Removing flavour from fish offcuts

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By Milthon Lujan

Nofima’s doctoral research fellow Silje Steinsholm has used a magnetic tongue to identify flavours that may make fish offcuts suitable for human consumption. On 12 April, she publicly defended her thesis and presented useful findings for the industry that wants to create food from fish offcuts.

Large amounts of offcuts are created from fillet production within the food industry. Some of this residual raw material is further processed into feed products, but significant amounts go to waste. This is not compatible with a circular bioeconomy, where all constituents of food resources should be utilised in the best possible manner. A greater proportion of the raw material should therefore be used for human consumption. To increase this proportion, Steinsholm has used enzymatic protein hydrolysis in her doctoral work.

Brief information about protein hydrolysate

The proteins found in filleting offcuts are difficult to access, but the process of enzymatic hydrolysis helps convert these proteins into water-soluble peptides. This takes place by adding enzymes, which act as scissors that cut the proteins into smaller and more water-soluble peptides (protein hydrolysate). The water phase can be separated out and dried, and this leaves a protein-rich powder that has many areas of application.

Flavour challenge

The fact that the hydrolysates have an unappealing and bitter taste is a challenge, and this also means that their use is rather limited. The flavour depends on hydrolysis parameters and the residual raw material being used during production. In order to remove the flavour, one must understand the relationships that exist between taste and chemistry. The development of different flavours, chemical composition and functional properties have therefore been the starting point for this study. The flavour and nutritional value of a certain product are important factors in terms of consumer choice, while the functional properties, such as the ability to form and stabilise emulsions, can be important production factors when changing the texture of a product.

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Useful findings for the industry

In the project, Steinsholm has evaluated the importance of enzymes, residual raw material and membrane filtration in relation to the end product. She has used the magnetic tongue (NMR spectroscopy) to find out which chemical substances produce flavour. She has connected these substances with objective measurements made by the taste judges on Nofima’s sensory panel. With the help of chemical analysis and advanced statistics, Steinsholm has got a good overview of the substances that produce different flavours.

In the study, Steinsholm found a link between several metabolites (different small molecules found in all living organisms) and flavours, and that it is possible to remove the very smallest metabolites by nanofiltration. The study shows that the intensity of bitterness is produced by small peptides and depends on the choice of enzyme and the degree of hydrolysis. Knowledge about the production of hydrolysates with low flavour intensity will benefit the industry in relation to protein hydrolysate production for human consumption.

NMR spectroscopy has been used in trials to define flavour in tomatoes, coffee beans and olive oil, but this is probably the first study that has been conducted on protein hydrolysates. The technology is not quite there yet, but NMR spectroscopy may help simplify the interpretation of flavour in the future.

One of the scientific articles on the findings made by Steinsholm and scientists at Nofima, the University of Bergen and Roskilde University has been published in the renowned ‘Journal of Agricultural and Food Chemistry’.

Silje Steinsholm publicly defended her PhD on 12 April at the University of Bergen, Norway, with the thesis ‘Sensory and physicochemical properties of enzymatic protein hydrolysates’. Steinsholm, who is 32 years old, completed a master’s degree in marine biotechnology at the University of Tromsø in 2014. The doctoral project was conducted at the Nofima food research institute in Bergen and the Department of Chemistry at the University of Bergen (UiB). The main supervisor was Tone Aspevik (Nofima) and the co-supervisors were Åge Oterhals (Nofima) and Jarl Underhaug (UiB).

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The doctoral degree has been included as part of Nofima’s self-financed project PEPTEK, but is also linked to the EU project AQUABIOPRO-FIT (financed by BBI-JU (Horizon 2020)) and the RCN project WHITEFISH.

Contact person
Silje Steinsholm
Ph.D. Student
Phone: +47 92068442

Tone Aspevik
Phone: +47 971 55 527


Silje Steinsholm, Åge Oterhals, Jarl Underhaug, Ingrid Måge, Anders Malmendal, and Tone Aspevik. 2021. Sensory Assessment of Fish and Chicken Protein Hydrolysates. Evaluation of NMR Metabolomics Profiling as a New Prediction Tool. Journal of Agricultural and Food Chemistry 2020 68 (12), 3881-3890
DOI: 10.1021/acs.jafc.9b07828 

Source: Nofima

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