Fisheries Post-Harvest Technology and Management
This domain covers spoilage, preservation, quality assessment, and the management systems that protect product safety from harvest to market. Questions combine biochemistry (rigor, autolysis, bacterial action) with processing calculations and HACCP principles.
Spoilage sequence and indices
- Rigor mortis: ATP depletion stiffens muscle; handling during rigor causes gaping and soft texture.
- Autolysis: endogenous enzymes break down proteins and lipids, softening tissue.
- Bacterial spoilage: bacteria reduce TMAO to trimethylamine (TMA), and TVB-N rises with volatile amines; K-value tracks ATP degradation.
- Histamine forms from histidine in scombroid fish and is heat-stable, so cooking does not make spoiled fish safe.
Preservation principles
Chilling slows bacterial growth; freezing halts growth but not enzymes; salting, drying, and smoking lower water activity; canning relies on a heat process (botulinum cook) and hermetic sealing.
Worked example
A cold-smoked sample contains 4 g salt and 65 g moisture per 100 g. Water-phase salt = salt ÷ (salt + moisture) × 100 = 4 ÷ 69 × 100 = 5.8%. That exceeds the 3.5% WPS target for cold-smoked fish, but the sample should still be checked for pathogens, because WPS is a hurdle, not a guarantee.
Traps that cost marks
Believing freezing kills spoilage bacteria; treating TVB-N and TMA as the same test; using smell alone as a safety decision; confusing HACCP with end-product testing rather than a preventive system; and ignoring temperature abuse before icing.