Rheological and structural trends on encapsulation of bioactive compounds of essential oils: A global systematic review of recent research

Essential oils (EOs) contain different types of chemical compounds such as alkaloids, isoflavones, flavonoids, monoterpenes, carotenoids, phenolic acids, and aldehydes with biological properties. However, when exposed to harsh environmental conditions, these compounds can become chemically unstable and susceptible to degradation, volatilization, and oxidation. Encapsulation technology has been largely employed to maintain the biological activities of EOs during the processing and development of novelty-enriched food products for industrial application. In this review, a brief description of EOs is presented and the main encapsulation methods used to protect them are highlighted. In addition, the structural characteristics and stability of encapsulated EOs were evaluated based on the rheological behavior, such as flow behavior, viscosity, and viscoelastic properties determined by two types of tests: oscillatory dynamic measurements (e.g., strain/stress sweep, time, temperature, and frequency sweep, including determination of storage modulus (G′), loss modulus (G″), complex modulus (G*), and complex viscosity (η*)), and static tests (creep and recovery). This work also contains information about fundamentals, principles, and importance of rheology for the evaluation of stability, strength, and structural characteristics of encapsulated EOs before the drying process to obtain nano(micro)particles. The knowledge of rheological behavior revealed to be important for large-scale industrial production, and application of encapsulated EOs, since during the processing and production, food products are submitted to high stress, temperature, and long-time operations.