Encapsulation of gallic acid in alginate/lactoferrin composite hydrogels: Physical properties and gallic acid diffusion

Alginate hydrogel is commonly utilized to encapsulate hydrophilic polyphenols because of its biocompatibility and flexibility. However, encapsulation with neat alginate gel is prone to uncontrolled compound diffusion during gel formation and storage. Previous research have demonstrated the electrostatic complexation of lactoferrin and alginate, nonetheless, no study has been reported on the combination of these polymers as hydrophilic polyphenol encapsulation agent. Therefore, this research aims to explore the encapsulation of gallic acid (GA), a representative of water-soluble polyphenol, in the lactoferrin-alginate composite hydrogel. The composite hydrogel of sodium alginate-lactoferrin (S-L) was prepared in solid-basis ratios of 1:0, 1:1, 2:0, 2:1, 2:2, and 2:3. The evaluation was conducted on the alginate-lactoferrin mixture viscosity, gel syneresis, gel strength and stiffness, dried gel rehydration properties, porosity, GA diffusion, and gel microstructure. Images of SEM and CLSM microscopy revealed relatively compact structures created by evenly distributed lactoferrin in the hydrogel system. According to the gel electrophoresis analysis, composite alginate-lactoferrin gel hindered the diffusion of compounds with molecular weight >50 kDa. The addition of lactoferrin to the GA-loaded alginate composite hydrogel significantly increased the retention of GA (87.1-92.2%) in the gel. The GA-loaded composite hydrogel with the alginate to lactoferrin ratio of 2:1 and 2:2 (pH 5.24-5.43) exhibited significantly better (P > 0.05) gallic acid retention compared to the neat alginate hydrogel (pH 5.16) in their natural pH. FTIR analysis revealed a hydrogen bond between lactoferrin and the gallic acid phenolic group, while the zeta-potential analysis showed the intermolecular interaction between positive-charged lactoferrin and negative-charged alginate. This work provides important information for the development of hydrogel-based polyphenol encapsulating materials.