# Microencapsulation of Polyphenols and Their Application in Food Technology
## 4 Microencapsulation of Polyphenols  
### Microencapsulation Techniques  
Microencapsulation is a technique of enclosing the active substances (e.g., polyphenols) in a thin-film structure, forming microcapsules. The purpose of microencapsulation is to protect the substances from adverse external conditions, such as light, oxygen, high temperature and pH changes [134, 135]. The process also allows for the controlled release of substances, which increases their bioavailability and biological effectiveness [136, 137]. Microencapsulation is based on several key principles. It ensures that bioactives are protected from degradation, allowing their retention of health properties for a longer periods of time [138]. Further, with the proper design of capsules, the active substances can be released under specific conditions, improving their bioavailability [139]. From a technology approach, microcapsules should retain their stability both during storage and food processing in order to preserve their health promoting properties. Moreover, the materials used to produce microcapsules should be safe for health, which is particularly important for food applications [140]. Microencapsulation can be carried out using a variety of methods that vary in terms of technique, materials and applications. The microencapsulation methodsinclude spray drying, freeze drying, emulsion-based encapsulations, encapsulation by entrapment in liposomes, coacervation, fluidized bed coating and ionic gelation [141; 142]. Extrusion is a process in which a mixture of ingredients (active ingredients, encapsulating materials and possible additives) is heated and passed through moulds to form microcapsules. This is one of the simplest methods, but may require high temperatures, which can affect the stability of some polyphenols [143]. The efficiency of the protection of polyphenols using this method is at an average level. Taking into consideration the degradation of polyphenols caused by high temperature, the biggest limitation of this method is the need for temperature monitoring and optimization during the process [144]. In the emulsion-based method, the active ingredient is dissolved in oil and then emulsified in water using emulsifiers. This process allows the formation of microemulsions, which can then be hardened to form microcapsules. This method is particularly useful for polyphenols with low water solubility. Emulsification is an effective method for the microencapsulation of polyphenic compounds under various conditions. An important advantage of polyphenols is their high stability, which supports their efficacy in various applications. However, the primary limitations of this approach include the necessity of using suitable emulsifiers and stabilizers to maintain their functionality and bioavailability. [145; 146]. Spray drying is one of the most widely used microencapsulation methods, involving spraying a solution of the active ingredient in hot air, which leads to the evaporation of the solvent and the formation of microcapsules. This method is effective in preserving the properties of polyphenols but can lead to their degradation if the drying temperature is too high. For this reason, it is necessary to monitor and optimize the temperature used in order to limit thermal degradation of bioactive compounds, which can be a significant limitation [147; 10]. The freeze-drying process involves freezing the material containing the active substances and then evaporating the water by sublimation, which is the transition of water directly from a solid state to a gaseous state. During this process, the active substances, encapsulated in a protective matrix remain stable, as the action of low temperature and vacuum minimizes their degradation. However, the freeze-drying process requires specialized equipment and a large amount of energy, making it time consuming and generating high cost, which can be a disadvantage of this method [148; 149].