ICAR AIEEA PG 2024 - Fisheries Science

In fish skeletal muscle, Cathepsin D is the major intracellular lysosomal endopeptidase belonging to the Aspartic acid protease family (active at acidic pH ~3.0–4.0). Cathepsins B, H, and L are cysteine/thiol proteases, and Cathepsin A is a serine carboxypeptidase.

Pre-rigor frozen fish still retains high levels of glycogen and ATP. During thawing, ice crystal disruption of the sarcoplasmic reticulum membrane triggers a sudden, massive release of Calcium ions ($\text{Ca}^{2+}$) into the sarcoplasm. In the presence of remaining ATP, $\text{Ca}^{2+}$ activates myosin ATPase, triggering severe, irreversible muscle contraction and drip loss known as 'thaw rigor'.

Gamma and electron beam irradiation in seafood preservation effectively damages microbial DNA without significantly affecting inorganic elements. Minerals (such as calcium, phosphorus, iron, and iodine) are chemically indestructible by ionizing radiation, whereas vitamins (especially thiamine and vitamin A) and polyunsaturated fatty acids (PUFA) are susceptible to free radical oxidation.

Aflatoxins are highly toxic, carcinogenic mycotoxins synthesized by molds belonging to the genus Aspergillus, predominantly Aspergillus flavus and Aspergillus parasiticus, which grow on improperly stored smoked and dried fish in humid tropical conditions.