ABSTRACT
The use of many active compounds of interest for nutraceutical and pharmaceutical applications is restricted by low solubility of these compounds in water, which contributes to low bioavailability, and makes it difficult to add these compounds to beverages or other water-based products. Thus, there is great interest in the development of water-soluble formulations of these compounds such as micellar solutions or other colloidal dispersions. Emulsion techniques have been particularly useful for the production of these formulations, since the emulsion can provide a template for
the morphology of the final product. This chapter presents the main techniques used for this purpose, starting with conventional emulsion evaporation and solvent displacement methods, and presenting recent developments, including novel emulsification techniques such as ultrasound emulsification and high-pressure homogenization, in the intensification of the process by increase in throughput and reduction of processing time through the processing of pressurized emulsions, and the application of supercritical fluids for extraction and antisolvent precipitation from emulsions. Finally, the application of several of these techniques for the preparation of water-soluble β-carotene formulations for application as natural colorant is presented as a case study. 8.1 Water-Soluble Formulations of Hydrophobic
Active CompoundsMany natural active compounds are characterized by high hydro-phobicity and, consequently, low solubility in water. This property can be an important limitation for the development of applications based on these compounds. In pharmaceutical applications, low solubility in water is generally associated with a low bioavailabil-ity of the compound, which can reduce its therapeutical activity and makes it difficult to dose the compound. On the other hand, many food products have an aqueous base in which hydrophobic active compounds cannot be dissolved. Therefore, there is a great interest in the development of formulations that can enhance the stability and solubility in water of hydrophobic active compounds of inter-est for food and pharmaceutical applications. Different methods for the development of such formulations are based on emulsions. Emulsions can provide a template for the final morphology of the product and enable an enhanced control over its size by controlling the size of the disperse phase droplets in the emulsion. Emulsion-template techniques are suitable for the production of different types of formulations (Fig. 8.1), including: ∑ Simple oil-in-water (o/w) emulsions, which can be suitable final formulations without further processing when the base product already presents a certain fat content (e.g., butter or milk)
∑ Micro-or nanosuspensions of a pure compound, which can be obtained with a controlled particle size distribution by elimination of the organic phase from an o/w emulsion with controlled droplet size ∑ Micellar solutions, formed by association of surfactant molecules in aqueous environment that create an inner hydrophobic cavity that can host water-insoluble compounds ∑ Liposomal solutions, formed by self-assembly of phospho-lipids in water, which can encapsulate both hydrophilic com-pounds in its inner aqueous cavity, as well as hydrophobic compounds in the lipid bilayer ∑ Hybrid systems, formed by a combination of hydrophilic and hydrophobic carrier materials, with the objective of stabilizing hydrophobic compounds in aqueous environments at the same time that a controlled delivery of these compounds is achieved This chapter presents the main emulsion techniques used to produce these types of formulations, starting with a brief presentation of the main conventional techniques and focusing on recently developed processes based on high-pressure and supercritical fluids, presenting the results obtained in the formulation of β-carotene as a case study.
