Solid-State Enzymes for Fiber Hydrolysis

Abstract

Lignocellulose degrading enzymes were produced by solid substrate fermentation (SSF) with Trichoderma and Gliocladium spp. on various agricultural by-products, such as spent brewing grain, corn fiber and wheat straw/wheat bran mixture. In a 10 day SSF, the hypercellulolytic mutant Trichoderma reesei Rut C30 produced 31 Filter Paper Unit (FPU)/g dry weight (DW) cellulase activity and 650 International Unit (IU)/g DW xylanase activity on corn fiber (corn seed hull), 55 FPU/g DW cellulase and 2400 IU/g DW xylanase activity on spent brewing grain. In a much faster 3 day fermentation, the wild strain Trichoderma hamatum TUB F-105 produced 7 FPU/g DW cellulase activity and 7600 IU/g DW xylanase activity on extracted (starch-removed) corn fiber. Gliocladium sp. TUB F-498 secreted 11 FPU/g DW cellulase activity in a 6 day SSF on a wheat straw-wheat bran 9:1 mixture. The hydrolyzing potential of SSF enzymes on native autologous substrates is substrate specific and does not always coincide with their filter paper activity. The F-498 and F-105 enzymes, at 5.0 FPU/g cellulose enzyme load hydrolyzed corn fiber and spent brewing grain more efficiently than the Rut C30 enzyme, although the Rut C30 enzyme hydrolyzed pure cellulose (Solka Floc) faster and more efficiently. The F-498 enzyme required lower enzyme loads for the hydrolysis of corn fiber and spent brewing grain than Rut C30. Due to adequate hydrolyzing potential, much reduced production cost and direct applicability, SSF enzymes are excellent candidates for enzymatic agrobiotechnological processes.