Authors Falguera, V., Quintero, J.P., Jiménez, A., Muñoz, J.A. and Ibarz, A.
Edible ?lms and coatings are thin layers of edible materials ap-plied on food products that play an important role on their conservation, distribution, and marketing. Some of their functions are to protect the product from mechanical damage, physical, chemical, and microbiological activities. Their use in food applications and especially highly perishable products such as horticultural ones, is based on some particular properties such as cost, availability, functional attributes, mechanical properties (?exibility, tension), optical properties (brightness and opacity), the barrier effect against gases ?ow, structural resistance to water and microorganisms and sensory acceptability, composition (polymers to be used in the structural matrix), including nanoparticles addition, and properties, An edible coating (EC) is a thin layer of edible material formed as a coating on a food product, while an edible ?lm(EF) is a preformed, thin layer, made of edible material, which once formed can be placed on or between food com-ponents, the main difference between these food systems is that the EC are applied in liquid form on the food, usually by immersing the product in a solution-generating substance formed by the structural matrix(carbohydrate, protein, lipid or multicomponent mixture),and EF are ?rst molded as solid sheets, which are then applied as a wrapping on the food product, The use of EC or EF in food applications and especially highly perishable products such as horticultural ones, is conditioned by the achievement of diverse characteristics-such as cost, availability, functional attributes, mechanical properties (?exibility, tension), optical properties (bright-ness and opacity), the barrier effect against gases ?ow, structural resistance to water and microorganisms and Author’s personal copy sensory acceptability. These characteristics are influenced by parameters such as the kind of material implemented as structural matrix (composition, molecular weight distribution), the conditions under which ?lms are preformed(type of solvent, pH, components concentration and temperature) and the type and concentration of additives (plasticizers, cross-linking agents, antimicrobials, antioxidants or emulsi?ers) , different compounds used in EF and EC are Carboxymethylcellulose, casein, casein derivates with beeswax and fatty acids , Locust bean gum, guar gum, ethyl cellulose ,Mesquite gum ,Gelatin with glycerol, sorbitol and sucrose ,Gelatin-casein cross-linked with transglutaminase ,Pectin , Cassava starch, Pre-gelatinized maize starch, Wheat gluten, Sodium alginate and pectin cross-linked with CaCl2 , HPMC with fatty acids, Beeswax ,Carnauba wax ,Chitosan, Chitosan-gelatin ,Maize starch-chitosan-glycerin , HPMC-tea tree essential oil ,Cashew gum ,Galactomannans, Galactomannans-collagen-glycerol, structural matrix: carbohydrates, proteins and lipids Edible coatings and ?lms are usually classi?ed according to their structural material. In this way, ?lms and coatings are based on proteins, lipids, polysaccharides, or composite. For example, a composite ?lm may consist of lipids and hydrocolloids combined to form a bilayer or cluster, In some recent studies the production of edible and biodegradable ?lms by combining various polysaccharides, proteins and lipids is considered with the aim of taking advantage of the properties of each compound and the synergy between them. The mechanical and barrier properties of these ?lms not only depend on the compounds used in the polymer matrix, but also on their compatibility , the optimization of edible ?lms composition is in one of the most important steps of the research in this ?eld, since they must be formulated according to the properties of the fruits and vegetables to which they have to be applied, thus, it is very important to characterize and test different coating solutions on fresh and minimally processed food, since each one of them has different quality attributes to be maintained and enhanced during the storage , hydrocolloids (proteins and polysaccharides) are the most widely investigated biopolymers in the ?eld of EC and EF, some of these are: carboxymethylcellulose, casein and its derivatives locust bean gum, guar gum, ethyl cellulose , mesquite gum , gelatin supplemented with glycerol sorbitol and sucrose as plasticizers , composite EF of gelatin casein cross-linked with transglutaminase , pectin, cassava starch with natural antimicrobial compounds , pre-gelatinized standard maize starch , wheat gluten and mixtures of sodium alginate and pectin, with the addition of CaCl2as a crosslinker material affecting mechanical properties, water solubility, moisture con-tent, ?lm thickness and its ability to contain calcium, hydroxypropylmethylcellulose (HPMC) has been used in combination with fatty acids to obtain composite ?lms with lower water vapor permeability (WVP) and less transparency in comparison with the same ?lm without lipids ,Polysaccharides and proteins are great materials for the formation of EC and EF, as they show excellent mechanical and structural properties, but they have a poor barrier capacity against moisture transfer. This problem is not found in lipids due to their hydrophobic properties, especially those with high melting points such as beeswax and carnauba wax, to overcome the poor mechanical strength of lipid com-pounds, they can be used in combination with hydrophilic materials by means of the formation of an emulsion or through lamination with an hydrocolloid ?lm lipid layer. The ef?ciency of an edible ?lm against moisture transfer cannot be simply improved with the addition of hydrophobic materials in the formulation, unless the formation of a homogeneous and continuous lipid layer inside the hydro-colloid matrix is achieved , In this way, it has been found that fatty acids can form stable layers in sodium caseinate or HPMC matrices, whose properties depend on their chain length: the lower the chain length, the greater the layers ,Emulsion-based ?lms are less ef?cient in controlling water transfer than bilayer ?lms, as a homogeneous distribution of lipids is not achieved. However, they exhibit good mechanical strength and require a simple process for their manufacture and application, whereas multilayer ?lms re-quire a complex set of operations that depend on the number of coatings. It has been proved, in emulsion-based ?lms, that the smaller the particle size or lipid globules and the more homogeneously distributed, the lower WVP, However, its permeability to water vapor can be similar to the values presented by the ?lms based on proteins or polysaccharides, among polysaccharides, bioactive compounds such as chitosan and its derivatives show a great number of applications focused on active coating systems, in view of the increasing concern about the production of poorly biodegradable plastic materials. Chitosan has a vast potential that can be applied in the food industry because of its particular physico-chemical properties such as biodegradability, biocompatibility with human tissues, null toxicity and especially its antimicrobial and antifungal properties , in addition to research based on its antimicrobial properties, some aspects such as mechanical and thermal properties and permeability to gases (O2,CO2) have been quantified, revealing that chitosan-gelatin ?lms plasticized with water and polyols suffer an increase in permeability as the amount of plasticizers in their formulation is increased
