10.1 Fish Meal
10.1.1 Fishmeal production
10.1.2 Quality of fish meal related to raw material and conditions of manufacture and storage
10.1.3 Salmonella control
10.1.4 The nutrient content of fish meal
10.1.5 Analysis and quality assessment of fish meal
10.1.6 The role of fish meal in animal feeds
10.1.7 Commercial value of fish meal
10.2 Fish Oil
10.2.1 Fish oil composition
10.2.2 Fish oil properties
10.2.3 Edible applications of fish oils
10.2.4 Technical applications of fish oils
10.2.5 Commercial value of fish oils
10.2.6 Fish oil quality
The two commercially significant products of the Industry are a protein-rich meal and oil.. In 1983 the values of the world production of these products were around US$ 2500 million and US$ 400million, respectively. The meal has a high content of protein which is of high nutritional quality, and is used to supplement other proteins, especially vegetable proteins, in diets for farmed animals. The oil is used principally for human consumption in margarines and edible oils, following refining and hardening. There is interest currently in the direct human consumption of refined fish oils with a high content of n-3 fatty acids for the prevention and treatment of coronary heart disease.
The production of fish meal in the main producing countries between 1979 and 1983 is shown in Table 11. There has been little change in overall world production (around 5 million tons) in the past five years, though there have been changes in certain parts of the world. The most noteworthy changes have been declining production in Peru and Iceland and increasing production in Chile. Adverse sea temperatures off the coast of Peru (El Niño effect) have reduced fish stocks, resulting in reduced fishmeal production.
About 90% of world fishmeal production is from oily fish species such as mackerel, pilchard, capelin and menhaden. Less than 10% is from white fish offal such as from cod and haddock. Only 1% is produced from other sources such as shellfish and whales. The majority of fish meal is "whole", that is, only water and some oil are extracted from the fish.
The quality of the protein in fish, that is the make-up of amino acids in relation to an animal's requirement, and their availability to the animal, are high, particularly in whole fish. The quality of the protein in skin, connective tissue and bone is lower; consequently, the quality of the protein in offal is somewhat lower than that in whole fish. For example. the proportion of the essential amino acids methionine and lysine in the protein in white fish offal is approximately 10% lower than that in whole oily fish such as anchovy and pilchard.
Table 11 Fishmeala: world production (in '000 t)
|Country or area||1976||1977||1978||1979||1980||1981||1982||1983||1984|
|St Pier Miqu||600||500b/||500b/||482||646||1069||954||809||1165|
|Germany, Fed. Rep.||53031||48550||44690||40008||36992||38514||36882||35803||36782|
a/ Meals, solubles and similar feedingstuffs or aquatic animal origin; including fish meals from "white fish", oily fish and fish solubles. Whale meal and solubles, crustacean and seal meal and fish silages are also included.
b/ FAO estimates
Freshness of raw material is important in its effect on the quality of the protein in the end product. The importance of minimizing the time between catching fish and processing, and of keeping the fish at low temperatures by icing has already been mentioned (see Chapter 2) as a means of reducing spoilage. As a guide to freshness of raw material the content of total volatile nitrogen in the fish can be measured; it should be less than 80 mg-N per 100 g raw material.
Process control in the factory is necessary for the manufacture of high quality fish meal. Excessive temperatures (over 120OC) for prolonged periods in the cooking, evaporating and drying should be avoided since fish proteins are sensitive to excessive heat. It has been shown that the rate of loss in available lysine (see Section 10.3.1) is less than 1% per hour at temperatures below 120 °C; above this temperature the rate increases very rapidly (10% per hour at 140°C) (Carpenter and Booth. 1973).
