Low-Temperature Spray Drying for the Microencapsulation of the Fungus Beauveria bassiana

Abstract

Low-temperature spray drying was used to microencapsulate the conidia of Beauveria bassiana. In order to prolong the activity of the conidia and improve their shelf life, various polymers (including hydroxypropyl methyl cellulose [HPMC], chitosan, dextrin, skimmed milk, and polyvinylpyrrolidone [PVP K90]) were examined as encapsulation matrices. Different inlet/outlet temperatures, compositions of the carrier systems, and conidia concentrations were examined with respect to spore viability. Moreover, the production characteristics, such as particle size distribution, entrapment efficiency, and shape, were investigated. The best encapsulated products were obtained using a matrix composed of 10% dextrin, 10% skimmed milk, and 5% PVP K90 as the coating material. The conidia exhibited 80% viability, even after storage for 6 months at 4°C. The microspheres obtained by spray drying were spherical with smooth or wrinkled surfaces. The mean particle size was in the range of 2.5–10 μm. The yield (%) using dextrin/SM/PVP K90 as coating material having maximum viability was 68 ± 4, whereas that with dextrin only as coating material was 85 ± 3.

Keywords:

• Beauveria bassiana
• Conidia
• Low-temperature spray drying
• Microencapsulation

ACKNOWLEDGEMENTS

We thank Zu-Hau Chan and Ya-Ching Wang for technical assistance. Financial support from the National Science Council of Taiwan (Grant No. NSC96–2313-B-276-002) is gratefully acknowledged.

Notes

^a CaCl₂ aqueous solution (10% w/v) was added to the submerged culture.

^b Measured at initial time (600 nm).

^c Measured at 7th day.

^a Inlet/outlet temperature.

^b Germination rate after 6 months of storage.

^c Dextrin (10% w/v), HPMC (0.03% w/v), glucose (2% w/v).

^d SM (10% w/v).

^e Chitosan (0.5% w/v).

^f Starch (4% w/v).

^g Sodium alginate (4% w/v).

^h SM (10% w/v), PVP K90 (5% w/v).

ⁱ Dextrin (10% w/v), SM (10% w/v), PVP K90 (5% w/v).

^a Coating materials: dextrin (10% w/v), SM (2.5% w/v), PVP K90 (10% w/v).

^b Microencapsulated conidia.

^c BK: The bare conidia.