2.2. Biodegradable Films Preparation

Active biodegradable films were obtained by casting method from filmogenic suspensions formulated with chitosan and corn starch, which were optimized in a previous work [40]. Briefly, chitosan (CH) was dispersed in aqueous acetic acid to obtain a 2.5% w/w solution. On the other hand, a 4% w/w corn starch (CS) suspension was gelatinized at 90 °C for 20 min in a thermostatic bath. Both biopolymers were mixed in a 75:25 CS:CH proportion. Glycerol was added as a plasticizer at 25% w/w. Two essential oils were chosen because of their antimicrobial activity: lemon essential oil (LEO) and grapefruit seed extract (GSE). The essential oils were added at 3% w/w in formulations according to a previous work [40]. The film forming dispersions were homogenized in a rotor-stator Ultraturrax T25 (Janke & Kunkel, Staufen im Breisgau, Germany). Then they were poured into rectangular plates of 10 × 15 cm² and dried in a convection oven (FAC, Buenos Aires, Argentina) at 50 °C until constant weight. The films were removed from the plates and thermo-sealed with an impulse sealer (Lepari, Santa Fe, Argentina) to obtain the active biodegradable packaging.

Synthetic PET containers, commonly called Clamshells, (125 g or 4.4 oz capacity, with dimensions of 106 × 106 × 40 mm³) and commercial bags suitable for modified atmosphere (DISEVAC SS MB Cristal 150 × 200, Plásticos DISE S.A., Córdoba, Argentina) were used as benchmark packaging systems. Barrier and mechanical properties of flexible film materials are included in Figure 1.

Blueberries packaging procedure using biodegradable active films and their relevant properties.