Fish spoilage: Enzymatic autolysis

Fish spoilage is a significant concern in the seafood industry, primarily driven by three fundamental mechanisms: enzymatic autolysis, oxidation, and microbial growth. Among these, enzymatic autolysis, driven by the activities of the fish's own enzymes, stands out as a principal contributor to the deterioration of fish quality.

Enzymatic autolysis in fish is accelerated compared to meat due to the presence of numerous enzymes that remain active postmortem. Phosphorylases, lipases, cathepsins, and gut enzymes are among the key players in this process. Rigor mortis, a natural consequence of death in fish, triggers a cascade of chemical changes in muscle tissue, leading to muscle softening and eventual breakdown of proteins by autolytic enzymes.

While enzymatic spoilage may not immediately produce off-odors or off-flavors, it significantly impacts the textural quality of fish during the early stages of deterioration. Even at low levels of spoilage organisms, enzymatic action can reduce shelf-life and compromise product quality. Notably, enzymatic degradation can manifest as "belly bursting," a phenomenon resulting from the action of digestive enzymes present in the fish's gut.

Proteolysis, a consequence of improper storage of whole fish, leads to the degradation of proteins and subsequent solubilization. Moreover, autolysis of fish muscle proteins yields peptides and free amino acids, providing substrates for microbial growth and the production of biogenic amines, further accelerating spoilage.

To combat enzymatic autolysis and preserve fish quality, various storage techniques and interventions are employed in the industry. Low-temperature storage inhibits enzymatic activity and microbial growth, while chemical methods control water activity and mitigate enzymatic, oxidative, and microbial spoilage.

In conclusion, understanding enzymatic autolysis is crucial for mitigating fish spoilage and maintaining product quality in the seafood industry. By employing effective storage techniques and interventions, we can prolong the shelf-life of fish products and ensure consumer satisfaction.
Understanding Fish Spoilage: Enzymatic Autolysis and Its Impact

Spoilage of fish: Definition and characteristics

Fish is highly perishable due to high moisture content, availability of the nutrients for the growth of microorganisms and ambient temperature. Fish spoilage results from three basic mechanisms:
*Enzymatic autolysis (reactions caused by the activities of the fish’s own enzymes)
*Oxidation (oxidation of unsaturated lipids)
*Microbial growth (metabolic activities of microorganisms)

One-fourth of the world's fish supply and 30% of landed fish are lost through microbial activity alone.

Fresh fish spoilage can be very rapid after it is caught. The spoilage process (Rigor mortis) will start within 12 h of their catch in the high ambient temperatures of the tropics.

Spoilage of fish can be considered as any change that render the product unacceptable for human consumption. When fish dies, the biochemical changes responsible for anabolism stop. As an inevitable consequence of this process of cessation of anabolism, catabolism starts bringing spoilage to fish flesh. The digestive enzymes still being active, instead of acting on the food present inside the gut, begin to digest tissue components such as lipids, carbohydrates and proteins. This process is called “autolysis”.

One important action determining the onset of spoilage in freshly caught fish is rigor mortis, the stiffening of the body. Usually, this develops within 1-7 hours after death. Rigor mortis sets in and passes quickly in very active fish but slowly in inert fish.

Characteristics of spoiled fish
*The flesh is soft to touch. When the flesh is pressed it leaves a permanent indentation.
*The skin looks dull and has slime on the surface.
*The gills look brownish.
*It gives a bad smell.

With the ever-growing world population and the need to store and transport the food from one place to another where it is needed, food preservation becomes necessary in order to increase its shelf life and maintain its nutritional value, texture and flavour.
Spoilage of fish: Definition and characteristics