Physicochemical, rheological, and biological properties of insect chitosans (Zophobas morio and Tenebrio molitor)...

Zophobas morio and Tenebrio molitor insects are promising sources of chitosan due to their ease of reproduction and breeding; however, optimizing their properties is necessary to expand potential applications. This study evaluated rheological, physicochemical, and biological properties of chitosans from T. molitor and Z. morio with different molecular weights (Mw), obtained by microwave irradiation. Native chitosans were depolymerized at different irradiation times (0, 6, 18, and 30 min) and compared with three commercial chitosans of high, medium, and low Mw. Depolymerization reduced Mw of both insect chitosans, with a more pronounced decrease in Z. morio (21.5% at 18 min) than T. molitor (10%). Physicochemical characterization revealed progressive reduction in Mw and apparent viscosity, without changes in degree of deacetylation. Structural (FTIR, XRD), morphological (SEM), thermal (TGA), and color analyses evidenced modifications associated with depolymerization. Regarding bioactivity, insect chitosans exhibited higher antioxidant capacity than commercial samples, with T. molitor showing lowest IC₅₀ value (0.30 mg/mL) compared to Z. morio (0.52 mg/mL) and commercial chitosans (4.2-5.2 mg/mL). However, microwave depolymerization did not enhance this activity. Antimicrobial assays revealed the following susceptibility order: Listeria monocytogenes > Staphylococcus aureus > Escherichia coli > Salmonella spp., indicating greater sensitivity to Gram-positive bacteria. Molecular weight reduction enhanced antibacterial activity, demonstrating comparable or superior activity to commercial chitosan under specific conditions. These findings highlight the potential of insect-derived chitosans as sustainable biopolymers for food preservation and pharmaceutical applications.