Evaluating physical pre-treatment methods for improving insect chitin hydrolysis using Streptomyces griseus chitinase

Chitin and particularly its derivatives, chitosan and chitoligosaccharides (COS), are gaining interest as highly functional biopolymers with many applications. Chitin, the main component of the exoskeleton of crustaceans and insects, has a resistant structure that makes access to chitinolytic enzymes extremely difficult, thus limiting the possibility of obtaining COS. Therefore, several pre-treatments have been investigated to interfere with the crystalline organisation of chitin and improve its enzymatic hydrolysis. This study tested different physical pre-treatment methods (ultrasonication, mechanochemical milling, and the use of pulsed electric fields) on different insect species (Hermetia illucens, Acheta domesticus, and Tenebrio molitor) compared to shrimp shells, aiming to intensify COS formation through the hydrolysis of the whole insects with chitinase from Streptomyces griseus. The findings of this study highlighted the importance of pre-treatments in enhancing the enzymatic hydrolysis of chitin and suggested the potential of insect-derived chitin as a sustainable source for COS production. In particular, different insect species produced different amounts of N-acetylglucosamine and N,N’-diacetylglucosamine, and mechanochemical pre-treatment on Hermetia illucens was the most effective. Additionally, this insect also had a lower degree of acetylation, calculated by 1H NMR, than the other species, indicating a possible influence on enzyme activity.