3.1 Fish meal and oil
3.2 Fish silage
3.3 Compost and other products from inedible fish waste
3.4 Effects of heat and pH on survival of aquaculture pathogens
3.4.3 Other Pathogens
3.5 Waste treatment in Norway
3.5.1 Norwegian regulations concerning the manufacture of fish silage and the disposition of fish waste
3.5.2 Specific Norwegian microbiological specifications pertaining to high and low risk offals
3.5.3 The Norwegian approach to dealing with fish offal
3.5.4 Aquaculture waste utilization from salmon and shrimp
The three most common methods for utilization of aquatic waste (either from aquaculture or wild stock) are the manufacture of fish meal/oil, the production of silage or the use of waste in the manufacture of organic fertilizer. Several other options have been proposed and in Norway (Section 3.5) much of the fish waste is manufactured into value added products. The problem of aquatic waste disposal was approached in Norway nearly a decade ago, at first with a view to waste disposal, then later with a view to manufacturing marketable products from waste. There is little doubt that at present, Norway is a world leader in the utilization of aquatic waste and has developed stringent guidelines as to the disposition of waste from the fishery. Many of these policies were developed to ensure that waste streams are handled so as to reduce the possibility of the spread of fish pathogens to cultured or wild fish species.
Rather than dealing with the detailed processes per se, this section is intended to deal with the potential transfer of fish pathogens through the manufacture of meal, silage and fertilizer.
The traditional manufacture of fish meal usually involves the comminution and cooking of waste in order to separate the oil from the rest of the material and to ensure the destruction of both pathogenic and spoilage organisms. Although there are a wide variety of processing conditions, in practice most fish meal cookers are designed to heat the minced fish to 95-100°C over a period of 18-20 minutes. Following this, the cooked material is pressed to separate solids (press cake) from liquids (press liquor) containing oil and water. The press liquor is further clarified by centrifugation to separate oil, water and solids, the water being subsequently evaporated and all solids are re-combined with the press cake which is then dried in an evaporator. The standard evaporator operates at 90-95°C whereas the evaporator for so-called "low temperature" (LT) meal is operated at 60-65°C.
The final product contains very little oil or water and is considered to be sterile or nearly so by virtue of the initial cooking process. This does not mean that problems related to non-sterility have not occurred in the manufacture of fishmeal. However, these problems are inevitably related to recontamination of the finished product by rodents or birds.
In Norway and in the European Union the safety of using fish meal as an ingredient in aquaculture feeds is ensured with a number of regulations (see Section 3.4.1). In general, aquaculture waste is not permitted for the manufacture of aquaculture feed and must be processed in facilities which are entirely separate from waste streams from the wild fishery. Also, special consideration must be given to offal which may reasonably be expected to contain chemical residues such as therapeutant drugs and antibiotics. Offal which is destined for fish feed production must be heated to an internal temperature of at least 90°C to prevent the survival of fish pathogens which may be present.
In the E.U. "high risk" offal such as mortalities from fish farms, fish which show clinical signs of disease or animals which are slaughtered as a part of a disease control program, must be thermally processed to an internal temperature of at least 133°C and cannot be used for any type of meal in the E.U. (EU Council Directive, 1990).
Shrimp meal is usually manufactured from heads, guts and tail hulls and can be processed in a variety of ways. It may be manufactured by simple sun drying or may be cooked as in the traditional fish meal process. It is considered as an ingredient for aquaculture feed for two reasons. First, its amino acid profile is ideal for the culture of crustaceans, while the pigment (largely astaxanthin) is desirable in certain cultured fish. The pigment is however heat labile and the low temperature processes sometimes used for shrimp meal production cannot be considered adequate for the destruction of shrimp pathogens. A good practical reference for the processing of fish waste into meal, oil and silage can be found in Windsor and Barlow (1981).
Fish silage is produced by acidification of fish waste using organic acids such as formic acid which is added at a rate of about 3.5% (w/w) or mineral acids such as sulfuric which is added at slightly lower levels. A third method sometimes used in tropical climates involves the addition of simple sugars such as molasses and a lactic acid bacterial culture which generates lactic acid through the natural breakdown of the sugar. The use of acid is necessary to inhibit spoilage bacteria which could produce off odours, flavours such as trimethylamine or ammonia and/or toxins such as histamine if left to ferment at neutral pH. An excellent review of the technology of silage manufacture was presented by Raa and Gildberg (1982).
