prevalence and molecular characteristics of vibrio species in pre ...

A. Cooling and freezing
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Rapid and efficient cooling to 5 °C will prevent the growth of V.
parahaemolyticus. Vibrio vulnificus is more sensitive to cold storage than V.
parahaemolyticus and reduces with approximately 0.04 log units/day under normal
cold temperature storage. Even though V. cholerae be reduced in cold storage, they
should not be relied on as preventive measures (FAO, 2003). It has been shown that
V. cholerae can survive under chilled and frozen temperatures on shellfish due to
presence or absence of the chitin-containing carapace of shrimp, which has a
cryoprotective effect on the pathogen (Shimodori et al., 1989). Sodium-
metabisulphate is traditionally used in shrimp to control non-microbiological spoilage
known as black spot. A study reported significant decreases (up to 1.8 log units) of V.
cholerae on chilled sodium-metabisulphate- treated, compared to untreated chilled
prawns (Januário and Dykes, 2005).
B. Heating
Vibrio is very sensitive to the heat (Table 8). Boiling temperature is very
harmful to the V. cholerae O in shrimp samples with or without carapace and
complete destruction occurs within 1-2 minutes after exposure to the temperature
(Nascumento et al., 1998). V. parahaemolyticus shows a >7 log reduction in viable
cell count when heated at 55 °C for 2 minutes (Yeung and Boor, 2004). Therefore
low heat pasteurization (50 °C for up to 15 min) can be applied for reduction of
Vibrio in the seafood (Andrews et al., 2003).
Table 9: Heat resistance of Vibrio spp. (FAO, 2003)
Vibrio species Heat resistance (D value)
V. cholerae D55 =0.24 min
V. parahaemolyticus D60 =0.71 min
V. vulnificus D50 =1.15 min (buffer); 0.66 min
(oysters)