Criticism of the purification process of bivalve shellfish. Literature review and our industrial research experiences

Worldwide bivalve shellfish production reached 14.4 million tons in 2011, of which about 12.9 million tons came from aquaculture; therefore, this sector has an important role in ensuring food to humans and good occupational opportunities. Bivalves are obligate filter feeders, gaining nourishment from microalgae, bacteria and organic particles present in the surrounding water. In this way, they can also accumulate chemicals, marine biotoxins, bacteria and viruses that are pathogenic for humans. In order to protect consumers, two main actions are applied, although there are some differences depending on the country of production: monitoring of growing areas, and the treatment of bivalves after harvesting. Adequate heat treatments ensure the elimination of viruses and pathogenic bacteria, but they are obviously not applicable to bivalves when they are commercialized alive. In this case, to allow microbial contaminants to be purged, there are two alternatives: natural depuration in less-contaminated areas, the so-called “relaying”; and “controlled depuration” by immersion in tanks containing clean seawater, which is also known as purification. Depuration is the preferred option for bivalve shellfish sold alive, and is practiced extensively throughout the world, including Europe, North America, Asia and Australia; however, it is generally accepted that the results of this treatment are only adequate for shellfish with moderate levels of fecal contaminants, as it has very limited effectiveness on viruses and marine bacteria, such as Vibrio spp. This represents a criticism of the assurance of food safety, given that viruses, particularly those in the genus Norovirus (NoV) and Hepatitis A virus (HAV), as well as pathogenic vibrios, such as V. parahaemolyticus and V. vulnificus, are the most common illness-causing agents when shellfish are consumed raw, lightly cooked or have been cross-contaminated. This chapter presents an overview of the state-of-the-art analyses for the purification process, including our industrial research experiences, the sanitary relevance of the most threatening contaminants of bivalves, NoV, HAV, V. parahaemolyticus and V. vulnificus, and the advances in analytical methods for the control of such pathogens.