3.5.4. Biodegradation of substrates during cultivation process
The analysis of biodegradation of substrates was done when
cropping period was finished showing that G. pampeanus had a
strong capacity to degrade sawdust and decrease the percentage
of organic matter. When ashes content was compared between
treated and untreated sawdust, a strong increse in ashes content
of treated substrate was observed reaching 1278% for ES and 666%
for PS. The increase of ashes, considered as mineral residue of
incinerated organic matter, could be explained by two factors: (i)
exogenous supply of minerals through watering since blocks were
exposed to tap water which is rich in minerals and salts; (ii) fictitious
relative increase of minerals. The latter due to the increase of
minerals that fungal biomass contains and concentrates as part of
its metabolism. After 4.5 months of growing, mushroom degraded
an important amount of organic matter. From the total amount of
energy obtained from the substrate, one part is used to produce
mycelia and the rest is lost as CO2 and H2O during cellular respiration
process. As a consequence, when a mass of treated substrate
is weighted for the ashes analysis, it contains part of the degraded
sawdust and part of fungal biomass. The latter accumulate minerals
which are originally in sawdust but which are finally obtained during
fermentation process by fungal metabolism. The same results
are found in many other studies. Rajarathnam et al. (1997) has
mentioned that a relative increase in the ash content was observed
in the course of degradation of the substrate and utilization of its
components in shiitake strains. Chantaraj (2000) and Sánchez et al.
(2002) proposed that an increase in mineral content is one of the
changes that substrates undergo during enzymatic breakdown and
the resulting organic matter is utilized while the fungi are in the
vegetative development stage.