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United States Department of Agriculture

Agricultural Research Service

Research Project: AUGMENTATIVE BIOLOGICAL CONTROL AND MASS REARING FOR BENEFICIAL AND PEST INSECTS

Location: Biological Control of Pests Research Unit

Title: Microencapsuling aerial conidia of Trichoderma harzianum through spray drying at elevated temperatures

Authors
item Jin, Xixuan
item Custis, Dan -

Research conducted cooperatively with:
item Advanced Biological Marketing, Inc.

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2010
Publication Date: November 8, 2010
Citation: Jin, X., Custis, D. 2010. Microencapsuling aerial conidia of Trichoderma harzianum through spray drying at elevated temperatures. Biological Control. 56:202-208.

Interpretive Summary: Aerial conidia of Trichoderma harzianum are produced by solid fermentation and then used to control root and foliar pathogens of plants. Conidia of T. harzianum must be dried to prevent spoilage by microbial contamination. Drying conidia of Trichoderma spp. in large scale production remains the major constraint because conidia lose viability during the drying process at elevated temperatures. Moreover, caking must be avoided during drying because heat generated by milling conidial chucks will kill conidia. A method was developed for microencapsulation of Trichoderma conidia with sugar through spray drying with sugars, such as sucrose, molasses or glycerol. Microencapsulation of conidia with 2% sucrose solution resulted in the highest survival percentage when compared with other sucrose concentrations and had about 7.5 X 1010 cfu in each gram of dried conidia, and 3.4 mg of sucrose added to each gram of dried conidia. The optimal inlet/outlet temperature setting was 60/31oC for spray drying and microencapsulation. The particle size of microencapsulated conidia balls ranged from 10 to 25 µm. The spray dried biomass of T. harzianum was a flowable powder with over 99% conidia, which could be used in a variety of formulation developments from seed coatings to sprayable formulations.

Technical Abstract: Trichoderma conidia are mostly produced by solid fermentation systems. Inoculum is produced by liquid culturing, and then transferred to solid substrate for aerial conidial production. Aerial conidia of T. harzianum are hydrophilic in nature, and it is difficult to separate them from the solid substrate by sieving. Washing conidia from the solid fermentation substrate and then centrifuging the suspension has become the choice for harvesting. Conidia of T. harzianum produced from either solid or liquid fermentation must be dried to prevent spoilage by microbial contaminations, and to induce dormancy for formulation development and prolonged self-life. Drying conidia of Trichoderma spp. in large scale production remains the major constraint because conidia lose viability during the drying process at elevated temperatures. Moreover, caking must be avoided during drying because heat generated by milling conidial chucks will kill conidia. It is ideal to dry conidia into a flowable powder for further formulation development. A method was developed for microencapsulation of Trichoderma conidia with sugar through spray drying. Microencapsulation with sugars, such as sucrose, molasses or glycerol, significantly (P < 0.05) increased the survival percentages of conidia after drying. Microencapsulation of conidia with 2% sucrose solution resulted in the highest survival percentage when compared with other sucrose concentrations and had about 7.5 X 1010 cfu in each gram of dried conidia, and 3.4 mg of sucrose added to each gram of dried conidia. The optimal inlet/outlet temperature setting was 60/31oC for spray drying and microencapsulation. The particle size of microencapsulated conidia balls ranged from 10 to 25 µm. The spray dried biomass of T. harzianum was a flowable powder with over 99% conidia, which could be used in a variety of formulation developments from seed coatings to sprayable formulations.

Last Modified: 7/25/2014