Self-Assembled Protein Micelles for Encapsulation of Docosahexaenoic Acid (DHA): The Improvement of Bioaccessibility and Lipid-Lowering Activity

Abstract

Docosahexaenoic acid (DHA; 22-carbon-6) is renowned for its diverse biological activities and essential role in human wellness. However, owing to its highly unsaturated structure, dietary DHA is susceptible to oxidation and degradation in the gastrointestinal tract. Proteins are considered ideal carriers for protecting sensitive bioactive compounds like DHA from environmental factors. In this study, we prepared self-assembled micelles of ovalbumin (Ova), myosin (Myo), 7S soy globulin (Ssg), and β-lactoglobulin (β-la) to encapsulate DHA, resulting in O(DHA), M(DHA), S(DHA), and β(DHA) micelles via the chymotrypsin hydrolysis. We evaluated the encapsulation effectiveness of these micelles by assessing their encapsulation efficiency, storage stability, and bioaccessibility of DHA. The results indicated that O(DHA), M(DHA), S(DHA), and β(DHA) formed uniform, monodisperse nanospheres, with an outer shell composed of hydrolyzed micelle material and an inner core of encapsulated DHA. The secondary structures of Ova, Myo, Ssg, and β-la micelles were altered during the micelle formation process. The encapsulation rates for DHA in Ova, Myo, and β-la micelles were all above 70%, with Ssg micelles achieving over 90%. The zeta potential values of O(DHA), M(DHA), S(DHA), and β(DHA) remained between 20 and 30 mV over 4 weeks of storage. The particle diameters of O(DHA), S(DHA), and β(DHA) remained relatively stable throughout the storage period, while the diameter of M(DHA) showed significant changes. Additionally, the bioaccessibilities of O(DHA), M(DHA), and β(DHA) were all above 50%, with S(DHA) reaching 71.36 ± 4.27%. The encapsulation of DHA in Ova, Myo, Ssg, and β-la micelles enhanced the retention of DHA in gastrointestinal fluid. Ova, Myo, Ssg, and β-la micelles significantly improved the efficiency of DHA transport across a Caco-2 cell monolayer. Micelles containing DHA were more effective than free DHA in reducing total cholesterol (TC) and alanine aminotransferase (ALT) levels, increasing the number of autophagosomes, and upregulating the mRNA expression levels of PPARα and CPT1A in HepG2 cells, thereby reducing lipid accumulation. These findings support the use of Ova, Myo, Ssg, and β-la micelles as effective carriers for DHA.