Sustainable Encapsulation of Biocontrol Agents: Cross-Linker Influence on Carboxymethylcellulose-Based Microbeads

The use of biopolymers for encapsulating active ingredients is a well-established approach, with ionotropic gelation representing a viable technique. This method allows the use of various cross-linking agents, though the physicochemical properties of the resulting materials can vary depending on the cross-linker selected. This study aimed to evaluate calcium (Ca²⁺) and aluminum (Al³⁺) ions as cross-linkers for the formation of carboxymethylcellulose (CMC) microbeads that can carry biological agents. Following comparative analyses, the most effective cross-linker was used for encapsulating the entomopathogenic fungus <i>Beauveria bassiana</i> strain IBCB66. Encapsulation of <i>B. bassiana</i> within a biopolymer bead matrix was found to be a promising strategy to preserve its biological control properties. Beads cross-linked with Al³⁺ (CMC_Al³⁺) demonstrated superior thermal stability (<i>T</i>_max of 165.76 and 386.71 °C) and swelling capacity (≈800%) compared to those cross-linked with Ca²⁺ (<i>T</i>_max of 211.78, 223.22, 309.29, and 368.95 °C, and swelling capacity of ≈200%). CMC_Al³⁺ beads also exhibited a uniform average size (1.92 ± 0.11 mm), in contrast to the heterogeneous conglomerates observed in CMC_Ca²⁺ beads. Blastospores of <i>B. bassiana</i> were efficiently encapsulated in CMC_Al³⁺ beads via a simple and rapid method, with 85% germination observed on the bead surface after five months of storage at -18 °C. These findings indicate that aluminum is a promising cross-linking agent for CMC-based encapsulation matrices in biological control applications.