Avaliação do potencial antioxidante de extrato de folha de oliveira nanoencapsulado frente a oxidação lipídica de óleo comestível

Abstract

Olive leaves (FO) are a bio-residue from the production of olive oil and olives and a source of antioxidant compounds, that can lose their activity. Aiming to prolong their effect the olive leaf extract (OLE) was submitted to nanoencapsulation by nanoprecipitation. The extraction and OLE nanoencapsulation were performed concomitantly, optimizing the time and solvent amount. FO and zein were mixed with the solvent (ethanol: water, 80:20) under stirring in a rotor-stator system to guarantee the compound's extraction and zein (encapsulanting agent) interaction with them. After the mixture centrifugation, nanoprecipitation was performed by dripping this solution into an aqueous sodium caseinate (surfactant) solution at 12,000 rpm, and finally, nanoparticles (NPs) were dried in an oven. OLE was obtained under the same proportion of FO/ethanol/water used for encapsulation, same stirring rate, centrifugation, and drying conditions. The OLE and NPs were characterized by FTIR (Fourier Transform Infrared Spectroscopy), DSC (Differential Scanning Calorimetry), and TGA (Thermogravimetric Analysis). The NPs were also analyzed by TEM (Transmission Electron Microscopy) and DLS (Dynamic Light Scattering). With thermal characterization, it was possible to verify a higher residual mass for NPs at the end of the analysis when compared to OLE, indicating higher thermal resistance. By FTIR, it was verified an intensity reduction of the characteristic bands of OH, CN, and NH groupings, indicating an interaction between components and effective encapsulation, in addition to zein crosslinking by hydrogen bonding with the phenolic compounds. The DLS indicated a polydispersion index (PDI) equal to 0,9 ± 0,1 and the average diameter Dz equal to 638,5 ± 55,8 nm, and TEM images confirmed the morphology of spherical format and the nanometric dimensions (100 to 500 nm), however with particle agglomerates. OLE and NPs were applied to edible oils at the concentrations of 47.1, 94.2 e 141.3 mgOLE/kgoil. To allow a comparison BHT (butylated hydroxytoluene) was added at 300 mgBHT/kgoil, and as a control the oils without antioxidants. The oils were analyzed by Rancimat, being BHT the best antioxidant for soya oil, free OLE at 141.3 mgOLE/kgoil for palm oil, being statistically equal to BHT. To palm kernel oil the samples that were added with 94.2 mgOLE/kgoil of free OLE and 141.3 mgOLE/kgoil of NPs presented a similar stability to the BHT added sample. The ABTS, DPPH, and FRAP analyses confirmed the antioxidant capacity of NPs. Finally, the Schaal Oven Test was performed with the NPs in the palm kernel oil. The UV-Vis spectra were then analyzed by the PARAFAC chemometric method, where it was determined higher stability of the oil added with 300 mgBHT/kgoil and 141.3 mgOLE/kgoil of NPs (300 mgNPs/kgoil). It can be concluded that the NPs can be produced using green solvents and edible polymers by the integrated process of extraction/encapsulation, guaranteeing the antioxidant capacity with great potential to be explored compared to the antioxidant capacity offered by BHT.