High pressure processing at ultra-low temperatures: Inactivation of foodborne bacterial pathogens and quality changes in frozen fish fillets

High pressure processing (HPP) at ultra-low temperatures was conducted against Listeria monocytogenes and Salmonella enterica in frozen pink salmon fillets. Quality changes, such as drip loss, color and odor attributes were recorded in non-inoculated pollock, pink salmon and tuna fillets. Pressures at 250 and 400 MPa were applied from 0.5 to 10 min. Reductions up to 3.5 log cfu/g were recorded for the treatments performed at -32 degrees C, in contrast to -50 degrees C where the reductions were only up to 1.5 log cfu/g. Higher pressure did not cause higher reduction. It was apparent that the main factor contributing to the bacterial inactivation is the phase transition of ice structure from I to III, in contrast to transition from I to II. Drip loss was not higher than the expected with HPP at temperatures above 0 degrees C, while color changes were negligible. Finally, the odor evaluation did not exhibit considerable differences between untreated and treated samples. Industrial relevance: High pressure processing at ultra-low temperatures is a promising treatment for bacterial inactivation and retention of quality attributes of frozen fish. Treatment at 250 MPa for only 3 min at temperatures just below -22 degrees C, which is feasible and affordable, caused a more than 3-log reduction against Listeria monocytogenes and Salmonella enterica, without affecting considerably the quality properties. Thus, the application of low pressure and shorter processing times gives a great potential for industrial application for frozen fish or fish that wouldn't be undesirable to freeze before pressurization.

Automated summary

The study demonstrated that high-pressure processing at ultra-low temperatures is effective in reducing bacterial counts in frozen pink salmon fillets without significantly affecting quality attributes. Results showed that higher pressure does not necessarily lead to higher reduction rates, and temperature plays a significant role in bacterial inactivation effects.