Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) films, plasticized with PEG, incorporating 13 wt. % of active compounds (carvacrol-CA, eugenol-EU) were obtained by spraying the active between PHBV layers and their subsequent adhesion. Release kinetics of CA and EU in food simulants of different polarity was analysed and the films' antimicrobial activity was predicted, taking the minimal inhibitory concentration against some foodborne pathogens into account. Overall migration values were also determined. At equilibrium, an almost total release of both CA and EU occurred in 50% ethanol, about 20 and 50 % of CA and EU, respectively, was delivered in the more aqueous simulants and 65-70 % in fatty systems. The release rate increased when the polarity of aqueous simulants decreased, but it fell markedly in fatty systems. EU was released faster than CA in the less polar simulants, but more slowly in the more aqueous systems.

Bilayer films using polyester blends (P) and starch (S) were obtained and characterized, incorporating carvacrol as active compound. Carvacrol was incorporated by spraying it between melt blended and compression moulded sheets or through its incorporation into the chloroform P solution used to obtain P cast films. Different PLA-PHBV ratios (75:25 and 65:35) were tested, with and without 15 wt% of PEG1000, whereas the 75:25 ratio with PEG was only used for cast sheets, based on its better overall properties. Mono and bilayers were characterized as to their tensile and water vapour barrier properties and thermal behaviour. Release kinetics of carvacrol in different food simulants and in in vitro antibacterial activity against Listeria innocua and Escherichia coli were also analysed. Incorporating carvacrol by spraying it between the polyester and starch sheets was not effective at retaining the compound in the bilayers. However, the incorporation of carvacrol into cast P films, and the subsequent formation of bilayers with the S sheets, was highly effective at providing practically total carvacrol retention. These active bilayers exhibited highly improved tensile and water vapour barrier capacity with respect to the S monolayer (87% reduction in WVP, 840% increase in elastic modulus) and inhibited the growth of L. innocua and E. coli from both P or S contact sides of bilayers, depending on the internal diffusion of carvacrol through the bilayer and its adequate release of the compound into the culture medium.

a b s t r a c tPoly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is a promising bio-based, biodegradable polymer for replacing synthetic polymers, but its brittleness limits its application range. With the aim of improving the mechanical properties of PHBV films, different plasticizers (polyethylene glycol (PEG 200, 1000 and 4000), lauric acid (LA) and stearic acid (SA)) were incorporated into the film formulation at 10 wt%. All plasticized films showed lower melting temperature and crystallization degree than pure PHBV films. All plasticizers, except SA, reduced film stiffness and resistance to break, and increased the films' water sorption capacity and solubility as well as their water vapour permeability, but only PEG1000 yielded more extensible films. PEG1000 and PEG4000 gave rise to the most heat-resistant plasticized films, while LA and SA highly promoted the heat-sensitivity of PHBV. PEG1000 was the most effective at plasticizing PHBV films, and it was the only plasticizer that partially mitigated the ageing effects. However, a greater ratio of plasticizer would be required to adapt PHBV mechanical properties to some packaging requirements.

The incorporation of natural antimicrobials, especially carvacrol and oregano essential oil, into bilayer films of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] could be a promising option for the development of active biodegradable films.

The thiazolyl blue tetrazolium bromide (MTT) assay was used to study the potential interactions between several active compounds from plant essential oils (carvacrol, eugenol, cinnamaldehyde, thymol and eucalyptol) when used as antibacterial agents against Escherichia coli and Listeria innocua. The minimum inhibitory concentration (MIC) of each active compound and the fractional inhibitory concentration (FIC) index for the binary combinations of essential oil compounds were determined. According to FIC index values, some of the compound binary combinations showed an additive effect, but others, such as carvacrol-eugenol and carvacrol-cinnamaldehyde exhibited a synergistic effect against L. innocua and E. coli, which was affected by the compound ratios. Some eugenol-cinnamaldehyde ratios exhibit an antagonistic effect against E. coli, but a synergistic effect against L. innocua. The most remarkable synergistic effect was observed for carvacrol-cinnamaldehyde blends for both E. coli and L. innocua, but using different compound ratios (1:0.1 and 0.5:4 respectively for each bacteria).