Release kinetics and antimicrobial properties of carvacrol encapsulated in electrospun poly-(ε-caprolactone) nanofibres. Application in starch multilayer films.

Carvacrol (CA) was encapsulated in polar (corn starch-Sodium caseinate, CS:NaCas) or non-polar (poly-εcaprolactone, PCL) matrices by electrospinning (ES). Electrospunable formulations were prepared with CS:NaCas (9:1 w/w ratio), at 2, 4 and 6 wt. % in water, or PCL at 5, 10 and 15 wt.% in glacial acetic acid using different CA ratios (0, 5, 10 and 15 wt.% with respect to the polymer). The liquid formulations were characterized for electrical conductivity, rheological behaviour and surface tension, and ES process conditions were established. The electrospun structures were analysed as to their nanostructure and CA retention. Geometry of the nanostructures obtained from the PCL systems was nanofibrillar with some beads, whereas it is particles that are mainly deposited for starch systems. PCL systems yielded better CA encapsulation efficiency (EE) than the polar ones, where greater variability was observed. The best EE (around 80%) was obtained for 15% PCL regardless of the CA ratio.

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Poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVA) present complementary barrier properties, and their combination in multilayer assemblies (laminates) could provide materials with more effective barrier capacity for food packaging purposes. However, their low chemical affinity compromises adequate polymer adhesion. Surface free energy modification of thermoprocessed PLA films through treatment with 1,6-hexanediamine was used to enhance adhesion with polar PVA aqueous solutions. Treatments of 1 and 3 min increased the polar component of the solid surface tension, while treatments above 10 min provoked a corrosive effect in the films' structure. Extensibility analyses of PVA solutions loaded with carvacrol (15 wt.%) and different Tween 85 ratios on PLA-activated surfaces allowed the selection of the 1-min aminolysed surface for obtaining PLA-PVA bilayers, by casting PVA solutions on the PLA films. This study revealed that despite aminolisation enhancing the PLA surface affinity for aqueous PVA solutions, casting-obtained bilayers presented limited oxygen barrier effectiveness due to heterogeneous thickness of PVA layer in the laminates.