Advances in Food Mycology

60 M. H. Taniwaki et al.
lowest; about a 12 fold difference. On PDA, F. oxysporum produced
the highest ergosterol content, with A. flavus the lowest, about a 22
fold difference.
For some species, medium composition greatly affected ergosterol
content. This was most evident for E. chevalieri, which produced 25
times as much ergosterol on PDA (670 µg/colony) from colonies less
than 50 mm in diameter, than from 86 mm diameter colonies on
CY20S (25 µg), despite comparable hyphal lengths on the two media.
In contrast, ergosterol production by A. flavus was much higher on
CYA than on PDA, again with comparable hyphal lengths.
3.7. Mycelium Dry Weights
Mycelium dry weights of 83-86 mm diameter colonies varied
between species. On CYA, A. flavus and F. oxysporum produced
colonies with a high mycelium dry weight (approximately 300
mg/plate). On CY20S, E. chevalieri colonies were equally heavy. The
weights of M. plumbeus colonies, however were only 12% of these values
(Table 5). For the vigorously growing Aspergillus, Penicillium and
Fusarium species, mycelium dry weights on PDA were lower than values
obtained on CYA. However, mycelium weights for M. plumbeus
and B. nivea were much higher on PDA than on CYA. In the case of
B. nivea, this difference was more than 8 fold.
3.8. Relationship Between Hyphal Length and
Mycelium Dry Weight
The relationship between hyphal length and mycelium dry weight
over time of growth was reasonably constant within species (Table 4)
except for very small colonies of Penicillium roqueforti, and varied
only four fold between the four species shown in Table 4. When all
nine species were compared, on more than one medium, much
greater variability was seen. This appears to be due mostly to variation
in hyphal length measurements, which is not so precise as the
other techniques used here. Increases in hyphal length sometimes
occurred with little increase in mycelial dry weight, e.g. for
M. plumbeus when grown on CYA and E. chevalieri grown on PDA.
These observations were reproducible (data not shown). As discussed
by Schnürer (1993), vacuole formation and autolysis of cell
contents may occur in aging cultures which would lead to a reduction
in weight per unit length.