Utilization of marine by-product

Abstract

There has been an increasing interest in fish by-products during the past years. Today it is seen as a potential resource instead of a waste. Much research is being done in order to explore the possible uses of different by-products.Today overexploitation of fish resources is a large problem, only about 50-60% of the catch is used for human consumption. Globally more than 91 million tons of fish and shellfish are caught each year. Some of the by-products are utilised today, but huge amounts are wasted. Annual discard from the world fisheries were (FAO) estimated to be approximately 20 million tonnes (25%) per year. Therefore it is a great potential for the fishing industry to utilise more of what is landed. This includes "waste" or by-products or what should really be called rest raw materials. In 2001 a total of 232 000 metric tons of by-products were created by the Norwegian cod fisheries alone, of this 125 000 tons were dumped while 107 000 were utilised. Only 36 000 tons of the by-products were used for human consumption which amounts to about 15,5% of the total The rest is used for the production of fishmeal, silage and animal feed. In Iceland fisheries are the single most important industry. The total catch is about 2 million tons, accounting for 62% of the value of exported products and around 49% of the foreign earnings each year. Increasing the proportion of the catch used for human consumption and other value added products (pharmaceuticals, feed ingredients etc.) would increase the profitability and reduce the amount of waste. Marine by-products contains valuable protein and lipid fractions as well as vitamins and minerals. To get a profitable utilisation of rest-raw material from the fish industry the final products demands a market interest. Knowledge about quality and composition is a necessity. There are major on-going research on searching of bioactive compounds in marine organisms and development of new technology for utilisation of this so we can assume that the future will bring more value out of what is today considered a waste. In order to evaluate possible applications for the products and conservation techniques of the rest-raw material, it is important that the raw material is characterised based on its chemical composition and enzymatic activity. The quality of the raw material at the processing site will determine the manufacturing possibilities. The handling onboard is very important. Marine by-products are extremely reactive and will be degraded by microbial spoilage, enzymatic reactions and oxidation if the conservation and handling is not satisfactory.

Full text

Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377 458
ISSN: 1579-4377
UTILISATION OF MARINE BY-PRODUCTS
Rustad, T.
Department of Biotechnology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
E-mail: turid.rustad@biotech.ntnu.no
KEYWORDS
by-products, fish, lipids, proteins, utilisation
ABSTRACT
There has been an increasing interest in fish by-products during the past years. Today it is seen
as a potential resource instead of a waste. Much research is being done in order to explore the possible
uses of different by-products.Today overexploitation of fish resources is a large problem, only about 50-
60% of the catch is used for human consumption. Globally more than 91 million tons of fish and shellfish
are caught each year. Some of the by-products are utilised today, but huge amounts are wasted. Annual
discard from the world fisheries were (FAO) estimated to be approximately 20 million tonnes (25%) per
year. Therefore it is a great potential for the fishing industry to utilise more of what is landed. This
includes “waste” or by-products or what should really be called rest raw materials. In 2001 a total of 232
000 metric tons of by-products were created by the Norwegian cod fisheries alone, of this 125 000 tons
were dumped while 107 000 were utilised. Only 36 000 tons of the by-products were used for human
consumption which amounts to about 15,5% of the total The rest is used for the production of fishmeal,
silage and animal feed. In Iceland fisheries are the single most important industry. The total catch is about
2 million tons, accounting for 62% of the value of exported products and around 49% of the foreign
earnings each year. Increasing the proportion of the catch used for human consumption and other value
added products (pharmaceuticals, feed ingredients etc.) would increase the profitability and reduce the
amount of waste.
Marine by-products contains valuable protein and lipid fractions as well as vitamins and
minerals. To get a profitable utilisation of rest-raw material from the fish industry the final products
demands a market interest. Knowledge about quality and composition is a necessity. There are major on-
going research on searching of bioactive compounds in marine organisms and development of new
technology for utilisation of this so we can assume that the future will bring more value out of what is
today considered a waste. In order to evaluate possible applications for the products and conservation
techniques of the rest-raw material, it is important that the raw material is characterised based on its
chemical composition and enzymatic activity. The quality of the raw material at the processing site will
determine the manufacturing possibilities. The handling onboard is very important. Marine by-products
are extremely reactive and will be degraded by microbial spoilage, enzymatic reactions and oxidation if
the conservation and handling is not satisfactory.
