and the metabolism of the microorganism [138]. Another important factor to be considered is the extraction of these biopolymers, which may influence their properties and applicability [139]. Figure 2.2 presents the steps to obtain PHA, its structure, and the most common PHA derivatives. Additionally, polymerization through the opening of β-butyrolactone chains using zinc or aluminum can be performed to produce PHA derivatives [140].
Figure 2.2 Polyhydroxyalkanoate (PHA) extraction and its general structure, where R is variable, and n can be from 1 to 13.
Food packaging materials based on PHA are the most common application of this biopolymer. PHA has interesting physicochemical due to the monomeric composition of its copolymers. The PHA-based materials properties vary from fragile and crystalline thermoplastics (PHB) to elastomeric ones (PHV, PHBV) [141]. PHA is considered biodegradable and biocompatible [140–142]. In addition, hydrophobicity property makes PHA-based materials insoluble in water and provides good water barrier properties. PHA is a semi-crystalline material with crystallinity degree between 30% and 80%, and melting temperature oscillating between 50 and 180 °C [133, 138]. Beyond PHAs, PHB is the most studied one regarding food packaging applications. PHB has similar properties to those found in conventional plastics; hence PHB can be extruded and molded to manufacture films at industrial scale. However, since this biopolymer has high crystallinity, the films and coatings become rigid and brittle [143]; in this sense, the incorporation of 3-hydroxyvalerate, producing PHBV, or other monomers has been used to overcome its shortcoming. The blend with other biopolymers or incorporation of other types of materials to produce composites is also studied in the food packaging area [133]. Table 2.7 shows an overview of studies that applied PHA and its derivatives as food packaging materials, highlighting the main results obtained by the authors.
The PHA derivatives have been used as food packaging materials; most studies have focused on the application of this biopolymer such as film for direct or indirect food contact, as well as barrier to coat paper-based packaging (Table 2.7).
Table 2.7 Films and coatings based on polyhydroxyalkanoates for food packaging applications.
| Components | Production approach | Main results | References |
|---|---|---|---|
| PHAa)/long alkyl chain quaternary/graphene oxide Nanocomposite | Casting | Films with improved mechanical, thermal, and oxygen barrier properties. Films with antimicrobial activity against S. aureus and E. coli | [144] |
| PHBb)/PEGc)/organobentonite or organovermiculite | Casting | Increase on the processability of the PHBb)with the improvement of the thermal resistance and crystallinity degree | [145] |
| PHBVd)/PHBb)/PLAe)/catechin | Electrospun/thermo-pressing molding | The addition of PHBb)increased the PLAe)-based fibers crystallinity. The film presented antioxidant activity related to catechin release on fatty food model. The incorporation of PHBb)/PLAe)layer improved the mechanical properties | [146] |
| PHAe)/apple extract/cellulose | Casting | The PHAa)increased the hydrophobicity and transparency of the films whereas the tensile strength was reduced. The apple extract gives an antioxidant property to the coating | [147] |
| PHBVd)/cellulose/TECf)or PEGc) | Extrusion | A sufficient adhesion (cohesion break) between paper and PHBVd)layer was obtained. The use of TECf) or PEGc) produced PHBV layers with lower defects and with increase of grease barrier property | [148] |
| PHBb)/bacterial cellulose/zinc oxide nanoparticle | Thermo-pressing molding/plasma | Films with better mechanical properties and antimicrobial activity against E. coli and S. aureus | [149] |
| PHBb)/starch/montmorillonite/eugenol | Extrusion | Reinforced films with antimicrobial properties manufactured at industrial scale | [150] |
| PLAe)/PHBb)/cinnamaldehyde | Casting | Films with better mechanical properties and slower release of the active compound. These films were used to extend the shelf life of salmon dices | [151] |
| PHBb)/palladium nanoparticles | Electrospinning/thermo-pressing molding | Films with oxygen scavenging capability and good barrier properties | [152] |
| PHBb)/silver nanoparticles |