Utilization of by-products from the salmon industry: The chemical composition and storage stability of Atlantic salmon (Salmo salar) heads

Previous studies have indicated the current situation and the need of utilizing by-products from the salmon industry. Awareness of the potential values behind these by-products is rising, but most of the by-products ended up in low-value silage for animal feeding or simply wasted. The main goal of this project is to investigate the possible utilization of heads from locally farmed Atlantic salmon (Salmo salar) in Iceland. Obtaining knowledge of the physiochemical properties of the different parts from salmon heads and their quality and stability as affected by frozen storage conditions are a prerequisite for further value-adding. There were three major parts of this project. The first part was to determine the yield, content of water, protein, ash, lipid, fatty acid, free fatty acid, phospholipid, peroxide, thiobarbituric acid reactive substances in brain, tongue, eyes, pectoral fins, and gills. The second part was to trace these contents for those five parts individually every two months from October 17th, 2018 to February 26th, 2019. The third part was an attempt to extract collagen from 5 whole salmon heads. The contents of water, lipid, protein and ash had wide ranges among the five analyzed parts and water, protein and ash were stable for all five parts during the 4-month storage at -25°C. Brain, tongue and eyes showed high amount of lipid, and tongue and eyes could be interesting sources for lipid extraction considering the size and removability. Bony tissues like tongue, fins and gills contained more protein and ash than soft tissues like brain and eyes. And gills possessed large varieties of interesting minerals like zinc and calcium, and the content of calcium was high. Fins were very prone to lipid oxidation and the major part of primary oxidation was finished already before the samples were sent to Matís. Gills and eyes also had high level of both primary and secondary oxidation during the 4-month storage. Collagen extracted from whole salmon head was slightly yellowish and had a relatively satisfying yield of 6.4%. The results above revealed the potential value behind salmon heads to some extent and processing these parts separately in line with their physiochemical properties would lead to the value creation from salmon head.Fyrri rannsóknir hafa gefið til kynna að nauðsynlegt sé að nýta hliðarhráefni úr laxavinnslu betur en nú er gert. Þekking á vinnslumöguleikum þessa hráefnis fer aukandi, en þó endar meirihluti hliðarafurða í vinnslu ódýrra afurða eða er jafnvel fleygt. Meginmarkmið verkefnisins var að rannsaka hvernig nýta megi hausa úr eldislaxi á Íslandi með því að afla þekkingar á efnasamsetningu og eðliseiginleikum mismunandi hluta hausanna og stöðugleika þeirra í frostgeymslu. Verkefninu var skipt í þrjá meginþætti. Í fyrsta hluta verkefnisins var nýting og efnasamsetning (vatn, fita, prótein, aska, fríar fitusýrur, fosfólípíð og oxunarafleiður) greindar í heila, gellum, augum, uggum og tálknum laxafiska. Í öðrum parti verkefnisins var stöðugleika þessara innihaldsefna fylgt eftir í gegnum frostgeymslu í fjóra mánuði. Í þriðja og lokahluta verkefnisins var skoðað hvort nýta mætti laxahausana til kollagenútdráttar. Efnainnihald haushlutanna var æði misjafnt, en það var stöðugt í frostgeyslu við -25°C. Heilinn, gellurnar og augun reyndust vera fituríkir vefir, og gellurnar og augun gætu nýst vel til vinnslu á lípíðum vegna nýtingar og stærðar þessara vefja og því hve einfalt var að fjarlægja þá úr hausunum. Vefir með hærra hlutfall beina, s.s. tálkn og uggar laxanna, innihéldu meira prótein og ösku en mýkri vefir hausanna, s.s. augu eða heili. Tálknin innihéldu einnig áhugaverð steinefni, svo sem sínk og kalk. Uggarnir voru sérstaklega viðkvæmir fyrir fituoxun. Tálknin og augun urðu einnig fyrir oxun við frostgeymsluna. Kollagen sem unnið var úr heilum laxahausum var gulleitt og ásættanlegar heimtur við útdráttinn fengust (6.4%). Niðurstöður verkefnisins sýndu að nýtingarmöguleikar laxahausa eru mun víðari en áður var haldið og að vinnsla hvers parts haussins (tálkna, auga, heila, gella, ugga) gæti ýtt undir verðmætasköpun í laxavinnslu.AVS (Added Value of Seafood) fund from the Ministry of Fisheries Agriculture in Icelan