Growth and ochratoxin A accumulation by two isolates of
Penicillium verrucosum, IBT5010 and IBT12803, were examined in
co-cultures with the antagonistic yeast Pichia anomala or
baker's yeast Saccharomyces cerevisiae. Each yeast was co-cultured
with
Penicillium verrucosum in malt extract agar supplemented with
1% yeast
extract and incubated at 25°C for 14 d. Ochratoxin A was
found to be stable at 25°, whether or not yeast was present.
Pichia anomala and Saccharomyces cerevisiae reduced mould
growth to
about the same extent in vitro. Both yeasts significantly reduced
the growth of Penicillium verrucosum isolates at 3×103
yeast
c.f.u./plate. In all co-cultures in vitro accumulated
ochratoxin A was reduced to below the detection limit (100 ng/plate)
by yeast
amounts as low as 3×103 c.f.u./plate. In wheat,
the growth of Penicillium verrucosum IBT5010, measured as c.f.u.,
was not reduced in
the presence of Pichia anomala, whereas the growth of
Penicillium verrucosum IBT12803 was clearly inhibited by this
yeast. A similar
pattern was observed for ochratoxin A accumulation in wheat when the
two mould strains were co-cultured with Pichia anomala.
Mycotoxin production was more sensitive to the presence of yeasts
than was mould growth. Co-cultivation with yeasts gave no
detectable stimulation of ochratoxin A accumulation in agar or wheat.