## 3 Characterization of Food-Grade Systems
### Technological Characterization
#### 3.1.3 Encapsulation Yield and Solid-State Characterization  
It is well known that bioactive constituents, including vitamins, bioactive lipids, bioactive peptides, essential oils and even probiotics, have a number of potential health benefits. These, however, are sensitive to heat and possess poor chemical stability. Several encapsulation methods have been applied to protect these constituents from thermal and chemical degradation. Encapsulates prepared by different methods and/or under different conditions have different microstructures, which in turn affect the efficiency of encapsulation, the retention of encapsulated substances, and the controlled release behavior of encapsulates differently [97]. In this context, the determination of specific parameters such as encapsulation efficiency (%EE) and drug loading (%DL) through the following Equations (1) and (2) allow the quantification of encapsulated material [98; 99; 100]. \[\%EE=\frac{\left(\text{Total drug added to the beads}-\text{Amount of free drug}\right)}{\text{Total amount of drug added to the beads}}\times 100 \tag{1}\]  
\[\%DL=\frac{\text{Amount of drug loaded in the beads}}{\text{Total weight of the beads}}\times 100 \tag{2}\]  
Figure 12: Zeta potential of zein NPs in the absence and presence of dextran sulphate at different mass ratios and at pH = 4.0. Adapted with permission from Ref. [60]. 2019, Elsevier B.V.  
During the encapsulation process, constituents reorganize into the neostructure of the system. This is dependent on the nature of the substances to be encapsulated and the encapsulants and the encapsulation process. In this sense, the assessment of any interactions between the carrier constituents and the carrier active substance and the nature of its solid state (crystalline or amorphous) within the system and the system itself are of crucial importance to the processes of development, formulation, activity, and storage. These, for example, affect not only the preparation of the system but also the possible dissolution-erosion mechanisms of the carrier, the mechanisms and profiles of release of the filler, its dissolution and thus its bioavailability and stability. For this purpose, the constituents of the system, their physical mixture(s), empty and loaded system are subjected to specific analyses, among which FT-IR, DSC and PXDR are the most common. FT-IR analysis provides information about the chemical bonds present in the sample giving us important information about the formation of any interactions between the constituents of the system [98; 101; 102]. DSC allows to assess the temperatures at which characteristic endothermic and exothermic transitions occur and that are specific for a certain substance and its structure. These can indicate the melting point of the sample or more generally a state transition (e.g., a rubbery-glass transition) and its purity, and confirm any interactions between samples in mixture or neostructured in a carrier system [103; 104; 105]. PXDR analysis provides information about the structure of the solid state, allowing to observe crystalline or amorphous transitions following the formulation production process [106; 107; 108; 109]. All these techniques synergistically allow the evaluation of the encapsulation process of the carrier substance [110]. For instance, absence of the characteristic peaks of the active substance in the spectra of the loaded system indicates its complete and uniform encapsulation in the carrier matrix. To this end, Curcio et al. used FTIR, DSC and PXDR in the technological characterization of microparticles based on EUGB and EUGC prepared for quercetin (QUE) delivery to the colon. The study investigated different formulation approaches by mandating fixed concentration of QUE and predetermined QUEcopolymer weight ratios (1:5, 1:10 and 1:25). The system consisting only of EUGB had a %EE of 97.6%. The FT-IR spectrum of the loaded system was superimposable with that of EUGB, and the characteristic QUE peaks were not present.