The meal should be allowed to cool gradually with air circulation, that is, controlled "curing" after leaving the dryer. Use of an antioxidant such as ethoxyquin at 700 ppm is desirable for the oily fish species, especially in hot climates, for the purpose of stabilizing the oil in the fish meal by preventing oxidation. Rapid oxidation in fish meal can result in overheating in the stored product. Use of antioxidant is required by the International Maritime Organization if fish meal is to be shipped in a low hazard category. Correct "curing" and/or antioxidant treatment of fish meal will produce a product which can be stored indefinitely under dry conditions without deterioration.
During cooking and drying, any harmful bacteria in fish are killed. Subsequently, contamination of fish meal is possible; good hygiene is necessary at all stages in handling and storage if this is to be avoided.
Precautions must particularly be taken against Salmonella contamination. This organism is destroyed in the cooking plus pressing process provided the temperature is raised above 80°C, but poor hygiene beyond this point could result in re-infection of the meal. It must be stressed that although high air temperatures are reached in the dryers, the fish material in the dryer may not reach a sufficiently high temperature for sufficient time to destroy Salmonella. To minimize the risk, the manufacturers should observe the following precautions:
In summary, it is desirable to keep the wet and dry areas of the plant separate and to reduce to a minimum the passage of personnel and equipment from one section to the other.
A proper factory cleaning scheme is necessary. Empty storage bins and unloading areas should be cleaned as soon as possible after use. Process machinery should be cleaned regularly by high pressure jets of hot water and detergent solutions.
Stickwater concentrate and decanter sludge must be heated to 93°C or more before adding to the presscake. For about three quarters of an hour after the start of operations, while the machinery is warming up to normal operating temperature, all presscake produced must be returned to the cooker intake for recooking and repressing in case contamination might have occurred.
Should Salmonella, nevertheless, be detected in fish meal, the contaminated lots must be disinfected, for example in special apparatus in which the meal is heated at about 90°C with live steam for 10 to 15 min and then redried. Alternatively, biocides such as formic and propionic acids can be used to treat infected fish meal. These are expensive processes, however, and it is far more economical to comply with the outlined precautions. Another way of ridding infected fish meal of Salmonella is to expose it to suitable doses of ionizing radiation. This will obviously depend on the availability of irradiation facilities and should, perhaps, be regarded as a method for the future.
As well as being a rich source of high quality protein, fish meals have a relatively high energy content and are rich in important minerals such as phosphorus, in B vitamins and in essential fatty acids. The nutrient analysis of the main fish meals in world trade (herring type, South American type) and white fish offal are shown in Tables 12a, 12b, 12c and 12d along with figures for the cereals, wheat and barley, and soyabean meal for comparison (IAFMM, no date). Fish meals made from offal have a higher content of ash and a lower content of protein. The amino acidcontents of fish meals are shown in Table 12b. All values are given on an "as received" basis.
The protein figures given in Table 12a represent average values; a range of ±2% to ±3% protein units is possible. This range can be greater for offal meals. It is recommended that the amino acid content of a fish meal be adjusted for protein content, using the figures in Tables 12a and 12b; for example, for an offal meal with only 59% protein the lysine content can be calculated as follows:
Lysine content = 4.49 × 59 ÷ 65 = 4.08%
Similarly, where protein content is higher than shown in the table, amino acid contents should be adjusted upward.
The energy content of fish meals depends upon the protein and oil content. Where these differ from those shown in Table 12a, they may be adjusted by using the regression equations as follows:
ME adjusted = ME tabulated + (Fa - Ft) ÷ 100 × ME fat + (Pa - Pt) ÷ 100 × ME protein
where Fa and Ft are the actual and tabulated fishmeal fat (oil) contents, and Pa and Pt are the actual and tabulated fishmeal protein contents.
