###### Abstract  
A typical emulsion contains oil and water phases, and these two phases can be combined by an emulsifier with both lipophilic and hydrophilic groups to form a mixture. If the component of water is more than oil, the mixture is termed as o/w emulsion. The water is called the continuous phase and the oil is called the dispersed phase. Oppositely, if the component of oil is more than water, the mixture is termed as w/o emulsion. The oil is called the continuous phase and the water is called the dispersed phase. Chitosan, which is biocompatible and non-toxic, was modified as an amphoteric emulsifier to replace sodium acrylates copolymer in the preparation of emulsions. Both sodium acrylates copolymer and the modified chitosan were used as emulsifiers, respectively, and the properties of moisturizing, transmittance, the number of bacteria, and emulsion stability were measured. The experimental results showed that the amount of amphoteric chitosan is less than that of sodium acrylate copolymer by 20% under a similar degree of emulsification. The measurement of spatial moisture showed the difference in equilibrium humidity was in the range of 2.05 to 2.20 gH\({}_{2}\)O/kg dry air, indicating that the moisture retention of the modified chitosan is better. In addition, the calculation of bacterial growth confirmed that the number of bacteria in the amphoteric chitosan emulsion and the sodium acrylate copolymer emulsion were 80 and 560, respectively. The emulsion stability was tested by the separation of oil and water phases in the diluted emulsion and by centrifugal accelerated sedimentation. The results showed that, for both emulsifiers, no separation of the oil and water phases occurred within one hour, and the stability of the modified chitosan emulsion was better. Therefore, the modified chitosan successfully substitutes sodium acrylates copolymer as an emulsifier in the preparation of emulsion. chitosan; emulsion; bacterial growth 2022125249 202212  
play an important role in the emulsification process, and emulsifiers were modified by some studies to maintain the stability of emulsions. For example, different weight ratios of sodium stearyl 2-lactylate to chitosan were used as emulsifiers [10], and optical microscopy and rheological measurements of emulsions were performed to analyze the stability of the emulsions. Similarly, anionic surfactant-chitosan complexes were used as the emulsifiers to improve the stability of oil-in-water emulsions [11]. To stabilize the emulsions at lower temperature, the chitosan/lithium dodecyl sulfate complex was used as an emulsifier [12], and the turbidity, size, and Zeta potentials of the emulsions were measured to discuss the effects of operating variables on the stability of the emulsions. Unlike the chitosan/surfactant complex, a series of chitosan-graft-oligoN-isopropylacrylamide-graft-oligolysine copolymers have been synthesized and used as the emulsifiers for preparing emulsions with high internal phases, and this kind of emulsion has been applied in pharmaceuticals, food, cosmetics, and biologics [13]. Both chitin and chitosan are non-toxic and antimicrobial and hydrating agents [14]. Since chitosan is a biopolymer made from natural organisms, it has good biocompatibility with biological cells [15; 16]. The functional groups of -OH and -NH\({}_{2}\) in chitosan can be substituted easily. Therefore, chitosan was used as the backbone to modify the -OH group as a hydrophilic end, such as -COOH, -SO\({}_{3}\), or -H\({}_{2}\)PO\({}_{4}\), and to modify the -NH\({}_{2}\) group as a hydrophobic end, such as 1-12 carbon alkyl, so as to form amphoteric chitosan. Higher capacities of amphoteric chitosan in water absorption and moisture retention were previously reported [17; 18], and the hollow nanocapsule of acylated carboxymethyl amphiphilic chitosan transformed from solid nanoparticle was observed as a result of the hydrophobic effect, which improved the affinity toward drug encapsulation [19].