Microbial spoilage of fish and fish products and its preservation

Fish is one of the most consumed seafood and it is a highly perishable food product. Fish and fish products are widely consumed as they are a good source of nutrition due to their high protein content, unsaturated fatty acids, especially omega-3 fatty acids.

The biological and chemical nature of fish leads to its deterioration after it is caught. The spoilage process starts within 12 hours. The deterioration occurs very quickly due to the metabolic activity of microorganisms, endogenous enzymatic activity (autolysis), and the chemical oxidation of lipids .

Fresh fish and shellfish are highly perishable products due to their biological composition. Under normal refrigerated storage conditions, the shelf life of these products is limited by enzymatic and microbiological spoilage. Therefore, particular care is required during harvesting and all along the supply chain in order to preserve nutritional attributes, to avoid contamination and loss and waste, and to deliver high quality fish products.

There are several mechanisms that make fish a highly perishable commodity. Some of them are:

  • Fish live underwater where the temperature is low and some microorganisms are adapted to low temperatures. These microorganisms, called psychrotrophs, can survive and grow in refrigerated conditions and cause spoilage of fish.
  • Fish contain a chemical called trimethylamine oxide (TMAO) that protects them from the protein-destabilizing effect of water pressure. When fish dies and its tissues get exposed to air, TMAO is degraded by bacteria into trimethylamine, which gives fish a strong, fishy odor.
  • Fish have a high water content (75–85%) and a high water activity (0.98–0.99) which makes them prone to microbial growth. Fish also have a low acidity (pH > 6) which favors the growth of spoilage and pathogenic bacteria.
  • Fish contain important nutritional and digestive proteins, essential amino acids, lipid-soluble vitamins, micronutrients, and highly unsaturated fatty acids. These compounds are susceptible to degradation by microorganisms and enzymes that result in undesirable changes in appearance, texture, flavor, and odor, reducing its quality.

In this article, we will discuss the three modes of fish spoilage: Oxidation, Enzymatic and Microbial spoilage. We will also describe the spoilage of different fish products and explain various preservation methods used to stop the spoilage of fish. We will conclude on the importance of preservation methods in extending the shelf life of fish and fish products.