Post harvest
fatty acids, in contrast to mammals which contain a higher percentage of omega-6 fatty acids compared with the omega-3 fatty acids found in marine species. The omega-3 fatty acids are good for cardiovascular health, but they are also much more susceptible to oxidizing and turning rancid during refrigerated and frozen storage.
Refrigerated Storage: Microorganisms are found on all surfaces (skin and gills) and in the intestines of live fish or fresh fish. The total numbers of microorganisms vary greatly. There are several different types of spoilage bacteria, but one of the main types of spoilage bacteria belong to the genus Pseudomonas and can be found on meat, poultry, seafood and milk and dairy products. Spoilage bacteria are generally harmless, but can cause changes in the color, flavor, odor, and texture of food. In contrast, pathogenic bacteria are illness-causing bacteria that can produce toxins or cause infections.
Problem Unpreserved raw fish and unpasteurized cooked fish and fishery products spoil rapidly during refrigerated storage. Solution Maintaining low constant storage temperatures. First-in First-out (FIFO) management schemes to shorten the time fish are kept in refrigerated storage. A trained workforce that understands the importance of following Good Manufacturing Practices (GMPs) and having and following Sanitation Standard Operating Procedures (SSOPs) and implementing following, and monitoring the 8 Key Sanitation Conditions and Practices mandated by the USFDA. (NOTE: Packaged products such as refrigerated unpreserved raw fish and refrigerated unpasteurized cooked fishery products require a film with a minimum Oxygen Transmission Rate [OTR] of 10,000 cc/ m2/24hr or 3,000 cc/m2/24hr, or higher to prevent formation of toxin from C. botulinum).
Effects of Freezing Method and Frozen Storage on Quality of Fish Storage at 0°F (-18°C) is satisfactory for maintaining adequate shelf life for most frozen foods. At that temperature, chemical changes that degrade food quality occur at a slower rate which eventually terminates shelf life. High barrier packaging films for frozen product and lower constant storage temperatures will help to lengthen the shelf life of these type products. Freezing does not destroy all microbes present, but temperatures below about +15°F (-9.4°C) preclude microbial growth, as the water activity (Aw) at this temperature is 0.90. However, enzymatic and non-enzymatic chemical reactions occur even at 0°F (-18°C). Q10 Effect The effect of temperature on the biochemical reaction rate is called the temperature accelerating effect. (i.e., Temperature Accelerating Factor: 66 »
Q10). The biochemical reaction rate is increased 2-3 fold when temperature is increased by 10°C (18°F). Conversely, the reaction rate is reduced 2-3 fold when temperature is decreased by 10°C (18°F). Problem Changes in fish texture, lipid (fat) oxidation, loss of pigment color, etc., are caused by a combination of dehydration, ice crystal formation, increased extracellular salt concentrations, etc. Dehydration can be caused by the removal of water during a slow freezing process, along with poor packaging, and low humidity levels in the room. Large ice crystals form during a slow freezing process and fluctuating storage temperatures by diffusion of water from the surrounding muscle fibers. These large ice crystals distort cells and muscle fibers, and create spaces in between the muscle fibers. The large ice crystals are formed during slow freezing, because the cell exteriors cool faster than the cell interiors. During this slow freezing of extracellular water, extracellular salt concentrations may increase as much as tenfold in the unfrozen solute. The higher extracellular salt concentrations will osmotically draw intracellular water into extracellular spaces causing extracellular space expansion. Solutions A high barrier packaging film to prevent oxygen transmission and dehydration (freezer burn) to help maintain texture, color and lipid (fat) quality. Quick freezing rates and low constant storage temperatures, to ensure lower extracellular salt concentrations, resulting in smaller ice crystals, less disruption of muscle fibers, and protection of pigments and lipid (fat).
Texture Changes in Gadoid Species
Problem The Gadidae family of fish includes some of the most important commercial species of fish such as haddock, pollock, cod, whiting, cusk and hakes.