63. Quick freezing process in shellfish: Total volatile basic nitrogen and algal biotoxins values in scallops frozen on board in Argentina

Freezing on-board has made it possible to expand commercial fishing to new species that were not widely utilized until the late 1970s. Shellfish are one of the commercial fishery products that can be harvested from natural beds located in far offshore ocean areas by factory trawler fleet where shellfish is processed and frozen quickly. In this way large volumes of frozen products can be obtained with optimal commercial quality and good sanitary conditions. In Argentina, scallop harvesting followed by on board quick freezing started in 1996. The aim of this presentation is to describe the quick freezing process applied by factory trawlers to scallops harvested from the Argentine Sea and to report the results obtained from the total volatile basic nitrogen (TVB-N) and biotoxin analysis of samples of these products. These data were collected at the National Animal Health and Agri-Food Quality Service (SENASA)-Regional Laboratory at Mar del Plata city, Argentina, and they cover a 14-year time span, from 1997 to 2011. Captured specimens were selected by size according to commercial criteria, and those smaller than 55mm were returned to the sea within 5–10min of capture. Scallops were water vapor-opened in order to separate the adductor muscle from the rest of the soft tissues (viscera, gonads and mantle). Adductor muscles enter a freezing tunnel where a fast flow of cold air induces a shock freezing of the tissue (at −26°C/−30°C), thus allowing to obtain in some 20min individually quick frozen adductor muscle units. The time elapsed since scallops selected by size enter the processing line until the final commercial product is stored is about 30min. This short processing time allows an optimal preservation of all organoleptic characteristics and at the same time prevents phytoplankton biotoxin diffusion from viscera (the primary storage region in the live animal) to muscle. TVB-N determinations were carried out by the Antonacopoulos method. The mean values recorded in the quick frozen scallop muscles ranged from 8.0 to 9.0mg%. Measurements performed in muscle tissue from scallops stored in freezing chambers (−18°C) gave TVB-N values between 12mg% and 13mg%, whereas TVB-N values in adductor muscles stored at 4°C were above 30mg%. Biotoxin determination was performed by the mouse bioassay (MBA) employing the AOAC 959.08 method for Paralytic Shellfish Poison (PSP) and the procedure described by Yasumoto et al. in 1986 for Diarrheic Shellfish Poison (DSP). None of the adductor muscle samples tested had detectable PSP or DSP levels. This was so even on occasions when high PSP concentrations were detected in whole scallop samples. Our results show that the quick freezing process on board Argentinian factory trawler ships are suitable for obtaining a commercial product that fully retains freshness parameters as well as the sanitary characteristics required for human consumption.