Characterization and shelf life of β-carotene loaded solid lipid microparticles produced with stearic acid and sunflower oil

Solid lipid microparticles were tested as microencapsulation systems for protecting β-carotene from degradation. Blends of long-chain (C18) solid lipids (70% stearic acid) and sunflower oil (30%) were used to produce lipid microparticles encapsulating the carotenoid. Polysorbate 80 (4%) was employed to stabilize the stearic acid microparticles. The concentration of β-carotene was monitored using spectrophotometry, the particle size distribution was measured by laser diffraction, the crystal structure was determined by wide angle X-ray diffraction (WAXD), and the thermal behaviour was characterized by differential scanning calorimetry (DSC) over a period of seven months. All of the systems had an average particle size smaller than 5 µm. To avoid β-carotene oxidation, α-tocopherol was added to the formulations and its action as an oxygen trap was crucial for the antioxidant effect. For stearic-acid microparticles with a-tocopherol, more than 90% of the initial amount of β-carotene was preserved after seven months under refrigerated storage (7-10°C) in the dark. Significant microstructural alterations were detected using WAXD and DSC only in the stearic acid microparticles without alpha-tocopherol. These results seemed promising and suggested that the blends of long-chain solid lipids and liquid lipids were suitable for the production of stable solid lipid microparticles.