Encapsulation of curcumin in casein-dextran sulfate nanocomplexes for enhanced acid stability and bioaccessibility

Abstract

Casein is commonly used to encapsulate lipophilic polyphenols such as curcumin. However, casein capsules precipitate at ∼ pH 3–5.5. Sodium caseinate (NaCas)-dextran sulfate (DS) nanocomplexes were studied in this work to encapsulate curcumin for acid stability and bioaccessibility. Compounds were dissolved at pH 13.0, followed by adjusting pH to 7.0, 4.6, and 3.0. The chosen formulation (3.0 mg/mL curcumin, 5.0 mg/mL NaCas, and 5.0 mg/mL DS) led to an encapsulation efficiency (EE) of 94.8%, 90.2%, and 77.3% and loading capacity of 38.1%, 35.3%, and 34.5% at pH 7.0, 4.6, and 3.0, respectively. The EE of curcumin-loaded NaCas/DS nanocomplex dispersions remained similar (P > 0.05) at pH 7.0 and 4.6 during 31-day ambient storage while at pH 3.0, slight precipitation decreased the EE by about 9% after 31 days. The Z-average diameter of dispersions was bigger at a lower pH and was smaller than 225 nm. During ambient storage, the Z-average diameter of dispersions was mostly stable. Encapsulation had no impact on the antioxidant capacity of curcumin but increased the bioaccessibility of curcumin to more than 53%, resulting from the amorphous curcumin structure. Therefore, NaCas/DS nanocomplexes have the potential of delivering curcumin in functional beverages, especially in acidic conditions.