Influence of the degree of inulin polymerization on the ultrasound-assisted encapsulation of annatto seed oil

•The effect of the DP of inulin was evaluated on its encapsulant characteristics.•The influence of ultrasonic power on the formation of O/W emulsions was assessed.•The XRD and TGA analyses proved the effectiveness of inulin as a wall material.•The highest DP promoted larger protection against annatto seed oil oxidation. The effect of the degree of polymerization (DP) of inulin was evaluated on its encapsulant characteristics. We assessed the influence of the average inulin DP (DP ≥10 and DP ≥23) in the ultrasound-assisted encapsulation of annatto seed oil using the freeze-drying technique for particle formation. The intensification of the homogenization process with ultrasound did not improve the characteristics of the emulsions due to the physicochemical limitations of the inulin molecular chain (molecules do not exhibit surface activity). The particle morphology, oil entrapment efficiency, encapsulation efficiency, X-ray diffraction, thermogravimetric analysis and Rancimat analyses proved the effectiveness of inulin as a wall material. The properties influenced by the DP were the surface oil, encapsulation efficiency, water activity, particle size and oxidative stability of the encapsulated oil because the highest DP promoted the formation of microparticles with lower surface oil content, greater encapsulation efficiency, low water activity, larger size and greater protection against oil oxidation.