ABSTRACT
The solid state fermentation (SSF) parameters of defatted soybean flour (DSF) with Aspergillus oryzae IOC 3999/1998 or Monascus purpureus NRRL 1992 was evaluated using a rotational central composite experimental design to optimise the production of ß-glucosidase and convert glycosidic isoflavones in aglycones. Variables investigated were initial pH of DSF, volume of water added to 10 g of DSF and incubation temperature. ß-Glucosidase activity was measured using the synthetic substrate, p-nitrophenyl-ß-D-glucoside. The content of isoflavones was determinate by ultra performance liquid chromatography. The highest production of ß-glucosidase for both strains occurred when adding 10 mL of water to the DSF, incubating at 30 °C and using 6.0 as the initial DSF pH. A. oryzae IOC 3999/1998 expressed ß-glucosidase activity at 10.7 times higher than M. purpureus NRRL 1992. The DSF fermentation was more efficient in converting isoflavones with M. purpureus NRRL 1992.
Subject(s)
Aspergillus oryzae/enzymology , Flour/microbiology , Fungal Proteins/metabolism , Glycine max/microbiology , Industrial Microbiology/methods , Isoflavones/metabolism , Monascus/enzymology , beta-Glucosidase/metabolism , Aspergillus oryzae/metabolism , Biotransformation , Culture Media/chemistry , Culture Media/metabolism , Fermentation , Flour/analysis , Hydrogen-Ion Concentration , Industrial Microbiology/instrumentation , Monascus/metabolism , Glycine max/metabolismABSTRACT
An extracellular beta-glucosidase produced by Monascus purpureus NRRL1992 in submerged cultivation was purified by acetone precipitation, gel filtration, and hydrophobic interaction chromatography, resulting in a purification factor of 92-fold. A 22 central-composite design (CCD) was performed to find the best temperature and pH conditions for enzyme activity. Maximum activity was observed in a wide range of temperature and pH values, with optimal conditions set at 50 degrees and pH 5.5. The beta-glucosidase showed moderate thermostability, was inhibited by HgCl2, K2CrO4, and K2Cr2O7, whereas other reagents including beta- mercaptoethanol, SDS, and EDTA showed no effect. Activity was slightly stimulated by low concentrations of ethanol and methanol. Hydrolysis of p-nitrophenyl-beta-D-glucopyranoside (pNPG), cellobiose, salicin, n-octyl-beta-D-glucopyranoside, and maltose indicates that the beta-glucosidase has broad substrate specificity. Apparently, glucosyl residues were removed from the nonreducing end of p-nitrophenyl-beta-Dcellobiose. beta-Glucosidase affinity and hydrolytic efficiency were higher for pNPG, followed by maltose and cellobiose. Glucose and cellobiose competitively inhibited pNPG hydrolysis.