INTRODUCTION
Today overexploitation of fish resources is a large problem, only about 50-60% of the catch is
used for human consumption. Globally more than 91 million tons of fish and shellfish are caught each
year. Some of the by-products are utilised today, but huge amounts are wasted. Annual discard from the

Rustad, T. EJEAFChe, 2 (4), 2003. [458-463]
Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377 459
world fisheries were (FAO) estimated to be approximately 20 million tonnes (25%) per year. Therefore it
is a great potential for the fishing industry to utilise more of what is landed. This includes “waste” or by-
products or what should really be called rest raw materials. In 200 a total of 232 000 metric tons of by-
products were created by the Norwegian cod fisheries alone, of this 125 000 tons were dumped while 107
000 were utilised. Only 36 000 tons of the by-products were used for human consumption which amounts
to about 15,5 % of the total (RUBIN; 2001). The rest is used for the production of fishmeal, silage and
animal feed. Increasing the proportion of the catch used for human consumption and other value added
products (pharmaceuticals, feed ingredients etc.) would increase the profitability and reduce the amount
of waste.
There is no single definition of what it is that constitutes marine by-products, usually we talk
about viscera, heads, cut-offs, bone and skin. In the regulations we sometimes divide between by-
products that can be used for human consumption and waste/discards/viscera. In Norway the definition is
given as: By-products are products that are not regarded as ordinary saleable products (fillet, round,
eviscerated or beheaded fish), but which can be recycled after treatment. Waste: products that cannot be
used for feed or value added products but which have to be composted, burned or destroyed. Fish
byproducts have often been regarded as fish offal or waste, but this is not how it should be. The term by-
products indicates something that can be utilised. Today the most common understanding of by-products
are all the raw material, edible or inedible, left during the production of the main product. When
producing fish fillets – fillet cuts, backbone, head, liver, gonads and guts are all byproducts (Gildberg,
2002). The by-products are highly perishable, and enzymatic processes are important determinants of
quality of the raw material. The quality and freshness limits the possibilities for utilisation, and
controlling autolysis in the by-products is therefore of crucial importance. Knowledge of enzymatic
activities and variations according to species, season and fishing ground, is needed. pH and temperature
influence enzymatic activities co-operatively, and thereby offer possibilities for controlling it.
USE OF BY-PRODUCTS – HISTORY
The use of by-products is not new. In the Nordic countries a lot of the by-products have been and
some are still being used for various purposes. Fish skin has been used for clothing – shoes, trousers etc.
Also bags, carrier packs and sacks etc were made from this material. The production of fertiliser and feed
from dead fish and by-products was industrialised. In 1903 13 – 14 million cod heads were collected in
Norway and used for production of feed and fertiliser. In the middle of the 1600s, the boiling of liver oil
became usual. Some fish by-products that are used for human consumption include roe (canned, or as cod
roe emulsion), liver (Eastern Europe), cleaned stomach, fried fish milt (as a snack).
It is possible to categorise byproducts in several different ways. One way is to divide into
material used for fertiliser, for feed, for food and for speciality products. Use as fertiliser has as already
mentioned – given good results for crop growth, but the profitability in this is low. The major fraction of
byproducts is used for feed production – in making fish meal/oil. This production also has a low
profitability. There is normally a far better profitability in making products for human consumption while
the highest profitability is in producing bioactive compounds (extracting and purifying) such as enzymes,
bioactive peptides, biopolymers for biotechnological or pharmaceutical application.
The by-products contain valuable protein and lipid fractions in addition to minerals and vitamins.
