The stimulation of extracellular carbohydrases of edible mushrooms by the hot water-soluble fraction from corn fiber

Corn fiber (CNF) is an abundant by-product of the wet corn milling process in the production of cornstarch. We have shown that the hot water-soluble fraction (HWSF) from CNF has a promoting effect on the mycelial growth of various edible mushrooms, including mycorrhizal fungi. To reveal the promoting mechanisms, the effect of CNFHWSF on the stimulation of extracellular enzymes was examined. The production of extracellular carbohydrases such as amylase, CMCase, and xylanase was markedly enhanced by the addition of low molecular weight fractions (less than MW 500) prepared from CNF-HWSF. The enzymatic stimulation and enhancement of mycelial growth appeared during 3-15 days after inoculation. Furthermore, a fraction of less than MW 500 was separated by gel filtrate chromatography into five fractions (A-E), and the effect of each fraction was investigated. Promoting effects were shown from C and D fractions; mycelial growth and enzyme production of Lentinula edodes were indicated although fraction D has no sugars and amino acids in CNF-HWSF. From these results, the promoting effect of CNF-HWSF seems to be a two-step reaction. The first step could be achieved by rich nutrients such as free amino acids and monosaccharides from CNF-HWSF. The second step (during 3-15 days) is considered to be that the marked promoting effect was caused by the stimulation of extracellular enzymes.