**1.5 Control release of active agent from antimicrobial package**

Direct incorporation of active/antimicrobial compounds into the polymer matrix or into the biopolymer coating is the most common type of food active packaging system. In this system, the active substance and a biopolymer/polymer are combined to



*Overview of Food Antimicrobial Packaging DOI: http://dx.doi.org/10.5772/intechopen.108666*


#### **Table 1.**

*Examples of bio-nanocomposite films in food packaging applications.*

form a composite matrix. There are three types of release mechanisms of active additives from a matrix [55, 85] 1. A diffusion-induced release in which the active agents diffuse through the macro-porous or micro-porous structure of the matrix from the film/coating surface into the food. 2. A swelling-induced release in which the incorporated active compounds are unable to diffuse within the polymer matrix. Due to its diffusion coefficient being too low. In this case, if the polymer/biopolymer matrix/ coating is placed in a compatible liquid medium, the polymer/biopolymer starts swelling because of the penetration of the fluids into the matrix/coating. The swelling causes an increase in the diffusion coefficient of the active substance, then diffusion of the active agents may begin. In addition, this type of release mostly occurs in moisture-sensitive packaging materials, such as polysaccharide-based or protein films/coatings. 3. A disintegration-induced release, which is caused by the cleavage,

degradation, or deformation of a polymer/biopolymer. This type of release occurs in reactive nonbiodegradable polymers or biodegradable types, such as poly(lactide) (PLA), polyanhydrides, and poly(lactide-co-glycolide) [55]. Several approaches have been proposed to achieve a more controlled diffusion of active compounds from the polymer/biopolymer matrix. Each of them focuses on a factor that influences the release rate. There are techniques that may be used to improve active packaging material characteristics. Multi-discipline techniques, such as nano-reinforcements, micro- or nano-encapsulation, which alter the properties of the active agents and decrease their volatility, diffusivity, or a chemical modification of a polymer/biopolymer, such as irradiation, cross-linking with selected agents and the lamination of films can lead to a more controlled release of active/antimicrobial substances [55]. Physical techniques, such as corona discharge, ultraviolet (UV) radiation generating carboxylic acid groups, gamma-ray, electron beam, and plasma forms that break the covalent bonds at the surface, leading to hydrogen abstraction and the formation of surface radicals and laser treatments can change the chemical structure of polymers [86]. Wet chemical methods using strong acids, such as chromic, permanganate or nitric acid, and bases, such as potassium base, have also been found to be an effective surface modification that generated various groups, such as hydroxyl, carbonyl, and carboxylic acid groups [87]. A good example may be a modification performed by Mulla et al. [88] who modified a LLDPE film surface by chromic acid treatment and coating it with clove essential oil. The chromic acid made the surface of the film more porous, allowing it to be coated with clove essential oil as an antimicrobial agent. This packaging material was confirmed to be effective against *S. Typhimurium* and *L. monocytogenes*. Another example of active layer modification is described by Fajardo et al. [89] who fabricated gliadin films cross-linked with cinnamaldehyde, as a carrier of lysozyme. The gliadin film cross-linked with cinnamaldehyde preserved its integrity in water and led to a prolonged release of antimicrobial compounds. The authors confirmed that the cross-linking process led to a slower release of lysozyme exhibiting greater antimicrobial activity compared to an unmodified film.
