Chemical nature and composition of compost during mushroom growth

Improvement of the process of mushroom composting is of importance in order to provide an optimal growing medium needed for the mushroom. Since composting produces a food source for the mushroom, the compositional changes of mushroom compost occurring during the growth cycle of the button mushroom, Agaricus bisporus, were studied. Samples were collected during spawning, casing and the following four flushes. Samples were analyzed for their elemental composition, carbohydrates, FTIR, ¹³C-NMR, pyrolysis-GC/MS and tetramethylammonium hydroxide (TMAH) thermochemolysis-GC/MS. The carbohydrate analysis revealed a decrease in the total amount of about 40% of the identified monosaccharides during mushroom growth. The ¹³C-NMR data also confirm that polysaccharides are the main fraction degraded (or utilized by the mushrooms) during the cropping period. These findings were also confirmed by changes in the absorbance of functional groups observed in the FTIR spectra. Pyrolysis data revealed chromatographic peaks related to polysaccharides-, proteins- and lignin-derived compounds. Both pyrolysis and TMAH thermochemolysis data show degradation of lignin structures during the growth period. Lignin alteration primarily involved a preferential degradation of syringyl units and oxidation of side chains of guaiacyl moieties. This study suggests that the polysaccharide fraction of the mushroom substrate is the main organic fraction utilized during the process. In addition, alterations of lignin structures have occurred although its relative content usually increases during mushroom cropping.