PROTEIN FRACTIONS
Fish sauce: A large variety of different fish protein hydrolysates are being produced. The oldest
is fish sauce which have long traditions in South-East Asia. Fish sauce, which is the major fermented fish
product, was known in ancient Greece and Rome. Fish sauce is produced in a quantity of about 250 000
tons pr year. It is made by mixing three parts of fish raw material with one part of salt and storing at
ambient tropical temperatures for 6-12 months. Both endogenous enzymes and microbial enzymes
contribute to the degradation of the proteins in the fish and the resulting fish sauce is an amber liquid with
8-14% digested proteins and about 25% salt. The production is simple and requires little sophisticated
equipment, but there is a need for a large storage space (Gildberg, 2002).
Fish silage: Fish silage can be produced from all kinds of low-value fish and fish by-products. It
is almost entirely used for feed. Fish silage is normally made by mixing 2-3% formic acid into the minced
raw material and storing at ambient temperatures till endogenous enzymes have dissolved the fish tissue.
A well-preserved fish silage will normally have a pH of 3-4 which is the optimum pH for fish pepsins.

Rustad, T. EJEAFChe, 2 (4), 2003. [458-463]
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The process usually takes a few days, provided that the raw material has a sufficiently high content of
pepsins and other acid proteases (cathepsins). The silage may be used directly in feed or processed further
by separation of the oil and evaporation to give a protein concentrate. The advantage of producing fish
silage is the low capital investment and simple processing equipment. The disadvantage is the high
transport costs due to the high water content. Norway is the major fish silage producer – producing about
140 000t pr year, mainly from aquaculture byproducts (salmon). Fish silage is a low price product, but is
a good alternative for utilising byproducts that might otherwise have been wasted.
Fish provides about 14 % of the world’s needs for animal proteins and 4-5 % of the total protein
requirements (Venugopal, 1995). The amino acid composition and digestibility of fish proteins is
excellent. It is a challenge to utilise the protein fractions from the by-products as food ingredients. In
order to achieve this, the protein fractions will have to have functional properties. Functional properties
include water- and fatbinding properties, emulsifying properties, viscosity, foaming properties etc.
Flesh from backbones and cut-offs can be used for surimi. This is mechanically deboned fish
flesh that has been washed with water or dilute salt solutions and to which cryoprotectants has been
added. These fractions can also be used for the production of thermostable protein dispersions (Shahidi,
1998). Both surimi and proteins dispersions have good functional properties.
By-products are used to produce protein hydrolysates, both from viscera and fish frames from
the fish-filleting industry (Gildberg, 1992, Liaset, Lied & Espe, 2000). Proteolytic modification of food
proteins to improve palatability and storage stability of available protein resources is an ancient
technology (Adler-Nissen, 1986). Hydrolysates can be defined as proteins that are chemically or
enzymatically broken down to peptides of varying sizes. Chemical and biological methods are most
widely used. Biological processes using added enzymes are employed more frequently and enzymatic
hydrolysis is promising because it results in products of high functionality and nutritive value. Fish
protein hydrolysates can be made in two ways. The first depends on the digestive enzymes of the fish
itself while the second method is based on the hydrolysis of the raw material with added commercial
enzymes (Mohr, 1978). The autolytic process depends on the action of digestive enzymes on the fish
itself. Today much of the fish flavour, fish soup and fish paste products available on the market are
prepared by enzymatic hydrolysis (Shoji, 1990). Protein hydrolysates can be used as emulsifying agent in
a number of applications such as salads dressing, spreads, and emulsified meat and fish products like
sausages or luncheon meat (Badal and Kiyoshi, 2001). Enzymatic hydrolysis has several advantages over
other processing methods for recovering protein from under utilized fish biomass and fish by-products.
However the hydrolysis process often leads to bitter taste in the product. The bitterness restricts the
practical uses of these hydrolysates. The presence of bile in hydrolysis of whole fish and fish viscera may
also cause bitterness in fish protein hydrolysates.
Collagen/gelatine:The demand of collagen and gelatine from the industry throughout the world is
considerable and still rising. By-products from fish processing are a potential source of collagen.
