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| Model | H2S-producing Shewanella*: Microbial spoilage model for aerobically stored fresh fish |
| Reference | Dalgaard P. (1993) Evaluation and Prediction of Microbial Fish Spoilage, Ph.D-thesis, Technological Laboratory, Danish Ministry of Fisheries, Lyngby, Denmark, 169 p. |
| Primary growth model | Log-transformed 3-parameter Logistic model |
| Secondary growth model | Square-root model |
| Factor in model | Temperature |
| Product validation studies | Cod, Haddock, Hoki, Orange roughy, Smooth oreo dory, Sea bream and Snapper (Dalgaard, 1999). |
| Range of applicability | Fresh seafood from temperate/cold waters stored aerobically at chill temperatures. The range of applicability in FSSP is 0-10°C |
| FSSP includes a simple square-root model for the effect of temperature on the maximum
specific growth rate (µmax, h-1) of
H2S-producing Shewanella spoilage bacteria
when growing in fresh fish under aerobic storage. The range of applicability has been set
to 0 - 10°C in FSSP although the more exact spoilage domain remains to be
determined in storage trials. The maximum population density has been set to 109
cfu/g. * H2S-producing Shewanella bacteria from chilled seafood were previously often identified as Shewanella putrefaciens. However, based on more recent taxonomy most of the H2S-producing Shewanella bacteria from chilled cold-water fish is more correctly identified as Shewanella baltica (Ziemke et al. 1998; Fonnesbech et al. 2005). |
| Primary growth model: |
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| In eqn. 1, Nt (cfu/g) is the concentration at time t, N0 (cfu/g) the initial concentration, Nmax the maximum concentration (cfu/g) and mmax the maximum specific growth rate (h -1). |
| Secondary growth model: |
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| This model for growth of H2S-producing Shewanella bacteria has been validated by comparison of observed and predicted growth rates in different fresh seafoods. The model predicted growth rates accurately in fresh fish stored aerobically at low temperatures. Data for higher temperatures remain to be evaluated in validation studies (See Table below). The model substantially overestimated growth rates in tropical seafood (bias factor = 1.44) and it can not be used for accurate shelf-life prediction for fresh fish from tropical/warm waters. |
Evaluation of microbial spoilage model for growth of H2S-producing Shewanella bacteria in aerobically stored fresh fish
Origin of seafoods |
Atmosphere |
Temp. (oC) |
na |
Bias factor |
Accuracy Factor |
Temperate/cold waters |
Air |
0 - 3 |
19 |
1.13 |
1.21 |
Tropical/warm waters |
Air |
0 – 30 |
15 |
1.44 |
1.60 |
a) Number of growth curves evaluated in product validation studies (Dalgaard, 1999)
| To predict shelf-life, the initial concentration of H2S-producing Shewanella bacteria is required and it can be determined using Iron agar Lyngby (Gram et al., 1987) or Peptone Iron agar (Levin, 1968). For H2S-producing Shewanella bacteria, minimal spoilage levels from 106 cfu/g to 108 cfu/g has been reported in the literature and FSSP uses a minimal spoilage levels of 107 cfu/g. Eqn. 3 is used to calculate product shelf-life. |
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Eqn. 1
Eqn. 2
Eqn. 3