MECHANICAL PROPERTIES AND SOLUBILITY OF CHITOSAN-BASED ACTIVE FILMS CONTAINING ROSIN RESIN AND ZnOnano

Passion fruit (Passiflora edulis Sims) is a tropical fruit widely consumed in Brazil. However, the reduced fruit shelf life is one of the problems pointed out by the productive value chain, affecting its external appearance, as the water loss gives the fruit a wrinkled appearance. In addition, passion fruit is also susceptible to be attacked by deteriorating microorganisms such as fungi. therefore, this work aimed to develop nanocomposite films to be used as an active coating on yellow passion fruits in order to increase their shelf life. The films were produced by casting. Six filmogenic solutions were prepared using chitosan as polymer base, glycerol as plasticizer, carnauba wax and rosin resin as hydrophobicity promoting agents and zinc oxide nanoparticles as antimicrobial agent. Acetic acid and Tween 80 were also used to facilitate the dissolution and mixing of the components. The six filmogenic solutions contain CH at 1.2% w/v, wax or resin content from 0 to 0.6% m/v and ZnOnano from 0 or 0.05% m/v. The dried films were characterized according to their chemical, mechanical and optical properties. All treatments resulted in homogeneous and flexible films. Wax and resin films were less transparent than the chitosan-only films. The films thickness ranged from 85.71 ± 5.35 to 152.86 ± 7.56 μm. The addition of either wax or resin resulted in an increase of film thickness. No significant differences were observed in film thickness when ZnOnano was incorporated in the formulation. Wax or resin films were less water soluble than chitosan-only films with values of 12.36% ± 0.08 and 16.47% ± 0.18 for wax and resin films, respectively. On the other hand, the addition of ZnOnano in the formulations increased the solubility of the films. The sorption degree was in line with the solubility results, i.e., films with ZnOnano presented higher sorption degree and solubility values. Regarding light transmission, at 280 nm, all treatments showed low or non-light transmission, indicating that the films provide good barrier to UV light. In the visible light region (350-800 nm), resin films showed the lowest transmittance values, hence offering a good barrier to visible light. Among the evaluated films, wax films showed the highest tensile strength and elongation at break, followed by resin and chitosan films. In general, films produced with wax and resin showed potential improvements in barrier, mechanical and optical properties, mainly due to their low water solubility, higher elongation at break and good UV protection, which are suitable for use in formulations intended to produce edible films and coatings.