Stability of astaxanthin-loaded nanostructured lipid carriers as affected by pH, ionic strength, heat treatment, simulated gastric juice and freeze-thawing

Nanostructured lipid carriers (NLCs) offer many potential benefits for incorporating lipophilic molecules into clear/opaque food systems. In this study, the influence of pH, ionic strength, thermal treatment, simulated gastric juice (SGJ), and freeze-thawing on the stability of astaxanthin-loaded NLCs (Ax-NLCs) was examined. Ax-NLCs (containing α-tocopherol and ethylenediaminetetraacetic acid as antioxidants) were stabilized with Tween 80 and lecithin (Z-average size: 94 nm), and studied for the above mentioned purpose. The size of Ax-NLCs increased at low pH values (≤5), high NaCl concentrations (≥50 mM), and slightly at SGJ, mainly because of decreasing the ζ-potential. Moreover, thermal treatment at 80/90 °C led to an increase in Ax-NLCs size. Glycerol was found as an appropriate cryoprotectant for preventing aggregation of Ax-NLCs during freeze-thawing. pH, ionic strength, heat and SGJ had no drastic effects on the chemical stability of astaxanthin in NLCs. These results have valuable implications for the utilization of food-grade NLCs.