## 5 Ficin Use as an Exfoliant Agent in Cosmetic Applications
### Ficin Stabilizers and Inhibitors in Cosmetic Formulations  
The preservation of ficin's structural integrity and activity necessitates precise formulation strategies that incorporate stabilizing agents while mitigating the impact of potential inhibitors. Stabilizing compounds, including established co-solvents such as trehalose, sucrose, sorbitol, and xylitol, have been shown to enhance the thermal stability of ficin by increasing its denaturation temperature. Notably, trehalose demonstrated the most significant stabilizing effect, thereby effectively maintaining the enzyme's native conformation [90]. The microencapsulation of proteolytic enzymes like ficin, has also been confirmed as an alternative stabilizing method [92]. Plus, TPP with tertiary butanol (t-butanol) and ammonium sulfate not only purifies ficin, but also concentrates it, enhancing its stability by partitioning it away from contaminants that could destabilize it. Additionally, it has been shown that ficin immobilization, chemical additives, and non-ionic surfactants in cream formulations enhance their stability and activity [27, 75, 90, 93].  
Conversely, certain substances act as inhibitors and must be avoided in ficin-based formulations. Ficin is highly susceptible to inhibition by compounds that target its active site. For instance, E-64 is a known cysteine protease inhibitor that is able to block ficin's enzymatic activity [89]. Moreover, metal ions, specifically zinc ions (Zn\({}^{2+}\)), have been shown to completely suppress ficin activity at a concentration of 1 mM. This inhibitory effect of Zn\({}^{2+}\) is relevant when considering formulation ingredients, as certain compounds may contain trace amounts of metal ions [89]. In addition to specific inhibitors, surfactants can also denature ficin, with non-ionic surfactants being a better choice to minimize this effect [27]. The pH of the formulation is critical as well, as ficin demonstrates its optimal activity in pH values ranging from 6.5 to 8.5, indicating that slightly acidic or alkaline conditions can compromise its enzymatic activity. Therefore, the formulation's pH should be controlled to match ficin's optimum pH range of around 6.5, while also taking the skin's pH conditions of approximately 5 into consideration [27, 89, 94]. Furthermore, the temperature must be controlled, since temperatures over 40 \({}^{\circ}\)C can lead to the thermal degradation of the enzyme. Usually, its storage requires moderate temperatures (maintaining its stability up to 37 \({}^{\circ}\)C). In addition, ficin's autolytic ability may lead to concerns, considering the fact that the autolysis process increases with storage time, regardless of the storage temperature [86]. Finally, the concentration of ficin can influence its stability; higher concentrations may increase its susceptibility to changes, while lower concentrations are deemed as more stable [27, 89, 94]. Thus, a holistic approach that combines the use of appropriate stabilizers and the avoidance of inhibitors, as well as controlling parameters like pH, temperature, and concentration, is essential for ensuring that ficin remains stable and effective in cosmetic formulations [25, 27, 89, 94, 95].