4.1. Discussion We can see from the above calculations that raw material quality is very important. Fresh fish lose much less solids to the pumpwater than stale fish. In fact, for every 100 mg/l of protein + fat in the pumpwater, you will lose 0.22 kg of fishmeal per ton of fish.
Yield losses
- 4.1.1.
Based on research done in the fishmeal industry in other countries, we found that the pressure of the fish on each layer in the hold is one of the primary causes of raw material deterioration. The more fish in the hold, the more quickly the pressure will force the fish to compress and lose liquid. This liquid contains enzymes which will further digest (liquify) the mass producing more liquid. Deterioration increases with increased storage temperatures and time. While the data from other species such as sandeel, herring, pilchards and sardines may not be directly related to anchovy, the principle is the same; when the fish are stored at elevated temperatures under pressure, they will lose liquid which if not recovered leads to reduced yields and pollution of the surrounding waters.
For herring it was calculated that for each 5 centigrades increase in temperature, the daily loss of yield doubles.
Figure 15. Work done with pilchards showed an increase in solids in the blood water from 1.6% to 11.4% in 2 days at 15 centigrades. With broken fish or trimmings, the bloodwater weight increased from 2.6% in 6 hours to 5.06% in 24 hours and the lost solids went from 1% in 6 hours to 1.75% in 24 hours. The blood water can range from 10-15% of the weight of the raw material. Studies with cod, redfish and herring compared the weight losses over 17 days at three different temperatures. Figure 16. Danish studies with sandeels indicate that the loss in solids in the vessel bilge water discharged at sea could amount to as much as 3.5% of the weight of the fish. In Norway studies with herring and Norway Pout stored at three different temperatures, showed similar losses in weight when the temperature was increased. Figure 17.Spoilage of fish can be measured in a number of ways. The easiest way is to use your nose. The spoiled odor is due to compounds that form when bacteria and chemicals in the fish begin to breakdown the proteins. They can also increase the FFA in the oil. The resulting compounds are called volatile nitrogen compounds and biogenic amines. Ammonia is a volatile nitrogen compound and histamine is a biogenic amine. The volatile nitrogen compounds are usually measured as TVN. The analysis of the biogenic amines is more complicated and requires expensive instrumentation. When these compounds form, they come out of the fish and are lost in the stickwater, blood water and evaporator, and dryer condensates. For every 100 TVN units you lose 0.625% protein in the fish.
Figure 18. Fresh fish should have a TVN of 10-15 mg/100 g of fish.Norwegian studies with capelin showed large increases in TVN and oil FFA when the fish were stored in bulk. Figure 19. Danish studies with herring and mackerel showed that the biogenic amine content (histamine, cadaverine putrescine and spermidine) were 2-20 times higher in the fish at 10 centigrades than at 2 centigrades. In another Danish study the TVN content of small cod and herring was measured at three different temperatures over two-weeks storage. The lower temperatures resulted in increased storage times. Figure 20.
If the catch could be processed on-board the vessel immediately after capture, there would be no need for preservation techniques but this is not the case in the fishmeal industry. There have been many studies done to evaluate methods of preserving fish for edible use and fishmeal production. These include protection from contamination, icing, containerization, refrigerated seawater, and chemicals.
Figure 21. To reduce spoilage of the fish you must eliminate or reduce bacterial contamination and lower the temperature of the fish. You must also prevent the fish from crushing each other so that the enzymes in the fish do not come out and begin digesting the proteins.Anchovy present problems when it comes to preservation. They are small, the belly's burst very quickly after capture and they compress in the hold of the vessel. Experiments have been conducted with the "champaign" system of refrigeration where the chilled water is forced up through the fish rather than sprayed from the top. It appears that major modifications of the fleet will be necessary to effect some type of preservation of the fish. This might not be possible as retrofitting the existing fleet might be too costly or impossible. Such modifications should include insulation of the holds, compartmenting the holds so that fewer fish will be in each compartment and possibly the use of containers to further reduce the volume in each compartment.
4.1.3.1. Advantages of preservation
The advantages to preservation of the catch will be increased yields and higher quality fishmeal and oil. Fresh raw material carries through the process like money in the bank increasing with time. Figure 22. You can't collect on what you don't have.
4.1.3.2. Disadvantages
There are disadvantages to preservation of the raw material. Nothing is free. There will be increased capital costs in the construction of the vessels.
4.1.3.2.1 Reduced vessel carrying capacity
The vessels will carry less fish because the walls of the hold must be insulated, so the cost to catch a unit of fish will increase.
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