Abstract
Heteroglycans were extracted and isolated from the fruiting bodies of wild mushroom Daedalea quercina (L) Fr. These were obtained from sequential extraction with hot water, 1% Ammonium oxalate then 5% Sodium hydroxide solution followed by ethanol or acidic precipitation affording crude extracts which were further purified by dialysis membrane (MWCO 12 400). Separation by charge and size were done using DEAE-cellulose column and Sephadex G-100 or Sepharose CL-4B. This resulted to water soluble neutral (W1P-1A) and acidic (W1P-2A) glycan isolates, ammonium oxalate soluble (A1P-1) and two alkali soluble (N1P-1 and N1P-2) glycan isolates. Characterization of the hydrolyzed isolates using HPAEC-PAD and MALDI TOF MS showed glucan-rich heteroglycans (W1P-1A and W1P-2A); glucan and mannan rich heteroglycan, (N1P-1) and galactan-rich heteroglycan (A1P-1). The latter being the first reported galactan-rich glycan found in ammonium oxalate mushroom extract. The hydrolysates had approximately 4-5 degree of polymerization with molecular weights ranging from 689.680 to 851.788 Da. The hydrolysate of isolate N1P-2 is a glucan-rich heteroglycan which also contain N-acetyl glucosamine units. It is composed of polymers with 4-5 hexose units as well as N-acetyl glucosamine containing polymers of 6-8 hexose units with molecular weight range of 689.799 to 851.915 Da and 1055.718 to 1379.584 Da, respectively.
Highlights
Mushrooms are studied mainly for their health benefits
Five relatively pure fractions were obtained in this study: two from H2O extract (W1P-1A, W1P-2A), one from (NH4)2C2O4 extract (A1P-1), and two from NaOH extract (N1P-1, N1P-2)
Monosaccharide and MALDI-TOF Mass spectra (MS) analysis of the hydrolysates of each fraction showed that neutral (W1P-1A) and acidic (W1P-2A) water soluble fractions are glucan-rich heteroglycans (671.5-995.8 Da)
Summary
Mushrooms are studied mainly for their health benefits These were attributed to several bioactive compounds such as polysaccharides, polysaccharide-peptides, nucleosides, triterpenoids and other metabolites which have been identified in a number of species (Wasser, 2002). We report the isolation and partial characterization of polysaccharides from the wild mushroom Daedalea quercina (L) Fr. Sample specimen was lodged in the national museum for taxonomic identification. The marc from water extraction was re-extracted with 1% ammonium oxalate at 1000C for 6hrs, three times. The concentrated sample was added with 1 mL distilled water, diluted 20 times and analyzed for monosaccharide composition using HPAEC-PAD (Dionex BioLC system). Separate samples were hydrolyzed to low molecular weight oligosaccharides (2M TFA 50 oC, 2h) and purified by gel-filtration chromatography on a Sephadex G-15 (SigmaAldrich) column using double distilled water as eluent. The oligosaccharides were mixed with 10 mM of 2, 5-DHB (1:1) ran on MALDI-TOF MS (UltraflexTM TOF/TOF mass spectrometer) (Hung., et al, 2008)
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