289
harvested from more heavily contaminated areas (Singh and Nagalakshimi 2013).
Other studies have shown that it is more difficult to remove enteric viruses such
as hepatitis A virus (HAV) and norovirus (NoV) by purification from the infected
oysters (Hernroth and Allard 2007; Ueki et al. 2007; Mcleod et al. 2009; Correa
et al. 2012; Neish 2013).
High pressure treatment has been reported to be promising for hepatitis A virus
(HAV) and norovirus inactivation, and treatment of 460 MPa at room temperature
has been found to be sufficient to inactivate the 7 log10 PFU virus stock of HAV
(Kingsley et al. 2002). Inactivation effects of HHP on human viruses found in the
tissues of oysters, mussels, and clams have been shown (Prapaiwong et al. 2009;
Kingsley 2013, 2014). Under 350–400 MPa high pressure processing (HPP) at
8.7–10.3 °C for 1 min resulted in a 6-log reduction of hepatitis A (Calci et al. 2005).
Enteric viruses are more resistant to inactivation in water sources and are
removed slowly, or not at all, from bivalves by depuration process (La Bella et al.
2017). Methods such as depuration to remove bacterial pathogens in bivalve have
been used successfully, whereas had little effect on viral contamination. In a study,
after a 48-h depuration, the bacterial levels of the oyster decreased by 95%, while
the Norwalk virus levels only decreased by 7% (Schwab et al. 1998).
Many enteric human viruses, such as Hepatitis A and Norwalk, have been
reported to be heat resistant and that viruses can survive when mild cooked (Millard
et al. 1987; Peterson et al. 1978). However, there are studies reported that an effective cooking process inactivates viruses. Flannery et al. (2014) reported that domestic cooking practices based on shell opening alone do not inactivate infectious virus
in mussels, however, cooking mussels at high temperatures is effective to reduce
infectious virus concentrations and the risk of illness in consumers. In another
study, cooking for 3 min at >85 °C was found to be sufficient to inactivate poliovirus
and hepatitis A in clams (Millard et al. 1987). Lees (2000) reported that cooking
shellfish is an effective method for norovirus decontamination and at least 90 s of
heat treatment at 90 °C will be sufficient. However, a balanced heat treatment should
be applied to protect the sensory quality of shellfish (Richards et al. 2010).
5.3 Biotoxins
Some species of Cyanobacteria (blue-green algae) and Pyrrophyta (dinoflagellates)
produce toxic compounds which are not poisonous for fish but for human. Filterfeeding shellfish such as clams and mussels accumulate the poisons from the dinoflagellates when feeding on them. They are normally eaten whole, including the
intestinal tract, and raw or following a very mild heat treatment (Lees 2000). Marine
biotoxins are a naturally occurring phenomenon that is not associated with sewage
contamination of coastal waters but is produced by Dinoflagellates and diatoms
(Gosling 2015). The marine biotoxins comprise many distinct compounds, all produced by species of naturally occurring marine algae. The algae are at the bottom of
the marine food chain. Consequently, the biotoxins produced by some algae are
5.3 Biotoxins
harvested from more heavily contaminated areas (Singh and Nagalakshimi 2013).
Other studies have shown that it is more difficult to remove enteric viruses such
as hepatitis A virus (HAV) and norovirus (NoV) by purification from the infected
oysters (Hernroth and Allard 2007; Ueki et al. 2007; Mcleod et al. 2009; Correa
et al. 2012; Neish 2013).
High pressure treatment has been reported to be promising for hepatitis A virus
(HAV) and norovirus inactivation, and treatment of 460 MPa at room temperature
has been found to be sufficient to inactivate the 7 log10 PFU virus stock of HAV
(Kingsley et al. 2002). Inactivation effects of HHP on human viruses found in the
tissues of oysters, mussels, and clams have been shown (Prapaiwong et al. 2009;
Kingsley 2013, 2014). Under 350–400 MPa high pressure processing (HPP) at
8.7–10.3 °C for 1 min resulted in a 6-log reduction of hepatitis A (Calci et al. 2005).
Enteric viruses are more resistant to inactivation in water sources and are
removed slowly, or not at all, from bivalves by depuration process (La Bella et al.
2017). Methods such as depuration to remove bacterial pathogens in bivalve have
been used successfully, whereas had little effect on viral contamination. In a study,
after a 48-h depuration, the bacterial levels of the oyster decreased by 95%, while
the Norwalk virus levels only decreased by 7% (Schwab et al. 1998).
Many enteric human viruses, such as Hepatitis A and Norwalk, have been
reported to be heat resistant and that viruses can survive when mild cooked (Millard
et al. 1987; Peterson et al. 1978). However, there are studies reported that an effective cooking process inactivates viruses. Flannery et al. (2014) reported that domestic cooking practices based on shell opening alone do not inactivate infectious virus
in mussels, however, cooking mussels at high temperatures is effective to reduce
infectious virus concentrations and the risk of illness in consumers. In another
study, cooking for 3 min at >85 °C was found to be sufficient to inactivate poliovirus
and hepatitis A in clams (Millard et al. 1987). Lees (2000) reported that cooking
shellfish is an effective method for norovirus decontamination and at least 90 s of
heat treatment at 90 °C will be sufficient. However, a balanced heat treatment should
be applied to protect the sensory quality of shellfish (Richards et al. 2010).
5.3 Biotoxins
Some species of Cyanobacteria (blue-green algae) and Pyrrophyta (dinoflagellates)
produce toxic compounds which are not poisonous for fish but for human. Filterfeeding shellfish such as clams and mussels accumulate the poisons from the dinoflagellates when feeding on them. They are normally eaten whole, including the
intestinal tract, and raw or following a very mild heat treatment (Lees 2000). Marine
biotoxins are a naturally occurring phenomenon that is not associated with sewage
contamination of coastal waters but is produced by Dinoflagellates and diatoms
(Gosling 2015). The marine biotoxins comprise many distinct compounds, all produced by species of naturally occurring marine algae. The algae are at the bottom of
the marine food chain. Consequently, the biotoxins produced by some algae are
5.3 Biotoxins