**1.4 Biodegradable, active packaging materials**

Biodegradable packaging materials have emerged as an alternative to replace multilayer plastics left as waste. Biodegradable films are usually obtained from biopolymers of high molecular weight and classified according to the nature of their components. These biopolymers may be applied in the form of films, thermoformed, or as a cover/coating (thin layer), through immersion or spraying of a film-forming solution [52]. Starch was found to be one of the most promising biopolymers to replace nondegradable traditional plastics. Poly(butylene adipate-co-terephthalate) (PBAT), as an aliphatic-aromatic co-polyester, is also a promising biopolymer due to its ease of processing and good mechanical properties [66]. Biopolymers, such as PLA (polylactide), PHA (polyhydroxyalkanoates), or PBS (polybutylene succinate), also belong to the bio-based and biodegradable plastic family [53]. To obtain biopolymer packaging materials with antimicrobial activity, the active substances should be introduced directly into the polymer matrix. A good example is cassava starch chitosan films containing oregano essential oil incorporated in a polymer matrix, produced though an extrusion process. These packaging materials were found to be active against gram-positive bacteria (*B. cereus* and *S. aureus*) and gram-negative bacteria (*Salmonella enteritidis* and *E. coli*) [66]. Another example is starch/PBAT films incorporated with ε-PL by Gao et al. [67]. ε-PL is a homo-polyamide produced by *Streptomycetaceae* and *Ergot* fungi. As an antimicrobial agent, ε-PL exhibits a broad-spectrum of antimicrobial activity gram-positive and against gram-negative

bacteria, molds, and yeasts. The authors indicated that starch/PBAT films with ε-PL inhibited the growth of tested microorganisms, such as *E. coli*, *S*. *aureus*, *and B. subtilis*. Biodegradable polymers, polyvinyl alcohol, and starch were used to prepare blends with natural additives, such as propolis extract and anthocyanin incorporated into the blend matrix. Boric acid was used as a cross-linker. Five different concentrations of propolis extract ranging from 0.5, 2, 5, 10, to 20% were used to develop active composites. It was demonstrated that an active film based on PE containing 20% of propolis was active against *E. coli* and methicillin-resistant *S. aureus*, respectively [68]. These novel materials having at least one dimension of just a few nanometers belong to polymer bio-nanocomposites. Bio-nanocomposites are novel, high-performance, lightweight, and eco-friendly materials that can replace traditional nonbiodegradable packaging materials obtained from synthetic materials [51]. Bio-nanocomposites are mostly constructed on biopolymer matrixes reinforced by nanofillers. These materials were found to have improved mechanical, barrier, thermal, and even antimicrobial properties attributed to the presence of the nanomaterials in the polymer matrix. The bond between the nanoparticle and biopolymer results in improved mechanical and thermal properties of the packaging materials [1, 69]. Several of the aforementioned nanomaterials were used in food packaging materials. There were nanoparticles of silver, copper, zinc oxide, titanium dioxide [1, 30–33], silicon dioxide [34], nanocellulose, nanoclays, and chitosan [30–33, 70, 71]. Thymol and silver nanoparticles (Ag-NPs) were used by Ramos and coauthors [30] to develop poly(lactic acid) (PLA) based films with antibacterial activity. Various amounts of thymol (6 and 8 wt%) and 1 wt% Ag-NPs were introduced into the PLA matrix to produce active nanobiocomposites. The authors indicated that PLA-based nano-biocomposites showed dose-dependent slight antibacterial activity against *E. coli*. In addition, these films inhibited the growth of *S. aureus* 8325-A. Tarabiah and coauthors [72] used polyethylene oxide (PEO) as semicrystalline polymer and carboxymethyl cellulose (CMC) to develop the biodegradable, nontoxic PEO/CMC blend matrix (70/30 wt.%) as a host blend. ZnO nanorods as a filler were introduced into the polymeric matrix with various concentrations (upto 0.6 wt.%). The authors demonstrated that these PEO/ CMC/ZnO nano-biocomposites can be used as a UV-mask. They also showed that these films were active against *S. aureus* and *E. coli*. De Souza and coauthors [73] used ZnO and Ag-ZnO nanoparticles as fillers and introduced them into the PBAT, which is an aliphatic-aromatic completely biodegradable flexible polyester, synthesized from 1,4-butanediol, adipic acid, and terephthalic acid. The authors established that such nano-biocomposite was active against *E. coli*. They also confirmed the synergistic effect between ZnO and Ag nanoparticles. The active packaging from chitosan and chitosan containing titanium dioxide nanoparticles was developed by Kaewklin and his team [33] to extend the shelf-life of climacteric cherry tomatoes. They indicated that tomatoes packaged in a chitosan package with nanoparticles showed lower quality changes than those in a chitosan film and control. The results suggested that the chitosan films containing titanium dioxide nanoparticles as active compounds exhibited ethylene photodegradation activity when exposed to UV light and consequently delayed the ripening process and any changes in the quality of the tomatoes. Hu and coauthors [71] developed chitosan/ZnO bio-nanocomposite and then introduced several concentrations of this bio-nanocomposite (0–5wt %) into the matrix of starch to produce antimicrobial starch-based composite films. The authors confirmed that such bio-nanocomposite films offered antimicrobial activity. They were active against *S. aureus* and *E. coli*. In addition, the antimicrobial activity of the films positively correlated with the amount of ZnO-chitosan nanoparticles introduced into the
