**1. Introduction**

There is an increasing interest in green and bioactive materials that could be used in direct contact with aliments. Edible films can be produced from natural materials with film-forming ability that can be applied on food surfaces as a thin-layer edible film and can potentially extend the shelf life and improve the quality of food. Edible film as a solid sheet can be applied between food components or on the surface of the food system in order to inhibit migration moisture, oxygen, CO2, aromas and lipids.

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Edible polymer film is a thin layer of edible material formed on a food as a coating or placed (pre-formed) on or between food components; in this case, edible films can improve the quality of multicomponent foods. The sanitary condition of the edible packaging would need to be maintained during storage, transportation and marketing. The end result would be source reduction and or improved recyclability of the remaining elements of the packaging system.

One major advantage of using edible films and coatings is that several active ingredients (antimicrobials, antibrownings, texture enhancers and nutraceuticals) can be incorporated into the polymer matrix and consumed with the food, thus enhancing safety or even nutritional and sensory attributes [1].

Many potential uses of edible films can be described such as inhibit migration of moisture, oxygen, carbon dioxide, aromas; carry food ingredients (e.g., antioxidants, antimicrobials, flavor) and or improve mechanical integrity or handling characteristics of the food [2]. Practical uses of edible films include wrapping various products; individual protection of dried fruits, meat and fish; control of internal moisture transfer in pizzas, pies, which are based on the film's properties (e.g., sensory, mechanical, gas and solute barrier). Also, ingredients can be delivered to processors on water-soluble and edible packaging films in premeasured amounts of ingredients to food processors and foodservice operations. Future applications of the concept have been envisioned in consumer-sized pouches of dried products ready for reconstitution on water.

The functionality and performance of edible polymer mainly depend on their barrier, me‐ chanical and color properties, which in turn depend on film composition and its formation process. Polysaccharide (cellulose, starch, dextrin, vegetable and other gums) and protein (gelatin, gluten, casein) based films can have suitable mechanical and sensory properties, while wax (beeswax, carnauba wax) and lipid or lipid derivative films have enhanced water vapor barrier properties. It was shown that the incorporation of oil between plasticized starch layers could reduce oxygen and water vapor permeability of the films [3]. The film-forming technol‐ ogy, solvent characteristics, plasticizing agents, temperature effects, solvent evaporation rate, coating operation and usage conditions of the film (relative humidity, temperature) can also substantially modify the ultimate properties of the film [4].

Important properties to be evaluated in an edible coating are its microbiological stability, adhesion, cohesion, wettability, solubility, transparency, mechanical properties, sensory and permeability to water vapor and gases. In order to choose the best edible film to be employed in each case, it is necessary to take in account the characteristics of the food intended to be protected. For coating a fresh fruit, for instance, it will be desired to induce low water vapor permeability to preserve texture and moderated O2/CO2 permeability to permit respiration. On the contrary, when it is intended to protect dried fruits and nuts, low water vapor perme‐ ability is required to maintain crispiness and low O2 permeability to avoid oxidation.

Proteins as components of edible films (gelatin, zein, casein) has usually better performance than polysaccharides (chitosan, starch, pectin); lipids have excellent water vapor barrier but do not form stand-alone films, and can be used as coatings, such as waxes on fruit surfaces. Besides the barrier efficiency, edible films and coatings have to be also sensory acceptable.

In the food industry, there are commonly used starches, dextrins, alginates, protein and lipid materials edible films as encapsulating materials [5]. A wide variety of foods are encapsulated: flavoring agents, acids, bases, artificial sweeteners, colorants, preservatives, leavening agents, antioxidants, agents with undesirable flavors, odors and nutrients, among others. In order to protect the viability of the probiotic bacteria, for instance, several types of biopolymers such as alginate, chitosan, gelatin, whey protein isolate, cellulose derivatives are used for encapsu‐ lation and several methods of encapsulation such as spray drying, extrusion, emulsion have been reported [6].

Active edible films represent one of the current and future trends in the development of new polymers for selected applications, particularly food packaging [7]. The concept of active packaging is described as a type of packaging that alters conditions surrounding the food to maintain product quality and freshness, improve sensory properties or enhance product safety and shelf life.

Edible and biodegradable polymer-based films offer alternative packaging without the environmental cost. In that case, they must fulfil the food packaging requirements as help to contain, protect, preserve, distribute and describe food from fresh to highly processed ones. The potential of biopolymers for packaging application is often limited due to their poor processability, so edible polymers originated from natural products are added to plasticizers and surfactants. A careful selection of the plasticizer allows biopolymer films with improved processability and high or low permeabilities to be manufactured [8].

Shit and Shah in 2014 distinguished the edible polymers into any of the four categories: (1) hydrocolloids, (2) polypeptides, (3) lipids, (4) synthetic and composite edible polymers [9].

In the following sections, the interaction of ionizing radiation with polysaccharides and proteins, which are considered the most important edible materials, as well as the role that radiation plays on the development of new edible materials will be addressed.
