Chickpea aquafaba as a natural stabiliser for chilli oleoresin encapsulation: Stabilisation, rheological and microstructural characterisation

The underpinnings and applications of aquafaba (AF) as a stabiliser of chilli oleoresin-in-water emulsions have only started to be studied. Pickering stabilisation by British Kabuli chickpea AF incidental nanoparticles (formed during cooking) and denatured proteins was examined in the present study. This entailed optimisation of the composition of the most stable chilli oleoresin-in-water emulsions, and the characterisation of the rheological behaviour and morphological features of the optimised systems. To this end, optimised formulations of chilli oleoresin-in-water emulsions stabilised by freeze-dried and resuspended AF, in regard to AF (%), oil (%, oleoresin: MCT, 1:1 (w/w)) and water (%), were investigated using I-optimal mixture design. The instability index of emulsions, as probed by a centrifugation/laser scanning device (LUMiSizer), was used as the response variable. Based on the best-fit linear mixture model, the three most stable formulations, comprising 13.85 to 15.00% AF, 1.00 to 6.64% oil, and 78.36 to 85.15% water, with an overall desirability value ≥ 0.96, were selected for further rheological and microstructural analysis via CLSM and Cryo-SEM imaging. These emulsions gelled upon standing at 25 °C, as demonstrated by small-deformation oscillatory rheology showing a sharp increase in G′ over G″ and gel-like frequency dependence. Complex viscosity ( η *) also increased with rising AF content. After shear-induced breakdown, the gels reformed upon resting, suggesting reversible, physically driven network formation. Cryo-SEM images revealed the presence of raspberry-like surface topology at the surface of the oil droplets, consistent with the hypothesis of Pickering emulsion stabilisation by AF nanoparticles. Overall, emulsions formulated with 15% AF, 6.64% oil, and 78.36% water (Run 13) yielded superior stability, rheological, and morphological properties for further applications. In conclusion, the results provided compelling evidence that AF can function as a wall material for capsaicin oleoresins encapsulation, leading to gelled emulsions.