Conventional fishing cannot meet the growing demand for omega-3 oil for human consumption.
That is why a research team from DTU, led by senior researcher Ann-Dorit Moltke Sørensen, is investigating whether two unwanted species—starfish, of which there are too many, and the invasive black-mouthed goby—can be used as sustainable sources of fish oil containing omega-3 fatty acids.
Long-chain omega-3 fatty acids keep the human heart, brain, and cells healthy. They are found primarily in fish, where they are bound in the fats.
The researchers have made the most progress in studying starfish, which have a high content of the valuable phospholipids. Omega-3 fatty acids bound in phospholipids are considered to be of particularly high quality because they are generally more easily absorbed by the body compared to omega-3 fatty acids bound in triglycerides—which are also found in starfish.
Traditionally, fish oil is extracted by applying high heat and pressure to the fish, so that the fats are extracted as oil. However, this method is energy-intensive and ineffective because phospholipids cannot be extracted using heat and pressing alone.
Supercritical CO2 extraction
Instead, the research team uses supercritical CO2 extraction, in which carbon dioxide is subjected to sufficiently high pressure and an appropriately high temperature so that it behaves as both a gas and a liquid. This allows CO2 to penetrate the raw material as a gas and effectively dissolve and extract fats as a liquid—including phospholipids when the method is used with ethanol as a solvent.
The method is carried out at moderate temperatures and with short processing times and is therefore considered by researchers to be more environmentally friendly, energy-efficient, and gentler on the product than the traditional method.
Unfortunately, the method has so far only extracted 10 percent of the particularly valuable phospholipids at the pilot scale. This contrasts with laboratory experiments, where various modifications to the process have made it possible to extract all omega-3 fatty acids—both those bound in triglycerides and those in phospholipids.
The researchers expect to solve the problem in the future by using custom-built equipment where the settings can be precisely tailored to the raw material.
There is still hope
In addition to the limited extraction of phospholipids, the process is not yet as climate-friendly as desired because the current process has not been optimized for industrial scale. However, the project has provided valuable insights, and the potential remains, emphasizes Ann-Dorit Moltke Sørensen.
"I am confident that we can make the process more sustainable by capturing and reusing the CO2 and ethanol we use. At the same time, I believe that with customized equipment, we can extract more omega-3 fatty acids from starfish, so they can become a new and sustainable source of omega-3," she says.
The project was carried out in collaboration with industry partners Nordic Marine Nutrition and Sea Longevity.