Fish and shrimp silage is highly nutritious and is traditionally fed as a protein supplement to swine, mink and poultry. It consists of autolyzed fish offal and is normally manufactured by the addition of fresh fish viscera which contain the necessary enzymes for autolytic breakdown. The liquified product has a pleasant "malty" odour and is often blended with dry feed ingredients to form a semi-moist diet.
Silage has also been used successfully as a low cost ingredient in aquaculture diets (Lall, 1991; Espe et al., 1992). In fact, shrimp silage has been used as a source of pigment as well as nutrition for farmed salmon (Guillou et al., 1995). Fermented fish silage produced by the addition of lactic acid bacteria and a carbohydrate source has been produced from offal from tilapia (Fagbenro and Jauncey, 1993; Fagbenro et al., 1994; and Fagbenro and Jauncey, 1995), shrimp (Sachindra et al., 1994) and salmon (Dong et al., 1993) and subsequently used in aquaculture diets. One advantage of this process over the traditional organic acid processes is that there is a substantial saving in operating costs provided an inexpensive source of carbohydrate such as molasses. Another potential advantage of using silage rather than meal in aquaculture diets is the fact that most of the silage processes used to date (with a few notable exceptions) do not involve heat denaturation of the proteins. One exception is a Norwegian process in which silage is produced in the traditional manner and subsequently transported to a thermal processing facility where the silage is heated in a two-stage process to eliminate pathogen transfer.
Another exception is the mixing of silage with other dry feed ingredients and then processing by thermoplastic extrusion to produce feed pellets which are heated under pressure and then expand when exiting the extruder producing air voids and thus a lower density. This latter process also results in the evaporation of water which is a requirement for product stability since silage normally contains 65-80% moisture before mixing with dry ingredients (Jangaard, 1991).
Thermophilic fermentation is one way of dealing with problem waste such as municipal sewage and fish mortalities. Processes for the production of fertilizers and other useful end products have been developed in various parts of the world. Thermophilic fermentation is a process which involves particle size reduction followed by bacterial fermentation at high temperature (usually 50-70°C) accompanied with aeration. The thermophilic process not only breaks down complex materials such as proteins, fats, carbohydrates, etc., but also generates heat which may or may not be utilized for other purposes. The production of heat during the process may result in the destruction of pathogenic microorganisms. Unfortunately, it is not always possible to obtain details about such processes since those which are in commercial production often contain proprietary information.
One such process was developed in Norway and has recently become commercialized. The process was developed through research funded by the RUBIN Foundation (see Section 3.5), Trondheim, Norway, and involves the mixing of problem wastes such as animal manure, municipal sewage and aquaculture mortalities. A liquid compost is formed by aerobic fermentation at 60°C. The equipment for the compost manufacture was supplied by Alpha Laval and a description of the RUBIN composting process may be found in RUBIN (1998). The compost produced in the Norwegian process is currently used as an agricultural organic fertilizer. The Rubin Foundation claims that although the process is capable of destroying Aeromonas salmonicida and infectious salmon anemia, thermophilic fermentation was incapable of removing antibiotic residues sometimes found in aquaculture waste.
Another commercial composting process was developed by Thermo Tech Technologies in Langley, British Columbia, Canada. The process is patented and involves the aerobic thermophilic fermentation at approximately 70°C. The process has been used to compost municipal sewage sludges, fruits, vegetables, meats, dairy waste and fish products. The company claims that the process eliminates a variety of human bacterial and viral pathogens and is claimed to successfully destroy chlortetracycline, sulphamethazine and penicillin (Thermo Tech Technologies, 1998). It is therefore perhaps reasonable to anticipate that this process may be applicable to the destruction of fish pathogens. The finished product is dried, pelletized and used as an organic fertilizer.
Most bacterial fish diseases are spread through excretions of urine and faeces from one host to another although the survival rate for most pathogens is limited in a marine environment. Fish bacterial pathogens are killed rather effectively by moderate heating, contact with an acidic environment or through enzymatic degradation. As early as 1986, it was determined that improper pasteurization of moist feeds resulted in high bacterial loads. Moffitt-Westover (1986) found that at least in the Pacific northwest of the U.S., problems associated with high bacterial loads in aquaculture diets were sometimes related to faulty pasteurization equipment. One such protocol for heating consisted of a holding time of 15 minutes at 65°C followed by holding at 82° for 10 minutes (Whipple and Rohovec, 1994). This two-step thermal process resulted in complete destruction of the bacterial pathogens Aeromonas salmonicida and Mycobacterium chelonei at initial levels >108 CFU/ml. However, Renibacterium salmoninarum was significantly more heat resistant and was able to survive >15 minutes at 65°C. A second heating regime of 15 minutes at 65°C followed by 5 minutes at 82°C was effective in destroying >108 CFU/ml of R. salmoninarum.
