## 4 Discussion
Studies have demonstrated that the stability of emulsions when exposed to different pH values depends on the composition of the extract, which may have positively or negatively charged components induced to aggregation and greater stability when attracted by charged saponins [34]. The best results in terms of emulsification activity were found in the current study for the sweet almond oil at a NaCl concentration of 10% for both the biosurfactants tested. This result is of great importance because chemical surfactants undergo inactivation at NaCl concentrations \(\geq\)2% [33]. One relevant characteristic is that _C. quinoa_ has fatty acids similar to those found in soybean oil and is rich in essential fatty acids, such as linoleic and linoleic acids [35]. pH values are essential for determining the stability of a compound, as adequate organoleptic characteristics lead to the acceptance of a product by consumers [36]. Emulsions using oils components in aqueous solutions are found in numerous products, including personal hygiene products. This is a type of colloidal dispersion in which small droplets of oil are dispersed in the continuous aqueous phase [37]. Such oil-in-water systems must remain stable and could be submitted to reformulations if any sign of instability occurs. If approved, the emulsion can be exposed to other stability tests [38]. According to [PERSON] and [PERSON] [39], the stability of emulsions depends on the interaction of interfaces established by the emulsifying agent and the hydrophobic compound. Therefore, emulsifying agents must have affinity for the oil being tested in order to maintain its stability in the dispersing phase. Many plant extracts rich in biosurfactants can serve as emulsifiers, which is an advantage for the preparation of \"green\" cosmetic products. The literature reports emulsifying action with excellent performance for surface-active plant-derived substances, such as tea saponins, glutenin of hydrolyzed rice, and saponins from the genus _Quillaja_[18]. Oil-in-water emulsions are important constituents of numerous commercial products, including foods, supplements, pharmaceutical products, cosmetics, personal care products, and pesticides [37]. Each plant extract has its particularity in terms of stability. However, biosurfactants are known to exhibit good stability when submitted to different temperatures and pH values [3]. The stability results of the extracts studied here confirm this trend, as the variation occurred in pH ranges not generally used in formulations for oral use, showing that the surface-active molecules in the extracts did not lose their function. The pH of mouthwashes affects the metabolism of dental plaque. Thus, mouthwashes are used in combination with the mechanical cleaning of the teeth. These compounds with low pH are effective against the fermentation and production of extracellular polysaccharides by microorganisms [40]. However, a very low pH together with the absence of fluoride in the formulation could be harmful to dental tissues, which could cause the demineralization of tooth enamel [41]. The pH value of mouthwash formulations containing the vegetable biosurfactant (4.19) was close to that of commercial mouthwashes, which suggests that they would be effective against the proliferation of microorganisms. In contrast, despite the low pH (4.19), the positively charged chitosan and chitosan hydrochloride have a buffering effect and adsorption action on negative surfaces, such as tooth enamel. Thus, even with the absence of fluoride, the present formulation is expected to maintain the balance of the demineralization-remineralization process of the enamel due to the interaction between chitosan hydrochloride and the phosphate group in hydroxyapatite. This expectation is based on the work of [PERSON] et al. [42], who conducted an in vitro experiment to determine the influence of chitosan on the demineralization-remineralization process of tooth enamel.