मत्स्य प्रसंस्करण एवं मूल्य संवर्धन

Defects and spoilages of processed seafood products:

• Blue discoloration is a known defect in canned crab and lobster meat caused by the oxidation and complexation of hemocyanin copper with ammonia.
• Curding is a defect in canned salmon and tuna where coagulated sarcoplasmic proteins precipitate as an unsightly white curd on the surface of the fish.
• Dun spoilage is an aerobic fungal spoilage specific to salted and dried fish, caused by the halophilic xerophilic brown mould Sporendonema epizoum (Wallemia sebi) forming pepper-like dark brown/black spots on the surface. Because it is an obligate aerobe that attacks low-moisture dried products, it cannot occur inside commercially sterile, hermetically sealed canned products.
• Struvite formation is a defect in canned fish/crustaceans where magnesium ammonium phosphate crystals ($MgNH_4PO_4\cdot 6H_2O$) precipitate resembling broken glass.

Principles of fish preservation and seafood toxicology:
Statement (I) is true: Fish marinades are semi-preserved seafood products prepared by immersing fresh or salted fish in solutions containing acetic acid (vinegar) and edible salt (NaCl). The combination lowers pH below 4.5 and reduces water activity, effectively inactivating spoilage bacteria and tissue autolytic enzymes.
Statement (II) is true: Scombroid fish poisoning (histamine fish poisoning) frequently occurs following the consumption of improperly chilled scombroid fishes like tuna, mackerel, and bonito, whose dark muscle contains high levels of free L-histidine that bacterial histidine decarboxylase enzymes convert into toxic histamine.

Preservative additives in fish curing and drying:

• Sorbitol is a sugar alcohol used as a cryoprotectant in frozen surimi manufacturing.
• Polyphosphates are water-binding humectants used to prevent drip loss in frozen fish fillets and shrimps.
• Citric acid is an acidulant and metal-chelating antioxidant synergist.
• Potassium sorbate (salt of sorbic acid) is the primary permitted broad-spectrum antifungal and antimycotic food additive sprayed or dipped onto cured/dried fish products to inhibit mould growth and dun spoilage (Wallemia sebi / Sporendonema epizoum).