Preparation of Lemongrass Essential Oil Microcapsules by Synergistic Encapsulation with Sodium Carboxymethyl Starch and Sodium Caseinate and Its Antibacterial Properties

To investigate the application of lemongrass essential oil in extending the shelf life of pickle. This study used lemongrass essential oil as the core material, sodium carboxymethyl starch and sodium caseinate as wall materials to prepare lemongrass essential oil microcapsules, and examined the effects of the mass ratio of sodium carboxymethyl starch to sodium caseinate on physicochemical properties, microscopic morphology, thermal stability, and others of lemongrass essential oil microcapsules. Furthermore, the effects of microencapsulation on the chemical composition of the essential oil and the antibacterial activity against major pathogenic bacteria in pickle was evaluated. Results showed that when the mass ratio of sodium carboxymethyl starch to sodium caseinate was 1:5 and 1:9, there was no significant difference in the essential oil encapsulation rate (P>0.05), which was 98.29% and 96.90%, respectively. The appearance was spherical and blocky. With the increasing sodium caseinate content, the micropores on the surface of the microcapsules gradually decreased, and the cavities became smaller. The thermogravimetric curves showed that the temperature corresponding to the maximum weight loss rate of microcapsules was increased with the increasing casein content, reaching a maximum of 314.27 ℃, while that of pure essential oil was only 106.27 ℃. Gas chromatgraphy-mass spectrometry (GC-MS) results showed that essential oil microcapsulation treatment retained multiple antibacterial ingredients of essential oils such as nerol (34.69%), geranyl acetate (27.41%), linalool (5.65%) and caryophyllene (6.50%). This conferred lemongrass essential oil microcapsules strong antibacterial properties against the main spoilage bacteria Bacillus subtilis in pickle and Staphylococcus epidermidis, the bacteria that cause packaging bags to bulge, with the minimum inhibitory concentration of 97.66 µg/mL for Bacillus subtilis and 195.31 µg/mL for Staphylococcus epidermidis, and the maximum bactericidal concentration of 1562.5 µg/mL for both bacteria. In summary, it is feasible to use sodium carboxymethyl starch and sodium caseinate as encapsulating agents to prepare lemongrass essential oil microcapsules, with a desirable inhibitory effect on the main spoilage bacteria in pickle. This research would provide a new perspective for further exploring the application of lemongrass essential oil in extending the shelf life of pickle.