Degradation of lignin in wheat straw during growth of the oyster mushroom (Pleurotus ostreatus) using off-line thermochemolysis with tetramethylammonium hydroxide and solid-state C-13 NMR

The oyster mushroom (Pleurotus ostreatus) is widely cultivated on wheat str aw (Triticum aestivum); however, there is a need to better understand the r elationship between the chemical composition of the compost and mushroom gr owth. Wheat straw was degraded over a period of 63 days by P. ostreatus dur ing which time it was sampled at weekly intervals. Off-line thermochemolysi s with tetramethylammonium hydroxide and solid-state C-13 NMR were then use d in the molecular characterization of the undegraded wheat straw and the d egraded samples. The degraded wheat straw samples had a lower proportion of syringyl- to guaiacyl-derived moieties and cinnamyl- to guaiacyl-derived m oieties than the undegraded control. There were increases in both guaiacyl and syringyl acid to aldehyde ratios with composting time, which showed tha t side-chain oxidation has been mediated by P. ostreatus. The 13C NMR spect ra confirmed the increase in carboxyl content but indicated that the overal l lignin and methoxyl contents remained relatively constant, although some nonsystematic variations were observed. The spectra also showed a decrease in amorphous noncellulosic polysaccharides in relation to the crystalline c ellulose upon degradation.