ME fish fat = 27.0 MJ/kg
ME fish protein = 16.5 MJ/kg
Worked example: South American fish meal 68% protein, 10% oil
ME adjusted = 13.2 + (10 - 9)÷100 × 27.0 + (68 - 65) ÷ 100 × 16.5 = 14.0 MJ/kg
fish meals b/
|S. American type
fish meals c/
|PROXIMATE ANALYSIS (%)|
N.B. All data refer to "as received" basis
a/ Produced from offal and whole fish
b/ Generic term including whole fish of species capelin, mackerel, sprat, sand eels, Norway pout. Herring type meals may have a protein content in the range of 68% to 74% and a fat content in the range of 7% to 12%. For fish meals of different protein content, the total content of an amino acid can be assumed to be proportional to the protein content, the amino acid make-up of fish protein being similar; e.g., herring type meal 72% protein: lysine 5.56%, methionine 2.16%; herring type meal 68% protein: lysine 5.25%, methionine 2.04%
c/ Fish meals made primarily from whole anchoveta; fish meals made from whole sardine or horse mackerel are similar in nutrient analysis
d/ Rowett Research Institute Feed Evaluation Unit, Aberdeen, UK
DE adjusted = DE tabulated + (Fa - Ft) ÷ 100 × DE fish fat + (Pa -Pt) ÷ 100 × DE fish protein
DE fish fat = 32.0 MJ/kg
DE fish protein = 23.0 MJ/kg
Worked example: Offal meal 47% protein, 4% oil
DE adjusted = 15.6 + (5 -4) ÷ 10 × 32.0 + (47 - 65) ÷ 100 × 23.0
= 11,2 MJ/kg
(Further details of the nutrient analysis of fish meals are available from the IAFMM, Hoval House, Mutton Lane, Potters Bar, Herts EN6 3AR, UK.) The nutrient values given above are based on fish meals of good protein and fat quality.
|Wheat||Barley||Soya 45%protein||White fish meal||Herring type fish meals||S. American type fish meals|
|TOTAL AMINO ACIDS a/ (%)|
a/Amino acids in fish meals and soyabean meal are equally available (see Miller, 1970)
|Wheat||Barley||Soya 45% protein||White fish meal||Herring type fish meals||S. American type fish meals|
|Phosphorus % (total)||0.29||0.35||0.55||4.80||1.90||2.60|
|Phosphorus % (available)||0.12||0.14||0.22||4.80||1.90||2.60|
|Selenium ppm (mg/kg)||0.20||0.40||0.60||1.50||2.20||1.40|
|Iron ppm (mg/kg)||33.00||38.00||36.00||300.00||150.00||246.00|
|Copper ppm (mg/kg)||5.00||4.00||41.00||7.00||5.00||11.00|
|Zinc ppm (mg/kg)||29.00||31.00||67.00||100.00||120.00||111.00|
|Manganese ppm (mg/kg)||38.00||19.00||36.00||10.00||2.00||10.00|
|Wheat||Barley||Soya 45% protein||White fish meal||Herring type fish meals||S. American type fish meals|
|Choline ppm (mg/kg)||730.00||110.00||2840.00||4400.00||4400.00||4400.00|
|Panthothenic acid ppm (mg/kg)||13.00||6.60||14.50||15.00||30.60||9.30|
|Riboflavin ppm (mg/kg)||1.10||1.30||4.00||6.50||7.30||6.60|
|Nicotinic acid (Niacin) ppm (mg/kg)||58.00||52.00||32.00||50.00||126.00||95.00|
|Folic acid ppm (mg/kg)||0.40||0.60||3.60||0.50||0.50||0.16|
|B12 ppm (mg/kg)||0.00||0.00||0.00||0.07||0.25||0.18|
|Biotin ppm (mg/kg)||0.10||0.14||0.25||0.08||0.42||0.26|
|Pyridoxine ppm (mg/kg)||4.00||2.90||8.00||3.30||3.70||3.50|
|ESSENTIAL FATTY ACIDS (%)|
Recommended sampling and methods of analysing fish meals are given in IAFMM Technical Bulletins No 16 (sampling), 8 and 15 (crude protein), 9 (moisture), 10 (ash), 11 (sand), 12 (salt), 13 (fat). Fish meal is a brown powder. The colour is affected by fish species, particle size, fat and moisture content. A very dark brown colour, especially if accompanied by an acrid "scorched" smell, may be the result of overheating. This will not affect the amount of protein in the meal, but will damage its nutritional quality. Regarding particle size, the general practice is for meals to have less than 10% that will pass through a 1-mm sieve and more than 90% passing through a 10-mm sieve.
