284
been shown that combination of hot-water/cold-shock processes reduced V. parahaemolyticus in oysters to nondetectable levels within 22 min at 50–52 °C (Andrews
et al. 2000).
Ionising radiation is another way to eliminate vibrios in shellfish. In another
study, live oysters (Crassostrea virginica) with naturally incurred and artificially
inoculated pathogenic vibrios, were exposed to 0–3 kGy dose Cobalt-60 gamma
radiation. Vibrio vulnificus was reduced from 10
6
cfu/g oyster meat to non- detectable
levels with 0.75–1.0 kGy irradiation exposure. Vibrio parahaemolyticus required
1.0–1.5 kGy for reduction to non-detectable levels (Andrews et al. 2003). In a study
aiming to determine the radiation decimal reduction dose (D10) of toxigenic Vibrio
cholerae in pure culture, it is found that a dose of 1.0 kGy was optimal for choro
mussels and abanico clams, whereas 2.0 kGy produced the best results when treating common clams (Torres et al. 2001). Lopez (2001) stated that 1.0 kGy would be
enough to render Uruguayan mussels Vibrio-safe (Lopez 2001). Rashid et al. (1992)
found that the gamma-radiation dose needed to reduce by 10
4
the number of Vibrio
isolates is about 3 kGy in frozen shrimps. It has been reported that combination of
sodium hypochlorite (NaClO) and gamma irradiation reduce V. parahaemolyticus
in shucked oysters and clams (Park and Ha 2018).
Chilling can be effective in reducing the number of vibrios in shellfish products.
Vibrio vulnificus in cold stored shellstock oysters and shucked oyster meats reached
undetectable levels (MPN <3/g) within 14 days and 21 days respectively (Cook and
Ruple 1992). Bradshaw et al. (1974) reported that V. parahaemolyticus inoculated
onto the surface of cooked shrimp or crab gradually decline in numbers at incubation temperatures of 10 °C and below and multiply if held at 18.3 °C. In shellstock
oysters stored at 0, 2 and 4 °C, V. vulnificus levels have been reported 1-log unit
decreased after 3 days of storage, while remain unchanged for 14 days at 2 and
4 °C. However, after 10 days at 0 °C, a 2.5-log unit decrease was detected (Kasper
and Tamplin 1993). However, others stated quite the reverse reports. Thomas (2016)
found that the onboard icing using ice-slurry immediately after harvest did not
change the levels of V. parahaemolyticus and V. vulnificus in oysters (Crassostrea
virginica). Similarly, Melody et al. (2008) reported that on-board and dockside
icing did not reduce the levels of V. vulnificus or V. parahaemolyticus in oysters
(Crassostrea virginica).
Liu et al. (2009) reported that freezing and frozen storage is a widely used
method to protect the product quality by preventing the growth of bacteria, and that
V. parahaemolyticus can provide a certain degree of reduction in oyster meat. They
determined a reduction of a 0.22 log MPN/g in population of V. parahaemolyticus
in Pacific oysters cryogenically frozen. Parker et al. (1994) reported that freezing
oysters under vacuum-packaged conditions at −20 °C is significantly effective in
reducing loads of V. Vulnificus. A reduction of 3–4-logs in Vibrio vulnificus population in oysters inoculated with V. vulnificus and frozen at −20 °C was found in that
study. The frozen storage of oysters at −18 and −24 °C has been reported to be
effective in the inactivation of V. parahaemolyticus in oyster homogenates (MuntadaGarriga et al. 1995). Freezing of oysters at −40 °C and then storage for 8–10 weeks
achieved a 4- to 5-log reduction in the V. vulnificus population (Cook and Ruple
5 Shellfish Safety
been shown that combination of hot-water/cold-shock processes reduced V. parahaemolyticus in oysters to nondetectable levels within 22 min at 50–52 °C (Andrews
et al. 2000).
Ionising radiation is another way to eliminate vibrios in shellfish. In another
study, live oysters (Crassostrea virginica) with naturally incurred and artificially
inoculated pathogenic vibrios, were exposed to 0–3 kGy dose Cobalt-60 gamma
radiation. Vibrio vulnificus was reduced from 10
6
cfu/g oyster meat to non- detectable
levels with 0.75–1.0 kGy irradiation exposure. Vibrio parahaemolyticus required
1.0–1.5 kGy for reduction to non-detectable levels (Andrews et al. 2003). In a study
aiming to determine the radiation decimal reduction dose (D10) of toxigenic Vibrio
cholerae in pure culture, it is found that a dose of 1.0 kGy was optimal for choro
mussels and abanico clams, whereas 2.0 kGy produced the best results when treating common clams (Torres et al. 2001). Lopez (2001) stated that 1.0 kGy would be
enough to render Uruguayan mussels Vibrio-safe (Lopez 2001). Rashid et al. (1992)
found that the gamma-radiation dose needed to reduce by 10
4
the number of Vibrio
isolates is about 3 kGy in frozen shrimps. It has been reported that combination of
sodium hypochlorite (NaClO) and gamma irradiation reduce V. parahaemolyticus
in shucked oysters and clams (Park and Ha 2018).
Chilling can be effective in reducing the number of vibrios in shellfish products.
Vibrio vulnificus in cold stored shellstock oysters and shucked oyster meats reached
undetectable levels (MPN <3/g) within 14 days and 21 days respectively (Cook and
Ruple 1992). Bradshaw et al. (1974) reported that V. parahaemolyticus inoculated
onto the surface of cooked shrimp or crab gradually decline in numbers at incubation temperatures of 10 °C and below and multiply if held at 18.3 °C. In shellstock
oysters stored at 0, 2 and 4 °C, V. vulnificus levels have been reported 1-log unit
decreased after 3 days of storage, while remain unchanged for 14 days at 2 and
4 °C. However, after 10 days at 0 °C, a 2.5-log unit decrease was detected (Kasper
and Tamplin 1993). However, others stated quite the reverse reports. Thomas (2016)
found that the onboard icing using ice-slurry immediately after harvest did not
change the levels of V. parahaemolyticus and V. vulnificus in oysters (Crassostrea
virginica). Similarly, Melody et al. (2008) reported that on-board and dockside
icing did not reduce the levels of V. vulnificus or V. parahaemolyticus in oysters
(Crassostrea virginica).
Liu et al. (2009) reported that freezing and frozen storage is a widely used
method to protect the product quality by preventing the growth of bacteria, and that
V. parahaemolyticus can provide a certain degree of reduction in oyster meat. They
determined a reduction of a 0.22 log MPN/g in population of V. parahaemolyticus
in Pacific oysters cryogenically frozen. Parker et al. (1994) reported that freezing
oysters under vacuum-packaged conditions at −20 °C is significantly effective in
reducing loads of V. Vulnificus. A reduction of 3–4-logs in Vibrio vulnificus population in oysters inoculated with V. vulnificus and frozen at −20 °C was found in that
study. The frozen storage of oysters at −18 and −24 °C has been reported to be
effective in the inactivation of V. parahaemolyticus in oyster homogenates (MuntadaGarriga et al. 1995). Freezing of oysters at −40 °C and then storage for 8–10 weeks
achieved a 4- to 5-log reduction in the V. vulnificus population (Cook and Ruple
5 Shellfish Safety