Improved shelf life of dried Beauveria bassiana blastospores using convective drying and active packaging processes

Authors: MASCARIN, GABRIEL - Embrapa; Jackson, Mark; Behle, Robert; KOBORI, NILCO - Embrapa; DELALIBERA JUNIOR, ITALO - Universidad De Sao Paulo

Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2016
Publication Date: 5/20/2016
Publication URL: http://handle.nal.usda.gov/10113/5506261
Citation: Mascarin, G.M., Jackson, M.A., Behle, R.W., Kobori, N.N., Delalibera Junior, I. 2016. Improved shelf life of dried Beauveria bassiana blastospores using convective drying and active packaging processes. Applied Microbiology and Biotechnology. 100:8359-8370. doi: 10.1007/s00253-016-7597-2.

Interpretive Summary: The insect-killing fungus Beauveria bassiana is used as a non-chemical control agent (bioinsecticide) for many serious insect pests including whiteflies, aphids, and coffee berry borers. Currently, spores of B. bassiana, the active ingredient in this bioinsecticide, are produced by growing the fungus on moistened grains and harvesting the spores from the surface of this solid substrate fermentation. Solid substrate spore production has limited the commercial use of this bioinsecticide due to quality control issues, long production times, high labor requirements, and difficulties in process scale-up. We have developed a rapid, low-cost method for mass producing the yeast form (blastospore) of B. bassiana using liquid culture fermentation. Blastospores of B. bassiana were shown to be more effective than solid substrate-produced spores in infecting and killing whiteflies. In this study, we showed that liquid culture-produced blastospores of B. bassiana remained viable after air- or spray-drying, were stable at room temperature when properly dried and packaged, and were more effective than solid substrate-produced spores in killing whiteflies. These studies showed that stable blastospores of B. bassiana can be economically mass produced, formulated, and packaged using commercially-available industrial processes. The commercial adoption of these low cost production, formulation, and packaging methods for blastospores of B. bassiana will hasten their widespread use as a bioinsecticide in row crops, horticulture, glasshouses, and urban environments.

Technical Abstract: The yeast form (blastospore) of the dimorphic insect-pathogenic fungus Beauveria bassiana can be rapidly produced using liquid fermentation methods but is generally unable to survive rapid dehydration processes or storage under non-refrigerated conditions. In this study, we evaluated the influence of two convective drying methods, various modified atmosphere packaging systems, and storage temperature on the desiccation tolerance, storage stability and virulence of blastospores of B. bassiana ESALQ 1432. All blastospore formulations were dried to < 5% water content equivalent to < 0.3 water activity. The viability of B. bassiana blastospores after air drying and spray drying was greater than 80%. Vacuum-packaged blastospores remained viable longer when stored at 4°C compared to 28°C with virtually no loss in viability up to 15 months regardless the drying method. When a both oxygen and moisture scavengers were added to sealed packages of dried blastospore formulations stored at 28°C, viability was significantly prolonged for both air and spray dried blastospores. The addition of ascorbic acid during spray-drying did not improve desiccation tolerance but enhanced cell stability (~two-fold higher half-life) when stored at 28°C. After storage for 4 months at 28°C, air dried blastospores produced a lower LC80 and resulted in higher mortality to whitefly nymphs (Bemisia tabaci) when compared to spray dried blastospores. These studies identified key storage conditions (low water activity and oxygen availability) that improved blastospore storage stability at room temperature and will facilitate the commercial development of blastospores-based bioinsecticides.