ABSTRACT Arabinoxylans (AX) covalent gels are little affected by pH changes and fermentable by colonic microbiota, which make them suitable for insulin oral administration and colon‐targeted delivery. In this work, the tailoring of insulin aggregates size using glutamic acid and their loading in AX microspheres (2%w/v) prepared by triaxial electrospray is presented. Dynamic light scattering showed that insulin‐glutamic acid aggregates are reversible under intestinal conditions. AX microspheres presented a spherical shape, a mean diameter of 233 μm, a heterogeneous microstructure as shown by scanning electron microscopy, and a homogeneous distribution of insulin aggregates as observed by confocal laser scanning microscopy. In this AX‐insulin system, 20% of insulin is released under simulated gastrointestinal pH conditions, indicating that most of the insulin stays into the microspheres, available for colonic release. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47960.