Production of High Quality Fish Oil by Thermal Treatment and Enzymatic Protein Hydrolysis from Fresh Norwegian Spring Spawning Herring By-Products

Abstract

AcknowledgementsAuthors wish to thank the Norwegian Research Council (project 173326) and the Ministry of Foreign Affairs for financial support to carry out experiments and to prepare this paper. Grøntvedt Pelagic is thanked for kindly providing herring by-products for the experiments and for making it possible to run the experiments near their filleting factory. AbstractThere is an increasing demand for omega-3 containing fish oils. By-products from fish fillet production can be utilized for the production of fish oils and be a valuable source of omega-3 for human consumption. The aim of this work was to evaluate industrial processes for production of quality oil for human consumption made from Norwegian spring spawning herring by-products.A mobile production plant was used to compare two industrial processes, thermal treatment (wet immediately after filleting. Results show that high quality herring oil can be produced from fresh by-products. The use of by-products immediately after filleting resulted in a low amount of free fatty acids for all the produced oils (below 0.4 %). Thermal treatment at 70 °C resulted in an oil with lower oxidation status and higher stability compared to the oils produced by enzymatic protein hydrolysis. Nevertheless, both processing methods gave a crude oil of high quality compared to crude oils on the market.

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“…Oil obtained by thermal separation before hydrolysis (first stage) had several times lower PV values indicating the significance of the oil separation prior to hydrolysis (Table ). These results were in accordance with previous studies indicating that thermally separated oil from is more stable and has better oxidation status compared to oil obtained after enzymatic hydrolysis (Carvajal et al ., ; Slizyte et al ., ). Even oil obtained at a hydrolysis time of 0 (when the material is mixed with warm water and warmed up to the hydrolysis temperature) showed the first signs of oxidation, which increases with hydrolysis time leading to elevated PV value in the oil obtained after hydrolysis.…”

“…However, our results show that the amount of FFA increased with increasing separation temperatures (from 20 to 77 °C) with the highest amount measured at around 77 °C (Table ). The same development pattern was observed in the crude oil extraction from fresh herring by‐products where the highest amount of FFA was measured in the oil extracted at 80 °C (Carvajal et al ., ). The lipolysis could be caused by an activity of different lipolytic enzymes acting during the increase in temperature in the materials.…”

“…This indicates that temperature is an important factor for oxidative quality of fish oil, even the oil is exposed to elevated temperatures only for a few minutes. The same tendency was observed with separation of oil from fresh herring by‐products at different temperatures (Carvajal et al ., ) indicating that even 10 °C increase in oil separation temperature can lead to significant increase in oxidative status of the oil.…”

“…To obtain more sustainable utilisation of these by-products, a techno-economically feasible process leading to high-quality products is needed. Thermally separated oil from fish by-products is more stable and has better oxidation status compared to oil obtained after enzymatic hydrolysis (Carvajal et al, 2015;Slizyte et al, 2017). In addition to higher quality oil, separation of oil before hydrolysis will reduce the amounts of raw material directed for hydrolysis.…”

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“…Furthermore, marine oils are already in short supply, since both the health food industry and the producers of fish food have an increasing demand for this essential ingredient. Thus, a higher volume of marine oils also has to be produced and harvested from the oceans (Carvajal et al 2015). Because of the growing market for seafood and biomarine ingredients, the Norwegian fish farming industry is expected to grow fivefold within year 2050 (Olafsen et al 2012).…”