A. salmonicida, M. chelonei and R. salmoninarum are all potentially devastating to the farmed salmon industry, causing furunculosis, mycobacteriosis and bacterial kidney disease, respectively. Heating these bacteria in the presence of acid such as is common in the production of fish silage, affected each bacterium differently. A. salmonicida was less heat resistant when the pH was reduced from neutral to pH 4.0. However, M. chelonei survived slightly longer when heated at acid pH. R. salmoninarum survived for >3 hr at 55°C in buffer at pH 7 or 4, but was destroyed within one minute in fish silage heated to 55°C.
In a 1993 study, Smail et al. (1993a) found that the bacterial pathogens A .salmonicida, Yersinia ruckeri and R. salmoninarum were destroyed quickly when mixed with commercial salmon silage made with a blend of formic and propionic acids. However, the authors pointed out that bacterial destruction would no doubt depend on the more or less complete autolysis of the silage particulates and that a suitable time period should be established between the last addition of solids and utilization of the silage.
There is very little published data on the quantitative effects of temperature and pH on fish bacterial pathogen destruction. Ideally, survivor curves and thermal death time kinetics need to be established for a range of bacterial pathogens inoculated into both silage and meal. Such determinations are required worldwide for the development of thermal processes for low acid canned food to ensure safety from food-borne pathogens such as Clostridium botulinum. It should also be pointed out that the kinetics of destruction may be quite different when comparing silage prepared by addition of organic acids and that which is sometimes produced in the tropics by natural lactic acid fermentation. This is because many lactic acid bacteria produce probiotics which could possibly provide an additional "hurdle" to the survival of fish pathogens.
Another area which requires research is the treatment of wastewater from aquaculture processing facilities to eliminate the re-introduction of fish pathogens into the marine environment. Again, very little has been published in the technical literature on the resistance/susceptibility of fish pathogens to treatment with disinfectants such as the halogens (chlorine, bromine and iodine), ozone or the use of ultraviolet light.
Far more work has been published upon the transmission and survival of fish viral pathogens than bacterial pathogens. Unfortunately, most of the technical literature published to date on the disinfection of aquaculture waste has dealt primarily with viruses associated with farmed salmon. Smail et al. (1993a) compared bacterial pathogen survival to the infectious pancreatic necrosis (IPN) virus. In particular, Smail et al. were interested in the efficacy of ensiling salmon farm mortalities on the fate of fish pathogens. They found that the IPN virus survived for over 4 months in acidified silage stored at 4°C but was no longer detectable after 71 days at 20°C. The addition of a virucidal agent "Virkon" which is a blend of peroxidants, surfactants and organic acids (Merck) at 1% in silage reduced IPN levels by >105 plaque forming units within 30 minutes. Heating silage to 60°C for 2 hours accelerated IPN destruction but no quantitative data on the kinetics of thermal destruction over a wide range of temperatures were given.
In a subsequent article, Smail et al., (1993b) found that the IPN virus was indeed resistant to both enzymatic digestion and extremely low pH levels. Intact IPN virus was detected in the faeces of cows which had been fed IPN-infected fish silage. Neither the silage process (pH 3.8-4.0) nor the acidic conditions within the bovine digestive system (pH 1.1 - 1.3) were capable of destroying the IPN virus.
This is particularly alarming information since in many instances livestock which are raised in the vicinity of salmon farms could potentially infect the soil, ground water, streams and rivers flowing into the ocean if fed viral contaminated silage.
Another virus, the infectious salmon anemia (ISA) virus has been studied recently since it has been responsible for the partial destruction of the Norwegian farmed salmon industry in the early `90's and now threatens the eastern Canadian salmon farms. Christie et al. (1993) found that the ISA virus contained a lipid envelop which could be removed by treating with solvents such as chloroform thus destroying its infectivity. Nylund et al. (1994) showed that the ISA virus was still infectious after 20 hr in seawater and that it could be transmitted by parasitic "sea lice" (Caligus elongatus and Lepeophtheirus salmonis) from host to host. Experiments on the localization and isolation of the ISA virus were carried out by Spielberg et al. (1995) and Dannevig et al. (1995), respectively. This is an important detail since any future work on the destruction/survival of viral fish pathogens requires that simple, reliable methods for the cell culture and enumeration of viruses have been established.
