Some relatively new bioplastics have been used in the development of food packaging. These materials were developed to achieve sustainable packaging and replace synthetic polymers. Examples of such polymers include: polylactic acid (PLA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), polyglycolic acid (PGA), polyvinyl alcohol (PVA), polylactic acid-hydroxyethyl acid copolymer (PLGA), and polybutylene succinate adipate (PBS).
Polylactic acid (PLA)
PLA is a linear polyester synthesized from lactic acid monomers. Lactic acid monomers can be obtained from renewable materials such as corn and waste cellulose materials through fermentation. PLA has several important characteristics that make it attractive as a packaging material, such as low permeability to gases and water, high transparency, and moderate tensile strength. Some studies have explored the use of PLA as a material for encapsulating essential oils. Antonioli et al. (2020) [1] encapsulated lemongrass essential oil in PLA nanocapsules and evaluated its antifungal activity in vitro and in vivo. The results showed that this material exhibited in vitro antifungal activity against both Cladosporium and Pythium fungi, with the minimum inhibitory concentration for both plant pathogens being 0.1%. The in vivo experiments were conducted on post-harvest apples. Compared with apples treated with unencapsulated essential oil or the positive control group, apples treated with the nanocapsulated essential oil had three times smaller scab lesions.
Polyhydroxyalkanoates (PHAs)
PHAs are thermoplastic, biodegradable polymers produced by microorganisms. Currently, over 100 types of PHA have been identified, among which the most common ones are polyhydroxybutyrate (PHB), followed by poly(3-hydroxybutyrate) (PHB), polyhydroxyvalerate (PHV), and polyhydroxyhexanoate (PHH). Currently, research is underway to explore the use of polymer nanoparticles based on polyhydroxy fatty acid esters (PHA) for encapsulation, in order to obtain biodegradable materials for preparing active packaging. Zheng et al. (2022) 【2】 encapsulated Mexican oregano essential oil in polyhydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-hydroxyhexanoate (PHB-HHx), and studied its in vitro release in simulated food media. Both of the two nano-systems containing the essential oil showed antibacterial activity against Rhodococcus rhodochrous, and the nanoparticles based on PHB-HHx were more efficient than pure essential oil. Additionally, using PLA/PHA (polylactic acid/ polyhydroxy fatty acid ester) composites containing oregano essential oil, significant effects were observed in active packaging for pufferfish fillets.
Polycaprolactone (PCL)
PCL is obtained through the ring-opening polymerization of ε-caprolactone or the condensation reaction of 6-hydroxyhexanoic acid. The tensile strength of PCL is lower than that of PLA (polylactic acid), and it has higher water vapor and oxygen permeability than other biopolymers. For use in active packaging, PCL is usually blended with other biopolymers. Regarding its application as a nanocarrier material, PCL has been successfully used to develop nanofibers aimed at active packaging 【3】. Lavandula luisieri essential oil has been successfully used in museum packaging in the form of non-woven substrate, and it can potentially be extended to further research as food packaging.
Polyglycolic acid (PGA) and PLGA (polylactic-co-glycolic acid copolymer)
PGA is obtained through direct condensation of glycolic acid, ring-opening polymerization of ethylene lactate, and solid-state condensation of halogenated acylates. This polymer has high biodegradability and is similar to cellulose. The main application of PGA is as a copolymer, such as the obtained PLGA, with a ratio of 88:12, meaning that the polymer is composed of 88% lactic acid and 12% glycolic acid. Zhu et al. (2019) [4] encapsulated thymol (a component of oregano and rosemary essential oils) using PLGA particles, obtaining spherical and smooth particles, achieving the best efficiency when encapsulating 20% of thymol. These particles loaded with thymol showed significant antibacterial activity against Staphylococcus aureus and Escherichia coli. Therefore, PLGA particles loaded with thymol have the potential to be used as preservatives in food.
Polyvinyl alcohol (PVA)
PVA is a synthetic biopolymer. It is synthesized by polymerizing polyvinyl acetate and subsequently hydrolyzing the acetate groups. PVA has high polarity and hydrophilicity, so it is usually mixed with more hydrophobic components to obtain materials for active packaging. Lamarra et al. (2020) [5] prepared PVA electrospun nanofibers and a shellac-based emulsion, and functionalized them using essential oil from the wood of Myrocarpus fastigiatus. To overcome the problem of low oil solubility and protect it, the authors proposed a two-step process: first, an emulsion was formed by combining chitosan and PVA, and then ion cross-linking with sodium citrate was performed. The nanofibers were also manufactured by the electrospinning method. The electrospun nanofibers demonstrated the ability to act as an effective carrier for capreulava essential oil and the ability to control the release of compounds, which was proven to be effective against a broad spectrum of microorganisms (Candida albicans, Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis).
Polybutylene succinate (PBS)
PBS is a biodegradable polymer that can be obtained through the condensation reaction of succinic acid (or succinyl dimethyl ester) with 1,4-butanediol. These monomers can be derived from renewable or fossil resources. By using a mixture of PBS and geraniol, solid and porous plates with antibacterial properties can be prepared and placed in bread packaging. By adding 8% (by weight) of geraniol to the PBS matrix and inserting these solid and porous antibacterial plates, the shelf life of the bread was extended by 5 days and 10 days respectively [6].
There is still a long way to go in promoting the use of bioplastics. Globally, less than 1% of the plastics used are of biological origin. These materials are biodegradable in water. Although some of these materials have not received much research as nano-carriers for essential oils used in food packaging applications, interest in this topic is increasing significantly [7].
Antonioli G, Fontanella G, Echeverrigaray S, et al. (2020) Poly(lactic acid) nanocapsules containing lemongrass essential oil for postharvest decay control: in vitro and in vivo evaluation against phytopathogenic fungi. Food Chem 326:126997.
【2】Zheng H, Tang H, Yang C, Chen J, Wang L, Dong Q, Shi W, Li L, Liu Y (2022) Evaluation of the slow-release polylactic acid/polyhydroxyalkanoates active film containing oregano essential oil on the quality and flavor of chilled pufferfish (Takifugu obscurus) fillets. Food Chem 385:132693
【3】Ferreira RR, Souza AG, Quispe YM, Rosa DS (2021) Essential oils loaded-chitosan nanocapsules incorporated into biodegradable starch films: A strategy to enhance fruit shelf life. Int J Biol Macromol 188:628–638
【4】Zhu Z, Min T, Zhang X, Wen Y (2019) Microencapsulation of thymol in poly(lactide-co-glycolide) (PLGA): physical and antibacterial properties. Materials 12(7):113
【5】Lamarra J, Calienni MN, Rivero S, Pinotti A (2020) Electrospun nanofibers of poly(vinyl alcohol) and chitosan-based emulsions functionalized with cabreuva essential oil. Int J Biol Macromol 160:307–318.
【6】Petchwattana N, Naknaen P, Cha-Aim K, Sanetuntikul J (2021) Application of antimicrobial plates in food packaging as an alternative approach for minimizing food waste. Int J Sustain Eng 14(4):600–608
[7] Atta OM, Manan S, Shahzad A, Ul-Islam M, et al. (2022) Biobased materials for active food packaging: a review. Food Hydrocoll 125:107419
