*Enzymatic autolysis (reactions caused by the activities of the fish’s own enzymes)
*Oxidation (oxidation of unsaturated lipids)
*Microbial growth (metabolic activities of microorganisms)
Low temperature storage and chemical techniques for controlling water activity, enzymatic, oxidative, and microbial spoilage are the most common in the industry today.
Many different enzymes are present in living seafood species. They help build tissue, contract, and relax muscles, and digest food. Enzymatic spoilage is caused by the autolytic fish enzymes. Fishes are highly perishable than meat because of more rapid autolysis by fish enzymes, and favorable conditions for microbial growth due to less acid reactions.
Autolysis plays an important role in spoilage of fish. The enzymes involved in autolysis are many. However, phosphorylases, lipases, cathepsins and gut enzymes predominate.
The Rigor mortis is a physical effect on the muscle tissue of fish caused by chemical changes following the death. After the completion of rigor mortis, muscle stiffness gradually decreases accompanied by increase in pH, ending up in softening of muscle. This is followed by breakdown of proteins by enzymes. This process is called as autolysis.
Autolytic enzymes reduced textural quality during early stages of deterioration but did not produce the characteristic spoilage off-odors and off-flavors. Autolytic degradation can limit shelf-life and product quality even with relatively low levels of spoilage organisms. Enzymatic action also causes decomposition in the fish known as belly bursting. The belly bursting is caused by the action of digestive enzymes present in the gut of the fish.
In case of improper storage of whole fish, proteolysis is responsible for degradation of proteins and is followed by a process of solubilization. On the other hand, peptides and free amino acids can be produced as a result of autolysis of fish muscle proteins, which lead towards the spoilage of fish meat as an outcome of microbial growth and production of biogenic amines.
Fish spoilage: Enzymatic autolysis
