UNIVERSITÉ PAUL CÉZANNE, AIX MARSEILLE III - IMEP

Résultats et discussion. Chapitre 2: Optimisation de la production du spawn
The substrates used for L. edodes growth in both liquid and solid state culture exhibited
constant ergosterol content in mycelium. Mean value of ergosterol content in pure mycelium
3.57± 0.56 (mg.g-1 of dry weight) was within the range found in other experiments with other
microorganism (Pasanen et al., 1999; Barajas-Aceves 2000; Jasinghe and Perera 2005). While
some of fungal species exhibited large differences in ergosterol content between the isolates,
as can be seen from the relatively large standard deviation (Klamer and Bååth 2004; Mille-
Lindblom et al., 2004; De Ridder-Duine et al., 2006).
It would appear that culturing of mycelium on EbA could allow for operating nearly to
natural condition so as to gain insight into the magnitude of variation and hence the potential
error when calculating fungal biomass from ergosterol concentration measured in spawn
fermentation (Gessner and Chauvet 1993). Determination of ergosterol allowed for reducing
the use of hazardous organic solvents which involved in saponification step of ergosteryl ester
(De Ridder-Duine et al., 2006), and this thereby permeates for measuring of living fungal
biomass (Mille-Lindblom et al., 2004) based on the assumption that the ergosterol have been
considered as kind of lipids storage (Klamer and Bååth 2004). Furthermore, the recovery of
ergosterol with this simple protocol was exhibited in the most of case very high as could be
reported by several authors (Gong et al., 2001; De Ridder-Duine et al., 2006; Yuan et al.,
2007).
The identification of ergosterol with HPLC was achieved by comparing its retention
time and spectrum against ergosterol standard (Fig. 6). The ergosterol spectrum exhibited
characteristic pattern, because it has a conjugated pair of double bonds at carbons 5-6 and 7-8,
it absorbs UV light strongly between 240 and 300 nm. The interference of sterol containing in
wheat, as reported by Seitz et al. (1977), was eliminated by verification of purity of ergosterol
peak detected by HPLC, and verification of spectrum of peak corresponding to ergosterol.
The conversion of ergosterol, which was considered as precursor, to vitamin D2
(Ergocalciferol) by UV irradiation was reported by several authors (Jasinghe and Perera 2005;
Jasinghe and Perera 2006; Teichmann et al., 2007). Certain author investigated conversion
kinetics of ergosterol to vitamin D2 in natural products such as in L. edodes mushrooms so as
to modeling of conversion in order to predict the yield of vitamin D2 after the irradiation
process.
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