Endo -chitinase Chit33 specificity on different chitinolytic materials allows the production of unexplored chitooligosaccharides with antioxidant activity.

•Overproduction of endo-chitinase Chit33 to 0.6 g/L in yeast medium.•Chitinolytic polymers transformed in total/partial acetylated COS by Chit33.•Production of GlcN-(GlcNAc)1-6 and (GlcN)2-(GlcNAc)1-5 from chitosan by Chit33.•Production of chitinolytic derivatives with antioxidant activity using Chit33.