ISA can be carried by land-locked brown trout without developing typical symptoms of the disease (Nylund et al., 1995) and can be excreted through faeces and urine from infected salmon even before they develop symptoms of the disease (Totland et al., 1996).
Destruction of infectious pancreatic necrosis (IPN) virus and infectious hematopoietic necrosis (IHN) virus using low pH and heat was examined by Whipple and Rohovec (1994). Again, both of these viruses are salmon pathogens and IPN was found far more resistant than IHN. IPN survived more than 14 days in a pH 4 buffer or in fish silage, whereas IHN was not found after 7 hr and 30 sec when incubated in pH 4 buffer and silage, respectively at 22°C. IPN inactivated after 2 hr at 70°C or 10 minutes at 80°C, while IHN was quickly destroyed at 55°C. Unfortunately, the authors did not perform detailed time temperature experiments for either virus or the three bacterial salmon pathogens, which were being studied simultaneously.
Published studies of other viral pathogens of other aquaculture species are extremely rare. One interesting article (Hegde et al., 1996) which appeared in "Infofish" discussed several methods for the disinfection and viral pathogen control in the farmed shrimp industry. The authors state that most shrimp viral pathogens are destroyed in <1 hr at 55-65°C. They also state that Baculovirus pinaei (BP), a shrimp pathogen, survived in 32 ppt seawater for 7 days at 22°C but >14 days in seawater at 5°C. BP was inactivated by U.V. irradiation at 254 nm for 40 minutes. The IPN virus is apparently more resistant to U.V. irradiation than the PB virus, but no quantitative data were given. It would appear then that there could be application of U.V. disinfection provided that the kinetics of destruction for pathogens were determined and provided the turbidity of the water was low enough to facilitate U.V. penetration. Hedge et al. (1996) suggested that perhaps ozone was probably the most effective viral disinfectant. They gave anecdotal examples (no experimental results nor references) on the rapid destruction a number of viruses of aquaculture significance including Hirame Rhabdo virus, Onchorhyncus Masou virus, Yellowtail Ascites virus IPN virus and the Chum Salmon virus.
Other examples of chemical inactivation of aquaculture viruses using chlorine, iodine and formalin were given.
Other pathogens such as pathogenic yeasts and fungi are perhaps of less significance in aquaculture "grow-out" facilities but are perhaps more important in fish hatcheries. However, it is probably safe to generalize in saying that fungi are more susceptible to physical and chemical treatment than either bacteria or viruses. Thus, one can perhaps presume that most physical/chemical methods used to destroy pathogenic bacteria and viruses, would also inactivate infectious fungi.
Recent attention has been given to a "new" class of infectious agents call "prions" which has been shown to be responsible for transmissible spongiform encephalopathies (TSE) in cattle and Creutzfeldt-Jacob Disease (CJD) in humans. It is believed that prions are manufactured in normal healthy animals and become post-translationally modified in conformation in affected individuals to form rod-shaped fibrils in the brain (Schmerr et al, 1996). The fibril formation is fatal and the spread of prion proteins among British beef cattle recently was believed to be due to the practice of feeding rendered beef protein to farm animals. Although, at least in the U.K., this practice has been banned, two obvious questions emerge from the recent controversy over British beef:
Although prion-related illnesses have to date never been reported in aquaculture species, processes which are designed to eliminate fish pathogens should be conservative since recent data suggest that at least for thermal destruction, prions are more resistant to heat than most foodborne pathogens of bacterial and viral origin (Casolari, 1998).
According to Dr. Yngve Torgersen (personal communication, Norwegian Ministry of Agriculture), the waste streams from the "open sea" or "wild" fishery must be kept separate from the aquaculture industrial waste at all times. At present, Norway produces about 200,000 MT of conventional fishmeal and 80,000 MT of fish oil from the open sea fishery. About 70% of the meal from the open sea fishery is used for aquaculture feeds while 30% is used for domesticated farm animals. The fish oil from the meal plants is utilized for both aquaculture feed and for human consumption in a ratio of about 1:1.
The production of waste by-products and transportation of aquaculture waste in Norway is regulated by the Ministry of Agriculture. By Norwegian law, separate processing facilities must be established to handle either aquaculture waste or "open sea" waste but no one facility may handle both. Thus the potential for cross-contamination of raw material is minimized to keep the waste streams separate.
In Norway, animal offal is divided into two major categories: "high risk" and "low risk".
