Turid Rustad, Professor NTNU in Norway, explains the opportunities and challenges when it comes to the full utilisation of the catch of pelagic fish to meet the increasing demand for food
The world population is increasing and is expected to reach 10 billion by 2055. This leads to an increased demand for food, especially high-value proteins and lipids. Today, only 5% of protein consumed comes from the ocean, while about 17% of the animal protein is supplied by fish and marine food. To increase the availability of high-value protein, there is a need to increase the amount of food coming from the ocean. Since most fish stocks are already fully exploited or overexploited, we cannot expect to increase the amount of captured fish. One way to increase the amount of food from the ocean is to improve the utilisation of the catch. Up to 50% of the fish is commonly discarded when preparing seafood industrially. Others claim that seafood processing discards and by-products make up around 75% of the total weight of the catch.
Today, the potential of rest raw material is not fully exploited. There is no single definition of marine by-products. Usually, we talk about viscera, heads, cut-offs, bone, skin and fish that is damaged or unsuitable for human consumption (or further processing) and bycatch. In Norway, ‘by-products’ are defined as products that are not regarded as ordinary saleable products (fillet, round, eviscerated or beheaded fish), but which can be recycled after treatment. ‘Waste’ includes products that cannot be used for feed or value-added products, but which have to be composted, burned or destroyed. Marine by-products intended for human consumption are not included in this definition and the term rest raw material should, therefore, be used.
Increasing demand for more convenient products – fillets, ready to heat/ready to cook meals leads to a higher proportion of fish that is being processed before sale. The trend in the Norwegian pelagic industry is towards more processing instead of exporting the fish as frozen whole fish. In 2018, Norway generated approximately 205,000 tonnes of rest raw material from the pelagic industry out of a total catch of 1,296,000 tonnes (Richardsen et al., 2018). However, a large part of the mackerel is still exported as round frozen fish.
The rest raw material from pelagic fish contains high amounts of beneficial and healthy long-chain omega-3 fatty acids, high-quality protein and other valuable components such as nucleic acids, calcium and phosphorus. The rest raw material, therefore, has high potential in the production of high-quality bio-molecules with various applications within the food, pharmaceutical and cosmetic industries.
This upward trend in filleting of pelagic species, mainly herring and mackerel, will produce higher amounts of rest raw materials. It is, therefore, highly important to study different ways of utilisation in order to utilise this resource to the fullest of its potential. The main challenges with the utilisation of rest raw material from pelagic fish are the high-fat content and the high content of dark muscle.
The quality of the raw materials and retaining the quality of the rest raw materials is one of the key factors for successful utilisation where fresh raw material gives better products. Rest raw material can be divided into two main groups: fractions with a high concentration of different endogenous enzymes (fractions containing viscera or blood) and more stable fractions such as heads, skin and bones. The first group is especially susceptible to fast degradation even at low storage temperatures.
In Norway, the main part of rest raw material from pelagic fish is used to produce fish meal and oil. The fish oil is currently the main product generated from the rest raw material of fatty fish and has traditionally been produced by cooking and pressing followed by centrifugal separation. However, the high temperatures used may be hard on the sensitive marine lipids, leading to faster degradation and oxidation. Carvajal et al. (2015) showed that high-quality herring oil could be extracted from fresh herring rest raw material with more gentle heating (60-70°C).
Different types of protein fractions can be produced from fish rest raw material. Flesh from backbones and cut-offs can be used for the production of fish mince and surimi. Recovery of proteins with good functional properties from rest raw material and small fatty pelagic fishes has been difficult due to the high content of heme proteins and lipids, resulting in pressure lowering and oxidation problems. The pH shift method where the proteins are solubilized at either high or low pH and then precipitated at isoelectric pH has been shown to give good yields and be a good method for removal of heme and lipids (Abdollahi and Undeland, 2018).
Enzymatic hydrolysis is a processing method for recovering both fish oil and protein from fish rest raw materials. Fish protein hydrolysates (FPH) have good functional properties (water-holding, texture, gelling, foaming and emulsification) as well as high nutritional value. Hydrolysates from pelagic rest raw material have also been shown to have bioactive properties such as antioxidant activity and blood pressure-lowering effect.
Some of the challenges related to producing protein hydrolysates are related to taste. The production of tasteless hydrolysates from pelagics has been studied in several projects. Both the bitter peptides and the lipids and lipid oxidation products in the hydrolysate fractions have been shown to contribute towards the unwanted bitter taste.
The current primary use of pelagic rest raw materials is towards low-end products – for production of fish meal used for aquaculture feed and pet food. A shift towards the production of higher-quality products for human consumption will generate a higher value as well as resulting in higher efficiency in the bio-economy.
Abdollahi, M. and I. Undeland (2018). “Structural, functional, and sensorial properties of protein isolate produced from salmon, cod, and herring by-products.” Food and Bioprocess Technology 11(9): 1733-1749.
Carvajal, A., et al. (2015). “Production of High Quality Fish Oil by Thermal Treatment and Enzymatic Protein Hydrolysis from Fresh Norwegian Spring Spawning Herring By-Products.” Journal of Aquatic Food Product Technology 24(8): 807-823.
Richardsen, R.; Myhre, M.; Nystøyl, R.; Strandheim, G. and Marthinussen A. 2019. Analyse av marint restråstoff 2018. SINTEF Ocean report 2019:00475 https://www.fhf.no/prosjekter/prosjektbasen/901336/
Rustad, T., et al. (2011). “Possibilities for the utilisation of marine by-products.” International Journal of Food Science & Technology 46(10): 2001-2014.
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