N₂-vacuum cold plasma-assisted OSA modification of rice starch: structural changes, emulsifying properties, and fat...

Native rice starch (RS) is a potential carbohydrate-based fat replacer, but its high hydrophilicity, retrogradation tendency under frozen conditions, and weak interfacial adsorption limit its performance in reduced-fat ice cream. This study investigated nitrogen vacuum cold plasma (N₂-VCP) pretreatment to enhance octenyl succinic anhydride (OSA) esterification of RS and improve its functionality as a 50% fat replacer. RS was pretreated with N₂-VCP at 400 or 800 W for 10 or 20 min before OSA esterification. The structural, surface, physicochemical, and emulsifying properties of the modified starches were characterized, and their performance was evaluated in reduced-fat ice cream. VCP pretreatment increased the degree of substitution (DS) and reaction efficiency (RE), with the highest values obtained for 800-20-OSA (DS = 0.0128, RE = 55.25%). However, 800-10-OSA showed the best functional performance, with the highest emulsifying activity index (16.31 m²/g) and emulsion stability index (63.25 min), whereas 800-20-OSA showed lower values of 16.09 m²/g and 54.93 min, respectively. Structural analyses indicated that moderate VCP pretreatment roughened the starch surface, altered ordered structures, and changed apparent molecular size, which was associated with improved esterification efficiency while maintaining molecular integrity for interfacial stabilization. In contrast, intensive VCP exposure at 800 W for 20 min was associated with greater apparent depolymerization and a less favorable balance between hydrophobic substitution and structural integrity. In reduced-fat ice cream, 800-10-OSA produced the highest overrun (36.92%), lowest melting rate (29.54%), reduced hardness, and improved cohesiveness, gumminess, and sensory texture/taste compared with RS and RS-OSA (p < 0.05). These findings suggest that N₂-VCP-assisted OSA modification is a promising non-thermal approach for developing rice-starch-based fat replacers in reduced-fat frozen dairy systems.