## 4 Natural Antioxidants and Their Role in Cosmetics
### Plant Stem Cells  
In cosmetics, plant extracts or bioactive compounds traditionally sourced from field-cultivated plants are predominantly used. However, the yield and quality of such raw materials are often suboptimal. The extraction of bioactive compounds from field-grown plants poses several challenges, including the limited availability of raw materials--particularly in the case of rare, endangered, or protected endemic species; plants from distinct climatic or geobotanical zones; or species with poor seed production or low germination rates. Additionally, field cultivation is subject to variability in plant growth, seasonal constraints, and inconsistent levels of bioactive compounds. Plant biotechnology offers a solution by enabling cultivation under strictly controlled and reproducible conditions that adhere to good manufacturing practices (GMPs) and good laboratory practices (GLPs). In vitro cultivation (conducted under sterile laboratory conditions) provides homogeneous plant material year-round, independent of seasonal or developmental cycles. Furthermore, in vitro-derived plant material is free from environmental contaminants, pathogens, and pesticides. Cultures maintained under laboratory conditions rarely contain toxic or allergenic compounds, enhancing their safety profile [242; 243; 244]. The production of secondary metabolites can be significantly accelerated and intensified in vitro through the application of advanced biotechnological methods. Compounds synthesized under these conditions retain the stereospecificity inherent to their natural counterparts, which is critical for preserving their biological activity. The extraction process from in vitro-derived biomass is more efficient and streamlined compared to field-sourced materials. In vitro plant biomass typically consists of undifferentiated cell cultures, such as callus tissues or suspension cells, cultivated under fully aseptic conditions. With optimized culture parameters, these cells exhibit rapid proliferation and produce substantial quantities of bioactive compounds, making in vitro systems a robust and scalable approach for obtaining high-quality plant-derived ingredients for cosmetic applications [242; 243; 244]. Reports highlight the cosmetic application of whole-cell contents derived from plant cell cultures, processed into homogenates through the high-pressure disruption of cell walls and membranes. Homogenates offer a key advantage by preserving the bioactivity of cellular components, including growth factors. Moreover, the use of whole-cell contents, as opposed to isolated pure compounds, provides the benefit of synergistic interactions among the diverse cellular constituents, such as salts, acids, phenols, sugars, lipids, proteins, and other biomolecules. These components collectively play a crucial role in protecting and supporting skin stem cell health [241; 243; 244]. This innovative technology has been pioneered and implemented by Mibelle AG Biochemistry, which produces homogenates from _Malus domestica_, _Vitis vinifera_, _Argania spinosa_, _Saponaria punila_, and _Rosa pendulina_. The process involves suspending cellular biomass in a solution containing liposomes, preservatives, and antioxidants, followed by high-pressure homogenization. During this process, lipophilic components are encapsulated within liposomes, while hydrophilic components dissolve in the aqueous phase, resulting in an amber-colored liquid. These plant cells, derived from apple, grapevine, organ, soapwort, or rose, are cultivated on a large scale using in vitro techniques that optimize explant selection and culture conditions to achieve efficient induction and proliferation. Remarkably, only minimal amounts of plant material are required to produce substantial quantities of high-quality active ingredients [241; 244; 245]. In a related advancement, the Institutio di Ricerche Biotecnologiche has developed a technology involving biomass homogenization, followed by extraction and concentration processes, to yield a yellow-amber powder.