Chitosan dispersed in aqueous solutions of acetic, glycolic, propionic or lactic acid as a thickener/stabilizer agent of O/W emulsions produced by ultrasonic homogenization

•Chitosan was dispersed in acetic, glycolic, propionic and lactic acid solutions.•Chitosan modified rheological characteristics and the microstructure of emulsions.•Small oil droplets were formed in emulsions with different consistency indexes using an ultrasound device.•Chitosan changed the hydrodynamic average diameter, PDI, and ζ potential values of oil droplets.•Chitosan improved emulsions stability over time and under stress conditions. Chitosan is a natural polycationic polysaccharide with several known biotechnological functionalities, but its application in food products as ingredient or additive remains nowadays unusual. Additionally, ultrasonic production of food-grade emulsions is still an open research field, so ultrasound applicability for such purpose must be evaluated case by case. In this study, chitosan was dispersed in acid aqueous media containing acetic, glycolic, propionic or lactic acid (50 mmol·L−1), then added of the emulsifier Tween 20, and finally mixed to sunflower oil, through ultrasonic homogenization (20 kHz, 500 W, 4 min), in order to prepare O/W emulsions (oil fraction = 0.25). In all studied systems, oil droplets with average hydrodynamic diameter