Using protein-fatty acid complexes to improve vitamin D stability.

Liprotides are complexes between lipids and partially denatured proteins in which the protein forms a stabilizing shell around a fatty acid micelle core. We have previously shown that liprotides stabilize small aliphatic molecules such as retinal and tocopherol by sequestering these molecules in the fatty acid core. This opens up the use of liprotides to formulate food additives. Here, we expand our investigations to the large and bulky molecule vitamin D3 (vitD), motivated by the population-wide occurrence of vitD deficiency. We prepared liprotides using different proteins and fatty acids and evaluated their ability to protect vitD upon exposure to heating or intense UV light. Additionally, we determined the stability of liprotides toward pH, Ca(2+), and BSA. The best results were obtained with liprotides made from α-lactalbumin and oleate. These liprotides were able to completely solubilize vitD, increase the stability toward UV light 9-fold, and increase the long-term stability at 37°C up to 1,000-fold. Native α-lactalbumin binds Ca(2+), making Ca(2+) potentially disruptive toward liprotides. However, liprotides prepared by incubation at 80°C were stable toward Ca(2+), in contrast to those made at 20°C. Nevertheless, the fatty acid binding protein BSA reduced the ability of both liprotides to protect vitD; the amount of vitD remianing after 20d at 20°C decreased from 79±3% in the absence of BSA to 49±4 and 23±3% in the presence of BSA for liprotides made at 80 and 20°C, respectively. Both classes of liprotides were able to release their vitD content, as demonstrated by the transfer of vitD encapsulated in liprotides to phospholipid vesicles. Importantly, liprotides were not stable at pH 6 and below, limiting the useful pH range of the liprotides to >pH 6. Our results indicate that vitD may be encapsulated and stabilized for enrichment of clear beverages at neutral pH to improve the intake and bioavailability of vitD.