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

Abstract

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 CNF-HWSF 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.

Biomass, laccase and endoglucanase production by Lentinula edodes during solid state fermentation of reed grass, bean stalks and wheat straw residues

“…The supplementation of the tested substrates with wheat bran and soybean flour increased N pool and readily available carbohydrates level, stimulating so initial endoglucanase and biomass production (Silva et al 2005a, Arai et al 2005. The deceleration of growth rate after the 3rd week of colonization, being in agreement with previous results (Leatham 1985), indicates the limitation of utilizable nutrients and soluble carbon sources (Mata and Savoie 1998).…”

“…This is further supported by the positive correlation of biomass and endoglucanase production found in the present study, as the higher endoglucanase level could be due to higher biomass production. Arai et al (2005) demonstrated that exocarbohydrase and particularly xylanase production correlate with growth promotion of L. edodes mycelium.…”