**5. Radiation and nano technology on synthetic and composite edible polymers**

Two classes of biodegradable polymers can be distinguished: synthetic or natural polymers. Recent developments in biopolymer-based food packaging materials include natural biopol‐ ymers (such as starches and proteins), synthetic biopolymers (such as poly lactic acid), biopolymer blends and nanocomposites based on natural and synthetic biopolymers [60]. The combination of synthetic and natural polymers to form films are of remarkable importance in producing composite polymers with permeability or mechanical properties according to the need of a specific application that can be applied either in the form of an emulsion, suspension or dispersion of the non-miscible constituents, or in successive layers, or in the form of a solution in a common solvent [61].

Biodegradable synthetic aliphatic polyester, like polylactide (PLA), has been studied exten‐ sively for a number of applications like drug delivery system. Frequently renewable resourcegenerated monomers possess better mechanical properties and easy processability by conventional methods like thermoforming, injection and blow molding with non-toxic degradation products, which have made it superior than the other conventional thermoplastics [62].

In addition to traditional plant materials for biodegradable polymer production, it is worthy to mention the advances in synthesizing novel polymers within transgenic plants, especially those in the polyhydroxyalkanoate class [63].

Application of nanoscience and nanotechnology to the agriculture and food sector is relatively recent compared with their use in drug delivery and pharmaceuticals [64, 65].

In the food industry, nanotechnology can be utilized in order to enhance the delivery of food ingredients to target sites, increase flavor, inhibit bacterial growth, extend product shelf life and improve food safety.

Applications of nanomaterials that do not involve direct addition of nanoparticles to consumed foods, and thus more likely to be marketed to the public in the short term, are related to food packaging and food safety. These applications include polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents and nanosen‐ sors and nanomaterial-based assays for the detection of food-relevant analytes (gases, small organic molecules and food-borne pathogens) [66].

Other emerging topics of nanotechnology for food and agriculture are smart delivery of nutrients, bioseparation of proteins, rapid sampling of biological and chemical contaminants and nanoencapsulation of nutraceuticals, as well as advances in technologies, such as DNA microarrays, microelectromechanical systems and microfluidics [67, 68].

Nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) are promising candidates for bio-nanocomposite production due to their abundance, high strength and stiffness, low weight and biodegradability [69].

Several reinforcing nanoparticles such as clays, silica or silver have been used for industrial applications, but cellulose nanocrystals (CNCs) are a better choice for food industry due to their biodegradable and biocompatible nature as well as their outstanding potential in improving mechanical and barrier properties of nanocomposites [70–72]. Also, cellulose nanofibers (CNF) reinforcement improved mechanical properties, except elongation of mango puree edible films [73].

The development of nanoscale systems for the encapsulation, protection and delivery of lipophilic nutrients, vitamins and nutraceuticals was recently reported [74]. A promising route to the synthesis of protein-mimetic materials that are capable of complex functions, such as molecular recognition and catalysis, is provided by peptoid nanosheets polymers structurally related to biologically occurring polypeptides [75].

The conjunction of radiation and nanotechnology for the improvement of biomaterials are drawing special interest [76]. Gamma radiation and nanocrystalline cellulose was used for the reinforcement of poly(caprolactone) composites [77]. Also, the radiation synthesis of gelatin hydrogels containing Ag nanoparticles was reported [78]. Grasielli and his group synthesized nanoparticles of seroalbumin via intramolecular cross-linking using gamma rays technology [79]. The radiation synthesis of a composite prepared from the algae polysaccharide alginate and clay nanocomposite was also described [80].