High risk offal includes farm animals which have died of disease, were destroyed in order to prevent the spread of disease, were still born, died in transport, were known to contain chemical residues at the time of slaughter or in the case of farmed fish, individuals which displayed clinical symptoms of transmissible disease or which reveal pathological signs of diseases upon inspection after death. Special regulations pertain to the handling of high risk fish which normally ensures the thermal destruction of biological hazards such as bacteria, viruses and fungi. Special consideration is given to offal which may reasonably be expected to contain chemical residues such as therapeutant drugs and antibiotics. In this case, appropriate measures must be taken so as to ensure that the residues cannot re-enter the food chain. High risk offal considered to contain harmful bacteria or viruses must be sterilized or incinerated.
Many of these residues are not destroyed by heat sterilization and therefore other methods of treatment must be developed. One suggestion has been the use of such "problem" waste as mink feed.
Low risk offal refers to animal waste derived from the slaughter of healthy animals destined for use in the human food chain. Aquaculture waste must be processed at a facility which is separate from open sea waste. All waste must be processed as soon as possible to reduce spoilage and must be ground to particle sizes not greater than 50 mm before processing. Processing is normally carried out initially by heating or by the addition of acid (usually formic) so that the final pH £ 4.0. An exception is made for low risk waste which is destined for the production of "technical" or "pharmaceutical" products, in which case, heating or acidification may not necessarily be appropriate.
Low risk offal which is destined for fish feed production must be heated to at least 90°C throughout the batch before being mixed with other feed ingredients. Exceptions to this thermal process may be approved by the Department of Agriculture if alternative treatment methods are used with the same bactericidal/viricidal effects.
Low risk offal which is destined for the production of feed for warm-blooded animals is exempt from the requirement for heat treatment.
Regulations concerning feed, technical and pharmaceutical products as well as products from sterilization plants and high-risk offal from aquaculture fish are as follows:
Salmonella - None in 25 g and n = 5, c = 0, m = 0, M = 0.
Enterobacteriaceae - n = 5, c = 2, m = 10, M - 300 per g.
Clostridium perfringens - None in a 1 g sample.
n = the number of single samples from a lot.
m = lower value which should not be exceeded (colony forming units). It separates acceptable counts from marginally acceptable counts.
M = lower value which must not be exceeded. It separates marginally acceptable counts and unacceptable counts.
c = maximum number of samples with analytical results between m and M which can be accepted without rejecting the lot.
In 1990, the various Norwegian fishing organizations and government established a research foundation called "RUBIN" A/S in Trondheim with an endowment of 25 million Nkr. The acronym RUBIN, roughly translated from Norwegian means "recycling utilization of organic products in Norway". The RUBIN foundation identified and funded waste elimination and waste utilization projects which were carried out by private companies, research organizations and universities. The initial phase of the endeavour was aimed at eliminating waste in environmentally acceptable ways. The second phase targeted projects in which cost savings could be realized in the area of waste utilization. The third phase which was nearing completion at the time of writing this report, was focused on commercial gain from the processing of waste through value added strategies. Some of the most significant projects are summarized below in addition to the thermophilic compost project described in Section 3.3.
Fish oil utilization
Edible virgin cod liver oil is treated with an enzymatic process which gives stability from oxidative rancidity. The oil is stored in oxygen impermeable bags which are nitrogen flushed before sealing. Subsequently, the fish oil is blended with butter to produce a popular "healthy" dairy spread which is packaged in heart-shaped plastic containers and marketed in both Norway and the U.K.
Pelleted wet fish feed
RUBIN has patented a process for the manufacture of a soft aquaculture feed consisting of protein, oil, a vitamin pre-mix and uncoated astaxanthin. The mixture is blended with alginate and cross-linked through a gelling process in a formic acid bath. The gelled feed particles are fluidized in a slurry and fed to salmon as a spray, the gelled particles holding together even when in contact with seawater. The advantages of the new soft fish feed are the better weight gains for salmon even during winter feeding, presumably because of increased palatability. Pigmentation of the flesh of fish on moist feed is enhanced as compared to similar pigmentation levels in dry feed. The moist feed is more economical to manufacture although has a shorter shelf life as compared to pelletized dry feed. Of course, the fish offal used in the feed must not come from the processing of Atlantic salmon.
Processing of fish silage
Companies such as Reiber & Sons in Tromso process acid silage collected from all over Norway and abroad. The silage is transported to Tromso and pasteurized in a 2-stage process before manufacture into various types of animal feeds.
