Obtaining antimicrobial bilayer starch and polyester-blend films with carvacrol

Abstract

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.

Development of Electrospun Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Monolayers Containing Eugenol and Their Application in Multilayer Antimicrobial Food Packaging

“…It can be observed that the multilayer presented a significant inhibition reduction (R ≥ 1 and <3) against both bacterial strains in the all days of evaluation, reaching at day 15 R values of 1.84 for S. aureus and 1.47 for E. coli. Compared with the monolayer materials, lower values were obtained since the release rate was slower due to the presence of the food contact layer, which potentially hindered the diffusion of eugenol (96). In any case, the R values obtained for these multilayers systems, ranging between 1.24 and 2.19, were still significant (R ≥ 1 and <3) against both bacteria and in both tested systems.…”

Enhancement of PLA-PVA Surface Adhesion in Bilayer Assemblies by PLA Aminolisation

“…The incorporation of the active compound in the polymer matrix modified the barrier and Fig. 1 Mechanism of aminolisation by 1,6-hexanediamine, occurring at the polylactide's surface mechanical properties of the film to a different extent, as reported by Requena et al (2018) and Tampau et al (2018) when carvacrol was incorporated into starch-polyester-blend bilayers and starch-PCL-starch multilayers, respectively.…”

“…Several authors have reported obtaining multilayers with improved physical properties, based on starch and polyester combinations. Requena et al (2018) obtained bilayers by thermo-sealing cassava starch sheets, and polylactic acid-polyhydroxybutyrate-co-hydroxyvalerate blend films, with low WVP and good oxygen barrier capacity. Muller et al (2017a) also obtained bilayer assemblies from thermo-processed cassava starch and amorphous PLA with improved barrier capacity with respect to the corresponding monolayers.…”

The Effects of Nanoclay on the Mechanical Properties, Carvacrol Release and Degradation of a PLA/PBAT Blend

“…It is worth noting that in both cases the final amount of carvacrol released at the equilibrium is lower than the nominal content in the films (i.e., 50 mg per 1 gram). This aspect, abundantly discussed in the scientific literature, can be ascribed to two phenomena [13,[35][36][37]: (i) Carvacrol tends to volatilize, especially at the high temperatures required for melt-processing; (ii) A certain aliquot of carvacrol remains entrapped inside the matrix.…”