Fish products and Byproducts Technology

Unit 5- Hurdle technology in fish preservation

5.1.3. Basic aspects of Hurdle technology
Homeostasis and hurdle technology
Homeostasis is the tendency to uniformity and stability in the internal status of organisms. For instance, the maintenance of a defined pH is a prerequisite and feature of living cells, and this applies to higher organism as well as to micro organisms. In food preservation the homeostasis of microorganism is the key phenomena which deserves much attention, because if the homeostasis is disturbed by preservative factors (hurdles) in foods, they will not multiply, i.e they remain in the lag phase or even die, before homeostasis is repaired (re-established). Therefore food preservation is achieved by disturbing the homeostasis of micro organisms in a food permanently.
Metabolic exhaustion and Hurdle technology
Hurdles or preservative factors disturb the Homeostasis of microorganisms, and they try to repair them by every possible means, by doing so that they spend all the energy and die finally. This metabolic exhaustion leads to auto sterilization of foods. Due to auto sterilization hurdle technology foods, which are micro biologically stable, become safer during storage, especially at ambient temperature.
Stress reaction and Hurdle technology
Some bacteria become more virulent and resistant under stress, since they generate stress shock proteins. Synthesis of protective stress shock proteins induced by heat, pH, water activity, ethanol, oxidative compounds, etc. The various response of micro organisms under stress might hamper the food preservation and could turn to be problematic for the application of hurdle technology. Simultaneous exposure to different stresses will require energy-consuming synthesis of several or at least much more protective stress shock proteins which inturn may cause the micro organisms to become metabolically exhausted. Therefore, multi target preservation of fish could be the key to avoiding synthesis of of stress shock proteins which otherwise could jeopardize the microbial stability and safety of hurdle technology fish and fishery products.
Multi-target preservation
A synergistic effect could be achieved if the hurdles in a food hit, at the same time, different targets (e.g., cell membrane, DNA, enzyme systems, pH, aw, Eh) within the microbial cells and thus disturb the homeostasis of the micro organisms present in several respects. If so the repair of homeostasis and activation of stress shock proteins become more difficult. Therefore employing simultaneously different hurdles in the preservation of a particular food should lead to microbial stability. It is more effective to employ different preservative factors (hurdles) of small intensity than one preservative factor of large intensity.