Advances in Food Mycology

High Pressure Inactivation of Fungi 243
gradual decline with increasing treatment times to 1-2 × 10 4 cfu/ml
after 60 sec, and 10 3 after 120 sec (Figure 1b).
3.2. Inactivation of heat sensitive moulds
Both P. expansum and F. oxysporum were pressure treated at
400 MPa. P. expansum was quite sensitive to pressure treatment.
A 3-4 log 10 reduction was achieved after 15-30 sec (Figure 2). After
60 sec, the reduction was >5 log 10 and by 120 sec, no survivors were
detected (limit of detection 10 cfu/ml). F. oxysporum conidia and
chlamydoconidia were even more sensitive to pressure treatment. A
suspension of 2.5 × 10 7 mixed microconidia and chlamydoconidia was
reduced to 1.4 × 10 2 cfu/ml after 15 sec at 400 MPa, and after 30 sec,
no survivors were detected (results not shown).
3.3. Inactivation of heat resistant moulds
As the ascospores of heat resistant moulds are known also to be
pressure resistant (Butz et al., 1996; Reyns et al., 2003; Voldrich et al.,
2004), both B. fulva and N. fischeri spore suspensions were pressure
treated at 600 MPa. Spore suspensions were divided into two portions,
and one of each was blanched at 95°C for 5 min. Both blanched and
unblanched spore suspensions were then pressure treated simultaneously
to ensure that they were exposed to exactly the same conditions.
B. fulva ascospores were more pressure sensitive than those of
N. fischeri (Figure 3). Unblanched ascospore suspensions of B. fulva,
Survivors (cfu/ml)
1.00E+08
1.00E+07
1.00E+06
1.00E+05
1.00E+04
1.00E+03
1.00E+02
1.00E+01
1.00E+00
Penicillium expansum
0 15 30 45 60 75 90 105 120 135
Time (seconds)
Figure 2. Effect of pressure treatment of 400 MPa at 25°C on Penicillium expansum
conidia. Cells were suspended in 20 °Brix sucrose solution, pH 4.2 (acidified with citric
acid). Graphs show replicates 1 (◆) and 2 (■) for each pressure run.