Optimising microencapsulated formulation stability of Bacillus thuringiensis subsp. kurstaki (Bt-KD2) against ultraviolet condition using response surface methodology

Abstract

In this paper, microencapsulated formulation of Bacillus thuringiensis subsp. kurstaki were prepared by the emulsion gelling method. Stability of formulation under ultraviolet (UV) radiation by spore viability and mortality teston Ephestia kuehniella Zeller larvae are investigated. Response surface methodology was used for optimising the formulations. Calcium Chloride (0.1 and 0.3 M) and sodium alginate (2 and 3% w/w) were used in the formulations, and stirring speed was selected between 1500 and 2000 rpm. Morphology of the microcapsule was evaluated by light microscopy. The optimal values for the variables were: sodium alginate = 2.15%, CaCl₂ = 0.24 M, speed = 1606 rpm and spore viability, mortality and diameter of 68% ± 1.73, 85% ± 1.5 and 9μ ± 1.3, respectively; while the predicted values by the software were 70% for spore viability, 87% for mortality and 8.3 μ for diameter.

Keywords:

• Bacillus thuringiensis
• microencapsulation
• stability
• ultraviolet

Acknowledgements

The authors are grateful to Dr. HeidaryAlizadeh of Iranian Research Institute of Plant Protection.