The quality of protein in fish meal can be measured using Sanger's reaction with fluorodinitrobenzene (FDNB), as modified by Carpenter and Booth (1973). The FDNB binds with the epsilon amino group of the amino acid lysine to produce a yellow compound, the amount of which indicates the amount of "FNDB reactive" lysine. Damaging a protein will reduce the "FDNB reactive lysine", which should be over 85% of total lysine (see Table 12b) in good quality fish meal. Recently a modified dye binding method (modified dye binding lysine) has been developed using Orange G dye. Both methods are satisfactory for a laboratory wishing to compare the quality of fish meals of known history, for example within a single fishmeal factory. They are not suitable for a comparison of fish meals of unknown history by different laboratories (Barlow et al. 1984).
Occasionally, samples of fish meal are found which have been adulterated with cheap diluents. Types of adulterants which have been encountered include poor quality proteins, e.g., feather meal, dried poultry manure. non-protein nitrogenous compounds, for example urea-formaldehyde, and non-nutritive diluents such as sand. Presence of other proteins in fish meal can be detected under the feed microscope. Presence of non-protein nitrogen may be indicated by a low lysine content (total and available) in relation to the crude protein content which is usually determined as N × 6.25. Non-nutritive diluents reduce all other nutrients in the fish meal.
Fish meal is used in feeds for poultry, pigs, ruminants, farmed fish and fur producing animals. It increases productivity and improves the efficiency with which feed is converted to animal produce (feed conversion). It is of special value in diets for young animals, for example in broiler starter diets, diets for early weaned pigs, and for farmed fish and fur producing animals.
Fish meal is particularly beneficial in situations which are less than ideal, for example, where feed mixing and quality control of ingredients is poor, where husbandry standards are less than ideal and where disease problems are prevalent. A detailed assessment of fish meal in diets for poultry, pigs and ruminants is given in IAFMM Technical Bulletins.
In diets for very young animals such as early weaned pigs (weaned before four weeks of age), ruminants. fish and fur animals, it is recommended that special quality fish meal is used. It should be made from very fresh raw material and, for ruminants, have a low content of soluble nitrogen.
Ruminants can make better use of forage if fish meal is included in their diets, particularly if forage is a major part of their feed. Fish meal has been shown to be superior to other proteins, specially vegetable proteins. in supplying a high quality protein. a large part of which escapes breakdown in the rumen. As well as providing a high quality protein with a near ideal balance of amino acids for farmed fish. antioxidant treated fish meal provides a valuable source of n-3 long chain fatty acids which are essential for fish such as trout, salmon, carp, catfish and eels.
Although often traded on a price per unit of protein. the commercial value of fish meal is determined not only on the basis of protein. Its value is affected by fishmeal supply, price of other proteins and, of course, demand.
The demand for fish meal and the use to which it is put reflects the special nutritional properties referred to earlier. Many feed formulators calculate a value for fish meal using linear programmes on computers which take into account all its nutrients. In some diets which have a high nutrient concentration, for example starter diets in intensive farming systems, raw materials with a high nutrient concentration are preferred; this is taken into account in computer formulated feeds. For these diets the higher protein fish meals (65% protein and above) attract a premium.
Most feed formulators throughout the world ensure that fish meal inclusion does not fall below a minimum level in certain diets. for example for young poultry, young pigs, fish and breeding stock.
The prices of fish meal (65% protein) and soyabean meal (44% protein) in Europe in the past five years are shown in Table 13. These prices reflect world prices. Although the prices of proteins vary and prediction of future protein prices is difficult, it is anticipated that the price ratio fish meal (65% protein): soyabean meal (44% protein) is likely to be in the range of 1.8 to 2.0. continuing the trend of the past two years.