Fine chemicals from the sea
A variety of fine chemicals are being manufactured from Norwegian fish waste. A Tromso company, KS Biotec-Mackzymal was established in 1990 and has annual sales of approximately 30 million Nkr of which most (80%) are exported to countries such as the US, Japan and other countries in Europe. The main areas of production and marketing are animal health and nutrition, human health and nutrition as well as industrial enzymes. Biotec produces feed additives such as the immunostimulant ß 1,3 glucan and a hydrolyzed fish protein product used as a feed ingredient for young pigs. They produce a variety of proteolytic enzymes from waste raw materials which are presently used to skin and tenderize squid, remove the scales from finfish, to de-clump caviar and to enzymatically remove the parasites from the surfaces of cod livers. The proteases are primarily derived from fish viscera and from the thaw water in the shrimp industry. Another product is DNA for the pharmaceutical industry produced from salmon roe sacs.
It is perhaps because of the problems associated with the use of antibiotics in farmed fish which resulted in Norwegian research on immunostimulants. In the early 1980's, as much as 80 MT of oxytetracycline was used annually in the Norwegian aquaculture industry. At present, it is estimated that the entire industry uses only about 600 kg of antibiotics per year. Vaccines and immunostimulants have replaced antibiotics for two reasons. First, the safety and reliability of antibiotics is in question and secondly, the antibiotics are persistent and difficult to eliminate from the waste stream. Vaccines and immunostimulants are now far more common in Norwegian aquaculture. According to Biotec, the best immunostimulants are derived from polysaccharides and lipopolysaccharides.
Although somewhat dated now, Strom and Raa (1993) published a review of the Norwegian marine biotechnology industry which is in part founded by upon projects funded by RUBIN. The list of products produced from marine sources includes vaccines, diagnostic test kits, enzymes for fish processing, immunostimulants, veterinary supplies, DNA and nucleotides, amino acids, peptides and peptones, alginates, chitin/chitosan, flavours, and omega-3 fatty acid concentrates. Many of these products are on the market today.
One of the most interesting products is chitosan which is manufactured from shrimp and lobster waste. Chitosan is used in large quantities for water treatment. It acts as a cationic flocculent to remove negatively-charged particles in the water purification process. Chitosan has also been used as a stiffening agent for the manufacture of paper, a water impermeable coating for fruit and seeds to retard dehydration, a processing aid for the clarification of fruit juices and wines and a thickening agent or stabilizer for manufactured foods. Chitosan has also been used as a skin replacement in the treatment of burn victims, a carrier for drugs and has antimicrobial properties which have been applied to food preservation and as an antibacterial coating for textiles. See Table 3.1 for further applications of chitosan.
Of course, the manufacture of chitin and chitosan from shrimp waste is not restricted to Norway. Perhaps one advantage of the manufacture of chitin/chitosan from shrimp waste is that rather severe extraction conditions are used and may possibly be expected to destroy at least many of the shrimp pathogens in the process.
Table 3.1 Some Practical Applications for Chitosan
|Antimicrobial||Oyster preservation (bacterial inhibition)||Chee et al. (1998)|
|Fruit coating (antifungal)||Donglin and Quantick (1998)|
|Textile deodorizer||Sakurai et al. (1997)|
|Immunostimulant||Vaccine adjuvant||Illum (1996)|
|Binding/gelling agent||Binding agent for surimi||Katoaka et al. (1998)|
|Immobolized enzymes (ß galactosidase)||Carrara and Rubilo (1997)|
|Microencapsulation (enzymes)||Gonzales-Sisto et al. (1997)|
|Edible packaging||Butler et al. (1996)|
|Drug delivery (controlled release)||Elson (1996)|
|Control enzymatic browning in fruit||Donglin and Quantick (1997)|
|Cationic flocculent||Waste water treatment||Skaugrud and Sargent (1990)|
Apart from the common processes for the manufacture of meal, oil, silage, chitin and chitosan, there are a number of interesting possibilities for the utilization of shrimp and salmon processing waste.
Mandeville et al. (1991) proposed a unique process for the fractionation and purification of pigments, lipids and flavour components from shrimp processing waste.
A variety of salmon oil products have been developed including encapsulated omega-3 enriched health supplements which are marketed world-wide through health and natural food stores, pharmacies and even supermarkets (Ocean Nutrition Inc., Bedford, NS, Canada).
Salmon DNA is currently being extracted from roe and marketed to the pharmaceutical industry (BioTec, 1998). Salmon skin is tanned and used for products manufactured from fish leather such as purses and key cases.