Encapsulation of Beauveria bassiana conidia in carboxymethylcellulose beads: Advancing UV protection and thermal resilience in bioinsecticide applications.

The encapsulation of entomopathogenic fungi in polysaccharide matrices is a promising green strategy for protecting them from environmental stressors such as UV radiation and high temperatures (>35 °C). This study presents a novel formulation for encapsulating Beauveria bassiana conidia within a sodium carboxymethylcellulose matrix cross-linked with Al³⁺ or Fe³⁺. Beads produced via ionic gelation were subjected to air-drying or freeze-drying and characterized using SEM-EDX, FT-IR, TGA, and XRD. Freeze-dried beads were larger and exhibited a higher swelling capacity than their air-dried counterparts. SEM imaging revealed that freeze-dried beads possessed a spherical, rough surface with a microporous internal structure, whereas air-dried beads appeared flattened and wrinkled. TGA confirmed that encapsulation did not compromise the thermal stability of the CMC matrix. XRD analysis indicated that Al-based beads were semi-crystalline, while Fe-based beads were amorphous. The Al-based beads significantly outperformed the Fe-based ones, encapsulating a 20-fold higher load of B. bassiana conidia. These conidia subsequently produced ten times more new conidia (10⁸ per bead) after 7 days of incubation. Importantly, the Al-based beads provided robust protection to B. bassiana conidia against high dose UV radiation (485.78 kJ/m²) and extreme heat (55 °C). This protection effect ensured that the B. bassiana conidia retained their insecticidal efficacy against Tenebrio molitor larvae and remained viable after six months of storage.