Olive oil by-product shows functional food potential

By Tim Cutcliffe contact

- Last updated on GMT

© iStock/ leonori
© iStock/ leonori
Adding an industrial by-product of olive oil dramatically improves the nutritional content of fish burgers, but an additional extraction process is needed to achieve satisfactory taste, say researchers.

Enriching fish burgers with 10% dried olive pomace flour (DOPF) increased their content of phenolic compounds by a factor of 13, according to a study published in Food Science and Nutrition​.

The addition of the olive paste also enhanced the flavonoid content and antioxidant activity of the burgers.

“The addition of olive by-products leads to an increase of the phenolic content and the antioxidant activity,”​ wrote the team, a collaboration between the University of Foggia and the Institute of Sciences of Food Production (ISPA), National Research Council of Italy (CNR).

However, the bitterness from the added olive paste gave the enriched burgers an unpleasant taste. The odour of the cooked burgers was also unacceptable, while colour and texture also suffered a deterioration compared to the ‘control’ burgers without the DOPF.

“As expected, the DOPF enrichment considerably improved the fish burger quality, but it negatively influenced the sensory properties due to a very bitter and spicy taste that became the products unacceptable,”​ explained corresponding author Professor Matteo Alessandro Del Nobile of Foggia University.

The researchers eventually produced fish burgers which had a balance of acceptable sensory properties and enhanced nutritional quality (total phenols content and antioxidant activity) using a combined hydration/ extraction technique with water or milk. This removed the bitter taste and unacceptable odour.  


Volumes of waste from food processing are large and can potentially create disposal and pollution problems. Thus, the utilisation of a by–product which contains nutritionally beneficial bioactive compounds makes sense from both health and economic standpoints.

The authors suggest that the nutritional benefits of the enhanced phenolic content provide the possibility “to consider the new fish burger suitable for a balanced diet with the possibility to be regarded as a new functional food.”

Taste improvement process

To overcome the sensory quality issues, the researchers tried pre-treating the burgers with either water or milk. Although taste improved, the odour of the cooked burgers actually worsened.

Consequently, they tried a two-stage process of hydration and extraction which resulted in significant improvements in sensory quality (particularly using milk). In particular, the bitter taste was substantially decreased.

“The hydration/extraction with either water or milk leads to a substantial decrease of the bitter taste related to DOPF,” ​observed the researchers.

Both cooked and uncooked final products had palatability scores only marginally below those of the DOPF-free burgers.

Although the extraction process lowered the bioactive compound content and antioxidant activity in the burgers, the total phenols content of the DOPF-enriched burgers was still over 3.5 times that of the olive-paste-free controls.

The extraction process therefore enabled production of burgers with a balance between enhanced nutritional content and acceptable sensory quality.

Source: Food Science and Nutrition
Volume 5, Issue 4   Pages 837-844   DOI: 10.1002/fsn3.461
“Fish burger enriched by olive oil industrial by-product”
Authors: Annamaria Cedola, et al

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