Following a request from the European Commission, the Panel on Biological Hazards (BIOHAZ Panel) was asked by the European Food Safety Authority to deliver a Scientific Opinion on the evaluation of heat treatments, different from those currently established in the EU legislation, that could be applied to live bivalve molluscs from B and C production areas, that have not been submitted to purification or relaying, in order to eliminate pathogenic microorganisms.
The current EU rules state that live bivalve molluscs from B and C production areas that have not been submitted for purification or relaying may be sent to a processing establishment, where they must undergo treatment to eliminate pathogenic microorganisms. The permitted treatment methods are (a) sterilisation in hermetically sealed containers and (b) heat treatments involving: (i) immersion in boiling water for the period required to raise the internal temperature of the mollusc flesh to not less than 90°C and maintenance of this minimum temperature for a period of not less than 90 seconds (s); (ii) cooking for 3 to 5 minutes (min) in an enclosed space where the temperature is between 120 and 160°C and the pressure is between 2 and 5 kg/cm2, followed by shelling and freezing of the flesh to a core temperature of –20°C; and (iii) steaming under pressure in an enclosed space satisfying the requirements relating to cooking time and the internal temperature of the mollusc flesh mentioned under (i).
EFSA is requested to evaluate, in the light of the current EU and international rules, different time–temperature conditions from those currently established in the EU legislation, which could be applied to live bivalve molluscs from B and C production areas that have not been submitted for purification or relaying in order to eliminate pathogenic microorganisms. It was clarified by the EC that the heat treatment of relevance (and for which alternative time–temperature conditions will be evaluated) is the achievement of at least 90°C for at least 90 s in the mollusc flesh. The focus of the assessment is on the thermal inactivation of viruses. The permitted heat treatments were not aimed at eliminating bacterial spores as these would require a more profound heat treatment. Furthermore the effects of heating on phycotoxin concentration in bivalve molluscs are outside the remit of this assessment.
Hazard identification was performed to list the most important viral hazards associated with bivalve molluscs. The hazard analysis used as data sources the EU food-borne outbreak data, the EU Rapid Alert System for Food and Feed (RASFF) data and scientific literature. It was concluded that the most important viral hazards associated with the consumption of bivalve molluscs are Norovirus (NoV) and Hepatitis A virus (HAV) acquired from human faecal pollution of bivalve production areas. Prevalence and concentration for NoV and HAV in bivalve molluscs from commercial production areas can vary significantly depending on the geographic region, the period of the year, the prevalence of infection in the local population, the effectiveness of sewage treatment systems, and the local environmental conditions. For example bivalve molluscs imported from HAV endemic areas, for which there is little data, may contain much higher levels of virus than non-endemic European areas. The current 90°C for 90 s requirement applies to a broad range of bivalve molluscs from Class B and C production areas in the EU and third countries importing into the EU, which will likely vary substantially in prevalence and concentrations of the viral hazards. Little data exists for virus concentrations in the worst case, i.e. molluscs from Class C areas. Epidemiological data indicate that human outbreaks with viruses have not been reported following consumption of commercially heat-treated bivalve molluscs. In contrast, viral outbreaks have been associated with raw products.
Among NoV and HAV, the latter was most appropriate to evaluate the heat treatment of bivalve molluscs because NoV is not effectively culturable and data on surrogates may not be representative in evaluating thermal resistance. The quantity of available data limited the modelling options for the effect of temperature on the HAV thermal inactivation. A HAV thermal inactivation model based on data in molluscs matrices during isothermal heat treatment was developed. The model estimates for the mean D-value at 90°C and the z-value for HAV inactivation in bivalve molluscs were 54 s (0.9 min) and 27.5°C, respectively. Evaluation of the model performance using independent non-isothermal temperature studies with whole bivalve molluscs showed that the observed HAV inactivation is in general higher than predicted and was in most cases within the quantified prediction intervals. The limited data suggest that under the conditions and matrices studied HAV is generally more heat tolerant than NoV surrogates. The estimated z‑value was used to identify equivalent time–temperature profiles to the ‘notional’ heat treatment of 90°C for 90 s without considering the effect of heat-up and cool-down times on virus inactivation leading to the same log reduction of HAV. The model indicated a range of equivalent processes between 72°C and 100°C such as 72°C for 407 s (246–1,879 s) (mean value and confidence interval (CI)), 76°C for 291 s (197–956 s), 80°C for 208 s (157–487 s), 86°C for 126 s (113–177 s), 94°C for 64 s (46–72 s), and 98°C for 46 s (23-58 s).
The ‘notional’ profile of 90°C for 90 s is theoretical. As confirmed by industrial temperature profiles, in practice, there is a heat-up and cool-down time that will further enhance the safety of the final product. The model showed that realistic 90°C for 90 s processes, that that include a heat-up and cool-down time can lead to significant variations in HAV log reduction depending on the process design (rate of temperature increase and decrease). The evaluation of alternative equivalent heat treatments that could be applied to live bivalve molluscs based on ‘realistic’ time–temperature profiles would be facilitated by the establishment of a Performance Criterion (PC), which is the required log reduction during heat treatment. A risk assessment case study was developed for illustrative purposes only to show the relationship between a PC for the reduction of HAV during heat treatment of bivalve molluscs and the human risk at consumption. If risk managers establish an Appropriate Level of Protection (ALOP), this can be translated to a PC and a Process Criterion (PrC) using the HAV thermal inactivation model. An F-value (the equivalent processing time of a hypothetical isothermal process at a reference temperature) is a more appropriate PrC than the current time–temperature combination (i.e. 90°C for 90 s) since it takes into account the whole time–temperature profile during heat treatment. The use of an F-value allows the food business operators (FBOs) to best balance product safety and quality. The estimated reduction of HAV for two industrial temperature profiles commercially used in the EU during bivalve mollusc heat treatments was > 4 logs. These two examples indicate that it is possible to design a commercial process to achieve such log reductions.
Uncertainties for the equivalent thermal processes and the F-values were analysed. The uncertainty related to the model fitting is quantitatively expressed for both the equivalent times and the F-value using the CIs of the models’ parameters. Apart from model fitting there are several additional uncertainty sources, which can lead to under or overestimation of HAV inactivation. The evaluation of model performance using independent non-isothermal temperature studies with whole bivalve molluscs showed that the observed HAV inactivation is in general higher than predicted and was in most cases within the quantified prediction intervals.
It is recommended to generate more data to improve the HAV thermal inactivation model (strain and food matrix effects) and reduce the uncertainty. In addition it is recommended to develop a Quantitative Risk Assessment (QRA) model for viruses, both Norovirus and HAV, in bivalve molluscs taking into account the differences across classification classes (A, B or C) and geographical regions with differing endemicity of HAV in human populations and sewage treatment, to provide necessary information for the establishment of a PC for heat treatment. Such a QRA would require the additional collection of data for virus prevalence and levels of contamination in raw/live molluscs, dose response relationship, consumption data, consumer handling, and variability in the heat processing.