Solid-state fermentation of Ginkgo biloba L. residue for optimal production of cellulase, protease and the simultaneous detoxification of Ginkgo biloba L. residue using Candida tropicalis and Aspergillus oryzae

Abstract

Ginkgo biloba L. residue (GBLR) is a by-product generated from flavonoids extraction of G. biloba L. Although it contains a high amount of nutritive components, it has toxic compound of ginkgolic acids which restricts its application in the food or animal feed industries. Also, the disposal of huge quantity of GBLR is a major environmental problem in the future. This study investigated the potential of a utilization of GBLR as substrate for cellulase and protease productions by solid-state fermentation (SSF) with Candida tropicalis and Aspergillus oryzae. The study simultaneously is focused on the biodetoxification of toxins in GBLR. The optimum SSF conditions for enzyme production were evaluated as, supplementation with 2 % maltose and peptone, inoculation with 1 × 107 fungi per 5 g residues, 7.0 pH, 40 % moisture content, 25 °C incubation temperature, and 4 days incubation time. Under these conditions, cellulase and protease activities reached up to 1,168.26 and 3,145.68 U/g, respectively. The main toxic compound ginkgolic acid content in the GBLR was reduced from 14.8 to 1.5 mg/g after SSF. The cytotoxicity of the fermented GBLR evaluated by methyl thiazolyl tetrazolium testing on abelson murine leukemia virus-induced tumor cells showed almost 100 % of cellular viability after 4 days of fermentation. Our results indicate that SSF of GBLR could produce industrial enzymes and the detoxified fermented GBLR could be potentially applied to animal feed.