Solid Lipid Nanoparticles in Food Applications: Challenges, Optimization Strategies, and Emerging Supercooling Technologies.

Solid lipid nanoparticles (SLNs) have gained attention as a promising delivery system for bioactive compounds due to their ability to improve stability and bioavailability of encapsulated molecules. However, their application remains limited by several challenges, including physical instability at both colloidal and crystalline levels, low loading capacity, and rapid initial release of encapsulated compounds. To address these limitations, both chemical and physical strategies have been developed. Chemical approaches primarily involve optimization of lipid and surfactant composition, whereas physical approaches include control of production methods as well as cooling and storage conditions. Among these physical strategies, supercooling technology has recently emerged as a potential approach for stabilizing SLN systems by maintaining the aqueous phase in a supercooled state at subzero temperatures while preserving the solid lipid matrix of nanoparticles. However, maintaining a supercooled state remains challenging due to spontaneous ice nucleation. Accordingly, various supercooling approaches, including magnetic field-assisted, isochoric, and temperature-controlled methods, have been investigated to enhance the stability of the supercooled state in food and biological systems. This review provides a comprehensive overview of SLNs in food applications, their main challenges, and the chemical and physical strategies developed to address them. In addition, it discusses supercooling technology as an emerging but still insufficiently validated physical strategy for improving the stability of SLN-based delivery systems and highlights the need for independent validation under standardized and directly comparable conditions.