Collagen is the main component in the skin (Norland, 1989; Sikorski and Borderias, 1994), that can be
collected separately from other by-products. Collagen in its purified form has found a number of
pharmaceutical and cosmetical applications. Similarly, gelatine, the hydrolysed form of collagen, is an
ingredient extensively used in the food industry. Gelatine is used as a food additive to increase the
texture, the water-holding capacity and stability of several food products (Borderias et al., 1994). Both
gelatine and collagen have been derived from fish skins and bones, but have been much less studied than
mammalian gelatine and collagen (Norland, 1989, Gudmunsson and Hafsteinson, 1997). The quality and
specific application of the extracted collagen and or gelatine is highly related to their functional properties
and its purity. Known problems with the extraction of collagen from fish skins are the abundance of
pigments and the presence of fish odours, which would restrict its potential use. The uniqueness of fish
collagen from cold water fish lies in the lower content of amino acids, proline, and hydroxyproline (Haard
et al., 1994). Although fish gelatine does not form particularly strong gels, it is well-suited for certain
industrial applications, as for example micro-encapsulations, light-sensitive coatings and, low-set-time
glues. There is also a market for non-gelling gelatine, which has a potential in the cosmetic industry as an
active ingredient (i.e. shampoo with protein). Using fish collagen and gelatine generates new applications
as a food ingredient, because it has properties different from mammalian collagen and because it can be
used in food where mammalian gelatine from cultural or safety point of view is not wanted.
Bioactive peptides: Protamine is a basic peptide containing more than 80% arginine. Protamine
has been found in the testicles of more than 50 fish species. Protamine has the ability to prevent growth of
Bacillus spores. Protamine is being used as an antibacterial agent in food processing and preservation. It
has been reported that many proteins possess antioxidative activities, and fish protein hydrolysates have
been found to possess antioxidative activity (Amarowicz and Shahidi, 1997; Kim et al., 2001).

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Fish enzymes: Proteolytic enzymes from cold-adapted fish have received a lot of interest during
the last decades. These enzymes have been found to be more catalytically active at relatively low
temperatures compared to corresponding enzymes from mammals, thermophilic organisms and plant
sources (De Vecchi & Coppes, 1996, Gudbjarnason, 1999). Fish enzymes have found use as digestive
aids in feeds for fish larvae, cosmetics as well as in the fish industry.
MARINE LIPIDS
Marine lipids have well documented beneficial health effects. High amounts of long chain
polyunsaturated fatty acids (PUFA) like eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic
acid (DHA, C22:6n-3) makes marine lipids unique compared to other lipid sources. These omega-3 fatty
acids have been found to reduce the risk of cardiovascular diseases, hypertension, autoimmune and
inflammatory diseases. It has also been found that fish oils in the diet may help protect against various
cancers. Dietetic research has shown that most people do not have enough n-3 fatty acids in their diet
(Garcia, 1998). The typical American diet has a ratio of 20-30:1 n-6 to n-3 fatty acids while the
recommended ratio is closer to 6:1 (Aparicio et al., 1998; Garcia, 1998). The liver of lean white fishes
such as cod species and the muscle of fatty fish (i.e. herring, mackerel, salmon) are good sources of
marine lipids – as well as blubber oil from marine mammals such as seal. In the last years the industry
have shown a growing interest in new product development where they include different lipid
components from fish in healthcare products (eg. capsules) and in functional foods as microencapsulated
lipids. n-3-products are being used in infant formulas, dietary supplements and in “functional” foods and
beverages. These are foods that provide a health benefit beyond basic nutrition. Phospholipids,
glycolipids, squalene and vitamins are other lipid components from marine rest raw material which have
properties that might make them interesting for the food and health care market. In addition to using the
fish oil as a food supplement, it is also an option to enrich everyday products like bread, egg, margarine
etc. with n-3 long chain fatty acids. There are already several such products on the market today.
The main factor limiting the application of these PUFAs in food products is their susceptibility to
lipid oxidation, which may effect the flavour and decrease the nutritional value. Fish lipids are susceptible
to oxidation because of the high content of polyunsaturated fatty acids. Oxidation is influenced by factors
like atmosphere (oxygen), temperature, light and chemical composition of the material (unsaturation of
fatty acids, pro-and antioxidants). In order to inhibit oxidation in marine lipids, synthetic antioxidants
have been widely used, but there is an increasing tendency toward using natural antioxidants such as
rosemary and salvie. This is currently being investigated in the ongoing EU-project Fishery by-products.
