## 3 Characterization of Food-Grade Systems
### Technological Characterization
#### 3.1.5 Stability  
Due to various environmental factors, including temperature, humidity, light, pH, etc., dietary supplements and pharmaceutical products can undergo degradation processes (chemical, physical, and microbiological) that affect their efficacy and/or safety. In general, we can define stability as the ability of a product to maintain its chemical, physical, and microbiological properties during its storage and use period. Specifically, chemical stability refers to the ability to maintain chemical identity and bioactive properties, physical stability to the retention of shape, color, odor, taste, and other physical characteristics, mind microbiological stability to retain sterility (or a low level of microorganisms) [127; 128]. EMA (European Medicines Agency) and EFSA (European Food Safety Authority) for EU, FDA (Food and Drug Administration) for the USA, and PMDA (Pharmaceuticals and Medical Devices Agency) for Japan are concerned with the regulation and safety of food and pharmaceutical products. The International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH), along with the World Health Organization (WHO), has provided a set of guidelines (ICH Q1A-E, Q3A-B, Q5C, Q6A-B) intended to unify the standards for the European Union, Japan, and the United States to facilitate the mutual acceptance of stability data that are sufficient for registration by the regulatory authorities in these jurisdictions [129]. Finally, with particular emphasis on microbiological stability, the International Organization for Standardization (ISO) with its ISO 14,698 standard outlined the importance of microbiological risk assessment in airy environments and on products. In summary, stability assessment aims to investigate the maintenance of parameters (chemical, physical and microbiological) of the system over time. Therefore, the stability of active ingredients, nutraceuticalts, pre- and probiotics, and other bioactive substances can be compromised by environmental factors for which encapsulation in appropriate systems in addition to enabling targeted delivery to the target site allow for improved stability [130; 131; 132]. Systems produced in this way are also subject to degraded phenomena, so careful monitoring of specific parameters over time is necessary. For example, in assessing the physical stability of micro- and nano-emulsions, colloidal systems, and solid-liquid dispersions of microsystems, size, PDI, and PZ are of relevant importance. In fact, their monitoring makes it possible to assess the occurrence of phenomena such as sedimentation, creaming, rupture, flocculation, and so on that compromise the stability of the preparation. To avoid the occurrence of these phenomena and thus increase stability, it is possible, for example, to minimize and homogenize the particle (or droplet) size, increase the viscosity of the dispersing medium, increase the stability at the droplet interface, give the system PZ values of \(\pm\)30 mV to ensure proper electrostatic repulsion, the inclusion of the dispersing put of inert polymers with high steric bulk, and so on [133; 134; 135; 136]. Therefore, as stability assessment is particularly important for food and pharmaceutical products, as their efficacy and safety can be compromised by chemical, physical, and microbiological processes, we propose some examples of stability assessment of food-grade polymer-based colonic-targeted systems found in the literature. Kong et al. proposed an interesting stability study of chlorophyll encapsulated in shellac nanoparticles immobilized in an agarose gel and encapsulated in calcite crystals. The chlorophyll-loaded nanoparticles (83 and of 108 nm) were tested for 56 days. Both samples showed 80% chlorophyll retention after 28 days at 4 \({}^{\circ}\)C and subsequent 28 days at room temperature. The pure chlorophyll dispersion, prepared as a reference following the same procedure, exhibited a gradual shift of the absorption peak from 670 nm to 690 nm over time.