The study on the antioxidant effect of microencapsulated sodium selenite by solvent evaporation during one-year soybean oil storage

Microencapsulation is represented as a technology of packaging solids, liquids, or gaseous materials in miniature sealed capsules that can release their contents at controlled speeds under specific conditions. The packaged materials can be pure materials or a mix, which are also called coated material, core material, actives, internal phase (Fang & Bhandari, 2010). Selenium is a micronutrient essential element for human health, which is toxic in high concentrations. Selenium is a component of selenoproteins that plays an enzymatic and structural roles in human biochemistry. Selenium is known as an antioxidant and catalyzer for active thyroid hormone production. The aim of this study was to optimize the microencapsulation of sodium selenite (100-900 mg per 20 mL final spray solution) using a combination of Arabic gum (25-29% per 20 mL final spray solution) and Persian gum (1-5% per 20 mL final spray solution) as capsule wall applying modified solvent evaporation method to produce microcapsules with the highest encapsulation efficiency (EE) and the smallest possible particle size using the response surface method (RSM) with central composite design (α = 2 with 6 central points and 2 repetition in axial and factorial points).

In this research, production of encapsulated sodium selenite at different concentration (100, 300, 500, 700 and 900 mg/20 cc) with Arabic gum (25%, 26%, 27%, 28% and 29%) and  Analogous Farsi gum (5%, 4%, 3%, 2% and 1%) as wall materials by solvent evaporation method was studied. The optimization of microcapsules based on the highest encapsulation efficiency and smallest microcapsules size was studied using RSM. Based on the mentioned parameters, 2 optimum conditions were chosen. The first one was a condition where the samples produced with 135 mg sodium selenite in 20 ml sprayed solution, 27% and 3% Arabic and Farsi gum, respectively. In this condition the encapsulation efficiency was 79.63% whereas the microcapsules size was 49.98 µm.  The second condition was followed by producing samples with 109 mg sodium selenite in 20 ml sprayed solution, 28% and 2% Arabic and Farsi gum with result of 95.10% encapsulation efficiency and the size of 46.71 µm. Finally 390 ppm capsules of the first condition and 480 ppm capsules of second condition (equal to 8.6 ppm sodium selenite salt), synthesized BHA (200 ppm) and sodium selenite salt (8.6 ppm) were added to a free anti-oxidant soybean oil and were kept at 55°C at 0, 23 and 46 days which was equal with 20°C at 0, 180 and 360 days. In this condition, peroxide value, acidity, Thiobarbituric acid, Anisidine value, Totox value and anti-oxidant activity of free anti-oxidant soybean oil were evaluated using SPSS software.

The results achieved by RSM showed that sodium selenite concentration had reverse relation on encapsulation efficiency whereas there was direct relation with Arabic and Farsi gum concentration. Also the size of microcapsules with had direct relation on sodium selenite concentration whereas Arabic and Farsi gum concentration had reverse relation. The result of SPSS analyses showed that with presence of the encapsulated sodium selenite anti-oxidant and synthesized BHA anti-oxidant in soybean oil, peroxide value, acidity, Thiobarbituric acid, Anisidine value, Totox value decreased whereas anti-oxidant activity of soybean oil increased. Based on anti-oxidant characteristics in soybean oil, recommended treatments in this research are: condition 2 ˃ condition 1 ≥ BHA ˃ sodium selenite salt ˃ control sample without anti-oxidant. The results of this study recommend the incorporation of encapsulated sodium selenite (condition 1 and 2) for increasing the shelf life of soybean oil as an alternative to synthesized BHA.