Inventing uses for mussels too small to eat

Mussel farming in the Baltic Sea could potentially help to counteract eutrophication while at the same time providing economic opportunities for small and medium enterprises using mussels as food, feed, and fertiliser.

Exploring the potential of mussel as feed is an academic with an unusual background. Indrek Adler is earning his Ph.D at the Estonian Maritime Academy, a part of the Tallinn University of Technology. His interest is potential applications for mussels as feed or in the pharmaceutical, cosmetic, or nutraceutical industries.

An unconventional path to academia

He comes to his doctorate with a degree in business studies and a working life spent on the commercial side of different companies. But he wears a second hat too, that of a coastal fisherman, an identity he has carried for many years having fished recreationally since he was a child. He represents the fourth generation of fishers in his family, his grandfather was in fact a full-time professional fisherman, and for his father too it was almost an occupation. Today, Mr Adler lives on the Pärispea peninsula, the northernmost tip of Estonia, where he has ready access to the sea and can indulge his hobby whenever possible.

Fishing even for sport has over the years showed Mr Adler how the stock status of the species he targets has been changing. Catches fluctuate from year to year with some species in abundance one year and absent the next, new species enter the area and gradually take over, but the overall trend has been one of decline. So, three or four years ago Mr Adler began to wonder how he could contribute to improving the situation for the benefit of fishers and the wider coastal community. He recognised that catches were not big enough for a fisher to make a living and part of the reason for this development was pollution in the water. Solving the pollution problem would contribute to rebuilding the fisheries so that coastal fishers could once again expect to catch enough fish to support themselves. Researching possible ways to improve the coastal environment, Mr Adler came across aquaculture but noted that it too tended to add to pollution levels unless it related to the production of macroalgae or mussels.

Low salinity in the Baltic hinders mussel growth

However, the low salinity levels in the Eastern Baltic meant there were not many species that thrive in this environment. Further research showed that the blue mussel (Mytilus edulis/M. trossulus) was about the only species that would be feasible. Mr Adler then joined the masters programme at the Estonian University of Life Sciences with a view to gaining a better understanding of the issues and to identifying a possible solution.

Eutrophication in the Baltic Sea is widespread; Helcom assesses over 97 of the sea to suffer from eutrophication due to past and current inputs of excess levels of the nutrients, nitrogen and phosphorus. The nutrients boost the production of algae, cyanobacteria, and benthic macro vegetation leading to greater turbidity and increased creation of organic material that in turn depletes oxygen levels at the sea bed as it decomposes. Nutrient inflows from land have decreased significantly over the last decades, but the effects of this decline have not yet manifested themselves. A more recent source of nutrients is the aquaculture industry where uneaten feed and faecal matter contribute to eutrophication locally as well as in a wider area as the particles spread.

However, addressing the problem by farming seaweed or mussels is still a challenge, partly because low salinity hinders the rapid growth of the biomass, but also because there is no regulatory framework in place that will enable the allocation of space in the sea for this activity. More importantly, though, farming mussels is not economically viable because the biomass produced has no value. It could be used as fertiliser on fields, but that has little or no added value. It cannot be used for human consumption because the mussels in the Gulf of Finland are too small due to the low salinity. Extracting the meat is very expensive because of the small size of the mussels. It can be done with, for example, enzymes, but that pushes the price up. So, there are few uses to which the biomass can be put unless a valuable and easily extractible ingredient can be identified in the mussel. Mr Adler’s research at the masters level focused on finding suitable techniques to extract the meat from the shell simply and economically. This area had not really been explored before as countries where mussels are grown in the Baltic Sea do not use the biomass as food for human consumption.

Three potentially useful (and valuable) end products

He developed a method in which the mussels were first ground in a meat processor to create a paste. When mixed with water the particles of shell in the paste sink faster to the bottom than the meat. The meat and water can thus be decanted while most of the shell will stay back. For a small or medium enterprise this would be an economically viable way of separating the shell from the meat. The end products at this stage of the experiment are the crushed shell, and the meat and water mixture. The crushed shell also contains a certain level of protein and Mr Adler thinks it could be used as poultry feed either on its own or as an ingredient. It offers calcium, nutrition in the form of protein, and the grit that birds need to digest their feed. The water is another potentially useful product as some studies have shown that it contains a compound that could, for example, prevent the oxidation of cut fruit (the discolouring that occurs when the cut piece is exposed to air). This may be useful to the retail sector as the water is organic and has no side effects. However, the water has a certain off taste. To remove it Mr Adler is experimenting with the addition of citric acid to the mixture of mussels and water. The really interesting end product, however, is the meat which, after centrifugation and drying, appears as a powder with a very high (65-70) content of protein. It can potentially be used as a standalone product or more likely as an ingredient in other products to increase their protein content. This powder is intended for human consumption as it will earn a higher price than if it were used for animal or bird feed.

The experiments have also resulted in several other interesting observations. One is that the harvest season influences the yield from the mussels and the colour of the final protein powder. Powder samples from the spring and fall batches of the mussels have now been sent for chemical analysis to investigate the reasons for these differences. That there should be a difference is not surprising as in the spring the mussels are coming out of the winter season, they have not been feeding, while in the fall they are well fed, the water is a bit warmer, and this could lead to differences in the chemical composition. In addition, the spring harvest has a much higher proportion of barnacles in the biomass compared with the autumn harvest. Currently Mr Adler removes the barnacles (manually) as they do not add any nutritional value to the final product. The yield of protein powder from a batch of spring mussels is 5-8, while an autumn batch delivers better than 8.

Solutions must be reliable, cost-effective, and industrially scalable

The overall goal of the experiments is to identify readily scalable ways of producing useful products from the mussel biomass. This means that fancy or expensive ingredients or techniques are ruled out. The off-taste issue is an example of a challenge that can be addressed in different ways, but for Mr Adler the solution needs to be industrially scalable. The protein powder can be marketed as a sustainable product as it is produced without harming the environment. On the contrary, the raw material (the mussels) from which it is derived has a beneficial impact on the environment. Even the ropes to grow the mussels will be made of coconut fibre to ensure the sustainability of the operation, while buoys and anchors will also be made of environmentally friendly material. If everything works out as planned farming mussels could be a way for communities to cheaply improve their coastal environment and at the same time earn something from it—which was the outcome Mr Adler hoped to achieve when he embarked on this journey.