ANTIOXIDANT ACTIVITY OF NANOEMULSION CONTAINING STRUCTURED LIPID

Structured lipids (LE) are restructured triacylglycerols, synthesized for various purposes, such like, to modify its physical and/or chemical characteristics or to alter its nutritional properties. The LE are obtained through a chemical or enzymatic interesterification process. The enzymatic interesterification exhibit high catalytic activity which reduces the thermal damages to reaction products. Emulsions when at nanoscale (nanoemulsions), with globules size ranging from 20 to 200 nm, are kinetically stable and are widely used in the transportation of pharmaceuticals, nutraceuticals and have several advantages over conventional emulsions in food and beverage applications. Thus, the objective of this study was to evaluate the antioxidant capacity of the two samples of nanoemulsion: LE and a simple oils mixture (blend), composed of olive oil, soybean oil and fully hydrogenated crambe oil. For the enzymatic interesterification reaction the oils were mixed in the ratio 43:43:14 (m/m) and added in a vacuum glass reactor at 350 rpm for 4 hours at 60 °C using 10% Lipozyme TL IM. After the reaction, the enzyme was removed by filtration with filter paper. Nanoemulsions were prepared using water, LE or the blend of oils and Tween 80 emulsifier. These mixtures were emulsified in a ultra turrax homogenizer and then brought to high pressure homogenizer (3 cycles at 800 bars). Nanoemulsions were characterized by particle size through the laser diffractometer using a Mastersizer 2000 and zeta potential (ZP) by photon correlation spectroscopy using a Zetasizer Nano-ZS. The particle size of LE was 159±0.00 nm and the blend of oils were 169±0.01 nm, in consequence, it is considered nanoemulsions. Particle size is essential in a nanoemulsion, since this parameter determines characteristics such as the physical stability and solubility of these molecules. In relation to ZP, the values obtained were -30.57±0.76 mV for LE and -25.77±2.76 mV for the blend oils. The ZP is used for gauging charge on nanoemulsion surfaceis and is an indirect measure of the physical stability of the nanoparticles, more than ± 30 mV provides good stability and gets excellent when ZP reaches toward ± 60 mV. In the case of the ZP ranging ± 20 mV decreases the general stability, while ±5 mV range indicates fast aggregation of the globules. The antioxidant activity was analysed through the iron ion reduction power (FRAP) and the oxygen radical absorption capacity (ORAC). The results showed that there were no statistical differences at the 95% significance level in the antioxidant activity by the ORAC method and the values were 3109.6±259.5 µmol TE/ml for LE and 3170.7±199.6 µmol TE/ml for the oil blend. But by FRAP the antioxidant capacity of the LE was lower (3330.0±277.6 µmol TE/ml) when compared to blend (5028.2±490.7 µmol TE/ml), probably due to loss of bioactive compounds during interesterification, which can be justified by the long reaction time at 60oC, without light protection. A small loss of carotenoids before the preparation of the nanoemulsions was also observed in LE (13.42±0.03 mg/kg) compared to the oil blend (15.28±0.49 mg/kg). Thus, the interesterification process slightly decreases the antioxidant capacity.