Preparation of encapsulated bovine milk exosome microcapsules and their resistance to environmental stability

Bovine milk exosomes (BME) have great potential for application in food and medicine due to their functional activities, such as immunomodulation and antioxidants. Still, their lack of stability in processing, storage, and digestive environments seriously restricts industrialization. In this study, sodium alginate (SA) and guar gum (GG) were used as wall materials to construct a BME microencapsulation system with a protective effect by the calcium ion cross-linking method. The optimized embedding parameters were determined by response surface methodology as 0.5 % w/v for GG, 1.5 % w/v for SA, and 4 % for CaCl₂, which achieved an encapsulation efficiency rate of 91.32 ± 0.32 %. Characterization results showed that the SA-GG-BME microcapsules had a dense network structure, and the microcapsules exhibited excellent water-holding and textural properties as well as pH-responsive swelling properties. Inverse experiments showed that SA-GG-BME microcapsules significantly improved stability compared with free-bovine milk exosomes (Free-BME): protein and RNA retention were 75 % and 45 % after simulated in vitro gastrointestinal digestion for 6 h, Macrophage metabolic activity reached 145.19 ± 0.42 % in the heat-treated group at 65 °C/30 min (vs. 137.50 ± 0.73 % in the free group, P < 0.05), and the SA-GG-BME microcapsules exhibited excellent water holding properties and pH-responsive swelling properties after storage at 4 °C for 28 d. The microcapsules had a dense network structure. After 28 d of storage at 4 °C, the active components in the SA-GG-BME group were 12–14 times higher than those in the Free-BME group. The macrophage-promoting metabolic activity (120.37 ± 0.57 %) was significantly better than that of the SA-BME group (105.09 ± 0.73 %) vs. the Free-BME group (inactive) (P < 0.05). By revealing the hydrogen bonding-hydrophobic synergistic protection mechanism of SA-GG wall materials, the present study provides a theoretical basis for applying BME in functional dairy products and orally targeted formulations.