Improving the thermal tolerance of biocontrol spores, <i>Akanthomyces lecanii</i>, by encapsulation

Akanthomyces lecanii is an entomopathogenic fungus, and spores of this fungus could be incorporated into films generated using cast film extrusion for biocontrol applications. However, the extrusion process involves high temperature processing (150°C) although this only lasts for a few minutes. The elevated temperature destroys spores, thereby eliminating functionality, unless the spores are protected from this heat. Initial experiments revealed that the heat tolerance of free A. lecanii spores to be 60°C. The spores were therefore encapsulated into beads prepared using a combination of Gelrite, cellulose, and Cel-fine at different concentrations. The beads were freeze-dried and then immersed in hot glycerol for 2 min at a selected temperature within the range of 50°C-100°C. The results indicated that some combinations of encapsulating agents resulted in the spores retaining viability (plate counting) after heat treatment at 100°C. Beads stored at room temperature for 1 week showed a reduction in the upper temperature tolerance. This study revealed that the temperature tolerance of A. lecanii spores could be improved by 40°C by encapsulation in freeze-dried beads containing 2% Gelrite (purified gellum gum), 0.4% cellulose, and 0.4% Cel-fine.