Biodegradable materials based on poly(vinyl alcohol) (PVA) and poly (lactic acid) (PLA) with antioxidant and antimicrobial activity for food packaging applications

The massive use of synthetic plastics and their environmental impact, as well as the need of improving food preservation, makes necessary the development of biodegradable alternatives for food active packaging, to extend the food shelf life.The use of active compounds from natural origin to obtain this kind of materials is a new trend based of the consumer demand for safer and healthier products.The present Doctoral Thesis, has been focused on the development of multilayer active packaging materials, based on biodegradable polymers with complementary properties, in order to obtain materials with adequate mechanical and barrier properties to meet food packaging requirements.To this end, poly (vinyl alcohol) (PVA) (with high oxygen barrier capacity), of different molecular weight and acetylation degree, and poly (lactic acid) (PLA) (with high water vapour barrier capacity) were considered.Likewise, carvacrol (liposomal encapsulated or not) and ferulic and cinnamic acid, were chosen as antimicrobial/antioxidant compounds, which were loaded into the PVA sheets.The liposomal encapsulation of carvacrol, using different kinds of lecithin was evaluated in order to improve the carvacrol retention in the polymer matrix during the film formation step.Soy lecithin enriched in phosphatidylcholine was the most effective at maintaining the stability of the carvacrol emulsion during film formation, leading to its highest retention in the PVA films.Incorporation of carvacrol (lecithin encapsulated or not) at 5 or 10 %, with respect to the polymer, slightly modified the film microstructure and physical properties and polymer crystallinity and thermal behaviour.The fully hydrolysed PVA provided films with a better mechanical performance and oxygen barrier capacity, but with less carvacrol retention.In contrast, partially hydrolysed PVA gave rise to more homogenous films with a higher carvacrol content, while acetyl groups protect the polymer for thermodegradation, shifting the degradation temperature to temperatures above the melting point.This allows the production of films using the common industrial thermoplastic processing techniques.Therefore, partially acetylated PVA has a great potential for the production of active films with carvacrol, with a wider range of possibilities (casting or thermoprocessing) than fully hydrolysed PVA.Cinnamic and ferulic acids, with lower potential sensory impact than of carvacrol, were also incorporated into partially and fully hydrolysed PVA, at 1 and 2 % with respect to the polymer, by casting of aqueous solutions containing glycerol (10%) to improve the acid solubility.Glycerol plasticized PVA films exhibited poorer barrier capacity than those non-plasticized.