Fish oil, previously the main product from raw materials having high oil contents. is now of secondary value. The product, however, is versatile and finds many applications in the food and technical industries and is still of considerable economic importance to producers. Table 14 shows some statistics of production of fish oil during a number of years.
The oils contain mainly triglycerides of fatty acids (glycerol combined with three similar or different acid molecules) with variable amounts of phospholipids, glycerol ethers and wax esters. It is characteristic of the oils that they contain a wide range of long-chain fatty acids with the number of carbon atoms ranging mainly from 14 to 22, and high degree of reactivity (unsaturation) ranging up to six double bonds per molecule.
Table 13 Prices of fish meal and soyabean meal a/ Yearly averages of weekly quotations
|Year||Fish hamb||Soya rott||Fish hamb b/
as % of
soya rott c/
a/ Oil World Weekly, Hamburg
b/ Fish meal, 64-65% any origin, CIF Hamburg (interior price after deduction of a calculated wholesale cost after conversion at current DM/US$ exchange rate)
c/ Soyabean meal, 44% US, CIF Rotterdam.
d/ Seven monthly figures
Table 14 Production of fish body oils (in '000 t)
|Germany, Fed. Rep.||15||14||NA||10||17|
Source: Bowman, 1984
a/ Provisional data derived from miscellaneous sources
NA: Not available
The complex nature of fish oil depends upon a number of factors. The fatty acid patterns of the oils vary widely with fish species and, to some extent, with the composition of the plankton and the time of year. These influence the properties of oils both in regard to edible as well as technical applications. The oils contain variable, but small. amounts of unsaponifiable components, such as hydrocarbons, fatty alcohols, waxes and ethers, and these also influence the properties of the oils to some extent.
The condition of the fish at the time of processing affects the oil physically, chemically and nutritionally. Fish of poor quality yield a malodorous oil with high contents of free fatty acids (FFA) and sulphur. These latter undesirable properties affect both the economic value and the application of the oil. Some sulphur compounds have an inactivating effect on the nickel catalyst used for hydrogenation (called "poisoning of the catalyst"). thus the catalyst has to be replaced frequently.
In order to manufacture oil of desirable properties, one should observe the following:
Their nutritional and physical properties have made hardened fish oils attractive constituents in diets for man. Hardened fish oil is used almost entirely in margarines and shortenings. Margarines prepared from hardened vegetable oil sometimes recrystallize on storage. This makes the margarine crumbly and hard. Because fish oils have a widely varied chain length. margarines prepared from them have an excellent plastic consistency. Shortening and bakery margarines have properties different from those of table margarines. The value of hardened fish oillies in its creaming power, particularly in cake making.
Refined fish oils are rich in polyunsaturated fatty acids of the linolenic acid family. Current medical research suggests that these fatty acids might have a unique role to play in prevention of coronary artery disease and the growth of different types of cancers. More clinical studies will have to be undertaken before positive health claims can be made.
The highly unsaturated properties make the oils (and particularly their highly unsaturated fractions) suitable for a number of technical applications, particularly as drying oils and varnishes. The saturated fatty acid fraction is a disadvantage for these purposes and must be reduced. Several specialized processes for this reduction are available.
Fish oils are a significant source for the production of fatty acids with a wide spectrum of chain lengths. From these acids are produced several types of metallic soaps, some of which are used in lubricating greases while others are used as waterproofing agents. Small quantities of fatty; acids are used pharmaceutically and medicinally, and for scientific research purposes.
The market value of fish oil depends on its chemical analysis. Normally, a basic sales value is established for an oil containing a certain level of free fatty acids (2% to 3%), unsaponifiable matter (.3.5%), and water and dirt (0.3%). If these levels are exceeded. the price is reduced accordingly. The price may also be reduced if the oil is dark coloured or malodorous.
