Techniques based on the chemical control of microbial activity and loads
These techniques are designed to add anti-microbial agents or decrease the fish muscle pH to levels that are inhibitory to microbial growth and proliferation. Most bacteria stop multiplying at pH less than 4.5. The decrease of pH is obtained by fermentation, marinades or by adding acids (acetic, citric, lactic, etc.) to fish products. In addition to the decrease in fish pH, fish fermenting lactic bacteria also produce anti-microbial compounds such as nisin, which improve preservation. This technique is often referred to as bio-preservation. Other preservatives include nitrites, sulphites, sorbates, benzoates or natural ones such as essential oils.
Techniques based on the control of the oxydo-reduction potential
Some spoilage bacteria and lipid oxidation require oxygen. Reducing the oxygen around fish will increase its shelf life. This is possible by vacuum packaging or by controlling or modifying the atmosphere around the fish. Specific combinations of CO2, O2 and N2 characterize controlled (CA) or modified atmosphere (MA). Vacuum packaging, CA and MA storage are often combined with refrigeration for fish preservation.
Combination of several preservation techniques
Two or more of the above-described techniques can be combined to improve preservation efficiency while reducing undesirable effects such as the denaturation of nutrients by severe heat treatments. Combinations already in use include pasteurization-refrigeration, CA (or MA)-refrigeration, salting-drying, salting-smoking, drying-smoking and salting-marinating. Other process combinations are currently being developed along the “multiple hurdle theory”.