Encapsulation of Mānuka Essential Oil in Yeast Microcarriers for Enhanced Thermal Stability and Antimicrobial activity

Foodborne pathogens present in food and agricultural systems are recognized as a considerable burden for human health and socioeconomic development. Mānuka essential oil (MEO) exhibits antimicrobial, antiparasitic, photo-protective, and some medicinal effects. However, limitations associated with the use of MEO, such as volatility, instability in complex biological systems, and only being effective at high doses, have significantly affected its large-scale applications in the food and agricultural industry. In this study, we propose to use a rapid and non-thermal vacuum infusion method to facilitate the encapsulation of MEO in yeast microcarriers. The physicochemical properties of encapsulated MEO were characterized and the thermal stability and in vitro release profile of encapsulated MEO were evaluated. The confocal images demonstrated the success of MEO encapsulation. The thermal stability of MEO was significantly improved by approximately 43% due to the presence of yeast microcarriers. The results of the in vitro release assay illustrate the release kinetics of MEO from the microcarriers, demonstrating the controlled release of MEO provided by encapsulation. Spore-forming Bacillus cereus vegetative cells were selected as a model foodborne pathogen. The antimicrobial activity of the encapsulated MEO was tested on B. cereus vegetative cells with and without a high concentration of simulated soluble organic matter (COD = 1000 mg/L). The results suggest that the encapsulated MEO can inactivate 4-log CFU/mL of bacteria after 1-h treatment, regardless of the presence of soluble organic matter, while the non-encapsulated MEO at an equivalent concentration only achieved less than 1-log reduction in the presence of organic content. In summary, this study reveals the potential of using cell-based encapsulation for MEO as an antimicrobial system to treat B. cereus vegetative cells in an organic-rich aqueous environment.