ASSESSING THE IMPACT OF NATURAL ANTIOXIDANTS POLARITY ON THE OXIDATIVE STABILITY OF SPRAY-DRIED MICROENCAPSULATED FLAXSEED OIL

Lipid oxidation is one of the main factors limiting the stability of oils rich in polyunsaturated fatty acids, especially in spray-dried microencapsulated systems. In these systems, antioxidant efficiency may be influenced not only by the chemical structure of the compounds, but also by their spatial distribution within the particle microstructure. This study evaluated the effect of antioxidant polarity on the oxidative stability of microencapsulated flaxseed oil. Four formulations were produced: a control without antioxidants (FO-C) and formulations containing gallic acid (FO-GA, hydrophilic), ferulic acid (FO-FA, amphiphilic), and tocopherol (FO-TCO, lipophilic). Emulsions O/W were prepared using whey protein isolate and maltodextrin and subsequently spray dried. Samples were stored at 45 °C for 45 days, under accelerated oxidation conditions, with an O₂ availability of approximately 0.163 mmol/g oil. During storage, surface oil (SO) and total oil (TO) fractions were extracted and analyzed by Nuclear Magnetic Resonance (NMR), with quantification of hydroperoxides, aldehydes, and epoxides. For primary oxidation products, the maximum hydroperoxide levels were similar among FO-C, FO-GA, and FO-FA (~150 mmol/kg in SO and ~200 mmol/kg in TO), whereas FO-TCO showed significantly higher accumulation (~375 mmol/kg in SO and ~325 mmol/kg in TO). The maximum epoxide values found in the SO fraction were 153, 163, 197, and 193 mmol/kg for FO-FA, FO-GA, FO-C, and FO-TCO, respectively. In the TO fraction, the maximum epoxide values were 156, 146, 148, and 191 mmol/kg for FO-FA, FO-GA, FO-C, and FO-TCO, respectively. The results indicate a greater protective effect of FO-FA and FO-GA compared to FO-C, especially in the SO fraction, which is considered the most susceptible to oxidation. In contrast, FO-TCO, although widely described in the literature as one of the most efficient antioxidants in lipid systems, exhibited a pro-oxidant behavior due to its high concentration in this study. These findings reinforce that antioxidant efficiency in microencapsulated systems also depends on concentration, localization, and microstructural organization within the particle. The application of complementary oxidation assays, as well as the evaluation of different tocopherol concentrations, may contribute to a better understanding of possible transitions between antioxidant and pro-oxidant behavior.