Desenvolvimento de filmes biopoliméricos a base de goma de ora-pro-nóbis (Pereskia aculeata Miller)

Abstract

Pereskia aculeata Miller is a Brazilian perennial plant. From the leaves of this plant it is extracted the ora-pro-nobis gum (GOPN), which has the biopolymer arabinogalactan. Biopolymers are been studied to produce films and edible coatings in order to use them as complements or substitutes of traditional packaging materials originated from petroleum. This research aimed to development films using GOPN and glycerol, as plasticizer, characterizing them in order to obtain the best formulation. Films were developed by casting method using five treatments: 1.5% GOPN with 20% glycerol (GOPN1.5G20), 1.5% GOPN with 25% glycerol (GOPN1.5G25), 1.8% GOPN with 22.5% glycerol (GOPN1.8G22.5), 2.0% GOPN with 20% glycerol (GOPN2.0G20), and 2.0% GOPN with 25% glycerol (GOPN2.0G25). The films were characterized by rheological, optical, mechanical (tensile and puncture tests), barrier (water vapour permeability), solubility and thermal properties (differential scanning calorimetry (DSC) and thermogravimetric (TGA) analysis). Surface response methodology was used to determine the optimum variables combination (GOPN and glycerol concentrations). The film-forming solutions presented a shear-thinning behavior, and both GOPN and glycerol, contributed to increase the viscosity. Films made with GOPN can be used to protect sensitive food against light, because they are dark and opaque. The formulation containing 1.5% GOPN and 20% glycerol exhibited the best mechanical and water vapor permeability (PVA) results, presenting 46.10% of elongation at break, 2.42 MPa of tensile strength and 0,344 g•water•mm/day•m 2 •kPa for PVA. Glycerol showed an antiplasticizing behavior. TGA test showed that the glycerol contributed to accelerate the films decomposition. The film containing 1.8% GOPN and 22.5% glycerol presented more stable thermal decomposition than the others, because it had loss of mass in the second stage of degradation (more severe). DSC analysis demonstrated two glass transition temperatures, below to 0 ºC and around 60 ºC. It was observed that GOPN increases the stability of the films, because higher concentration of the gum increased the glass transition temperature. For this study, it was concluded that the best formulation used 1.5% GOPN and 20% glycerol. GOPN is able to form cohesive and nontoxic edible films, and it can be a potential source to replace packaging from petroleum.