3.3.1. Microbial analysis
The initial bacterial counts in the samples are described in chapter
3.1. No Listeria spp. was detected in unspiked-unpressurized control
samples, not even after 41 days storage at 5.5 C (Figs. 2 and 3),
indicating a good quality and safety of the raw material used in this experiment. Fig. 2 shows that L.innocua was reduced significantly (p< 0.05) after 60 s at 500 MPa. One log reductionwas observed and the number decreased during storage. No reduction was observed after 10 s and it remained unchanged until after more than 26 days.By increasing the treatment time to 20 and 30 s it appeared that the bacteria were shocked in some way as the total number decreased
during the first 12 days of storage but after that the bacteria recovered
and the number increased. No L.innocua was detected 5 days
after HPP treatment at 900 MPa (Fig. 3) but after storage at 5.5 C for
26–41 days low level (0.3–20 cfu/g)was detected. It is difficult to say
if this indicates thatsome of the cells survived and could recover after
some storage time or this difference is due to individual difference
between samples. Tables 2 and 3 depicts changes in the TVC and LAB
counts in the vacuum-packed cold smoked salmon after pressure
treatment and during storage at 5.5 C. The LAB count was considerably
higher than TVC or log 5.5 compared to log 3.7 in untreated samples indicating that by using LH at 15 C some LAB cannot grow (Table 2).Unfortunately the LABwere not identified downto species.
At day 5 the TVC count was 0.2–1.2 log lower in samples treated at 500 MPa compared to untreated samples (Table 2). During the storage the number increased steadily and after the 41 days storage about 0.8–2.7 log increases were observed. The number of LAB
reduced significantly (p< 0.05) compared to untreated samples but
during storage 4–6 log increasewas observed indicating that the LAB