4 °C - the National Sea Grant Library

negative bacteria such as Pseudomonas spp. (Herbert et al., 1971; Herbert and
Shewan, 1976). SA inhibits growth of gram-negative bacteria on refrigerated (4°C)
catfish fillets (Kim and Hearnsberger, 1994), while gram-positive bacteria are more
susceptible to inhibition by MKP than are gram-negative bacteria (Molins, 1991).
This microbial specificity demonstrates that SA is a better chemical treatment than
MKP to extend shelf-life of catfish. However, results indicate that a combination of
SA and MKP may prolong the microbiological shelf life of catfish at 4°C by keeping
counts below 10 7 CFU/g.
Combined effect of sodium acetate and bifidobacteria
The effects of various concentrations and species of BIF and SA on the shelflife
of refrigerated catfish fillets were studied on the basis of aerobic plate counts
(APC) and sensory data. When a 2.5% culture of B. infantis was used alone, little
impact on APC was noted with the exception of a significant (P0.05) from control fillets
(Fig. 6). Similar (P>0.05) extended lag phases and GT were noted for fillets treated
with 2.5% cultures of B. adolescentis or B. longum (results not shown). Hence,
further results only will report data from B. infantis treatments. Lag phase increases
of psychrotrophic populations were observed in ground poultry treated with
Lactobacillus plantarum or Pediococcus cerevisiae (Raccach et al., 1979). It was
assumed that inoculated BIF do not grow on refrigerated fish fillets and the extension
of lag phase may be due to compounds produced during culturing, i.e. acetic and/or
lactic acid, that were inhibitory to aerobic spoilage bacteria (Gilliland and Speck,
1975; Ray, 1992). Other reasons for inhibited aerobic growth might include nutrient
competition, unfavorable changes in oxidation reduction potential, or production of
other antimicrobial compounds.
Fillets treated with 0.5% SA had APC significantly lower and GT significantly
higher (P0.05) as the other two cultures when
combined with 0.5% SA (results not shown). The combined treatments could
increase GT by approximately 20 h. A previous report on SA combined with
potassium sorbate or lactic acid culture has attributed antimicrobial effects primarily
to SA (Kim and Hearnsberger, 1994). The present study shows that an additive
interaction occurs when BIF are combined with SA.