Enzymatic grafting of 5-O-succinyl erythorbyl myristate onto chitosan to improve its emulsifying properties

Chitosan (CS) is a versatile polysaccharide with numerous inherent biological activity, while the lack of amphiphilicity limits its application in emulsion-based systems. In this study, erythorbyl myristate (EM) with interfacial activity was chemically modified to 5-O-succinyl EM (EMS) and grafted onto CS to improve the emulsifying properties. The grafting reaction was conducted by the catalysis of protease, with the progress of the reaction monitored by HPLC analysis and UV absorbance measurement. Structural identification by FTIR and two-dimensional ¹H¹³C HSQC NMR spectroscopy confirmed the protease-catalyzed grafting of EMS onto CS. The grafting ratio of synthesized EMS-grafted CS (EMS-g-CS) was determined to be 13.30 ± 0.60 % according to the UV absorbance measurement and ¹H NMR analysis. Evaluation of the emulsifying properties of EMS-g-CS revealed that the grafting reaction significantly enhanced both emulsifying activity and emulsion stability, compared to the CS, EM, and their mixture. The oil-in-water emulsion stabilized with 1 % (w/v) EMS-g-CS exhibited emulsifying activity index of 6.03 ± 0.13 m²/g with homogeneous and stable droplet size distribution and exhibited a turbiscan stability index of 2.05 after 3 days. These findings suggested that EMS-g-CS synthesized via the chemoenzymatic process can be a promising polymeric emulsifier for utilization in emulsion-based systems.