MAIZE FLOUR, AN ALTERNATIVE CRYOPROTECTANT FOR FREEZE-DRYING BACILLUS THURINGIENSIS FOR COCOA FERMENTATION IN COTE DIVOIRE

Bacillus thuringiensis is an important micro-organism in organic farming and food fermentation due to its metabolites, which have fungicidal and insecticidal properties. To ensure stability and avoid genetic modification, the strains are freeze-dried. However, the cryoprotectants used are very expensive. The aim of this study was to design a more economical freeze-drying environment for Bacillus thuringiensis using local flours. Bacillus thuringiensis was grown and then centrifuged to recover the resulting cell pellets. Local flours were prepared individually and added to each pellet before freezing and lyophilisation. Survival after lyophilisation and survival over time at 30C were evaluated. Maize and sorghum flours gave survival rates after lyophilization of 93.05 0.69 and 92.07 0.35 respectively, close to those of sucrose (96.31 0.42) and mannitol (94.91 1.51). All flours maintained more than 50% of strain survival for 1.5 months. Sorghum and maize flours could be used as an alternative to cryoprotectants, which are too costly, to preserve Bacillus thuringiensis strains.