Processing fresh mussels (M. galloprovincialis) by sous vide technology: effect on the microbiological characteristics

Sous-vide cook-chilled (SVCC) is used to describe food that has been vacuum-packed and given mild heat treatment under controlled conditions of time and temperature and subsequently rapidly cooled and stored at chilled conditions until heated before serving (Rhodehamel, 1992; Hansen et al., 1995). Limited studies reported the application of this process in aquacultural products (Espinosa et al., 2016; Shakila et al., 2009), such as trout fillets (Gonzalez-Fandos et al., 2004), 2009) and carp (Can, 2011) and there are no reports on the opportunities to apply such process to molluscs. The aim of the present research was to test the effect of the application of the SVCC technique on fresh mussel microbiological characteristics. Commercial Mediterranean mussels (M. galloprovincialis) were individually inoculated with 100 µl suspension of Pseudomonas spp.(107 UFC/mL), packaged in a Oriented Polyamide/Polypropylene (OPA/PP, Orved S.p.A., Musile di Piave, VE, Italy) pouch and heat-sealed before being submitted to heat treatment in a steam oven (Lanoix Ali S.p.A., Treviso, Italy). After treatment, mussel pouches were immediately chilled at 3°C. Six different time temperature combinations (75/85/95 °C for 10 and 30 min), were tested in triplicate (3 specimens/group) and compared to raw and inoculated mussels. Total aerobic bacterial count (TBC), lactic acid bacteria (LAB), anaerobic sulphite-reducing clostridia, Pseudomonas spp. and pH were determined. All time/temperature combinations resulted in a substantial reduction of the Pseudomonas spp. population (<1 log CFU/g) both in raw (4.9 log CFU/g) and experimentally inoculated (5.7 log CFU/g) mussels. The homogenate pH values (6.22) resulted not affected by the heat treatment. Such results were confirmed on natural bacterial load of mussel. A TBC reduction (2.4 log and 3,5 log, respectively) was registered after treatment at 85 °C both for 10 and 30 min, while the highest reduction (4.8 log) was observed at 95 °C for 10 min confirming the efficacy of sous vide cook treatments even for fresh mussels. The technological and sensorial traits, as well the stability of these products both under refrigeration and thermal abuse conditions during storage need to be evaluated.