Versatility of emulsion-based encapsulation techniques: applications and mathematical modelling

Encapsulation can be defined as the entrapment of bioactive compound within another substance, which can be either liquid or solid. The objective is to incorporate the bioactive compounds in micro and nanocarriers to preserve their functional and physicochemical properties, to guarantee their vitality and stability, to provide protective barriers against the external environment, and to increase shelf-life. A wide variety of encapsulation techniques exists to address the requirements associated with the type of bioactive compound and the intended application. Indeed, by selecting the most appropriate encapsulation system, it is possible to produce a final product that exhibits all the desired characteristics, such as encapsulating materials, size, and formulation. For this Ph.D. work, emulsion-based techniques are selected as the methodology to be investigated. These methodologies utilize the emulsion structure to protect the bioactive compounds. In fact, emulsions are liquid dispersions composed of two immiscible liquid phases, where one phase is dispersed in the other as small spherical droplets. In emulsions, the bioactive compounds can be entrapped into the dispersed phase droplets, while the continuous phase provides a protective barrier to the loaded dispersed droplets. Beyond their role as a standalone encapsulation method, emulsification can also be the first step in the fabrication of polymeric particles via further processing. In this case, the active compound is homogeneously dispersed in the polymer matrix or entrapped in a central core and surrounded by the polymer matrix. Therefore, the objective of this PhD was to investigate and demonstrate the versatility of emulsion-based techniques for encapsulation. To this end, the techniques were investigated from different perspectives in order to provide a comprehensive overview of the potential of these technologies. The addressed challenges range from the study of different applications in food and nutraceutical fields, using specific bioactive compounds as case studies, to the study of predictive models of the average size of the produced systems, which are essential for the production processes optimization. Furthermore, different emulsification techniques were examined to evaluate the widest possible size range, from nano- to microsize, in order to determine the most appropriate method depending on the desired size. The topic addressed by this thesis is organized and subdivided into chapters as follows. Chapter 1 – State of the Art – this chapter was dedicated to an extensive literature review on emulsion-based techniques for encapsulation. The emulsions were described in terms of classification, composition and characterization. Finally, the existing production techniques were described in detail. Chapter 2 – Probiotic Encapsulation in Double Emulsions as Liquid Formulation – this chapter was focused on the optimization of emulsion for the encapsulation of a target probiotic, selected as specific case study. Chapter 3 – Encapsulation of Polyphenolic Extract in Polymeric Nanoparticles by Emulsion Drying – this chapter was aimed at the study of emulsion-based techniques for the polymeric particles production as encapsulating structure. Natural polyphenolic extracts were selected as case study. Chapter 4 – Validation of Existing Mathematical Models for Emulsions as Liquid Formulation – in this chapter, the effects of physico-chemical properties and operating conditions on the emulsion droplets were evaluated. In addition, the fitting of literature mathematical models was carried out. Chapter 5 – Development of a Mathematical Model for Emulsion Droplets and Polymeric Particles Mean Diameter Predictions – a new predictive mathematical model for emulsion droplets and polymeric particles was proposed. Chapter 6 – Microfluidic for Emulsion Production – the microfluidic emulsifier was investigated as innovative techniques for the production of emulsion with high precision and control. Chapter 7 – General Conclusions – a final discussion of the main obtained results was carried out in order to highlight the general evidence of this project.