He is also exploring possible ways of sustainably regulating the level of essential nutrients (such as selenium) in farmed fish.
Since its introduction in the nineteen-sixties, the Japanese oyster (Crassostrea gigas) has expanded its habitat to include the Flemish and Dutch coast. Controlled and sustainable farming of these oysters will require cultivation facilities on land, but this must not be allowed to compromise the flavour of the final product. The flavour is partly determined by the food ingested by the oysters. Unsaturated fats play an important role. Feeding suitable types and amounts of these fatty acids to the oysters, via specific algae for example, may provide a key to influencing the flavour profiles.
In order to achieve this, Professor Luten´s research will focus on the volatile compounds released during the consumption of Japanese oysters. The first job is for trained flavour specialists to define these aromas. The flat oyster (Ostrea edulis) will be subjected to the same analysis. According to experts, this oyster is a more exclusive product and therefore has a higher retail value than the Japanese oyster.
The research group is developing advanced techniques for acquiring a concentration of the volatile aromas, which are only present in very low amounts. This is expected to lead to the detection of dozens of volatile compounds in various concentrations and intensities, each of which will have its own aroma.
The first phase of the research will focus on drawing up a reliable distinction between the two sorts of oysters in terms of odour and taste. Experiments will then be set up to analyse the feeding pattern of cultivated Japanese oysters on the basis of the results. The tests will also provide insight into the duration of feeding and the best methods for feeding oysters. Algae may be too expensive as a source of feed for oysters, making a search for alternatives such as fatty acids micro-capsulated or emulsions vital. Adding amino-acids in a natural way may also have a positive impact on the flavour.
The ultimate aim of the exercise is to cultivate oysters with a range of flavour profiles, farmed on land using new feeding techniques, and to test them on consumers. This is the best way to find out which Japanese oysters will appeal to them most.
Selenium is an essential nutrient for humans and animals, and an important anti-oxidant that may also have anti-carcinogenic properties. Professor Joop Luten is therefore focusing his research on ways of increasing selenium levels in farmed fish. This research could also form the basis for finding ways of increasing levels of other essential nutrients such as iodine and vitamin D in farmed varieties of fish such as salmon, trout and sole. Generally speaking, farmed fish have lower amounts of these nutrients when compared with fish caught in open waters.
There are high hopes for selenium. Research on catfish headed by Joop Luten at IMARES showed that the selenium level could be increased by a factor of five in a 6-week breeding period. By feeding catfish suitable feed two weeks before slaughter, the researchers managed to increase the selenium level threefold. Products enriched in this way could make a significant contribution to satisfying the recommended daily intake of selenium, which is 55 micrograms per day. It was also noted that the availability of selenium from fish can vary.
The primary focus of the research is finding the best way for fish to absorb selenium from their diet, and to study the absorption and bioactivity in humans. Another aspect will be to examine whether selenium helps products to oxidise less rapidly; after all, it is an anti-oxidant. In this way, nutritional properties may go hand-in-hand with technological advancement.
Joop Luten is European Business Developer at Nofima - Norwegian Institute of Food, Fisheries and Aquaculture Research. In his academic career he has been leading research departments on seafood quality, technology and nutrition. Joop Luten was R&D-coordinator of the EU-project SEAFOODplus. He is editor of seven scientific books and is (co)author of more than 100 publications.