It has been reported that many proteins possess antioxidative activities, and fish protein hydrolysates have
been found to possess antioxidative activity (Amarowicz and Shahidi, 1997; Kim et al., 2001). Careful
handling and process modifications may also be of help in minimising the problems with oxidation.
WHAT IS NEEDED TO INCREASE THE UTILIZATION OF FISHERY BY-PRODUCTS FOR
VALUE-ADDED PRODUCTS?
To get a profitable utilisation of rest-raw material from the fish industry the final products
demands a market interest. Knowledge about quality and composition is a necessity. There are major on-
going research on searching of bioactive compounds in marine organisms and development of new
technology for utilisation of this so we can assume that the future will bring more value out of today’s
waste. The quality of the raw material at the processing site will determine the manufacturing
possibilities. A very important factor for the by-products will then be the handling onboard. Viscera from
marine fish are extremely reactive and will be degraded by microbial spoilage, enzymatic reactions and
oxidation if the conservation and handling is not satisfactory. Optimal logistical solutions for the bulk
product is therefore of major importance.
Sorting :One of the problems for utilisation of by-products today is the lack of gentle machinery
for evisceration. The equipment used today is too “rough” and the viscera are destroyed and it is difficult
to separate whole liver and roe. At SINTEF F&A in Trondheim research is being done on development of
automatic sorting equipment based on robotic technology. The aim is to develop a system that is able to
recognise the different by-product fractions and to sort these automatically.
In order to evaluate possible applications for the products and conservation techniques of the
rest-raw material, it is important that the raw material is characterised based on its chemical composition

Rustad, T. EJEAFChe, 2 (4), 2003. [458-463]
Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377 462
and enzymatic activity. In the EU-project Utilisation and stabilisation of by-products from cod species
(QLK1-CT-2000-01017), acronym Fishery by-products, the chemical composition and stability of by-
products from 5 different cod species at three different seasons and three different fishing grounds are
being characterised. Proteolytic activity in by-products from cod species caught at three different fishing
grounds was characterised and compared. Relationships between proteolytic activity and quality
parameters were examined. Median proteolytic activity was highest in viscera at pH 3 and 35°C. Activity
in cut off and liver samples was highest at pH 3, 35°C and 50°C, respectively. At pH 5 highest median
activity for all samples was at 50°C. Highest activity at pH 7 was at 50°C in viscera and 65°C in liver and
cut off. Proteolytic activity in viscera is more influenced by species, while proteolytic activity in cut off is
more influenced by fishing ground.
Keeping the by-products from all fractions at neutral pH and low temperature seems to be the
best way of keeping the proteolytic activity down. However, the activity in viscera is still high under
these conditions, so procedures for inactivating proteases should be undertaken.
Weight fractions and lipid composition has been evaluated in liver, visceras and cut offs. Weight
of the mentioned fractions, lipid content, amount of individual fatty acids and vitamin E were evaluated
and compared. Multivariate data analyses (PCA analysis) on weight, free fatty acids, total lipids, vitamin
E and fatty acid composition of selected by products, show that the samples from Norway and Iceland are
distributed differently in the PCA plot. This indicates significant geographical difference in the chemical
composition of the rest raw materials. Data from weight of liver and viscera showed differences between
all 3 fishing grounds evaluated.
There is not an endless amount of fish in the sea and therefore we need to manage our fisheries
better than in the past. There are many ways that are possible to achieve this. Today, the conditions
onboard the fishing vessels are not optimised for a cost effective utilisation. Increasing the proportion of
the catch that is used for human consumption and other value added products (pharmaceuticals, feed
ingredients etc.), will increase the profitability and reduce the amount of waste.
In order to achieve this it is necessary to:
• develop systems to sort and handle the by-products onboard
• find safe and cost-effective preservation methods
• improve the logistics to get the by-products from the vessels to the processing plants
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