Evaluation of interfacial properties, droplet size optimisation and rheological properties of chemically modified Bambara groundnut (Vigna Subterranea) starch in oil-in-water emulsions

Abstract

• Modified Bambara groundnut starches (MBGNS and BG-SC) function as effective stabilisers for oil-in-water emulsions. • High BGN starch concentrations (8-10%) significantly improved stabilisation • Modified BGN starches are surface active molecules. • The BG-SC complex demonstrated exceptional structural regeneration, reaching up to 95% viscosity recovery after high-shear stress. • The modified starches successfully address demands for clean label ingredients by serving as dual-function agents. Using starch stabilisers in emulsions offers a promising approach to enhancing their stability and performance. This study investigated the performance of Bambara groundnut (BGN) starch, modified with ascorbic acid and hydrogen peroxide (MBGNS) and a modified starch-catechin complex (BG-SC), as natural stabiliser for oil-in-water (O/W) emulsions. Using a three-dimensional component I-optimal quadratic mixture design, the research evaluated varying ratios of starch (2-10%), oil (10-65%) and water (25-88%) to determine their impact on interfacial tension, droplet size and rheology. Both MBGNS and BG-SC functioned as effective surface-active agents, reducing equilibrium interfacial tension to 8.19 mN/m and 6.61 mN/m, respectively. These values are comparable to commercial lecithin with 9.30 mN/m. MBGNS exhibited more efficient refinement with characteristic times (Θ) of 8-15 minutes, whereas BG-SC was slower, exceeding 20 minutes in several formulations. Higher starch concentrations (8-10%) significantly improved stabilisation. The smallest median droplet diameter (D [0.5] ) was 18.04 μm for MBGNS (10% starch, 28% oil) and 20.81 μm for BG-SC (10% starch, 10% oil). High oil formulations (65%) were unstable or produced coarser droplets up to 162.62 μm. All emulsions displayed shear-thinning behaviour with flow behaviour indices (n) ranging from 0.57 to 0.74. Yield stress values reached up to 17.31 Pa, indicating a structured network resistant to creaming. BG-SC formulations showed superior thixotropic recovery, reaching up to 95% viscosity regeneration after shear compared to a maximum of 83% for MBGNS. Frequency sweeps revealed storage moduli (G’) consistently higher that loss moduli (G”), thus confirming a robust gel-like microstructure that prevents droplet coalescence. These findings indicate that modified BGN starches, specifically at concentrations of 6-10% are viable, high performance, clean label alternatives to synthetic emulsifiers and OSA-modified starches for industrial, food and cosmetic applications.