Fish products and Byproducts Technology

Unit 1- Principles of Fish Preservation

1.5.4. Curing (drying, salting and smoking)
Unlike canning (which engenders the destruction of micro-organisms and their spores) curing preserves by rendering the medium unsuitable environment for microbial propagation. Increasing the concentration of soluble substances in the medium either by abstracting water or by causing soluble substances to diffuse in (salting, brining or sugar curing) are the principal means of accomplishing this. In addition to concentrating the soluble substances by brining and dehydration, smoking preserves by depositing bacteriostatic chemicals like formaldehyde and phenols in the system.
The addition of salt is more effective for weight than the addition of sugar because salt ionizes to a sodium cation and a chloride anion each of which attracts a sheath of water molecules. These ionically associated water molecules are unavailable for use by micro-organisms and there is a tendency for the ionic forces to pull water molecules from the microbial cells dehydrating them to the point where they die or sporulate and lie dormant. Sucrose also withdraws water molecules from the system and holds them by hydrogen bonding. However, far fewer molecules become bound or unavailable in this way than is the case for an equal mass of sodium chloride. This availability of water in the system for use by micro organisms directly relates to the effectiveness of preservation and can be represented physically by the water activity (a_w).