# Non-Thermal Methods for Ensuring the Microbiological Quality and Safety of Seafood
## 2 High Hydrostatic Pressure--HHP
### Microbiological Quality and Safety
(2007) [67] reported that HHP at 450 and 600 MPa reduced the total aerobic counts by 4 to 6-log CFU/g on rainbow trout and mahi-maink filties during cold storage at 4 \({}^{\circ}\)C. In another recent study, when salmon, cod, and mackerel fish were treated with 200 or 500 MPa for 2 min, in compliance with other studies [50; 68; 69], it was found that the shelf life of the fish extended during storage at 0.5 \({}^{\circ}\)C [70]. [PERSON] et al. (2014) [47] illustrated microbial reduction in 2-log CFU/g caused by HP treatment at 400 MPa for 30 min on sea bass (_D. labrax_) filties and, as reported, might result in extended shelf life. Additionally, [PERSON] et al. (2019) [48] found that treating sea bass filites at a higher pressure for less time (600 MPa; 5 min; 25 \({}^{\circ}\)C) led to 5-log CFU/g reduction of TVC during storage at 2 \({}^{\circ}\)C, and the shelf life of HP-treated sea bass was extended up to 2 months, compared to 11 days for the untreated control filties. As we mentioned earlier, the successful combination of HHP with other hurdles can lead to the successful inactivation of spoilage and pathogenic bacteria. The shelf life of high added value lobster tails increased after treatment with HHP (150 or 300 MPa, 10 min) and subsequent sous vide cooking at 65 \({}^{\circ}\)C, stored under refrigeration up to 28 days [57]. [PERSON] et al. (2020) [71] found another successful combination to increase the microbial shelf life of Coho Salmon (O. _isisutch_). They focused on applying HHP (150 MPa, 5 min) combined with CO\({}_{2}\) (50, 70, 100%) atmosphere and found that the salmon's shelf life increased in parallel with the elevated CO\({}_{2}\) levels. HP treatment and CO\({}_{2}\) had no synergistic effect. The increased shelf life attributed to the ability of CO\({}_{2}\) to inhibit aerobic bacterial growth [72], while [PERSON] et al. (2010) [53] also found that HP treatment \(<\) 200 MPa cannot extend the shelf life of chilled stored Coho salmon. When cold-smoked salmon fillets were treated with HHP at 600 MPa for 120 s in combination with nisin (10 \(\mu\)g/g) it resulted in 3.99 log CFU/g reduction in _L. innocua_, without any apparent synergistic effect [73]. [PERSON] et al. (2020) [28] investigated the synergistic effect of HHP at 200 MPa (15 min) with liquid smoke extracts and freezing and resulted in a more than 5-log reduction in CFU/g of the inoculated _L. monocytogenes_ strain on the surface of hot smoked trout fillet. In seafood products, the effects of HP processing on the inactivation of foodborne microorganisms are better documented for pressure treatments above 0 \({}^{\circ}\)C. However, the application of HHP at subzero temperatures to inactivate bacterial pathogens in seafood has been carried out, showing encouraging results. Satisfactory bacterial reduction with pressures as low as 200 to 250 MPa have been obtained [36; 56]. The effectiveness was attributed to the transition of ice structure I to III occurring at temperatures below \(-\)25 \({}^{\circ}\)C. Regarding subzero temperatures, combined treatments with HHP led to a high reduction in inoculated _L. monocytogenes_ on the surface of smoked salmon up to 4.89 log CFU/g (200 MPa, \(-\)18 \({}^{\circ}\)C, pH 4.5) [74]. The authors concluded that the bacterial reduction observed was due to the synergistic effect of pressure, temperature, and pH.