Long-term stable water-in-oil-in-water emulsion for effective protection and sustained release of lysine-calcium using chitosan and hydroxypropyl methyl cellulose

The poor tolerance to gastric acid and low absorption of calcium supplements in the intestinal tract remain a serious limitation in applications. Herein, lysine-calcium (Lys-Ca) has been synthesized via the chelation of Lys and high-temperature calcination scallop shell powder (HCSP), and subsequently encapsulated in a carefully designed water-in-oil-in-water (W/O/W) emulsion with a high encapsulation efficiency of 93 % using chitosan (CS) and hydroxypropyl methylcellulose (HPMC). Owing to the interfacial film formed by CS and HPMC between the droplets, the resulting emulsion demonstrates good acid and thermal stability, as well as long-term stability even after 60 d of storage at 25 degrees C. Meanwhile, the emulsion effectively protects the encapsulated Lys-Ca from damage in simulated gastric fluid (SGF). with only about 20 % Lys-Ca escaping into SGF (after 4 h). In simulated intestinal fluid (SIF), it sustainedly releases with a 61 % ratio at 1 h under the influence of bile salts and lipase, and near-complete release occurred after 6 h. Additionally, the emulsion presents no cytotoxicity and possesses appreciable calcium transport capacity. This work provides a well-designed double-emulsion strategy that offers a promising approach for developing efficient calcium supplements, aiming at improving the bioavailability of biomass calcium.