Structure-function relationship of pectin derived from red dragon fruit peel as a bio-based emulsifier for oil-in-water emulsions

Natural emulsifiers have attracted increasing attention due to their sustainability, biocompatibility, and non-toxicity; however, the structure-function relationship governing their emulsifying performance remains insufficiently understood, particularly for underutilized biomass such as red dragon fruit peel (DFP). This study aims to investigate the potential of pectin extracted from DFP as a bio-based emulsifier, focusing on its structural characteristics and emulsification behavior. Pectin was extracted using ultrasound-assisted extraction, yielding 5.70% under optimal conditions (pH 3, 60°C). The extracted pectin was identified as high-methoxyl pectin, with a particle size of 1.413 µm, indicating its suitability for interfacial adsorption. Comprehensive physicochemical characterization further revealed properties relevant to its emulsifying functionality. Its emulsifying performance was evaluated in oil-in-water systems under varying processing conditions. The optimal emulsification conditions were achieved at 0.3% (w/v) pectin concentration, 30% ultrasound amplitude, and 10 min emulsification time, resulting in the lowest creaming index (11.43%). Under these conditions, droplet size was significantly reduced (4.07-70.28 µm), indicating improved dispersion and resistance to coalescence. Despite a relatively low zeta potential (+8.52 mV), the emulsions exhibited good stability, suggesting that steric stabilization and interfacial adsorption play a more dominant role than electrostatic repulsion. Additionally, comparative analysis with previously reported pectin systems demonstrates the competitive emulsifying performance of DFP-derived pectin. Furthermore, this study provides new insights into the structure-function relationship of DFP pectin and highlights its potential as a sustainable and effective natural emulsifier for food and industrial applications.