Phytosterol nanoparticles with reduced crystallinity generated using nanoporous starch aerogels

Abstract

Food industry has placed a high priority on developing foods that are enriched with health-promoting bioactives such as phytosterols. However, the potential of phytosterols remains untapped due to their poor bioavailability. Incorporation of free phytosterols into foods is a major challenge because phytosterols are high melting point crystalline bioactives that are insoluble in water and poorly soluble in fats and oils. Poor water solubility severely limits phytosterols' bioavailability. The main objective of this study was to develop a novel approach to decrease the size and crystallinity of phytosterols in order to enhance their solubility and, in turn, their bioavailability. Nanoporous starch aerogels (NSAs) (19.6 nm pore size, 59.7 m² g⁻¹ surface area, 0.12 g cm⁻³ density) were generated using a green method based on supercritical carbon dioxide (SC-CO₂) drying. A phytosterol–SC-CO₂ solvato complex was precipitated in the NSAs using a SC-CO₂ impregnation process. The nanopores of the NSA act as a mold to prevent the formation of bigger phytosterol crystals and lead to the formation of phytosterol nanoparticles whilst decreasing their crystallinity, which later leads to the enhanced solubility of the phytosterols in water and gastrointestinal fluid. Impregnated phytosterols were 37 times more soluble than the crude phytosterols in water. Impregnation did not create any chemical bonding with the NSA matrix. This is a novel green approach to fabricate water-insoluble (lipophilic) bioactive nanoparticles with decreased crystallinity, which enables the addition of water-insoluble bioactives into low-fat foods and beverages to promote health and maximizes the utilization of water-insoluble bioactives.