Bioactive micro-structured lipid carriers for incorporation in biodegradable films for potential food application

Abstract

The main goal of this thesis was to obtain active lipid carriers by complex coacervation and incorporate them in biodegradable chitosan-based films plasticized with deep eutectic solvents (DES) based on the mixture of choline chloride:glycerol (ChCl:Gly) to potential food application. Two different systems based on chitosan (CS) and sodium alginate (SA), and CS and pea protein isolate (PPI) were formulated and optimized using the design of experiments (DOE) methodology to encapsulate açaí pulp oil (AO) and extra-virgin olive oil (EvO). The first system was investigated by a central composite design. It was formulated to study the effect of different amounts of AO (0.25 - 0.75%), and calcium chloride (CaCl2) (0 – 1.0%), in the formation of CS:SA polyelectrolyte complexes (PECs). CS:SA complex formation and AO encapsulation were confirmed by optical (OM) and electron scanning microscopy (SEM), as well as infrared spectroscopy (FTIR), thermogravimetric and derivative thermogravimetric analyses (TGA/DTG). In this system, AO and CaCl2 significantly influenced the size and polydispersity index (span) of the PECs, although the encapsulation efficiency (>99%) was not affected. These PECs exhibited a gel-like behavior, consistent with the complexes formation. AO and the optimum PECs (0.5% AO and 0.5% CaCl2) presented high antioxidant activity, >70% by the DPPH scavenging radical. The other microencapsulation system was formulated to study the effect of CS concentration (0.39 - 1.1%) and CS:PPI ratio (0.18 - 2.31) on the formation of PECs to encapsulate EvO using a central composite design. The particles size was significantly influenced by CS:PPI ratio, whereas span was influenced by both, CS and CS:PPI ratio. The results were optimized by response surface methodology (RSM) and desirability function (D), displaying optimum conditions of 0.75% CS, 2.31 CS:PPI ratio and 0.5% EvO, and D = 0.845. The optimized particles had a small size and narrow span, ~3 µm and 2, respectively. FTIR spectra and TGA/DTG curves of the complexes have confirmed the EvO encapsulation. The CS:PPI-EvO complexes exhibited moderate antioxidant activity, with the highest value ~117 mg Trolox equivalent (TE) L -1 by DPPH radical scavenging assay. As to the AO encapsulated in optimum CS/SA, PECs exhibited satisfactory physicochemical and antioxidant properties. Their incorporation in biodegradable films was evaluated. The casting method was used to produce CScomposite films plasticized with 1:2 ChCl:Gly and incorporated with different amounts (0 - 10%) of AO PECs. The OM, SEM and confocal laser scanning microscopy (CLSM) techniques were used to observe their microstructure and to confirm the presence of AO PECs. FTIR and X-ray diffraction patterns revealed interactions between CS, DES and AO PECs in the films by typical and shifted spectral bands, as well as by its decreased crystallinity (8 to 4%), respectively. The films exhibited good mechanical properties, high elongation at break > 100%, low tensile strength and Young’s modulus. All films exhibited antioxidant activities by using different assays, although the highest value was determined by DPPH radical scavenging, up to 17 mg TE g-1 of film. This could be associated to the higher antioxidant capacity of AO, 101.8 ± 8.2 mg TE L-1 oil, also determined by DPPH radical scavenging assay. Furthermore, these results have demonstrated the good structural, mechanical and antioxidant properties of the CS-composite films as a potential active food packaging.