Development, characterization, application, and degradation of sustainable active packaging: cellulose acetate and zein films incorporated with garlic essential oil

Abstract

Biodegradable polymers obtained from renewable sources are considered potential substitutes for conventional plastics. In the present work, cellulose acetate (CA) and zein films containing garlic essential oil (GEO) and different plasticizers (glycerol and tributyrin) were manufactured, characterized, and evaluated as active films aiming food preservation, as well as investigated regarding their degradation in soil. In the first chapter, CA and zein blends were manufactured by adding glycerol or tributyrin as plasticizers, and GEO, complexed or not with β-cyclodextrin. Blends plasticized with tributyrin exhibited a more homogeneous surface than those containing glycerol. The blends underperformed the CA films at mechanical properties and water vapor permeability. However, they were more flexible than the zein brittle films. The films added with GEO presented in vitro activity against Listeria innocua and Staphylococcus aureus. These findings suggest that the mixture of CA and plasticizers could increase the range of application of zein as a sustainable packaging component, while GEO acts as a natural preservative. In the second chapter, CA-based films containing GEO were tested in vitro against L. innocua to verify the occurrence of sub-lethal injury and/or homologous resistance to GEO. Two conditions were tested: 7 oC for 10 days, and 37 oC for 24 h. The active films were also tested on food. The in vitro trials showed that the incubation under low temperature enhanced the active films properties: log reductions of 4.3 and 5.7 were obtained for films containing 1% and 10% of GEO, respectively. Moreover, 86.3% of L. innocua cells were injured at sub-lethal level when exposed to films with 10% of GEO for 10 days at 7 oC. Despite this, no occurrence of homologous resistance was found. When the active films were tested on food, they resulted in fewer contaminants. This work suggested that GEO is a safe active compound from the point of view of homologous resistance. In the third chapter, the degradation in soil of blend films and CA-based films was studied. Films were buried for 150 days and were studied in terms of weight loss, macro and micro changes, molecular alterations, and thermal degradation profile. The polymer mass loss was more noticeable in CA:zein blend films and in films produced through glycerol incorporation. Also, there was significant interaction between the plasticizer choice and presence of GEO: incorporation of GEO in glycerol-added films reduced the mass loss due to polymer degradation, while, when tributyrin was used, no impact was observed. FTIR spectra evidenced plasticizer loss, as well as degradation of zein in blend films and oxidation of the CA remaining hydroxyls. This study showed that the polymeric film’s degradation in soil can be dependent on the polymer matrix, the type of plasticizer, and the presence of antimicrobial agent. Overall, the present study showed that the plasticizer choice can impact on the antimicrobial property of active films, and that additives as well as the polymer type affect the degradation rate of biodegradable films. Additionally, GEO, acting as antimicrobial agent in films, did not cause homologous resistance in L. innocua cells. Keywords: Food preservation. Food Packaging. Polymers. Microbiology. Bacterial resistance. Degradation.7