## 3 Vitamin A, Its Vitaminoids and Carotenoids' General Profile and Health Benefits
### Vitamin A, Vitaminoids, and Carotenoids from Microorganism Sources
Moreover, hydrogels, biodegradable polymers, and emulsions have also been exploited in topical applications for controlled release and sustained effects of retinol, retinoids, and carotenoids [244; 245]. Finally, microencapsulation has also been utilized for enclosing and rapidly delivering vitamin A, retinoids, and carotenoids to target cells (Figure 13) [15]. Microencapsulation and nanoencapsulation are two encapsulation technologies currently utilized for vitamin transportation, and many attempts towards overcoming their chemical instability have been conducted. The procedure of coating or enclosing tiny solid, liquid, or gas particles in a continuous polymeric layer is microencapsulation. The coated substance, also known as the payload, internal phase, fill, core material, or actives, can be encapsulated alone or in conjunction with additional substances, while the coating material is also referred to as an encapsulating agent, wall material, shell, or carrier and frequently takes the form of combined materials. Since vitamin A is a hydrophobic, fat-soluble compound, it can rapidly break down in the presence of water-based solutions, while it is poorly soluble in aqueous solutions due to its low polarity. Furthermore, it is an extremely sensitive substance that reacts with a variety of other substances, including oxidants, temperature, trace metals, light, heat, and moisture [15; 252; 253; 254]. By selecting the correct encapsulation method, vitamin A can be added to carriers with favorable chemical and physical characteristics to boost its remedial ability, bioavailability, dispersity, controlled release, accurate delivery at the intended spot, and maximum absorbance. Importantly, with a view to achieving the desired encapsulation efficiency, microparticle stability, and essential final product qualities in accordance with its applicability, the right encapsulating agent must be selected, which should not react with the core material, be eco-friendly, and be non-toxic. Spray-cooling, spray-drying, cochleates, coacervation (phase separation), emulsion systems, liposomes, and solid lipid nanoparticles are widely appealing microencapsulation techniques, while the most utilized microencapsulation method for carotenoids is spray-drying technology, with multiple studies globally documenting using a variety of biopolymers as encapsulating materials [244; 245; 255; 256; 257]. For instance, Arabic gum has been pointed out as a promising encapsulating agent due to its capacity to generate stable microemulsions of sufficient solubility and low viscosity for carotenoids' delivery (Figure 13) [257; 258]. Nanoencapsulation has also been proven as a highly efficacious approach for improving carotenoid's chemical stability, thereby safeguarding their bioactivity and stability against potential external influences throughout diverse processing and storage conditions. This method refers to the entrapment of active compounds like vitamin A, its vitaminoids, and carotenoids within nanoscale carriers including liposomes, polymeric nanoparticles, micelles, and solid-lipid nanoparticles for targeted and controlled delivery of bioactives, improved skin penetration, protection from degradation and sun exposure, reduced toxicity and irritation, enhanced stability, antioxidant activity, and bioavailability, as well as effective treatment of retinol deficiency, wound healing, and skin disorders (i.e., acne in topical, oral, or systemic delivery) [15; 197; 252; 259; 260]. The most frequently used nanoencapsulation methods are nanoemulsions of vitamin A and carotenoids, namely colloidal dispersions with nanometer-sized droplets (20-200 nm) in a continuous phase,  
Figure 13: Different formulations, microencapsulation, and nanoencapsulation for systemic delivery of vitamin A, retinoids, and carotenoids. stabilized with surfactants.