2014b), Arabic gum (Cruz et al�, 2015), cellulose (Atef et al�, 2015), and proteins (Hopkins et al�, 2015; Khanzadi et al�, 2015; Tong et al�, 2015) have been used as base materials to formulate edible coatings and films� It is known that polysaccharide- based films have poor water vapor barrier properties, whereas most single hydropho- bic coatings or films have high moisture resistance, although they form brittle films�
Moisture barrier properties of hydrophilic films can be improved by incorpo- rating hydrophobic materials such as waxes or long-chain saturated fatty acids through emulsion or lamination technology (Bosquez-Molina et al�, 2003)� The presence of wax compounds can reduce water vapor permeability, but it can affect coatings transparence and mechanical properties, besides its possible impact in the aftertaste—which may impair the sensory characteristics of food (Bourlieu et al�, 2009; Chiumarelli and Hubinger, 2014)� Among the range of different hydropho- bic substances, waxes provide the best barrier to moisture� Among these, beeswax, candelilla wax, and carnauba wax have GRAS status and are FDA approved for use as coatings in fruits and vegetables, or as additives in beverages and confectionery products (Kowalczyk and Baraniak, 2014)�
4.2 LIPIDS, WAXES, AND RESINS USED AS RAW