I
t should be possible to eat the whole fish, not only the fillets. And it should be possible for a major proportion of herring, sprat and blue whiting to be used directly as food, instead of taking the energy demanding route via fodder for fish farms.
Researchers at Chalmers Food Science are now looking at a method for isolating protein for use in food. The method can separate proteins from shell, bone and skin without any prior mechanical cleaning. The proteins are dissolved at extreme pH values and can then be separated from insoluble components such as pigment, fat skin and bones by centrifugation or filtration. The process is called pH-shift since it alters the pH values on a number of occasions.
Herring, fish offal and mussel
At Chalmers, the method has been tested on whole herring, blue whiting, cod frames and mussels, which are used far from optimally at present. Herring is a well known food fish, but large parts of herring that are caught are used for fish meal/fish oil which is mixed into fodder for e.g. fish farms.
The situation is worse still regarding blue whiting and sprat which are used as food to only a very small extent although they contain high quality protein. Their small size, the proliferation of bones and the dark pigmentation are some of the reasons.
When cod is filleted mechanically, the head and frame are left as offal. The head in particular contains large quantities of fine meat, only a small quantity of which can be pressed out mechanically. The meat-rich cod residues are generally used instead as food for mink or as fishmeal.
In Sweden, mussels are increasingly cultivated as water purifiers since they remove nitrogen and phosphorus from water. About two thirds of the harvested mussels are used as food while as much as one third is rejected because of damage or because they are too small. In order to increase mussel farming, there must be a profitable market for this third also which is used only as fodder today.
Increased storage life and safety
The proteins that are isolated have a very low content of impurities and fat. Removal of the fat may be seen as a strange idea as it largely consists of beneficial Omega-3 fatty acids. In a processed product, however, fat can cause a lot of problems since the polyunsaturated fatty acids easily oxidise and thus turn rancid, especially at low pH values. Reduction of the fat content can therefore increase shelf life.
Some contaminants found in the environment are also fat soluble, and it has been found that both dioxins and PCB have been removed from Baltic herring during the pH-shift process. Toxins in blue mussels have also been greatly reduced.
Surimi, marinade and coating
On the Swedish market there are as yet no pH-shift isolated proteins. Commercial efforts are however made in both the US and Iceland, for instance as an ingredient of surimi.
Surimi is a traditional raw material that normally consists of deep frozen washed fish mince stabilised with cryprotectants. In Asia, surimi has a huge market and has been used for a long time in gelled "kamaboko" products. The only example of this product category in Sweden is crab sticks. It is possible to use the pH-shift method instead of classic washing based methods to produce surimu. One advantage then is the higher protein yield.
Two other interesting fields of use for pH-shift produced protein at industrial scale are coating and injection marinades.
Coating is made by an American company which uses it on fried products such as fish fingers. The great advantage is that the proteins do not absorb the frying fat to such an extent as carbohydrates, and they also protect the water retention capacity of the fried fish/meat. It thus producess a juicier and less fatty product.
Injection marinades of pH-shift isolated protein are made in Iceland. The protein marinades can then be injected into fish fillets instead of salts or phosphates. The fish fillet then has better water retention properties in quite a natural way; quite simply, it becomes fish-in-fish. There are strict safeguards to ensure that both the marinade and the fillet are of the same fish species.
Now it is time for the Swedish market to become active. Some companies have already shown interest in research at Chalmers, and with the help of research funds that have been applied for, the team is planning scaling up tests from laboratory to pilot scale.
Author
:
Sofia Marmon
is a postgraduate student at the Department of Food Science, Chalmers University of Technology
E-mail:
sofia.marmon@chalmers.se
Ingrid Undeland
is project leader. She is Assistant Professor at the Department of Food Science, Chalmers University of Technology
E-mail:
undeland@chalmers.se