A number of chemical, physical and sensory methods have been developed for the assessment of quality. Analytical work is made difficult due to the labile nature of the unsaturated fatty acids, so oil sampled should be stored at low temperatures in an inert atmosphere before analysis. Saturated oil fractions tend to precipitate during cold seasons in large storage vessels. This necessitates thorough mixing of the oil before sampling.
The test methods employed by the user of fish oil for hardening purposes are often divided into two groups, the first being applied on receipt of a consignment to check the fundamental parameters and the second, more detailed, examination as soon as possible thereafter, but in any case before the oil is used in the refinery. The purpose of this second examination is to determine refining procedures.
The initial testing involves the following:
Moisture: For contractual reasons and because moisture in the oilleads to the formation of rust in storage tanks with consequent accelerated oxidation of the oil catalysed by iron. Thus, high moisture may be a contributory cause of high oxidation levels and a high trace iron content, which can also lead to colour problems in refining. Moisture in the oil is also responsible for the increase of FFA during storage.
Dirt: Usually only visually, unless excessive.
Appearance: Lovibond colour has not been found to be useful, but a golden brown oil is usually easy to refine whereas a dull brown oil gives difficulties. A frothiness can indicate a high phosphorus content and thus a tendency to emulsification problems.
FFA: for contractual reasons and because this is still the most reliable parameter for oil quality and yield assessment.
Soap: to check that the oil is not a blend of neutralized and crude oils.
Iodine value (I.V.): for hydrogen usage and to ensure that the I.V. is in the region expected for the type of oil stated, although these limits are very wide.
The second examination normally includes:
Peroxide Value (P.V.) and Anisidine Value (A.V.): to establish primary and secondary oxidation product levels. These compounds, with others resulting from further decomposition, are responsible for the rancid flavours that develop. Of the two values the A.V. is the more indicative of quality state.
Ultra Violet (U.V.) Extinction Values at 233 nm and 269 nm: these figures quantify the conjugated dienes and trienes, respectively, and are related to oxidation levels, but increases in these values are also obtained when an oil is overheated, resulting in colour fixation.
Trace Metals. Iron and Copper: both metals are pro-oxidants, that is catalysts for fat oxidation, copper being ten times more active than iron. It is, however, unusual to find high copper levels, but high iron levels occur all too frequently. A further problem with iron is that when sulphur is also present a darkening of the oil colour frequently occurs during deodorization. The trace metal level can be reduced using acids such as phosphoric and citric in the refining.
Sulphur: the effect of sulphur as a catalyst poison is recognized, but the poisoning effect depends on the chemical form in which the sulphur is present, and this is not as yet fully understood. All that can be said is that below 30 ppm in the crude oil (15 ppm in the neutralized oil) sulphur is not a problem, but that a significant poisoning effect is often encountered at higher levels.
Phosphorus: phosphorus is present in fish oil as phosphatides which are emulsifiers. These should be substantially removed from the oil by washing and/or phosphoric acid treatment prior to caustic soda refining so as to improve yields of neutral oil. The phosphorus content must be determined so as to calculate the required amount of phosphoric acid used to denature the phosphatides. The black residue which results from the treatment cakes the insides of solid bowl centrifuges and incomplete "degumming", as the reaction is known, can give separation difficulties when the soapstock is split with sulphuric acid.
"Standard" Hydrogenation Test: this test is the definitive test for the forecasting of plant hydrogenation performance but, as can be seen from the above, it does not give all the information needed by the refiner to produce a high quality oil at optimum cost for that oil. Other catalyst poisons exist, e.g., chlorine, bromine, iodine, which cannot easily be determined in a works laboratory and for this reason the hydrogenation test should be carried out in addition to the sulphur determination.
The determination of unsaponifiable matter in itself is of no great help apart from a high figure raising doubts about possible mineral oil contamination. Little is known about the quality effects of non-glyceride components of oils or of their degradation products and thus the content in the oil of these chemicals taken as a group is practically without value.