# Mechanistic Insights into Fish Spoilage and Integrated Preservation Technologies
## 3 Preservation Technologies and Optimization
### Physical Preservation
#### 3.1.1 Low-Temperature Preservation  
Low-temperature preservation is an essential method for extending the shelf life of fish by significantly slowing down the enzymatic and microbial activities responsible for  
\begin{table}
\begin{tabular}{l l l l} \hline \hline _Bacteria_ & **Major Spoilage Metabolites** & **Typical Spoilage Characteristics** \\ \hline _Pseudomonas_ spp. & Amines, aldehydes, ketones & Sweet, fruity odors, slimy texture \\ _Shewanella putrefaciens_ & TMA, H\({}_{2}\)S, sulfides & Strong ammonia-like, rotten-egg odors \\ _Photobacterium phosphorem_ & TMA & Fishy, ammonia odors \\ _Aerononas_ spp. & Amines, organic acids & Sour, off-odors, slime formation \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview of fish spoilage microbes and their sensory consequences.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Method** & **Parameter** & **Storage Duration** & **Microbial Reduction** & **Sensory Impact** \\ \hline Refrigeration & 0–4 \({}^{\circ}\)C & 3–9 days & \(\sim\)1 log CFU/g & Maintains fresh texture; short-term \\ Super-Chilling & \(-\)0.5 to \(-\)2.8 \({}^{\circ}\)C & 10–14 days & \(\sim\)2 log CFU/g & Excellent texture; minimal \\ Freezing & \(\leq\)\(-\)18 \({}^{\circ}\)C & 6–12 months & \(\sim\)5 log CFU/g & Potential drip loss; texture \\ High-Pressure & 300 MPa, 3 min & 21–28 days & \(>\)3 log CFU/g & Good texture; slight \\ Processing & & & & firmness change \\ Pulsed Electric Fields & 1–3 kV/cm & 7–14 days & \(\sim\)2 log CFU/g & Negligible sensory \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparative summary of physical preservation methods for fish.  
spoilage. This technique includes refrigeration, super-chilling, and freezing, each of which operates through distinct mechanisms to maintain the quality of fish.  
Refrigeration  
Refrigeration, which involves maintaining fish at temperatures just above freezing, typically between 0 \({}^{\circ}\)C and 4 \({}^{\circ}\)C, is one of the most common methods used to slow down spoilage processes. Refrigeration systems use stainless-steel tunnel or spiral chillers equipped with distributed evaporator coils and variable-speed fans to maintain uniform airflow (1-2 m/s) across trays of fish; coil spacing, airflow ducting, and insulation ensure \(\pm\)0.5 \({}^{\circ}\)C temperature control. This method significantly inhibits microbial growth and enzymatic activity but does not stop them entirely. The growth of psychotrophic bacteria, such as Shewanella putrefaciens, which are major contributors to spoilage, is considerably slowed at 0 \({}^{\circ}\)C compared to their optimal temperature, thus reducing spoilage rates. Additionally, the activity of autolytic enzymes responsible for breaking down proteins, lipids, and other molecules is reduced, preserving the texture and flavor of the fish [20]. Immediate icing of fresh fish is crucial to maximize shelf life, as delays can lead to rapid spoilage [51]. Methods like chilled seawater (CSW) and refrigerated seawater (RSW) provide uniform cooling and enhance shelf life better than ice alone due to the anaerobic conditions created.